Voltage in shower waste!

[purplemaf]

I hear you Marvo

Ive got all the externals to check through tomorrow then it'll have to be the bad news for the customer... sorry but I'm just going to rip your house apart :/

 

[UKMeterman]

I am starting from basics trying to find out what is causing elevated voltage with respect to true earth. 1Kohm or less should be significantly less than the impedance of the volt meter used to investigate the problem, this Ze is for the test lead ONLY. I am suspecting one or more of the following;


1. MET of the property is at an elevated potential, if this is the case then the DNO need to be got back.
2. Some water heater has got a small earth leak.
3. There could be some metal waste pipes that are either at some high potential or are earthed to true earth.

It should be quick to check point 1. if there are more than a couple of volts phone up the DNO and get them back.

The checks to the waste are to try to find out where the potential is coming from. If it is present when the buckets of water are poured down the waste then there is someting in the waste pipe that is causing the potential. If the volts go away when the main switch to the property is turned off then it is the installation at fault and time to get the megger out. If the volts do not go away get the DNO out again as there is a fault not under the control of the property owner.

Now check the volts between the test lead and taps and so on and see if any are found. If volts are found try turning the various circuits off in turn in the consumer unit. It could be the heater has split and particularly if there is a lack of earth bonding a shock hazard could occour.

 

[7029 dave]

By what you have described I would say external fault, try bonding anything metallic in the said area, also disconnect all circuits completely from db,keep cu off, to prove its worth a try.

 

[purplemaf]

I have carried out the process of turning on/off each circuit in turn to see when the problem arises. It is difficult to gauge exactly but it definately appears clearly on 3 or 4 of the 6 circuits...

The voltage does disappear when the main switch is off.

I'm 100% banking on an external issue.....I DO LOVE A CHALLENGE!

 

[Knobhead]

Have you measured the total leakage to earth for the installation at the service head?

Nothing to do with the MET, it’s a test on the incoming L&N tails.

 

[purplemaf]

Just checked outside electrics (only 1 twin skt on house wall)...no problem there. Also checked for voltage in the actual drainage outside the front door. No voltage present.

 

[UNG]

Have you tried an IR / continuity test on the waste to L & N and the main earth

Also what type of meter are you using to get your voltage readings

 

[Lucien Nunes]

If the voltage is absent with some circuits off, and remains absent even when there is load on other circuits, and the Ze is OK, that would suggest a localised insulation fault rather than external. If the insulation has broken down to some pipework or structural metal that is not bonded your original IR test might not have revealed it. How about earthing the water flow and repeating the IR test on suspect circuits.

 

[newbec]

If the voltage is absent with some circuits off, and remains absent even when there is load on other circuits, and the Ze is OK, that would suggest a localised insulation fault rather than external. If the insulation has broken down to some pipework or structural metal that is not bonded your original IR test might not have revealed it. How about earthing the water flow and repeating the IR test on suspect circuits.

I agree with this. Also have you completely removed all connections to the installation when carrying out Ze and also tested loop impedance of the supply between Line and Neutral and compared it with the Ze result to ensure the PME link in the service head is intact and the external return path is effective?

 

[purplemaf]

Hi Gents thanks for all the posts....unfortunately this is still not resolved.

I have once again worked through all circuits and was convinced I was closing in on he problem. I connected each circuit individually and switched on to see which were giving a voltage. I had done this before. I found that only the upstairs lighting gave me 16v. So I started looking closer at the lighting leg by leg taking r1+r2 readings as I went along. Each room increased the reading by roughly 0.4 ohms. Overall the Earth loop reading was 2.36. I put it back together adding each room to the circuit and testing the water. The voltage in he water started very low and increased every time I added another room. HOWEVER once I finished this process I decided to completely disconnect the lighting and power the rest of the house back up. The voltage again returned at 5/6v

I tried converting to TT.....still there. Ran a bond to upstairs straight from board...still there....