Socket Breaker Size?

Question

Hi Guys!!

I have a exam question paper here goes: -

What is the correct circuit breaker size for sockets:

a) 30mA

b)40mA

c)50mA

d)60mA

I know that normal sockets in a ring citcuit is connected to 32Amp breakers, but not sure how this works as "m" = mili doesn't it? which would equal 10^-3 ?? Help Please

Thanks

Answer 1

30mA is for an earth leakage unit as anything above 30mA is likely to kill you. Circuit breaker ratings could be anything depending on regulations.

Answer 2

Are you sure that you haven't missed the bit that says "earth leakage" as in ELCB or "residual current" in your reading of the question?

A UK ring main consists of a number of 13A sockets protected by a 30A fuse or 32A circuit breaker.  (UK plugs contain a individual cartridge fuse to protect the load)

For safety reasons, the circuit breaker often includes a 30mA earth leakage trip.

Edit:   30mA is fairly typical.  It gives reasonable protection with good resistance to false tripping.    Some older consumer units have an ELCB that doubles as the main switch.  If it trips, the whole lot goes off.

I have seen other values used for special purposes,  100mA supposedly for protection against fire, but no good for protecting individuals.  I've also seen 10mA types for use in special situations - e.g. stables, where there is a high risk of horses peeing on the electrics!

The more sensitive the trip, the more likelihood of false tripping.  In the labs of some schools and colleges, they use a special unit which uses a centre-tapped transformer and trips if there is an earth leakage greater than about 1.5mA, but these wouldn't be used in a domestic situation.

Answer 3

correct breaker size is determined by the load.

Typical sizes in the U.S. are 15 or 20 amps.

All of your answers are in mA, which is not correct, not even close.

"for sockets" is a meaningless phrase in this context, unless this is the UK and they use different terminology.