Socket Query

[CellophaneFlower]

I have a double socket in a kitchen cupboard. It has dishwasher and washing machine plugged into it. Recently 1 socket has failed so I need to replace.

2 things. When it failed it didn't trip the RCD. Is this normal? Also is there any benefit in replacing it with an RCD socket? Happy to pay the extra for added safety, but will just replace with a normal one if not!

Many thanks for any advice!

How did the socket fail? RCD only looks for (trying to explain in simple terms - it's not quite like this!) a difference in the electricity going into the appliance, or the circuit in the house, and the amount of electricity coming back to the fusebox.

If more is going out from the fusebox (or socket if that's where the RCD is) than is coming back then it trips as it assumes some of the electricity is going astray. Through a fault somewhere (or in worst case, through a person!).

So only certain types of failures will cause an RCD to trip. An appliance can sit burning through 13A of current and catch fire easily (think how hot an electric fire can get) without tripping anything, as that's seen as normal to the protective devices (the reason just sticking a 13A fuse in everything is a really bad idea - most things don't need that).

If you are worried the RCD isn't working, do you regulalry test it? It'll have a test button on it.

If you don't have a test button then it's not actually an RCD - maybe it's a MCB - miniture circuit breaker. This is basically a clever fuse, and trips when too much electricity is flowing. In a fuse box, on sockets it'll often be 32A. That's more than enough for serious issues, so they don't always trip!

Test the RCD, and it it trips it's probably fine. If you are really worried, get an electrician to test it properly. Adding an RCD socket isn't always wise if you have one at the fusebox as well, as having two on the same circuit can cause issues (confusion as to which will trip first etc). It also won't help unless rated as more sensitive than the main one - talk to an electrician.

Hope that helps a bit - I've probably not explained it very clearly!

When a socket outlet fails it won't necessarily trip your 'breaker' as it may be a simple breakdown of the socket itself, not a 'fault' as such.

I would just replace like for like.

ps. Sparkie for more years than I care to remember

Thanks both. The RCD definitely works. My partner has so far drilled through a cable in a wall and cut through the power cable when trimming a hedge and it tripped both those times Just wanted to check it shouldn't have with a failed socket.

The socket has possibly burnt out inside/worn out. It just stopped working and the switch doesn't click properly. So what fuse would be adequate for a washing machine and dishwasher? I know nothing about these things and now panicking I have 13A fuses everywhere and I'm going to burn 🙈

Hops onto thread as would be interested in knowing what sort of socket provision is best for a washer & dryer (similar to washer & dishwasher?)

Two separate sockets, not a double.

@PigletJohn so I should replace the double that was originally there with 2 singles? I assume that will be safer then? Thanks!

Also, as it might not be easy to do this, is it fine to change for a double for the time being, but only use 1 appliance at a time?

Yes but I bet you forget and it will overheat.

I promise I won't! I'm so paranoid about electricity... I'd turn my fridge and freezer off at night if it was possible! It's just it's in a kitchen cupboard and I'm not sure how accessible it would be to add an extra socket

Both a washing machine and dishwasher have decent heating elements, so will need a 13A fuse.

In theory two seperate is better than a double, but they'll probably both be on the same ring final circuit (or a radial), so limited in how much that helps. What does help is not using cheap sockets.

Decent quality decent brand double would out perform and out last 2 cheap singles. Decent double socket - maybe a fiver. Cheap one 1.50. It's not like the decent ones are expensive, avoid the cheap stuff!

The failure you describe is exactly the sort of failure that isn't really hard to detect automatically. RCD won't trip as the electricity appeared to the unit to be working fine (it was heating the socket instead of the water in the machine, but it can't tell that!).

The breaker didn't trip as it was still only pulling way under the max. A socket can get very hot without getting anywhere near a trip current.

More recently the Arc fault detection units that are around can help, but they are eye wateringly expensive at the moment... and time will tell what sort of failures they bring - effectively a computer "looking" for the signature of something sparking. Might stop a dodgy socket, but still a reasonable chance it wont :-(

See www.cef.co.uk/catalogue/categories/switchgear-distribution-arc-fault-detection-afdds for why they aren't popular yet - count your breakers in the fuseboard, and then multiply up by those prices. Ouch.

Each plug is rated at 13A

When both are running at full power heating cycle, the load may be about 26Amp

Single sockets are rated at 13A

Double sockets are not rated at 26A

Not a lot of people know that.

Thank you @jamie2001 ! Yeah, would only buy a decent socket, not that they're expensive anyway, as you say, hence why I asked if paying extra for the RCD socket was worth it. I was scrolling through Screwfix looking for a super duper socket and noticed those!

I'll just replace with a decent 1 and be mindful not to overload it constantly. We're hoping to extend in the near future so will definitely get all the wiring sorted then, (60s house) rewire/partial rewire or whatever's necessary. Will put my mind at rest anyway as can never be sure what's been bodged when you're a bit clueless like us!

Thanks again!

@PigletJohn

Each plug is rated at 13A

When both are running at full power heating cycle, the load may be about 26Amp

Single sockets are rated at 13A

Double sockets are not rated at 26A

Not a lot of people know that.

Indeed. IIRC, it's rated for 14A on one, and 6 on the other. Again, that's minimum spec - some will be better than that (I believe MK had a range that was spec'd at higher - although probably not 26A).

Diversity rules though - a decent socket will handle it far better for the few mins it's actually pulling top whack from both (unlikely to be full 13A on either). If this was a commercial laundry I'd be more worried. In a domestic kitchen use a decent brand, and don't worry about it too much. (but go for two singles if you get a rewire :-))

Toaster is more likely to catch fire IMO. How often do you clear crumbs out of that? :-)

Despite the fact that both applicances have 13A plugs, they will be drawing less power than this - for most of the operational time, neither a WM or a DW has the heating element running on high. If there is a moment when they do, the socket can handle it perfectly well.

Buy a good quality double like MK and replace like with like.

No reason for a failing socket to trip an RCD - depends on WHY it failed? Switch broken?

If it has a tumble dryer and a washing machine, it will run quite hot, and this will embrittle the plastic and shorten its life. It may well be the moving parts in the switch that failed. An ordinary tumble drier may well run at 3kW continuously for an hour or more. Few domestic appliances do that. The washing machine will do it for shorter periods that may coincide.

These two appliances on one double socket often lead to overheating of the socket.

Double sockets are required to comply with BS1363 part 2: 1995 and are rated at 13A.

It is often said that some brands are tested to 20A total but I haven't found this in a manufacturer's specification.

It's true I'm not an avid toaster de-crumber.... but I'm extremely thorough with my tumble dryer filter!

@notrub I'm not sure what happened to it. It stopped working mid washing machine cycle. The switch now won't click, but seems more stuck in 'on' position. It's probably at least 15 years old as I think that's when kitchen was installed (before I lived here). Probably bog standard socket too. Perhaps it had just had enough?

And thank you for all the very helpful replies!

@PigletJohn

If it has a tumble dryer and a washing machine, it will run quite hot, and this will embrittle the plastic and shorten its life. It may well be the moving parts in the switch that failed. An ordinary tumble drier may well run at 3kW continuously for an hour or more. Few domestic appliances do that. The washing machine will do it for shorter periods that may coincide.

These two appliances on one double socket often lead to overheating of the socket.

Double sockets are required to comply with BS1363 part 2: 1995 and are rated at 13A.

It is often said that some brands are tested to 20A total but I haven't found this in a manufacturer's specification.

Sorry but you're talking rubbish.

A double socket is rated to 20A.

It's EXTREMELY unlikely that BOTH appliances will draw this much power at the same time and if for a few moments both ran to their MAXIMUM load, the socket would have no issues with that.

I should add that MK double sockets are rated to 26A

I always use MK - for a few pennies more you get a MUCH better product.

@PigletJohn

If it has a tumble dryer and a washing machine, it will run quite hot, and this will embrittle the plastic and shorten its life. It may well be the moving parts in the switch that failed. An ordinary tumble drier may well run at 3kW continuously for an hour or more. Few domestic appliances do that. The washing machine will do it for shorter periods that may coincide.

These two appliances on one double socket often lead to overheating of the socket.

Double sockets are required to comply with BS1363 part 2: 1995 and are rated at 13A.

It is often said that some brands are tested to 20A total but I haven't found this in a manufacturer's specification.

A decent brand should cope fine with that (a cheap brand if to standard should also, but...). Even if both appliances are 13A max, it's very very unlikely they'll both pull that at the same time for long enough to ever cause anything but minor warming which will be fine.

MK say (from their catalogue):

All MK socket-outlets are manufactured to comply with BS1363 part 2: 1995 and are rated at 13A per unit. Double socket-outlets have been manufactured and tested to exceed this rating by margin that allows electrical safety and reduces the risk of heat and mechanical damage to components due to overloading. It should be noted that BS1363 part 2: 1995 does not allow double sockets to operate at twice the permissible maximum loading and it should be remembered that double socket-outlets are not manufactured to be able to withstand a 26A load for sustained periods of time.

Research by ourselves and third party organisations has shown that all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period. Increasing the load slightly will begin to cause heat and mechanical stresses on the components in a relatively short period. Testing showed that a load of 22.3A was sufficient to cause heat stress that would cause a browning of the faceplates and sufficient heat to cause insulation damage to cable cores. A load of 24A for 43 hours was sufficient to cause significant heat damage to the material in which the socket-outlet was situated and within 75 hours sufficient to cause significant damage that would lead to the very real potential of fire.

the relevant bit of the standard says:

"BS1363-2:1995 requires for double socket outlets that both socket outlets have loads applied via test plugs, 1 test plug having a load of 14 amps whilst the other has a load of 6 amps, making a total load of 20 amps on the cable supplying the double socket outlet. The double socket outlet is then subjected to this loading for a minimum continuous period of 4 hours or longer until stability is reached with a maximum duration of 8 hours (stability being taken as less than 1 degC rise within 1 h). The test is passed if neither the terminals / terminations, nor the accessible external surface, increase in temperature by more than 52 degC."

In summary, fit one of the more expensive double sockets and don't worry too much about it.

@jamie2001 Thanks