Theoretical electrics question

[Graham Jones]

Hello,

I've been pondering something for a few days and was hoping someone here could help. Please forgive me if any of the following is wrong.

The maximum load on a normal ring circuit for sockets is 32A. Lets assume that this circuit is fully loaded, there are appliances plugged in that are drawing a total of 32A.

Now each socket on this ring is rated as 13A, at least that is what it says on the back of the spare sockets I have. (13A 250V). They will probably cope with a bit more though.

So my question is, as the circuit is fully loaded does this mean that each socket on the ring have 32A "flowing" through it? If so will they catch fire or melt?

A similar question is lets say we have a 13A socket spurred off a 13A socket. Both sockets are fully loaded, does this mean that the first socket has 26A "flowing" through it? Will it catch fire or melt?

Thanks

Graham

[John Williamson]

Maybe, maybe not. The 13A is specified as the minimum capacity, and cheap plug/ socket pairs will often only just carry it within the specified rise in temperature. Some illegal imports won't even do that.

No, partly because the current flowing in the ring main is split (in theory, assuming no faults) into 2 x 16A parts, one coming to each socket from each direction, so in theory, the connections at the rear of the socket are carrying no more than 16A, unless it's a double, in which case they may be carrying 26A. Also, the connections at the rear of the socket are capable of carrying more current than the contacts, and

*should* be rated to carry the full 32A without overheating.

Not if the connections are sound. Loose screws on the connections can cause dangerous overheating as can other installation problems, not forgetting that the spring contacts inside the socket can weaken over time.

[Man at B&Q]

The only current "through" the socket is that to the load that is plugged in.

The two connections for the ring (or spur) go into the same screw terminal on the back of the socket. The total current in the ring stays in the ring, it doesn't go into the socket and back out again.

MBQ

[Graham Jones]

Thanks for the replies, I was missing the fact that the contacts can carry more than the rest of the socket. It makes sense now.

[John Rumm]

13A for a single, 20A for a double...

Depends on the quality of the socket and for how long...

No and no. If there is nothing plugged into the socket, then there will be no current drawn through it. The wires of the circuit may pass "through" the socket in the sense that they join at its terminals, but this current will not be flowing through the socket itself.

Also note in the case of a ring circuit, only some of the total current will be running past each socket, since there are two alternate cable routes to each socket.

Again no, because the spur is not plugged into the first socket, but connected directly to the cables feeding the socket instead. They are capable of carrying the full circuit current and some more typically.

[John Rumm]

If you think about it, the contacts are actually clamping a pair of wires together - chances are the joint would carry full circuit current even if the terminals themselves were actually insulating.

[Andy Champ]

I'm going from a different theory to you - and no knowledge of what part P says.

If the socket is near one end of the ring the resistance in the wires in the two directions will be very different, and most of the current will come from one direction.

As others have pointed out this probably doesn't matter.

Andy