SHOWER TRIPS RCD ITS NOT CONNECTED TO

[vitoboy]

Hi all

OK..did a cu change yesterday .. old wylex with an external rcd for a new amd3 dual rcd cu.

This morning the customer rings to say the shower has tripped the rcd.
Turn up on site..and the rcd that has tripped is not the one that the shower circuit is on.!
So i check for crossed over neutrals .. none.
i check with 500v IR test for connections between circuits between each rcd..none.

So.. the rcd only trips if the shower is running .. so i remove 1 element to check its not breaking down...all ok.

swap the elements ..all ok..

But any time both elements work together the rcd trips.

Put a clamp meter on the shower earth .. leakage just 8mA.

Ok ..im a bit stumped now...of course some interaction is going on between the 2 rcd's circuits .. but i cant measure any connection between them.

The install is in an old farm house 4 other dwellings around it all with TT systems including the 1 im working on.

Local supply transformer is in the field right next to the job .

All and any idea's please .

Many thanks in advance.

Vito

 

[Strima]

Loose supply neutral?

 

[Octopus]

accumulated leakage?

 

[Pete999]

Hi all

OK..did a cu change yesterday .. old wylex with an external rcd for a new amd3 dual rcd cu.

This morning the customer rings to say the shower has tripped the rcd.
Turn up on site..and the rcd that has tripped is not the one that the shower circuit is on.!
So i check for crossed over neutrals .. none.
i check with 500v IR test for connections between circuits between each rcd..none.

So.. the rcd only trips if the shower is running .. so i remove 1 element to check its not breaking down...all ok.

swap the elements ..all ok..

But any time both elements work together the rcd trips.

Put a clamp meter on the shower earth .. leakage just 8mA.

Ok ..im a bit stumped now...of course some interaction is going on between the 2 rcd's circuits .. but i cant measure any connection between them.

The install is in an old farm house 4 other dwellings around it all with TT systems including the 1 im working on.

Local supply transformer is in the field right next to the job .

All and any idea's please .

Many thanks in advance.

Vito

2nd Paragraph last two lines, what exactly do you mean by that statement? Agree with Strima could be loose N connection.

 

[marconi]

Are the white appliances (dishwasher, tumble dryer, washing machine, microwave) or electric hob (is it an induction hob?) - supplied by the RCD which trips?

Could you measure the L-E, N-E and L-N voltages at the CU main switch with the shower off and then on (all mcbs apart from shower one off) and let us know them? Shower on full flow and high heat so elements remain on.

 

[Midwest]

Global IR test result? And 8mA for just the shower.

 

[Midwest]

Another possibility, curtsey of @Richard Burns

 

[MDJ]

accumulated leakage?

this is also my opinion.

 

[vitoboy]

Neutrals in the cu .. all of them...are good.

Accumulated leakage ... wrong rcd for this.!

Cooker and kitchen ring circuit with all appliances is on the rcd that's tripping .. but that's not the one with the shower on it.
No induction hob..

Global IR test .. well the lowest IR for any of the circuit's is 60 meg ohms .. ..but the shower circuit is 999meg ohms.

Midwest... Yeh .. I've had this before ... but so far none of the circuit's on the tripping rcd side seems to have a significant neutral earth fault.

But so far I think this will be my next point of investigation. ..if only because I can't think of another.

Marcoi .. I could .. but what are you getting at with this..?

Thanks again for the input guys

Vito

 

[Yozza19]

Had exactly the same once turned out tncs system loose n in metre witch had recently been changed dam metre monkeys witch in turn under high load shower ect the high resistance made earth lower potential than n return try clamp metre on gas and water while shower is on or voltage indicator

 

[Lucien Nunes]

This is a classic symptom of an N-E fault on one of the circuits on the RCD that trips. The shower trips it because it is the heaviest load on the installation, that creates the greatest drop in the neutral, driving the most current through the fault. But the fault could be on any appliance plugged into the circuits on the tripping RCD, not necessarily on the circuit itself.

What I would do is get into a situation where the RCD trips, then immediately isolate the supply and check with an ohmmeter the global resistance N-E with everything still plugged in and switched on. If you get any kind of a low reading, start tracing before anything changes.

 

[Richard Burns]

Marcoi .. I could .. but what are you getting at with this..?

Vito

Measuring the voltage off load and on load would highlight a high resistance connection in the supply. You would ideally have no voltage drop, in practice the voltage may drop a couple of volts with a heavy load but if there is an unexpected resistance in the supply say from a contaminated loose connection then the voltage drop could be significant.

 

[marconi]

Appliance and Washing Machine Filters - EMI Filters - https://www.astrodynetdi.com/emi-filters/appliance-and-washing-machine

I concur it could be an undiscovered N-E fault. If the fault is not so simple, albeit may be difficult to locate, I was thinking about what happens when the shower turns on(off) and interactions with the EMI filters of white goods and induction hobs. The voltage measurements where to find out what Richard Burns said and also to see if the changes in potential of the mains L and N with respect to the local earth electrode where similar or different in sign and magnitude to gauge the ratio of volt-drop along the L path and the N path. And then how the EMI filters might respond.

Take a gander at the reference and study the electrical schematics of a few of the EMI filters. Then consider these filters connected in an installation with TT earthing and ponder changes in potentials of and currents in L and in N - for the RCD which trips - as a result of mains voltage transients and dips caused by the shower being turned on(or off) and the earth leakage currents (standing and transient) through the earth electrode. What sets the potential of the earth electrode with respect to the transformer earth electrode? What effect will a change in potential of the local earth electrode have?

Something along these lines is what went through my mind when I posted earlier. It'd be useful to know the earth electrode resistance.