New DEC museum entry :D

Tony Duell ard at p850ug1.demon.co.uk
Thu Feb 22 13:39:34 CST 2007


> Yeah, I was thinking about that too.. If you're drawing enough current to 
> blow a 100A breaker through a system power cord (18 - 14AWG here in the 
> states), you'd end up with a very melty power cable.

In the UK, the standard mains plug contains a cartridge fuse in series 
with the live wire (it's a 3 pin plug, polarised, so live and neutral 
can't be swapped by plugginhg it in upside-down or anything). The 
standard ratings for these fuses are 3A, 5A and 12A (others do exist). I 
would expect most micros would be happy with a 3A plug fuse (that's over 
700VA , after all). 

Now, if you have several protective devices (fuses, circuit breakers) in 
series, it's not always the case that the lowest-rated one blows in the 
event of a fault, but in general the characteristics of the MCBs used in 
house wiring are such that the plug fuse _will_ blow first in the event 
of a fault in the device.  The MCB is there to protect against faults in 
the fixed wiring.

In this case, I would be suprised if that '100A breaker' was not a 
100A-rated RCD, and that it doesn't trip on overcurrent anyway. I've 
never seen a domestic wiring installation where the main switch was 
anything other than either a plain on/off switch or an RCd.


> 
> I think it's gotta be a ground-fault that's causing Witchy's problems.

I am almost sure it is.

-tony



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