electric shower trips rcd

[joe79]

hi all,

just installed a new 8 way wylex rcd board for a friend turned on the circuits everything was fine, started to plug appliances in one by one and firstly when the fridge is plugged in it trips the 100a 30ma main rcd switch, i thought it was a faulty fridge, i left the fridge unplugged for 20 mins then when i plugged it back in the rcd stayed on, its tripped off twice since in the last 6 days always turning back on with the fridge unplugged, left out for a while then plugged back in. secondly when the mira sprint 8.5kw shower is turned on this also trips the rcd. i managed to get the shower running with power on but just on cold water setting as soon as power is turned up rcd trips!!! i told my mate he had a faulty fridge and shower (bit of bad luck) my mate decided to put up with the fridge but has gone straight out bought a brand new replacement mira sprint 8.5kw had it fitted an hour ago and he's just rang and told me the very same thing is happening!? at the min im feeling like quite a bad mate!! so has anyone got any ideas please i have tried ringing mira and wylex tech support but cant get thru. any help would be very appreiciated

 

[Adam_151]

What earthing arrangement is the supply?
And what values you get for insulation resistance?
RCD trip times in spec?

 

[ColJack]

nothing wrong with the appliances..
your friends choice of electrician is in doubt though..


did you part P?
did you fully test the installation before you changed the CU?
did you fully test after you installed the CU?
fitted a 17th edition compliant board with at least 2 rcd's or RCBO's?
find any borrowed neutrals?
put the neutrals back in the right place after testing?

 

[flameport]

As always, pictures of the new CU and surrounding area will be useful.

 

[joe79]

the property is a one bed bungalow with ring, lights, shower in question and a combi fuse spur so only fitted a 8 way mains with one rcd (didnt think it was necessary to split circuits over 2 rcds) tested before and everything was fine, tested after and everything was fine. obviously never did a test on the appliances (shower and fridge) the earthing arrangements are tncs

 

[Spark123]

It is frowned upon to have a single point of failure i.e. a single RCD covering the whole of the installation (see regulation 314).
Ideally you should either split circuits between 2 RCDs using one of those dual RCD boards, or use a number of RCBOs or a mixture of these. This will mean a single fault will not cut the power to all circuits.
My guess is that there could be a fault between neutral and earth at the moment, the voltage caused at the consumer unit by a large load such as the shower causes enough potential difference to be aparrent between the neutral and earth to cause enough current to flow through the parallel path back to the service head causing the RCD to trip.
The fault could be anywhere - could be on an appliance.

 

[joe79]

It is frowned upon to have a single point of failure i.e. a single RCD covering the whole of the installation (see regulation 314).
Ideally you should either split circuits between 2 RCDs using one of those dual RCD boards, or use a number of RCBOs or a mixture of these. This will mean a single fault will not cut the power to all circuits.
My guess is that there could be a fault between neutral and earth at the moment, the voltage caused at the consumer unit by a large load such as the shower causes enough potential difference to be aparrent between the neutral and earth to cause enough current to flow through the parallel path back to the service head causing the RCD to trip.
The fault could be anywhere - could be on an appliance.

so would you recommend swapping the mcb's for rcbo's? would that eliminate any build up of several inbalances across a number of circiuts all loading onto the one rcd like it is now

 

[electronicsuk]

power to all circuits.
My guess is that there could be a fault between neutral and earth at the moment, the voltage caused at the consumer unit by a large load such as the shower causes enough potential difference to be aparrent between the neutral and earth to cause enough current to flow through the parallel path back to the service head causing the RCD to trip.

Of course, if the OP did test before and after as he maintains, he would (should) have found this.

 

[electronicsuk]

so would you recommend swapping the mcb's for rcbo's? would that eliminate any build up of several inbalances across a number of circiuts all loading onto the one rcd like it is now

How will that fix the fault if it is, as Spark123 suggested, a linked N-E somewhere in the wiring other than the service head?

 

[Spark123]

power to all circuits.
My guess is that there could be a fault between neutral and earth at the moment........

Of course, if the OP did test before and after as he maintains, he would (should) have found this.

Depends where the fault is - if it is on an appliance then it wouldn't have been picked up as all appliances are unplugged for test purposes.

 

[Spark123]

so would you recommend swapping the mcb's for rcbo's? would that eliminate any build up of several inbalances across a number of circiuts all loading onto the one rcd like it is now

Sort of - if you were to swop all circuits for RCBOs (and the main switch to a normal isolator) then a fault would only take out the one circuit with the fault on it.

Using a board with 2 RCDs in it will limit the amount of circuits lost under a fault on one circuit.
Have a read of this here: http://download.hager.com/hagergrou...rmation/ConsumerUnitGuideToThe17thEdition.pdf

 

[chrishaworth]

1. Single RCD eliminates neutral on the wrong bus - would trip immediately anyway.
2. All TT systems have a single RCD and the brbfb doesn't say much on that.
3. Multiple faults are more common than you would think. Showers are an obvious source of tripping, but fridges, particularly with auto defrost, can give E-N problems. Keep the fridge unplugged for a while and if it doesn't trip, bin the fridge.

Cheers
Chris