Shower tripping RCD

This morning, roughly ten minutes after turning off power shower, the RCD blew and after narrowing it down, found it to be the shower itself. Tried fuse, checked wiring in shower unit and fused switch box and everything seems in order. Inside the shower unit is bone dry. The circuit trips whenever we try and turn it on at the fused switch box. The shower itself has been working perfectly for 6-7 years. Could it be inside the shower unit itself or is it more likely to be wiring???

Any help greatly appreciated..thanks!

Tracing RCD faults is not easy. The main tool is an insulation tester there is also special clamp-on ammeters able to measure the leakage.

The problem is it could well be something completely different to shower causing the problem.

Using RCBO's it's not so much a problem but with an RCD feeding many MCB's the MCB's are single pole so even when turned off a neutral earth fault can still exist.

Every wire has some resistance and as we increase draw current along the wire the voltage compared with a wire where there is no current draw will increase. An earth to neutral fault is rarely a full short circuit but is also a resistance. When no power is drawn the current between neutral and earth is less than 15 - 30ma needed to trip the RCD but as we draw current then the leakage current increases to a point where over 15 - 30ma needed to trip the RCD is flowing.

The shower draws about the maximum of all domestic appliances so with a earth neutral fault it will seem as if the shower is causing the trip. Where in fact it could be anything else on the same RCD even if switched off as most switches don't switch the neutral.

So for example a fault on a florescent lamp could cause the RCD to trip even when not switched on as you try to use the shower.

You can try first unplugging everything, as that does break the neutral, and items with FCU normally those switches are also twin pole. But if the fault is in something like a florescent lamp then you have no real way to find it without meters.

Thanks for your reply. I've unplugged everything else on that circuit and its definitely just the shower. I think the only answer is to get someone in who knows what they're doing.

Thanks again.

After more investigation, it is definitely the shower at fault. Any ideas what it could be? Another forum suggested motor/pump assembly. I really want as many opinions as possible before forking out on another shower unit!

Thanks again.

What were your further investigations? As Eric Mark has explained RCD tripping faults can be misleading as to what the actual faulty component is. Before buying a new shower, I would definitly get a sparky to double check that. It shouldn't take more than 30 minutes to confirm the shower as the problem! That could save you buying a new shower, having it installed, and then still having a problem!!

To investigate this fault requires specialist test equiptment mainly an insulation resistance tester also know in the trade as a "Megger" the electrician will check the insulation resistance on any suspect circuits to try and track down the fault.
I would also test to RCD unit in isolation with a ramp test to see if it has become oversensitive.
One other posable fault location would be inside the shower pullcord switch if you have one normally the terminations become loose and burn up causing this type of fault.

Thanks for your replies... Perhaps I was being a bit premature in my conclusions then! All I did was disconnect the shower from the ring main (inside the shower unit itself) and turn on the fused switch box and nothing blew. I therefore assumed that the shower was causing the tripping. (There is no pull cord switch, just a switched fuse box on the wall in a cupboard behind the shower).

(The Shower Doc forum suggested it was a short/fault in the motor/pump assembly).

fergus666 said:

Thanks for your replies... Perhaps I was being a bit premature in my conclusions then! All I did was disconnect the shower from the ring main (inside the shower unit itself) and turn on the fused switch box and nothing blew.

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It is unclear from your comments whether the shower is an 'electric shower' or a 'pump shower'. If it is the former then it should not be on the ring main but on its own circuit.

Its a 'pump' shower and its on a spur of the ring main.

Best to get somebody in to check same , but it sounds like the Problem will be at the Pump or maybe on the Spur (FCU if Fitted)

Lucky

I am a little confused by your contradiction:

First said:

This morning, roughly ten minutes after turning off power shower, the RCD blew

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Then said:

The circuit trips whenever we try and turn it on

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The first time it happened was shortly after turning the shower off on the switch on the actual shower unit.

I isolated the problem (or so I thought) by turning it off at the FCU. It trips when turning the FCU back on again while shower is connected to it. (No problem when disconnecting the shower completely).

Sorry for confusion.

My shower tripped out and after investigation i found out that the black wire in the pull cord had burnt the outer sleeve can anybody help me and explain why it has burnt out, if it is overloading have i got the wrong cable supplying the power

fytchea1 said:

My shower tripped out and after investigation i found out that the black wire in the pull cord had burnt the outer sleeve can anybody help me and explain why it has burnt out, if it is overloading have i got the wrong cable supplying the power

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Assuming it is the correct cable probably a loose connection.