Low Earth Voltage in bathroom from bonded fittings

[Kris Dor]

I have a hot/cold feed power shower in bathroom, shower frame and a radiator near by.
I'm measuring the voltage difference between the three things and getting the following and wondered if anyone could help. Had two sparky's out who have not thrown any light on it so far.
Shower hose (metal) to radiator 0.2v
Radiator to Shower frame 2v

When I run the shower for 2-5 mins I get these readings
Shower hose (metal) to radiator 5v
Radiator to Shower frame 12v

This voltage then very slowly drops back down to earlier figures over the course of mins/hours rather than seconds (in 5-10 mins it would drop from 12v to 10v)

I have this: Bonding from rad to both inlet pipes of shower
I was advised to do this which is now done: Bonding from earth in shower unit to the pipework feeds and supplementary bonding from pipework to two upstairs light rings which was advice sparky got from NIC

The shower is hot/cold so just a pump from a spur on ring main protected with switched fused 3a and RCCB on ring main circuit

If I switch off the bathroom lights the first 0.2v reading prior to running shower might drop from 0.2v to 0.1v

Nothing on the CU has tripped but there is a tiny spark when sparky took off an Earth from the (rail?) in the CU while he was looking at it.

No single circuit seems to be the cause of the low voltage readings but if everything is off on the CU the reading is 0v.

Any help ideas would be appreciated .
Cheers
Kris

 

[Deleted member 26818]

Has anyone mentioned induced voltage?

 

[Kris Dor]

Hi spinlondon,
Cheers - no one has mentioned this.

Could the shower motor be faulty?

If the shower is completely disconnected physically apart from the bonding the radiator to shower frame is still 0.2 - 0.4v
I measured it without the shower running at about 2am and radiator to shower frame showed 12v

There is another cable in the wall to a burglar alarm which may be close to the run for the shower. I could disconnect this quite easily but when I turn this circuit off on the CU it doesn't affect the earlier situation.

Cheers
Kris

 

[Wilko]

Hi Kris and Welcome to the Forum !
My first dumb question (of many, sorry) is why are you standing in your shower with a multimeter? Did you get a tingle?

 

[Deleted member 26818]

If the shower pump was faulty, I would expect a greater voltage and for the RCD to trip.
Some PLC controlled equipment will have Earth leakage under normal operation, but I doubt your shower pump is PLC controlled.

 

[Octopus]

Did any of them check the earth continuity back to the CU ?

 

[Midwest]

I'm wondering why 'we' are bothered about bonding shower frames and radiators?

 

[kingeri]

Might have been reading Cockburn.

 

[Bobster]

Are you measuring with a digital meter or analogue one?

 

[telectrix]

fit a usb socket between shower and radiator. free charger.

 

[Kris Dor]

Thanks so far for the interest,
Cheers spinlondon re the pump.
Wilko I got a tingle from the shower head in the shower and began investigating as I'm allergic to electricity )
Midwest I don't want to bond the shower frame - I'm using it as a 0v to measure the others in the absence of 100m of earth cable and a spade in the garden - I appreciate this is haphazard but I can feel a tingle from the showerhose and sometimes the rad too, never anything from the shower frame.
Rob - it's a LAP MAS830B digital multimeter from Screwfix
Murdoch - how can I check continuity back to the CU? Although if the voltage is registering on an earth cable at the CU I guess the voltage on the Earth is getting back to the CU somehow... (?)

 

[Octopus]

^ you need a competent spark, with a proper tester and knowledge to use it and finally a wander lead.

 

[Kris Dor]

Cheers Murdoch, my sparky has tested from the earth bond under the sink in kitchen back to CU and it was fine with wander lead and megger

 

[Wilko]

Hi Kris, thought you might've felt a tingle. How often do you feel them? Sometimes the earth provided by the electricity supplier may have a few volts on it relative to the local general mass of the Earth. But some external faults may increase it. Are you able to confirm the type of earthing used at your house?

 

[Kris Dor]

my sparky says Im TNS. I'm told that the setup will be that the earth is taken from the Neutral and in my box I have a 100amp fuse and the earth cable goes into a box and comes back out of it.

I have got solar panels linked into the supply but sparky checked it and said it wasn't that.

There was a cable (single core copper with steel armouring) I removed in the garden a couple of months ago, don't suppose Earth to the house would be via a separate cable? I showed sparky but he said this had nothing to do with it.