From Newsgroup: sci.electronics.design
On 8/7/2026 2:59 AM, Martin Brown wrote:
But, 2200VA is a 20A branch circuit.-a In a residence,
most are 15A (1440/1800W).
One advantage of UK 240v mains is that the currents are lower.
I have seen 3kW heaters used in cold rooms cause trouble with cables that were
not tightly crimped leading to red hot wire devoid of insulation and charring
of the interior of the plug.
Here, the emphasis on reducing cost (and labor) leads
to all sorts of "bad design choices".
For example, receptacles (typically duplex) tend to have
a pair of connections for each "conductor".
<
https://www.electrical-forensics.com/Receptacles/F10-052/ReceptacleConnections.jpg>
The connections used to be screw terminals though now tend to be
"back stab" self-securing fasteners (the bare end of the wire is
slipped into a hole in th4e back of the receptacle where a ratcheting
mechanism "grabs" the wire; to remove the wire, one inserts another
object -- typically a cabinet-tip screwdriver blade -- into a nearby
slot to mechanically disengage the "ratchet").
The metallic part of an outlet -- with all the plastic removed: <
https://www.electrical-forensics.com/Receptacles/F10-052/ReceptacleStabInConnection.jpg>
(Note the "link" at the top can be deliberately severed to allow
the two receptacles to be independantly wired -- like for an
"always-powered" and "switched" outlet to be colocated)
A consequence of this is the wiring at the receptacle is in series
with all other loads downstream from this point. So, a screw that
works its way loose (because the receptacle sees repeated mechanical disturbance as items are plugged and unplugged) leads to
a higher resistance connection AT the receptacle.
A better (though more labor intensive) practice is to secure the
upstream and downstream wires directly together and run a short
pigtail off to the receptacle. As such, any disturbance at the
receptacle only affects the load plugged into that receptacle
(which is likely smaller than the SUM of that load and all
downstream loads)
This is aggravated by the DIYers who *think* it's just a
matter of connecting a couple of wires...
OTOH, our branch circuits tend to be smaller -- lower power
(ampacity).
A typical home will have 15A (1440/1800W) circuits for lighting
and most receptacles; 20A (1920/2400W) for "small appliances at
the kitchen counter; 30A@220V for an electric clothes dryer;
50A@220V for a stove; etc. Few "corded" devices require a 20A
circuit -- the plugs have a "horizontal neutral" to ensure they
don't mechanically mate with a 15A-only receptacle (which has
parallel blades for hot and neutral)
<
https://cdn1.bigcommerce.com/server3900/wlejmk/product_images/uploaded_images/info-outlet-types-15a-vs-20-amp.jpg>
E.g., the 2200VA UPS has a plug with non-parallel blades. Removing
it to replace it with one with parallel blades is a code violation
as the device loses it's "listing" (hello insurers!)
A house typically has a 60A ("dated"), 100A or 200A (all at 220V)
"service" but this is distributed over 20 or 30 branch circuits.
IF I KNOW THAT I WILL NEVER EXCEED THE AMPACITY OF THE
BRANCH CIRCUIT, what risk to repurposing a 2200VA unit
to run off a 15A circuit?
US style mains is radial rather than ring isn't it so you will be sometimes
Yes.
pushing the limit if the UPS needs to supply 2.2kVA. OTOH the cable will just
run a bit warm when that happens. If it happens too often then it will shorten
the useful life of the cable.
The 15A circuit would barely support a 2200VA load (assuming a PF of ~0.8). But, I wouldn't have such loads powered simultaneously -- I would be exceeding the circuit's ampacity even if they were plugged into discrete outlets
in the absence of a UPS.
A UK mains ring circuit provides twice the nominal capacity of the cable used
provided that the ring isn't broken.
"cable" meaning "wiring internal to the residence"
The "cord" to the UPS would still see the full load.
Slow blow fuses can stand roughly twice their nominal rated current flowing through them for tens of minutes (though get rather hot).
I'm hesitant to just "try it" as the things are heavy
and lugging them into place (only to be disappointed)
is not something I look forward to doing -- let alone
sorting through all the cabling, etc.
You could do a test wherever it is presently located to see under what
<frown> I may have mentioned that I have a lot of kit? <grin>
These UPSs are all rack units -- typically 2U to 5U. Big. Heavy.
There's no easy way to store them other than to stack them atop
each other AS IF they were mounted in a rack.
The 5KVA units are >> 100f pounds -- even without batteries
(the batteries add another 100 pounds). The 2200, 3KVA, etc. units
are a bit lighter -- but, not the sort of things you would encounter
in most SOHO environments (that you can lift and transport without
much effort).
So, I'd have to test them "in place". Which means bringing power *to*
them. I have a 100ft #12AWG "cord reel" but *it* weighs almost 40 pounds! Then, getting access to the outlets on the back side, etc.
I.e., decide to use it (and invest the time to get it into position)
or NOT use it (and leave it where it is).
But, as I said in another post, I found several 1500VA units (same physical size but their magnetics are lighter weight). That will let me stage
them in different places, closer to their respective loads.
[Goal is to move all the machines -- and the BTUs they throw off -- out
to the lab and access them headless. There, I can be more deliberate
in how they are wired -- and make them more accessible, at the same
time (instead of hiding them under workbenches, etc.)]
circumstances and for how long it might draw 2.2kW. I don't understand the notation (1440/1800W) is that steady load and absolute peak load?
The 1800W is the rating of the circuit (15A @ 120V = 1800W) at nominal
line voltage. "Best practices" are to derate branch circuits by 20%,
hence the 1440W is the nominal "maximum expected load". This being
important where users can add loads to the circuit at will (vs.
dedicated circuits where the load is unalterable).
If it is then you may have your answer since insurerance loss adjusters love to
find a reason not to pay out if there is a fire.
There's a *reason* for those "requirements". They're not just
trying to bust your balls...
[I've a buddy who does a lot of DIY stuff. To his credit, he at least
makes an effort to make it *look* nice! But, he omits things like
conduit (EMC) as it's extra cost and labor. As if the *sole* reason
for its use is to drive UP that cost!]
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