RCD buzzes when immersion heater on - can I replace RCD?

[r_c]

I have just replaced the plug for our immersion heater. The plastic on one of the pins was melting and the smell alerted us to the problem. The RCD never tripped. I replaced the entire cable and plug as it didn't look like a great job had been done. When I opened up the old plug I noticed that there was a lot of exposed wires and a single hair of wire from the blue was touching the green & yellow! God knows how long this had been like that

I have now noticed that when I turn on the immersion heater I can hear a buzzing noise downstairs coming from the RCD consumer unit.

Can I just buy a new RCD and replace it or must an electrician do that?

 

[flameport]

You can replace it provided you are capable of doing so properly and safely.

However the fact it makes a noise does not mean it is faulty. It could mean the immersion heater has a fault which is causing enough current imbalance to hold the RCD near it's tripping point. Or the noise could be from an MCB in the consumer unit.

 

[r_c]

a fault which is causing enough current imbalance

Is there something I can buy from B&Q to test this?

 

[flameport]

No, but even if they did that type of test equipment is hundreds of pounds and therefore totally uneconomic to buy for a single use.

 

[winston1]

An immersion heater should not really be on a plug and socket.

 

[EFLImpudence]

Agreed - for the very reason the OP has found.

 

[ericmark]

An immersion heater should not really be on a plug and socket.

Depends what plug and socket. It was a standard way to wire an immersion heater in 1950's using a 15A plug and socket, this made it so a plumber could change the immersion heater without needing an electrician when in an age where demarcation lines were not crossed.

It was very rare to have problems with the 15A socket and plug, in the main due to there being no fuse in the 15A plug, the fuse was in the fuse box, when the 13A plug and socket came out the pins were solid brass and better able to get rid of the heat from the fuse, but even then it was common to find plugs where the full 13A is drawn for an extended time that the plug, overheated and this could also cause the socket to overheat and to lose the pressure required to grip the plug.

So yes one would not normally use a 13A plug on an immersion heater, and if used the plug would need to be in free air, where in the main the immersion heater is in a cupboard which makes it even worse, so there is a high likelihood that a 13A plug and socket in a cupboard would overheat. Using a fused connection unit (FCU) there is more mass in the device to dissipate the heat, so normally a FCU would be used.

So yes unwise to use a 13A plug and socket, but nothing to say you should not use it. And no reason why you should not use a 15A plug and socket.

As to noise I would say more likely to be what is being powered causing the problem than the RCD or MCB. Although it could be normal for that make, I have heard noisy MCB's in the past, but today seems rare.

 

[Echo the husky]

I have just replaced the plug for our immersion heater. The plastic on one of the pins was melting and the smell alerted us to the problem.

Replace the socket as well as this will also be damaged internally.

 

[deadshort]

IF you are replacing the socket you would be as well to replace it with a 20a DP switch. But first you need to confirm that the immersion is on it's own circuit at the CU and the mcb is 20a, or 16a.

Regards,

DS

 

[r_c]

Once again, thank you all for your advice. It sounds like I have some work to do before I start solving the problem of the buzzing. Please correct my understanding ...

• Check the MCB is 20A.
• Replace the 13A cable with a 20A cable.
• Replace the 13A plug & socket with a FCU.

If buzzing continues, then next step is to look at the immersion heater. It sounds like a pain to drain the tank, so I might try first just replacing the thermostat.

 

[winston1]

MCB need only be 16A.
No such thing as 13A cable or 16A cable. Immersion heaters are usually waited in 2.5 T&E though 1.5 would theoretically be OK.
No need for FCU with a 16A MCB, use a 20A double pole switch.