From Newsgroup: uk.d-i-y

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely enough
to turn on the LCD display on my power-monitoring plug!). NP say it is
due to a circuit breaker having tripped just one of the three phases in
the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?
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From Newsgroup: uk.d-i-y

On 2025-10-14 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely enough
to turn on the LCD display on my power-monitoring plug!). NP say it is
due to a circuit breaker having tripped just one of the three phases in
the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Assuming that your local neutral and earth are still at roughly earth potential, perhaps before your local transformer the imbalance between
phases somewhere in the higher-voltage supply has raised a neutral and
your supply transformer is working between that and one of the active
phases?

nib
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely enough
to turn on the LCD display on my power-monitoring plug!). NP say it is
due to a circuit breaker having tripped just one of the three phases in
the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

I think so, though I cant quite visualise exactly how right now (coffee infusion hasn't quite levelled out)

A three phase transformer takes all phases and magnetically couples them
not only to the output phases as you might expect, but also to each other.

"A 3-phase transformer or 3-a transformer can be constructed either by connecting together three single-phase transformers, thereby forming a so-called three phase transformer bank, *or by using one pre-assembled
and balanced three phase transformer*which consists of three pairs of
single phase windings mounted onto *one single laminated core.*

The advantages of building a single three phase transformer is that for
the same kVA rating it will be smaller, cheaper and lighter than three individual single phase transformers connected together. This is because
the copper and iron core are used more effectively."

https://www.electronics-tutorials.ws/transformer/three-phase-transformer.html


Now the analysis of what happens to such a beast when you lose a single
input phase is beyond me at this stage in the morning, but it certainly includes the possibility of weird shit on *all* the output phases.
--
"I guess a rattlesnake ain't risponsible fer bein' a rattlesnake, but ah
puts mah heel on um jess the same if'n I catches him around mah chillun".


--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely enough
to turn on the LCD display on my power-monitoring plug!). NP say it is
due to a circuit breaker having tripped just one of the three phases in
the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Happens quite regularly here. I've heard it blamed on incinerated
squirrels and - improbably - on a metallised balloon, tripping an 11kV breaker. My phase well below spec - the other two phases high - but
just in spec.

On the last brown-out I got the engineers to switch my house to one of
the other phases. No brown-out in the two years since.

Still plenty of brief cuts. A pretty pathetic service.
--
PA
--

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 10:53, nib wrote:

On 2025-10-14 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely
enough to turn on the LCD display on my power-monitoring plug!). NP
say it is due to a circuit breaker having tripped just one of the
three phases in the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Assuming that your local neutral and earth are still at roughly earth potential, perhaps before your local transformer the imbalance between phases somewhere in the higher-voltage supply has raised a neutral and
your supply transformer is working between that and one of the active phases?

nib

It's not *quite* like that. Upstream of the final three phase
transformer there IS no neutral. As such.

That final transformer - probably a grey or green box somewhere local,
will be a *single* iron core with six windings fed from three 11kV
(sometimes 33kV) lines.

The neutral is generated by the connection of three of the output phases
to a common point. Which is then earthed.

Whether or not you can regard that as 'raising a neutral ' under fault conditions when only two phases exist is moot. But it certainly isn't happening *upstream* of the transformer.

And as pointed out above, three phase transformers are *not* three
single phase transformers in the same box.

Their operation under fault conditions is not something I was ever
taught or had reason to study, so I can't say more than it isn't nearly
as simple as one would hope for it to be.
--
Ideas are more powerful than guns. We would not let our enemies have
guns, why should we let them have ideas?

Josef Stalin

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

"The Natural Philosopher" <tnp@invalid.invalid> wrote in message news:10cl6j1$2q6c4$13@dont-email.me...

On 14/10/2025 10:33, NY wrote:

We have an interesting power supply problem at the moment, which Northern >> Powergrid are trying to fix. Power to our village is present (for
everyone, AFAIK) but the voltage has dropped to 95 V (barely enough to
turn on the LCD display on my power-monitoring plug!). NP say it is due
to a circuit breaker having tripped just one of the three phases in the
supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

I think so, though I cant quite visualise exactly how right now (coffee infusion hasn't quite levelled out)

A three phase transformer takes all phases and magnetically couples them
not only to the output phases as you might expect, but also to each other.

"Also to each other" - that's the crucial thing!

"A 3-phase transformer or 3-a transformer can be constructed either by connecting together three single-phase transformers, thereby forming a so-called three phase transformer bank, *or by using one pre-assembled and balanced three phase transformer*which consists of three pairs of single phase windings mounted onto *one single laminated core.*

The advantages of building a single three phase transformer is that for
the same kVA rating it will be smaller, cheaper and lighter than three individual single phase transformers connected together. This is because
the copper and iron core are used more effectively."

https://www.electronics-tutorials.ws/transformer/three-phase-transformer.html

Now the analysis of what happens to such a beast when you lose a single input phase is beyond me at this stage in the morning, but it certainly includes the possibility of weird shit on *all* the output phases.

We definitely got "weird shit". My desktop PC switched off as if there had been a power cut but my LED desk lamp was still on, as were the router and
the various mesh network nodes around the house. My wife, in her home office in the bedroom, was not aware of any problem. I checked the "fuse box" for a tripped ring main - fine! The fridge and freezer were "on" (display of temperature but no motors... but then the thermostat may not have switched them on. Then I noticed that a mains power-monitoring plug was displaying a very faint "95.6 V". The miracle is that so many electronic devices were getting their full power - switched-mode power supplies are wonderful
beasts! I know a lot are rated for input voltages from about 80V up to 260
V, and either 50 or 60 Hz, so they can be used anywhere in the world - just with a greater duty cycle if the mains voltage is lower.

Reminds me of the switched-mode PSU project that we all did at university 40-odd years ago. Our PSU had to deliver 12 V at 5 A, with input voltage ranging from 50 V AC to 300 V AC, and drawing up to the full 5 A even with
50 V going in - almost 100% duty cycle! Our team won the prize for
regulation range and efficiency - because a genius on our team worked out
that rather than using resistors to perform potential divider somewhere, we could use capacitors which would be lossless - as long as the frequency remained around 50 Hz. I still have the book somewhere which everyone in our team won.

I would probably have known how to calculate the effect of losing one phase
of a 3-phase transformer - but it was 45 years ago and the "use it or lose
it" principle means I've forgotten.


power came back a little while ago so all computers, router, mesh nodes
etc - and washing machine! - are now working.

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 09:56, Peter Able wrote:

On 14/10/2025 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely
enough to turn on the LCD display on my power-monitoring plug!). NP
say it is due to a circuit breaker having tripped just one of the
three phases in the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Happens quite regularly here.-a I've heard it blamed on incinerated squirrels and - improbably - on a metallised balloon, tripping an 11kV breaker.-a My phase well below spec - the other two phases high - but
just in spec.

Round here it tends to be falling branches. The 11kV is too widely
spaced for a squirrel to stretch...

On the last brown-out I got the engineers to switch my house to one of
the other phases.-a No brown-out in the two years since.

Still plenty of brief cuts.-a A pretty pathetic service.

Well back in the day it was a reasonable way cost-benefit to string up overhead 11kV lines. With pole mounted transformers, when electricity
was a luxury. not a necessity.

Then the trees grew. And the demands grew. And the dependency grew.

No one lays out overhead 11KV any more if they can help it.

It's all undergrounded at quite considerable cost.

But you save an enormous amount in maintenance. Tree pollarding here is
now an annual preventative measure.

As are outages due to trees that are not on the annual schedule.




--
ItrCOs easier to fool people than to convince them that they have been fooled. Mark Twain



--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

NY wrote:

We definitely got "weird shit". My desktop PC switched off as if there
had been a power cut but my LED desk lamp was still on, as were the
router and the various mesh network nodes around the house.

Have had similar here (though I don't know whether it was a lost phase,
or lost neutral) anything "electronic" just carried on, the fridge was distinctly unhappy.

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On Tue, 14 Oct 2025 10:33:52 +0100, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely enough
to turn on the LCD display on my power-monitoring plug!). NP say it is
due to a circuit breaker having tripped just one of the three phases in
the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Indeed. Your 230v supply is the difference between 2 phases of a 380v
3 phase feed. So only the users on the two good phases will get
full voltage.
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

Andy Burns <usenet@andyburns.uk> wrote in news:ml6o4nFkfevU1 @mid.individual.net:

NY wrote:

We definitely got "weird shit". My desktop PC switched off as if there
had been a power cut but my LED desk lamp was still on, as were the
router and the various mesh network nodes around the house.

Have had similar here (though I don't know whether it was a lost phase,
or lost neutral) anything "electronic" just carried on, the fridge was distinctly unhappy.

Watch out for fridges & freezers on brown-outs, it can lead to a compressor stall & burnout. Common in India where power supply irregularities are more common is a little monitor box plugged in before fridges to cut the power
to them if it is badly out of spec. Possible that our modern appliances
will monitor the supply and do similar, I don't know.
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 11:16, NY wrote:

"The Natural Philosopher" <tnp@invalid.invalid> wrote in message news:10cl6j1$2q6c4$13@dont-email.me...

On 14/10/2025 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely
enough to turn on the LCD display on my power-monitoring plug!). NP
say it is due to a circuit breaker having tripped just one of the
three phases in the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

I think so, though I cant quite visualise exactly how right now
(coffee infusion hasn't quite levelled out)

A three phase transformer takes all phases and magnetically couples
them not only to the output phases as you might expect, but also to
each other.

"Also to each other" - that's the crucial thing!

"A 3-phase transformer or 3-a transformer can be constructed either by
connecting together three single-phase transformers, thereby forming a
so-called three phase transformer bank, *or by using one pre-assembled
and balanced three phase transformer*which consists of three pairs of
single phase windings mounted onto *one single laminated core.*

The advantages of building a single three phase transformer is that
for the same kVA rating it will be smaller, cheaper and lighter than
three individual single phase transformers connected together. This is
because the copper and iron core are used more effectively."

https://www.electronics-tutorials.ws/transformer/three-phase-transformer.html


Now the analysis of what happens to such a beast when you lose a
single input phase is beyond me at this stage in the morning, but it
certainly includes the possibility of weird shit on *all* the output
phases.

We definitely got "weird shit". My desktop PC switched off as if there
had been a power cut but my LED desk lamp was still on, as were the
router and the various mesh network nodes around the house.

Many of today's switched mode power supplies are habppy from 48vDC to
250vAC.

> My wife, in

her home office in the bedroom, was not aware of any problem. I checked
the "fuse box" for a tripped ring main - fine! The fridge and freezer
were "on" (display of temperature but no motors... but then the
thermostat may not have switched them on. Then I noticed that a mains power-monitoring plug was displaying a very faint "95.6 V". The miracle
is that so many electronic devices were getting their full power - switched-mode power supplies are wonderful beasts! I know a lot are
rated for input voltages from about 80V up to 260 V, and either 50 or 60
Hz, so they can be used anywhere in the world - just with a greater duty cycle if the mains voltage is lower.

Yup.

Reminds me of the switched-mode PSU project that we all did at
university 40-odd years ago. Our PSU had to deliver 12 V at 5 A, with
input voltage ranging from 50 V AC to 300 V AC, and drawing up to the
full 5 A even with 50 V going in - almost 100% duty cycle! Our team won
the prize for regulation range and efficiency - because a genius on our
team worked out that rather than using resistors to perform potential divider somewhere, we could use capacitors which would be lossless - as
long as the frequency remained around 50 Hz. I still have the book
somewhere which everyone in our team won.

Nice project!

I would probably have known how to calculate the effect of losing one
phase of a 3-phase transformer - but it was 45 years ago and the "use it
or lose it" principle means I've forgotten.

Precisely.
Same here. And my CH boiler just crapped out....

power came back a little while ago so all computers, router, mesh nodes
etc - and washing machine! - are now working.

Good work!
--
"What do you think about Gay Marriage?"
"I don't."
"Don't what?"
"Think about Gay Marriage."


--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 2025-10-14 12:20, crn wrote:

On Tue, 14 Oct 2025 10:33:52 +0100, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely enough
to turn on the LCD display on my power-monitoring plug!). NP say it is
due to a circuit breaker having tripped just one of the three phases in
the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Indeed. Your 230v supply is the difference between 2 phases of a 380v
3 phase feed. So only the users on the two good phases will get
full voltage.

If you imagine a 3-phase transformer with the three output sides forming
the star-connected final distribution to premises, with each domestic
property working from one phase to neutral...

and the input sides connected to a delta-connected incoming mains, and
just one of the incoming mains goes open circuit (say L3)...

then one of the output phases works as normal, giving 230V (the one with
the transformer input connected betweeen L1 and L2). The other two
output phases both see the outputs from transformers with inputs
connected in series between L1 and L2 (via the open-circuit L3), so you
would expect them to see half volts.

So I would expect one phase to keep working at 230/240V and the other
two to see 115/120V.

nib
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 2025-10-14 13:03, nib wrote:

On 2025-10-14 12:20, crn wrote:

On Tue, 14 Oct 2025 10:33:52 +0100, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely enough >>> to turn on the LCD display on my power-monitoring plug!). NP say it is
due to a circuit breaker having tripped just one of the three phases in
the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Indeed. Your 230v supply is the difference between 2 phases of a 380v
3 phase feed. So only the users on the two good phases will get
full voltage.

If you imagine a 3-phase transformer with the three output sides forming
the star-connected final distribution to premises, with each domestic property working from one phase to neutral...

and the input sides connected to a delta-connected incoming mains, and
just one of the incoming mains goes open circuit (say L3)...

then one of the output phases works as normal, giving 230V (the one with
the transformer input connected betweeen L1 and L2). The other two
output phases both see the outputs from transformers with inputs
connected in series between L1 and L2 (via the open-circuit L3), so you would expect them to see half volts.

So I would expect one phase to keep working at 230/240V and the other
two to see 115/120V.

nib

Too many words! Like this:

<https://drive.google.com/file/d/1VJCZ1jas8N7AbGCN2QwkqINinTX5quVq/view?usp=sharing>

nib
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 13:20, nib wrote:

Too many words! Like this:

<https://drive.google.com/file/d/1VJCZ1jas8N7AbGCN2QwkqINinTX5quVq/view?usp=sharing>

nib

Except those iron cores are not separate
--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx


--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On Tue, 10/14/2025 6:48 AM, Andy Burns wrote:

NY wrote:

We definitely got "weird shit". My desktop PC switched off as if there had been a power cut but my LED desk lamp was still on, as were the router and the various mesh network nodes around the house.

Have had similar here (though I don't know whether it was a lost phase, or lost neutral) anything "electronic" just carried on, the fridge was distinctly unhappy.

On a phase failure here, I switched off at the incomer until it was repaired.

I didn't even need to do repeated measurements with a meter, to determine the all clear.
Just watched a local traffic light, until the lighting on it was "normal again".

On the electrical system, the dining table serves up:

1) 0 volts. The one we all love and quite common.

2) A rise in voltage. Incandescent bulbs pop. Bad for motors (heat from excess voltage).
Bad for the audio power amp in your multimedia rack. Switch off at incomer and wait for service.

3) A fall in voltage. Electric motors lug and in some cases, don't start properly
and the motor can burn out. Switch off at incomer and wait for service.

Paul
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From Newsgroup: uk.d-i-y

On 14/10/2025 11:16, The Natural Philosopher wrote:

On 14/10/2025 09:56, Peter Able wrote:

On 14/10/2025 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely
enough to turn on the LCD display on my power-monitoring plug!). NP
say it is due to a circuit breaker having tripped just one of the
three phases in the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Happens quite regularly here.-a I've heard it blamed on incinerated
squirrels and - improbably - on a metallised balloon, tripping an 11kV
breaker.-a My phase well below spec - the other two phases high - but
just in spec.

Round here it tends to be falling branches. The 11kV is too widely
spaced for a squirrel to stretch...

If the squirrel story was true, it was a phase-to-earth, I guess.

On the last brown-out I got the engineers to switch my house to one of
the other phases.-a No brown-out in the two years since.

Still plenty of brief cuts.-a A pretty pathetic service.

Well back in the day it was a reasonable way cost-benefit to string up overhead 11kV lines. With pole mounted transformers, when electricity
was a luxury. not a necessity.

Then the trees grew. And the demands grew. And the dependency grew.

No one lays out overhead 11KV any more if they can help it.

It's all undergrounded at quite considerable cost.

That's no comfort to a user in an all-overhead area !

But you save an enormous amount in maintenance. Tree pollarding here

is > now an annual preventative measure.

As are outages due to trees that are not on the annual schedule.

--
PA
--

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 09:56, Peter Able wrote:

On 14/10/2025 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely
enough to turn on the LCD display on my power-monitoring plug!). NP
say it is due to a circuit breaker having tripped just one of the
three phases in the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Happens quite regularly here.-a I've heard it blamed on incinerated squirrels and - improbably - on a metallised balloon, tripping an 11kV breaker.-a My phase well below spec - the other two phases high - but
just in spec.

We used to get a lot of brief one-second power cuts - just long enough
to force all computer equipment to reboot :-(

The best excuse I had from Northern Powergrid was calves in a farmer's
field using a wooden HV pole as a scratching post. Which was plausible
if it made the wires swing so the touched each other or an overhanging
tree... except they specified a field which did not have calves in it at
that time. The truth was that (as so often happened until we kicked up a stink) NP were not pruning back branches *before* they got close enough
to cause shorting.


After the brownout problem had been fixed, our power came back
perfectly, but then later went off for three and a half hours while the engineers made further corrections. Been fine ever since.
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 11:03, The Natural Philosopher wrote:

It's not *quite* like that.-a Upstream of the final three phase
transformer there IS no neutral. As such.

That final transformer - probably a grey or green box somewhere local,
will be a *single* iron core with six windings fed from three 11kV (sometimes 33kV)-a lines.

Intriguingly, the woman who took my call and read the engineer's report
said it was a fault in "a 20 kV line". Is there such a thing? I know of
11 and 33 kV. Is there even 22 kV? I know OHLE for trains is 25 kV
rather than 22 kV (so not a multiple-of-11 voltage like 11, 33 or 132 kV).
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 11:48, Andy Burns wrote:

NY wrote:

We definitely got "weird shit". My desktop PC switched off as if there
had been a power cut but my LED desk lamp was still on, as were the
router and the various mesh network nodes around the house.

Have had similar here (though I don't know whether it was a lost phase,
or lost neutral) anything "electronic" just carried on, the fridge was distinctly unhappy.

I was sitting at my desk when my PC went off. Bugger: power cut, I
thought. Hang on, my LED desk lamp is still on. Has the ring main
tripped? No, the router and mesh node next door are still on (on same
ring main). No circuit breakers have tripped. Then I noticed my power-monitoring passthrough plug on my desk (*) had a barely visible
number. What did it say? 96 V? WTF!! I went upstairs to warn my wife and
she was completely unaware, so her wifi connection via another mesh node
and the one connected to the router was quite happy with 96 V instead of
240V. I bet the SMPSUs everywhere were struggling though, with the power transistors turned on for almost 100% duty cycle.

We switched off everything with SMPSUs to avoid them overheating. We'd
have turned off the fridge and freezer but those are on Kasa smart plugs
- mainly for the power-monitoring capabilities rather than the remote
switch on/off capabilities, and it means pulling the fridge/freezer out
to reach the switches (and there was too little mains to control the
switches remotely). So those had to stay on - or else empty the
fridge/freezer to make them light enough to move...

If I'd had a tungsten light bulb to hand, it would have been amusing to
see how dim and orange it was. I forgot about the dining room which is
the only room which still has tungsten bulbs, in the form of 40 W candle
bulbs in a candelabra. Or is it candelabrum if there's just one?


(*) I'd been using it to monitor how much power a 5 V Raspberry Pi PSU
used to see if I may have been overloading its 5 V output (if mains
power is less than 10 W then output power can't be any higher than that
so 5V at 2A is not being exceeded).
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 14/10/2025 12:34, fred wrote:

Andy Burns <usenet@andyburns.uk> wrote in news:ml6o4nFkfevU1 @mid.individual.net:

NY wrote:

We definitely got "weird shit". My desktop PC switched off as if there
had been a power cut but my LED desk lamp was still on, as were the
router and the various mesh network nodes around the house.

Have had similar here (though I don't know whether it was a lost phase,
or lost neutral) anything "electronic" just carried on, the fridge was
distinctly unhappy.

Watch out for fridges & freezers on brown-outs, it can lead to a compressor stall & burnout. Common in India where power supply irregularities are more common is a little monitor box plugged in before fridges to cut the power
to them if it is badly out of spec. Possible that our modern appliances
will monitor the supply and do similar, I don't know.

Ah yes, equipment being able to monitor mains voltage. My first
indication that something was up was a strange error code on the washing machine that I was about to switch on. I'd just got to my PC to look up
the code in the PDF instruction manual when the PC switched itself off.
I looked up the code later on: "mains voltage too low". There are also
other codes for "mains voltage too high" and "mains frequency out of spec".

Fridge and freezer are a bugger for us: the switches to turn them off
are behind the appliances and can only be reached by emptying the fridge/freezer to make them light enough to pull out to reach the
switches. They're on Kasa smart switches - but the mains voltage was too
low for those to be operated remotely.
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From Newsgroup: uk.d-i-y

On 14/10/2025 17:35, Paul wrote:

On Tue, 10/14/2025 6:48 AM, Andy Burns wrote:

NY wrote:

We definitely got "weird shit". My desktop PC switched off as if there had been a power cut but my LED desk lamp was still on, as were the router and the various mesh network nodes around the house.

Have had similar here (though I don't know whether it was a lost phase, or lost neutral) anything "electronic" just carried on, the fridge was distinctly unhappy.

On a phase failure here, I switched off at the incomer until it was repaired.

I didn't even need to do repeated measurements with a meter, to determine the all clear.
Just watched a local traffic light, until the lighting on it was "normal again".

On the electrical system, the dining table serves up:

1) 0 volts. The one we all love and quite common.

2) A rise in voltage. Incandescent bulbs pop. Bad for motors (heat from excess voltage).
Bad for the audio power amp in your multimedia rack. Switch off at incomer and wait for service.

3) A fall in voltage. Electric motors lug and in some cases, don't start properly
and the motor can burn out. Switch off at incomer and wait for service.

I should have switched off at the consumer unit, but I realised that if
I did so I'd never know when the mains came back full-strength - unless
I kept turning it on briefly to check.
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From Newsgroup: uk.d-i-y

On 14/10/2025 12:50, The Natural Philosopher wrote:

On 14/10/2025 11:16, NY wrote:

"The Natural Philosopher" <tnp@invalid.invalid> wrote in message
news:10cl6j1$2q6c4$13@dont-email.me...

On 14/10/2025 10:33, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is
present (for everyone, AFAIK) but the voltage has dropped to 95 V
(barely enough to turn on the LCD display on my power-monitoring
plug!). NP say it is due to a circuit breaker having tripped just
one of the three phases in the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

I think so, though I cant quite visualise exactly how right now
(coffee infusion hasn't quite levelled out)

A three phase transformer takes all phases and magnetically couples
them not only to the output phases as you might expect, but also to
each other.

"Also to each other" - that's the crucial thing!

"A 3-phase transformer or 3-a transformer can be constructed either by
connecting together three single-phase transformers, thereby forming
a so-called three phase transformer bank, *or by using one pre-
assembled and balanced three phase transformer*which consists of
three pairs of single phase windings mounted onto *one single
laminated core.*

The advantages of building a single three phase transformer is that
for the same kVA rating it will be smaller, cheaper and lighter than
three individual single phase transformers connected together. This
is because the copper and iron core are used more effectively."

https://www.electronics-tutorials.ws/transformer/three-phase-
transformer.html


Now the analysis of what happens to such a beast when you lose a
single input phase is beyond me at this stage in the morning, but it
certainly includes the possibility of weird shit on *all* the output
phases.

We definitely got "weird shit". My desktop PC switched off as if there
had been a power cut but my LED desk lamp was still on, as were the
router and the various mesh network nodes around the house.

Many of today's switched mode power supplies are happy from 48vDC to
250vAC.

DC? I suppose a simple 4-diode bridge rectifier (the input between the
mains and the step-down transformer) will pass DC no matter what the
polarity is, and if the step-down transformer is *after* the switching
circuit (making the transformer much smaller) then DC will reach the oscillator, control circuit and power transistor.

Yup.

Reminds me of the switched-mode PSU project that we all did at
university 40-odd years ago. Our PSU had to deliver 12 V at 5 A, with
input voltage ranging from 50 V AC to 300 V AC, and drawing up to the
full 5 A even with 50 V going in - almost 100% duty cycle! Our team
won the prize for regulation range and efficiency - because a genius
on our team worked out that rather than using resistors to perform
potential divider somewhere, we could use capacitors which would be
lossless - as long as the frequency remained around 50 Hz. I still
have the book somewhere which everyone in our team won.

Nice project!

Last year I came across the handwritten report that I'd written for our
team all those years ago. Our design used a mains-fed transformer, then low-voltage bridge rectifier, which may have been part of the "rules"
that everyone had to abide by. So we were AC-only. We were given a huge
Variac transformer to simulate the wide range of input mains voltages.
We wound ours up to quite a bit beyond the 300 V maximum in our design requirements, to make sure that we could exceed the spec! The control
circuit eventually switched the duty cycle off completely - it failed gracefully.

I remember us all being warned that the power transistor would not be
able to handle full load current if it was on permanently, as opposed to
being switched at 25 kHz. Before we finalised our design and made up a
printed circuit board, we were developing our control circuit on a
separate breadboard with a single-wire feed to the power transistor.
That wire became accidentally disconnected during full-load testing.
There was a noise like rustling leaves, a bit of magic smoke and then a rifle-shot crack. The transistor had exploded and fired itself into the ceiling of the lab 20 feet above us. After that, we were all made to
wear safety specs... The mark in the ceiling was still there two years
later in our final year!
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From Newsgroup: uk.d-i-y

On 14/10/2025 12:20, crn wrote:

On Tue, 14 Oct 2025 10:33:52 +0100, NY wrote:

We have an interesting power supply problem at the moment, which
Northern Powergrid are trying to fix. Power to our village is present
(for everyone, AFAIK) but the voltage has dropped to 95 V (barely enough
to turn on the LCD display on my power-monitoring plug!). NP say it is
due to a circuit breaker having tripped just one of the three phases in
the supply to our village.

Is it plausible that this could cause low voltage for everyone, as
opposed to full voltage for those houses that are on good phases and
total power loss for people on the phase that has tripped?

Indeed. Your 230v supply is the difference between 2 phases of a 380v
3 phase feed. So only the users on the two good phases will get
full voltage.

Hmmm. I can believe that. What is odd is that everyone in the village,
no matter which phase their house was on, got low voltage. You'd think
that one house in three (between the two good phases) would have been
OK. Certainly no-one in the village said on our Facebook group "it's
fine for us". Weird.
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From Newsgroup: uk.d-i-y

NY wrote:

The Natural Philosopher wrote:

Many of today's switched mode power supplies are happy from 48vDC to
250vAC.

DC?

I knew someone who made a portable battery pack to run their BBC micro.
It was a 5' long section of drain pipe with a stack of 100 NiCd cells
with a 13A socket araldited into one of the end caps. The beeb PSU was
happy to run on 240V DC ... ok it would have stressed half the diodes,
but it didn't seem to care.
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From Newsgroup: uk.d-i-y

On 15/10/2025 23:47, NY wrote:

On 14/10/2025 12:50, The Natural Philosopher wrote:

Many of today's switched mode power supplies are happy from 48vDC to
250vAC.

DC? I suppose a simple 4-diode bridge rectifier (the input between the
mains and the step-down transformer) will pass DC no matter what the polarity is, and if the step-down transformer is *after* the switching circuit (making the transformer much smaller) then DC will reach the oscillator, control circuit and power transistor.

Spot on. That is how it works.
The availability if ultra low resistance very high speed switching
MOSFETS jhas transformed the industry.
--
ThererCOs a mighty big difference between good, sound reasons and reasons
that sound good.

Burton Hillis (William Vaughn, American columnist)

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From Newsgroup: uk.d-i-y

NY <me@privacy.net> wrote in news:10cp8g3$pvr$1@dont-email.me:

Hmmm. I can believe that. What is odd is that everyone in the village,
no matter which phase their house was on, got low voltage. You'd think
that one house in three (between the two good phases) would have been
OK. Certainly no-one in the village said on our Facebook group "it's
fine for us". Weird.

That's not how it works, people are not fed with power between phases but between 'low' voltage[1] phase and neutral. On a low voltage supply that is
4 wires (each home normally getting only 2, 1 phase, 1 neutral). High
voltage supply (11kV+) is on 3 phase wires only (to save on copper) with
the final conversion from 'delta' to 'star' via the low voltage
transformer. Lose one of the input phases and the whole lot turns to shit (heavy mathematical vector proof omitted).

[1] In power distribution 230V counts as low voltage.
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From Newsgroup: uk.d-i-y

On 16/10/2025 15:38, fred wrote:

NY <me@privacy.net> wrote in news:10cp8g3$pvr$1@dont-email.me:

Hmmm. I can believe that. What is odd is that everyone in the village,
no matter which phase their house was on, got low voltage. You'd think
that one house in three (between the two good phases) would have been
OK. Certainly no-one in the village said on our Facebook group "it's
fine for us". Weird.

That's not how it works, people are not fed with power between phases but between 'low' voltage[1] phase and neutral. On a low voltage supply that is
4 wires (each home normally getting only 2, 1 phase, 1 neutral). High
voltage supply (11kV+) is on 3 phase wires only (to save on copper) with
the final conversion from 'delta' to 'star' via the low voltage
transformer. Lose one of the input phases and the whole lot turns to shit (heavy mathematical vector proof omitted).

[1] In power distribution 230V counts as low voltage.

I have seen some examples where individual houses (in rural areas)
are fed from the difference between phases. The main feed is 3 phase
11kV with no neutral. A branch takes two conductors at 11kV from the
available three and drives a transformer on a pole which then feeds
the house.
John

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From Newsgroup: uk.d-i-y

On 16/10/2025 20:56, John R Walliker wrote:

I have seen some examples where individual houses (in rural areas)
are fed from the difference between phases.-a The main feed is 3 phase
11kV with no neutral.-a A branch takes two conductors at 11kV from the available three and drives a transformer on a pole which then feeds
the house.

That seems to be a standard arrangement, especially obvious where there
is an outlying property which has two wires connected to two of the
three 11 kV overhead lines and a single-phase transformer to feed 240 V
(often by low voltage overhead lines) to the house/farm.

Our old house was the middle of a terrace of three. All four wires of
240 V along the street were tapped to four wires that ran along the back
of the houses, and you could see very clearly how each house took its
live from a different phase, plus a common neutral.

We had a really stupid arrangement in our server room at work. When it
was refurbished, someone in Site Facilities decided to supply each of
the several benches from a different mains phase. That meant that we
were forbidden to connect (for example) a terminal on one bench to a
server on another bench by RS-232 because of the risk of > 240 V (maybe
415 V) between benches if there was a wiring fault. So we had to invest
in loads of opto-isolators for connections between benches, and if we
took any test equipment in there temporarily, we had to make damn sure
it was plugged into a mains socket on the same bench as the server it
was connected to. I'm not sure how they handled the Ethernet Cat 5
cables, because the same hub/switch would have cables from benches on
all three phases. It would have been so much better if the whole of one
floor of the building had been on a single phase, which I think was how
it was before the refurbishment.
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From Newsgroup: uk.d-i-y

John R Walliker <jrwalliker@gmail.com> wrote in news:10crikm$7tdq$2@dont-email.me:

On 16/10/2025 15:38, fred wrote:

That's not how it works, people are not fed with power between phases
but between 'low' voltage[1] phase and neutral. On a low voltage
supply that is 4 wires (each home normally getting only 2, 1 phase, 1
neutral). High voltage supply (11kV+) is on 3 phase wires only (to
save on copper) with the final conversion from 'delta' to 'star' via
the low voltage transformer. Lose one of the input phases and the
whole lot turns to shit (heavy mathematical vector proof omitted).

[1] In power distribution 230V counts as low voltage.

I have seen some examples where individual houses (in rural areas)
are fed from the difference between phases. The main feed is 3 phase
11kV with no neutral. A branch takes two conductors at 11kV from the available three and drives a transformer on a pole which then feeds
the house.
John

Of course, there is no neutral in the HV network so that is how it will be done in rural areas, it is routine.
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