Replaced shower, and isolation switch. Rcd trips

[iforgot]

Ok i have replaced a 8.5kw shower with another 8.5kw shower. its running on 10mm cable, on a 40amp mcb, the isolation switch is 45amps.


When the shower was replaced, the rcd on the cu kept tripping the instant it was turned on. So after looking about, the isolation switch was found to be a bit dodgy and replaced.

Heres where the fun lies, the old isolation switch had two connection points for earth from both supply and load. The new one has 1 point, that both have to be pushed into.

With both earths connected to this single point, the rcd instantly trips the second the shower powers up. With either one or the other connected it doesnt trip.

Its current state is that the mcb is off, and the the supply earth is connected to the point, the isolation switch is off with the pull cord for the switch removed to stop anyone using it.

So what now ideas? suggestions ? or is it now time to call in a sparky?

 

[Adam_151]

It sounds like your new shower is faulty

Either that, or the cable between the shower and the local isolator has developed an insulation fault (which isn't too likely, but is possible if you were careless with the fixings for the new shower unit!)

DO NOT USE THE SHOWER WITH THE EARTH OPEN CIRCUIT!

 

[iforgot]

No its not going to get used!! The mcb is set to off, the isolation switch is off, with the cable removed so people cant turn it on, and the switch on the front of the shower is disconnected.

No ones going to be using the shower till its sorted out!

Have thought about replacing the cable from isolation switch to the shower, as access to its not too bad in the loft, just going to be a pain in the bum to feed it down the cavity to the shower and get it out!

 

[333rocky333]

check within the shower unit , that the wires are on the right terms
Neutral and earth crossed over could cause it.

 

[iforgot]

the cable in place has stranded earth, so its pretty much impossible to get neutral and earth confused. (t&e)

 

[333rocky333]

the cable in place has stranded earth, so its pretty much impossible to get neutral and earth confused. (t&e)

Apreciate that , meant more the terms they go in (if three)
Check the output sides that they are the same function as the in wires

With two terms and one post it is as you say hard to get wrong

 

[Softus]

When the shower was replaced, the rcd on the cu kept tripping the instant it was turned on. So after looking about, the isolation switch was found to be a bit dodgy and replaced.

What does "a bit dodgy" mean, exactly? Was the switch faulty or not?

With both earths connected to this single point, the rcd instantly trips the second the shower powers up. With either one or the other connected it doesnt trip.

Then you have a live-to-earth or neutral-to-earth fault, which is what the RCD is supposed to detect.

Its current state is that the mcb is off, and the the supply earth is connected to the point, the isolation switch is off with the pull cord for the switch removed to stop anyone using it.

It's unusual to be able to remove the pull cord. Is that really what you've done? Why have you left a suspect cable connected to a suspect appliance?

or is it now time to call in a sparky?

Yes, unless you're happy to carry out an insulation resistance test.

 

[iforgot]

What does "a bit dodgy" mean, exactly? Was the switch faulty or not?

Yes it was.

It's unusual to be able to remove the pull cord. Is that really what you've done? Why have you left a suspect cable connected to a suspect appliance?

Its been left connected for time. It was gone 11pm, with small people sleeping. Yes the cord is removed from the switch.

Yes, unless you're happy to carry out an insulation resistance test.

While i understand the principles of such testing, i lack equipment to test at a sufficient voltage.

Overnight have decided to replace the suspect cable with a new run.

Is there any reason why i should't simply run the cable through a dry bathroom to the shower from the isolation switch as a temp measure to see if its the shower at fault? (with the view that if the tripping continues must be the new shower, so replace that, if it stops must be the old run of cable, so replace that and see how good i am at feeding through the cavity!)

 

[ban-all-sheds]

Maybe I'm missing something, but if there was a fault in the cable, or it was miswired at the shower, wouldn't the RCD trip as soon as the isolator was turned on, whether the shower was on or not?

And tripping only on the shower itself going on would indicate the fault was in the shower?

 

[iforgot]

Sorry i didnt make myself clear, the rcd trips the second the isolator switch is turned on , which give me (an idiot) the idea that the cable as suggested is at fault.

 

[dannyboi2003]

Easiest way to test if its a cable fault without pulling the house apart is to disconnect the supply at the shower and make the ends safe with choc-blocks. Switch on the mcb, switch on the pull-cord isolator, if the RCD trips then you have a cable fault, if it doesn't then its the shower thats faulty.

 

[JohnD]

My interpretation is as follows (I have simplified the circumstances for emphasis)

Ok i have replaced a 8.5kw shower with another 8.5kw shower. .. When the shower was replaced, the rcd on the cu kept tripping the instant it was turned on....

So
1) You changed something
2) The RCD immediately tripped

Diagnosis:
You introduced a fault when you made your change.

Stop blaming the switch or the cable.

 

[iforgot]

So i didn't explicitly say the old shower was faulty, my mistake, i assumed the most people would realise someone swapping one item for an identical one, does so for a reason.

The old shower had started to trip the rcd intermittently (once or twice) and one of the heating elements had failed, (it gets a lot of use and is old) so time to replace it.

I didn't introduce a fault, i simply removed some others, and made an existing one worse.

After replacing it, intermittent rcd tripping became instant, once the isolator switch was activated. I happened to have a spare switch, so i swapped the switch to eliminate it as a problem.

So my logic says, new shower, new switch chances that they faulty is much less likely than then chance the existing cable is faulty. I assume that as i had to grapple with the cable to move it about a bit to fit the new shower (same model but moved the location of inputs ) , that any existing insulation problem (a live/neutral to-earth ) in the cable which was causing the old intermittent problem was made worse due to the movement of cable and now have a permanent something to-earth problem within the cable.

As it turns out i don't have sufficient cable to test the shower from the isolation switch to hand, so i will grab some later on, got to go past a few retailers on the way to work.

dannyboi2003's suggestion is prob better than my idea of running a cable across the bathroom floor as a temp see if it trips the rcd test!

 

[JohnD]

...So my logic says, new shower, new switch chances that they faulty is much less likely than then chance the existing cable is faulty. ...

but new connection has a high chance of error and should be the first thing to check when you get immediate RCD tripping after connecting something.

cables rarely go faulty unless someone has hammered a nail through them. Or they have melted from overload.

 

[iforgot]

Booked a local electrition to come Im past the point where i can do stuff now!