I have an Agilent U1241A VOM that I bought at a hamfest for only $20,
new, but the previous model and it seems to be missing its tilt stand.
It is so fancy I don't even understand all the ratings:
The amperage measurement is: 11A/1000 V 30 kA/fast-acting fuse
The milli and micro amp measurement is similar.
What does 30 kA mean? 30,000 amps? I dont' think so. ;-)
micky <NONONOmisc07@fmguy.com> wrote:
I have an Agilent U1241A VOM that I bought at a hamfest for only $20,
new, but the previous model and it seems to be missing its tilt stand.
It is so fancy I don't even understand all the ratings:
The amperage measurement is: 11A/1000 V 30 kA/fast-acting fuse
The milli and micro amp measurement is similar.
What does 30 kA mean? 30,000 amps? I dont' think so. ;-)
It does mean that. It's a "30 kA fast-acting fuse".
In other words, if you apply more than 11A (or whatever the fuse rating is) >but less than 30,000 amps the fuse promises to become open circuit. If you >apply more than 30kA then there is a risk the fuse blows closed-circuit.
Due to the destructive power of putting so many kW into a small space, you >could have problems like vapourising metal parts in such a way that it fails >'closed', or creates a sustained arc that means current flows even though
the fuse has supposedly 'blown'.
TL;DR: if you are measuring something that might allow more than 30kA to
flow if you accidentally shorted it, don't use this meter to measure it. >However you would probably know if you were in such a situation.
Theo
In other words, if you apply more than 11A (or whatever the fuse rating is) but less than 30,000 amps the fuse promises to become open circuit. If you apply more than 30kA then there is a risk the fuse blows closed-circuit.
I have an Agilent U1241A VOM that I bought at a hamfest for only $20,
new, but the previous model and it seems to be missing its tilt stand.
It is so fancy I don't even understand all the ratings:
The amperage measurement is: 11A/1000 V 30 kA/fast-acting fuse
The milli and micro amp measurement is similar.
What does 30 kA mean? 30,000 amps? I dont' think so. ;-)
HRC is "high rupture efficiency". ><https://www.google.com/search?udm=2&q=hrc%20fuses>
On 21/02/2026 16:14, Theo wrote:
In other words, if you apply more than 11A (or whatever the fuse rating is) but less than 30,000 amps the fuse promises to become open circuit. If you apply more than 30kA then there is a risk the fuse blows closed-circuit.
Well. The problem that might occur if the current exceeds 30kA is kind
of unspecified.
With all good safely made brands of HRC fuse it means the fuse should
stay intact if the peak current is under 30kA, and exceeding 30kA is
likely to cause the fuse to explode and potentially damage other parts
of the equipment it is a part of.
Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
With all good safely made brands of HRC fuse it means the fuse should
stay intact if the peak current is under 30kA, and exceeding 30kA is
likely to cause the fuse to explode and potentially damage other parts
of the equipment it is a part of.
...like the venetian blind slats on the other side of the room (yes, it happened to me whlst testing equipment with the covers removed).
On 22/02/2026 19:59, Liz Tuddenham wrote:
Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
With all good safely made brands of HRC fuse it means the fuse should
stay intact if the peak current is under 30kA, and exceeding 30kA is
likely to cause the fuse to explode and potentially damage other parts
of the equipment it is a part of.
...like the venetian blind slats on the other side of the room (yes, it happened to me whlst testing equipment with the covers removed).
Ouch!
Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
On 22/02/2026 19:59, Liz Tuddenham wrote:
Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
With all good safely made brands of HRC fuse it means the fuse should
stay intact if the peak current is under 30kA, and exceeding 30kA is
likely to cause the fuse to explode and potentially damage other parts >>>> of the equipment it is a part of.
...like the venetian blind slats on the other side of the room (yes, it
happened to me whlst testing equipment with the covers removed).
Ouch!
There was an earth strap hidden on the back of the fuseholder block and
my workshop was quite close to the electricity substation.
I only discovered the strap when I gathered up the remains of the
fuseholders and pieced them back together.
On 2/27/26 01:25, Liz Tuddenham wrote:
Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
On 22/02/2026 19:59, Liz Tuddenham wrote:
Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
With all good safely made brands of HRC fuse it means the fuse should >>>> stay intact if the peak current is under 30kA, and exceeding 30kA is >>>> likely to cause the fuse to explode and potentially damage other parts >>>> of the equipment it is a part of.
...like the venetian blind slats on the other side of the room (yes, it >>> happened to me whlst testing equipment with the covers removed).
Ouch!
There was an earth strap hidden on the back of the fuseholder block and
my workshop was quite close to the electricity substation.
I only discovered the strap when I gathered up the remains of the fuseholders and pieced them back together.
I wonder how much current it took to vaporize a 2KW wirewound resistor?
It had something to do with a pressurized waveguide that developed a
leak and arced internally... Impressive, nothing left but the metal end cylinders!
wmartin <wwm@wwmartin.net> wrote:
On 2/27/26 01:25, Liz Tuddenham wrote:
Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:I wonder how much current it took to vaporize a 2KW wirewound resistor?
On 22/02/2026 19:59, Liz Tuddenham wrote:
Brian Gregory <void-invalid-dead-dontuse@email.invalid> wrote:
With all good safely made brands of HRC fuse it means the fuse should >>>>>> stay intact if the peak current is under 30kA, and exceeding 30kA is >>>>>> likely to cause the fuse to explode and potentially damage other parts >>>>>> of the equipment it is a part of.
...like the venetian blind slats on the other side of the room (yes, it >>>>> happened to me whlst testing equipment with the covers removed).
Ouch!
There was an earth strap hidden on the back of the fuseholder block and
my workshop was quite close to the electricity substation.
I only discovered the strap when I gathered up the remains of the
fuseholders and pieced them back together.
It had something to do with a pressurized waveguide that developed a
leak and arced internally... Impressive, nothing left but the metal end
cylinders!
I once (well twice, actually) had to rebuild a starting controller for a
5 kW repulsion-induction motor. Water had got onto the resistors and
caused an arc to the earthed retaining bolts. The slate core had
shattered and the windings had exploded into short lengths (some with
welded blobs on the ends). Parts of the brass bolts had vapourised too
- it must have been quite spectacular.
The fragments of wire were so short that I had to use 4-terminal
measurements to calculate the resistance values. A resistance wire
supplier in N.E. England recognised the type of wire immediatley and
sold me the length I needed.
A slate quarry in Cornwall cut me some replacement slate bars and I
re-wound the resistors by hand, complete with tapping points for the
various stages of motor control.
The motor and controller were made in 1919 but I had no difficulty
obtaining the materials to repair them and restore them to full working order. The whole job onlu took about 3 weeks from start to finish. How
many modern electrical items will be so easy to repair in another 95
years time?
| Sysop: | Amessyroom |
|---|---|
| Location: | Fayetteville, NC |
| Users: | 59 |
| Nodes: | 6 (0 / 6) |
| Uptime: | 18:06:34 |
| Calls: | 810 |
| Calls today: | 1 |
| Files: | 1,287 |
| D/L today: |
10 files (21,017K bytes) |
| Messages: | 193,396 |