Products > Test Equipment
Big Clive's "Trashy" meter, unboxed ( Duratool D03047 multimeter )
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AVGresponding:

--- Quote from: Fungus on April 29, 2023, 07:49:59 pm ---
--- Quote from: IanB on April 29, 2023, 06:42:22 pm ---Fair enough. Which is why I would curious if any UK based electricians here could indicate what kind of prospective fault current would be measured at a typical UK 13 A wall socket? (It would be a range, obviously, but typical/min/max would be interesting.)

--- End quote ---

Wikipedia says typical UK ring circuits have 30A fuses and 2.5mm2 cable.

--- End quote ---

Wikipedia needs editing... what a surprise! Any installation still using fuses would for sure be a Code 2 on an EICR, maybe a Code 1 if the sparky is in a bad mood (yes, there's some wiggle room). Most are going to be MCBs at the least, or RCDs or RCBOs. In any case, for domestic installs they'll be 32A type B, with a 6kA breaking capacity.
The 2.5mm2 T+E has a CPC CSA of 1.5mm2, and in a ring of course there's two paths back to the board (barring fault conditions).
Radials (for socket outlets) are in 4mm2 which also has a 1.5mm2 CPC (used to be 2.5mm2, but hey, cost cutting), and will be protected by a 20A type B MCB/RCD/RCBO.
Fungus:

--- Quote from: AVGresponding on April 30, 2023, 05:27:08 am ---Wikipedia needs editing... what a surprise! Any installation still using fuses would for sure be a Code 2 on an EICR, maybe a Code 1 if the sparky is in a bad mood (yes, there's some wiggle room). Most are going to be MCBs at the least, or RCDs or RCBOs. In any case, for domestic installs they'll be 32A type B, with a 6kA breaking capacity.
The 2.5mm2 T+E has a CPC CSA of 1.5mm2, and in a ring of course there's two paths back to the board (barring fault conditions).
Radials (for socket outlets) are in 4mm2 which also has a 1.5mm2 CPC (used to be 2.5mm2, but hey, cost cutting), and will be protected by a 20A type B MCB/RCD/RCBO.

--- End quote ---

What it actually says is: " They are generally wired with 2.5 mm2 cable and protected by a 30 A fuse, an older 30 A circuit breaker, or a European harmonised 32 A circuit breaker. Sometimes 4 mm2 cable is used if very long cable runs"

But don't let your anti-Wikipedia bias get in your way.
AVGresponding:

--- Quote from: Fungus on April 30, 2023, 06:37:25 am ---
--- Quote from: AVGresponding on April 30, 2023, 05:27:08 am ---Wikipedia needs editing... what a surprise! Any installation still using fuses would for sure be a Code 2 on an EICR, maybe a Code 1 if the sparky is in a bad mood (yes, there's some wiggle room). Most are going to be MCBs at the least, or RCDs or RCBOs. In any case, for domestic installs they'll be 32A type B, with a 6kA breaking capacity.
The 2.5mm2 T+E has a CPC CSA of 1.5mm2, and in a ring of course there's two paths back to the board (barring fault conditions).
Radials (for socket outlets) are in 4mm2 which also has a 1.5mm2 CPC (used to be 2.5mm2, but hey, cost cutting), and will be protected by a 20A type B MCB/RCD/RCBO.

--- End quote ---

What it actually says is: " They are generally wired with 2.5 mm2 cable and protected by a 30 A fuse, an older 30 A circuit breaker, or a European harmonised 32 A circuit breaker. Sometimes 4 mm2 cable is used if very long cable runs"

But don't let your anti-Wikipedia bias get in your way.

--- End quote ---

I like Wikipedia, and I fund it from time to time. The article header mentions it needs additional verification and citations, and this is a fair assessment. There is some ambiguity and misleading information in it. A circuit breaker old enough to be rated at 30A would be just as bad as a rewirable fuse, and would attract similar comments on an EICR; the tripping times on these old things are so slow as to be positively glacial. I can't recall ever seeing pyro used in a domestic setting. A consumer unit is not the same thing as a distribution board; all consumer units are distribution boards, but not all distribution boards are consumer units.

4mm2 can be used for particularly long runs, but this is not ideal, and would be unlikely to be necessary in a domestic setting, and would be discouraged in any case, due to the negative impact on tripping times. I have seen 6mm2 used on a 20A radial socket circuit; it barely passed muster under testing.
Normally these situations can be avoided by having a better design, ie by having a DB nearer to the load.
IanB:

--- Quote from: AVGresponding on April 30, 2023, 01:00:36 pm ---4mm2 can be used for particularly long runs, but this is not ideal, and would be unlikely to be necessary in a domestic setting, and would be discouraged in any case, due to the negative impact on tripping times. I have seen 6mm2 used on a 20A radial socket circuit; it barely passed muster under testing.
--- End quote ---

How and why does cable size affect tripping times? For example, a 12 m run of 6 mm2 is going to have the same resistance and voltage drop as an 8 m run of 4 mm2 or a 5 m run of 2.5 mm2. Run lengths are going to vary a lot between a large house and a small shed.
themadhippy:

--- Quote --- I have seen 6mm2 used on a 20A radial socket circuit; it barely passed muster under testing
--- End quote ---
how come? the R1 R2 for 6mm is going to be lower than the same length of a bit of 2.5/1.5,meaning your fault current will be higher leading to a faster disconnection time,the only failure i can think of is the fault current being  to high for the protective device
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