Problem with shower tripping rcd

[benmatthews]

Hi Peeps. I'm having an issue wiring in a new shower in my house that I'm having trouble working out. I initially wired in a 8.5kw Tritn shwer thats a few years old but had never been used and kept in the box. I ran the circuit in 10mm T & E (circuit length 15 metres). I installed a 45A pull switch/Isolator between the consumer unit and the shower. The circuit is on a 40A MBC which is then protected by a 30mA RCD. Cable size and MBC size are exactly what it says in the instruction manual for an 8.5kW model.\
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I connected everything up and carried out the commisioning as per the manual where the shower is turned on the cold water setting where only the pump is engaged and not the heating element, and the water is pumped through the shower to eleiminate any air in the system etc. \
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The shower runs absolutely fine on the cold setting, but as soon as I turned the power setting to heat the water it's trips out the RCD. I checked all the connections which were fine. I initally thought perhaps the loading was tripping out the RCD when heating. However, I discovered that I could still trip the RCD when
\f1\b not
\f0\b0 under load by having the MCB turned off, the pull switch in the on position, the shower button off, and as soon as I turned the dial from cold to hot setting the RCD would trip? I assumed then that perhaps there must have been some sort of earth fault within the heating element of the shower so went out and bought a new triton 8.5kW shower.\
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I have plumbed/wired the new shower in, commisioned it on the cold setting which runs fine, and low and behold once again, as soon as I turn the dial to engage the heating element it trips out. With the new shower, it does not trip out the RCD when the MCB is isolated as with the older version, it only trips out when under load.\
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I'm at a bit of a loose end now as what to look for. I have checked the cable to see if there are any nicks anywhere and can't see anything obvious. There is about 60cm of cable hidden behind some plywood that has been tiled over I can't check without pulling it all down but I was careful screwing in the ply not to put any screws where the cable run was.\
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I would have thought that if I'd nicked the cable with a screw it would trip when on the cold setting but it doesn't\
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I don't have a megger so cannot IR test the cables (I would like to). Does anyone have any other ideas as to what the issue could be, otherwise I'm going to have to get in a spark with testing equiptment which I'd like to avoid if possible.\
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Thanks in advance\
\
Ben\

 

[telectrix]

my guess is that you've made a connection error. call in a spark. you should not have done this job yourself. without test equipment and the knowledge to use it, how are you going to be sure the work is safe, and how the hell do you ecpect to complete an installation certificate,

 

[Spoon]

As above, call in a spark.
I presume you have notified your Local Authority Building Control about the new shower circuit you have just installed...

 

[BlueToBits]

It is possible that you have a high impedance neutral to earth fault somewhere that only passes enough current to trip the RCD when the neutral voltage rises above earth. Such a fault is most likely to be noticed with a combination of high load (the shower heater) and a high phase to neutral impedance at the origin (distant sub-station) with a high impedance TNS, TT, faulty TNCS or absent earth system. This is not an uncommon fault, but finding such faults will almost certainly require professional test gear and the knowledge and experience to interpret the readings to diagnose and locate them. They could be anywhere in the house and could have been around a long time.

So, even though the shower may appear to be installed 'in accordance with the instructions', because of a fault somewhere else in the house there could still be reason to doubt it's safe, or at best it's functional operation. Indeed, the shower itself could introduce a detrimental influence somewhere else in the house. This is one of the main reasons why proper testing is important, and why the instructions say that it should be installed by a qualified electrician.

 

[Pete999]

As post 3

 

[camerabloke]

As post 5

 

[Octopus]

why did you post this twice??

 

[camerabloke]

Perhaps he's got an ensuite

 

[SirKit Breaker]

I am not trying to be clever, but it needs a R1+R2 test to confirm the integrity of the CPC and polarity, then an insulation resistance test, BEFORE it was powered up.

I appreciate that you are trying to save a few quid, but believe me, it will cost you a hell of a lot more when you have to go to court if as a result of your actions someone gets killed or injured by the work you have done, and that is before we even get onto the fact that you are in breach of building regulations, which is illegal. Your insurance company wont find it funny either if you have a fire.

The first ever prosecution under Part P of the building regs cost a qualified electrician £16,000 and 2 years in prison for installing a shower in Newcastle in which a woman got seriously injured. It was incorrectly installed and not notified.

Ask yourself, does an hour or two of a sparks time seem expensive now?

I can't believe that any one in their right mind wants to install a high powered electrical appliance (or any other for that matter) fill it with water, stand under it , and it hasn't even been tested properly, and hope it works OK :rifle:

Cheers.........Howard

 

[GMES]

i am not trying to be clever, but it needs a r1+r2 test to confirm the integrity of the cpc and polarity, then an insulation resistance test, before it was powered up.

I appreciate that you are trying to save a few quid, but believe me, it will cost you a hell of a lot more when you have to go to court if as a result of your actions someone gets killed or injured by the work you have done, and that is before we even get onto the fact that you are in breach of building regulations, which is illegal. Your insurance company wont find it funny either if you have a fire.

The first ever prosecution under part p of the building regs cost a qualified electrician £16,000 and 2 years in prison for installing a shower in newcastle in which a woman got seriously injured. It was incorrectly installed and not notified.

Ask yourself, does an hour or two of a sparks time seem expensive now?

I can't believe that any one in their right mind wants to install a high powered electrical appliance (or any other for that matter) fill it with water, stand under it , and it hasn't even been tested properly, and hope it works ok :rifle:

Cheers.........howard

well said howard

 

[telectrix]

sounds like a job for......................... SUPERKATE.

 

[Octopus]

sounds like a job for......................... SUPERKATE.

But where is she???????????

 

[Plonker 3]

I am not trying to be clever, but it needs a R1+R2 test to confirm the integrity of the CPC and polarity, then an insulation resistance test, BEFORE it was powered up.

I appreciate that you are trying to save a few quid, but believe me, it will cost you a hell of a lot more when you have to go to court if as a result of your actions someone gets killed or injured by the work you have done, and that is before we even get onto the fact that you are in breach of building regulations, which is illegal. Your insurance company wont find it funny either if you have a fire.

The first ever prosecution under Part P of the building regs cost a qualified electrician £16,000 and 2 years in prison for installing a shower in Newcastle in which a woman got seriously injured. It was incorrectly installed and not notified.

Ask yourself, does an hour or two of a sparks time seem expensive now?

I can't believe that any one in their right mind wants to install a high powered electrical appliance (or any other for that matter) fill it with water, stand under it , and it hasn't even been tested properly, and hope it works OK :rifle:

Cheers.........Howard

Do you have a link to that prosecution? Or anyone else for that matter.

 

[Octopus]

Electrician Fined for Part P breach | Options Skills Ltd

 

[SirKit Breaker]

Cheers Murdoch, i looked high and low for that.