Electric sockets overloaded? What's maximum load?

[justaboutsane]

I wonder if the Sparkies out there can help, I am just back after a weeks break and am up to my eyes in catch up so have not got time to go trawling..

A tenant has called complaining about Electric sockets not working.. the sparkie has been out and has a very strong suspicion they have been overloaded. Can anyone tell me what the maximum usage should be on a single and a double socket please.. and also in terms of appliances.. I want to send a short paragraph out in my next newsletter about the dangers of overloading! .. Will lay it on about Insurance companies and fire risks etc...

If you can post a website, law or whatever which I can quote that would be great.

Thank you x

[P.Pilcher]

It all depends!
Each socket (presumably for flat pin plugs) is designed to deliver a maximum of 13 amps - hence the 13 amp fuse you find in new plugs. Thus a double socket can supply no more than 26 amps. The current is given by dividing the power rating of the appliance connected by the voltage thus for a 250 volt supply a three kilowatt appliance will draw 12 amps.
Now, electric sockets are connected to the fuse/circuit breaker board by a ring main and this is fused (or circuit breakered) to a maximum of 30 amps (32 for circuit breakers) Hence one double socket supplying two three kilowatt appliances does not leave very much spare for other appliances connected elsewhere in the ring main. Depending on how old your wiring is, you may have one ring main wiring all the sockets in the house, or all the sockets on a floor, and in my house I have put a separate ring in for my kitchen. You can tell how many ring mains you probably have by counting the fuses you have at 30 amps (circuit breakers at 32).

In theory, then the internal wiring in the house cannot be overloaded because of the protection devices at the fuseboard. The plug fuses protect the appliance and its wiring, which is why you fit a smaller fuse in the plug supplying a lamp than the one supplying a 3 kilowatt kettle. Unfortunately however, although the connections to wall sockets are done up very tightly when installed, they tend to loosen with time. This impairs the connection so when a high current appliance is connected, the connection gets hot and damage can be done. As sockets wear, the same can happen to the connection between the live terminal of the socket and plug. Nowadays they are usually white and the telltake of a brown stain around the lower right hand socket hole indicates that said socket requires immediate replacement!
I suspect that this is the damage that your electrician is complaining about, so his advice to repair it should be heeded, however it should be impossible to overload a properly installed well maintained system.

P.P.

[justaboutsane]

:confused: Thank you PP!!! I have been away for a week.. I got back to a message from the property manager saying that the tenant called to say the Electrics had blown and the sparkie thinks they have been overloaded! .. The particular tenant is a pain... broke a kitchen drawer within days of it being installed and blamed the builder.... but kitchen drawers are not designed to be thrown across a room!!! Anyhow... i am awaiting a written report and will know more shortly! ... I have no voice so communication is a problem at the mo!

[Ericthelobster]

I agree with PP that you can't 'overload' a properly designed and maintained system, so difficult to see what the tenant's done wrong... if he's really 'blown the electrics' may I venture to suggest that your property's wiring needs some attention from a sparks pronto before you get into deep do-do? Have you had a 'Periodic Inspection' done recently?

The alternative scenario of course is that 'blown electrics' refers to nothing more than a tripped circuit breaker or blown fuse back at the consumer unit/fuse box, and if so you'll have paid handsomely for a sparks to go and reset it! And that is quite likely to have been caused by the tenant placing too much load on the circuit, as PP describes. But depending on the age and nature of your current wiring, even that may not be the tenant's fault - 30 or 40 years ago the power requirements and number of appliances in use in an average house were a fraction of what they are now.

Anyway, let us know what the spark's report says...!

[Stuart Urban]

BS1363 states that all outlets shall be labelled with their maximum rating in amps. In theory this could be anything but in practice a double socket outlet will usually be rated at 20 amps but could also be rated at 13 amps. The markings will only be visible if you remove the socket outlet from the wall and have a look (using the correct isolation procedure of course).

You can in theory, therefore, overload a socket outlet by plugging in two appliances that take a 13 amp load but in practice this would be unlikely because the loads appliances take varies and any overload would be of short duration. The only problem that I could envisage is if someone plugged in two 3kW fires into the same double socket outlet this would definately overload the socket.

However scorching marks on socket outlets and plugs is usually a sign of a loose connection in either the plug or the socket outlet.