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Been asked to find out why a new shower is tripping a new cu rcd,
new shower 9.8kw mira
supplied with 10mm T&E
40amp mcb protected by 63a RCD
Its a new cable thats been run in and I have no equipment to test the continuity etc I went right back to basics ,missed out the 45amp DP switch and it still tripped,then wired it straight into the DP isolator switch of the cu and the shower started straight away I should also say that this cu is fed from the main house but the shower did not trip the main cu.
The mira instructions say to fit a 30a rcd

Anyone any ideas ?

Ta
 
Thanks for the reply as I said I have no proper testing equipment I have a fluke ,continuity was fine with this,and yes you are right it is 30ma ....really should proof read posts I'll check the neutral is in the correct bar next time I'm out..
 
ok got that, would this occur even if the cu is split load ?
and if there is an N-E fault elsewhere why is this not tripping the rcd

things were much easier in the 70's sparky wise....a meggar for testing and a wire coat hanger and a piece of string with a plug chain for fishing cables...
 
Is it the MCB, RCD or both knocking out ?. Just googled Mira 9.8 kW install manuals & they specify a 45a MCB.
 
A 41A load on a 40A ocpd is not a good start!
Without test equipment you are going to waste a lot of time and effort.

If I've read the op correctly, which I hope I haven't, you have bypassed the protective devices by connecting the circuit directly to the main switch of the CU?
 
Think you've read it right Dave, if not we both need to learn to read. That's how I read it as well.

I don't really understand going to look for a fault without test equipment either, maybe I'm getting too old for this.
 
Really should take more notice but I was more concerned theat the rcd was tripping and didnt (or cant )remember if both had tripped I have a feeling the the mcb is 40a as it was one of those pre-populated CU's that he bought
and Ive just done a quick calc for a 9.8kw appliance and its 40.833333333a...
 
In reply to the above ,I'm doing a pal a favour in trying to find the fault, the original installer is not returning his calls
I think some of the problems have arisen due to my pal buying the materials himself to save money.
and ..FYI I don't have any test equipment as I've been effectively off the tools since 1986..save for the odd light fitting and extra socket
 
yes I agree but we didnt have all the all singing and dancing equipment in the late seventies /early eighties it was a case of disconnecting everything and starting from the cu ....
we only had one megger between two of us when on the tools, I completed a pyro installation and the only way I could bell out the cores was to connect to to the supply and hope that the cores had sealed properly and the pot was on straight...
 
You don't need anything all seeing & dancing just an Insulation tester & maybe a Clamp meter to check Earth leakage.
If the installer left it like that though, you have to wonder what else you might find.
 
Been asked to find out why a new shower is tripping a new cu rcd,
new shower 9.8kw mira
supplied with 10mm T&E
40amp mcb protected by 63a RCD
Its a new cable thats been run in and I have no equipment to test the continuity etc I went right back to basics ,missed out the 45amp DP switch and it still tripped,then wired it straight into the DP isolator switch of the cu and the shower started straight away I should also say that this cu is fed from the main house but the shower did not trip the main cu.
The mira instructions say to fit a 30a rcd

Anyone any ideas ?

Ta
Well wiring it into the CU M/S and it wont trip, cus there is nothing to trip
 
I dont have a megger, I have a fluke, Installation practices of 40 odd years ago are still practiced today,its the way they are installed ie bad workmanship that cause the problems,wiring systems have not changed since I was on the tools but certain regs have,earthing,testing,circuit discrimination I could go on but ultimately most of it is down to bad practice.
I would have had my a**e booted from my journeyman for some of the installations I have seen
 

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