50V On Garage Earth

[RumbleAndSway]

Hey guys,

Just wondered if anyone could give some advice from their experiences. I did a job today for someone, just involved putting a CU with RCBO for a new cooker the customers having delivered soon.

Anyway to the fault:

I had to upgrade the main earth terminal and as I removed the earth for the garage things got a little interesting. The garage is on it's own supply from a 5 way henley. I tested between the disconnected garage earth and the main earth terminal which still had all the other earths connected and got 50v.

This was right at the end of the day and I've told the customer I'll be back to have another look as soon as I can. He's told me he has his office in the garage with some computers in, a fridge and a load of sockets/lights.

The setup is old metal wylex CU inside the house fed from a henley which feeds externally over a archway into the garage where there's a fuse board.

Any advice appreciated or next steps to find what's going on quicker.

Thanks!

 

[Essex1]

What is the incoming earth arrangement?

 

[Andy™]

i hope you isolated power to the shed before removing the earth...

 

[Essex1]

i hope you isolated power to the shed before removing the earth...

What has that got to do with the op?

 

[Andy™]

What has that got to do with the op?

you cant see an issue with disconnecting an earth for a circuit thats energized?

 

[RumbleAndSway]

TNS, pilc cable.

 

[kerching]

What did you measure the 50V with?

Just saying

 

[Essex1]

you cant see an issue with disconnecting an earth for a circuit thats energized?

So are you going to ask every safety question to get a full detailed list of what the op has done? Then help him with his question? He says he is an electrician.

 

[RumbleAndSway]

you cant see an issue with disconnecting an earth for a circuit thats energized?

I can see the issue with that! I was being a little bit naive, had the house isolated and was moving each individual earth over to a main earth terminal with more points on it, didn't notice I hadn't isolated the garage as the CU is hidden behind the the customers kitchen country effect wood panelling. Obviously as soon as I saw something was up as I disconnected it's earth I isolated the garage straight away and told the customer to stay clear.

 

[Essex1]

TNS, pilc cable.

Did you measure Ze?

 

[RumbleAndSway]

What did you measure the 50V with?

Just saying

Fluke T110 initially then used a Fluke 1652c to get a accurate reading.

Did you measure Ze?

Not yet. I'm going back round in the morning.

 

[Lurch]

Stop playing with electrics and get a professional in.

 

[Andy™]

and was the earth still live after garage was isolated?

 

[kerching]

**joke on**

For anything below 100V i just use my tongue

for anything above 100V i just use monkees tongue 

**joke off*

I had an alarm fault on a ."Dark site" if anyone reading does not know what it is i cannot tell them

Anyway had to get the Big Fat Freshwater Fish Alarm Company out......their "engineer arrived'...teested elv alarm wires with his tongue....tw@! Not sure if he was trying to show off or not!...not arsed, not my problem. My problEm was a private 400mm^s AWA coming from the MV Sub with a metal fence post through it!

The fencing contractor had a bigger problem....MUCH bigger!

 

[RumbleAndSway]

and was the earth still live after garage was isolated?

Thanks for helping Andy, the earth wasn't live after isolation.

The garage is still isolated now.

 

[Andy™]

So are you going to ask every safety question to get a full detailed list of what the op has done? Then help him with his question? He says he is an electrician.

yes. the answer to my question is 2 possibilities. each has a completely different outcome: 'no' may be completely normal and to be expected, 'yes' could be an issue requiring further investigation. kind of hard to give more advice without knowing the answer

and the more detail the better anyway

Thanks for helping Andy, the earth wasn't live after isolation.

The garage is still isolated now.

so you know he has computers, which are well known to leak current to earth, which you disconnected, leaving the power nowhere to go, so it became live. probably no issue there to be found

or it could simply be inductance, again, no issue

 

[Essex1]

You need to test the Ze. Being a TNS it could be a poor incoming earth.

 

[RumbleAndSway]

yes. the answer to my question is 2 possibilities. each has a completely different outcome: 'no' may be completely normal and to be expected, 'yes' could be an issue requiring further investigation. kind of hard to give more advice without knowing the answer

and the more detail the better anyway

so you know he has computers, which are well known to leak current to earth, which you disconnected, leaving the power nowhere to go, so it became live. probably no issue there to be found

or it could simply be inductance, again, no issue

Okay thanks for the help! I haven't seen as much as 50v before, maybe upto 20v before.

 

[Lurch]

You need to test the Ze. Being a TNS it could be a poor incoming earth.

Can't see how that will make any difference when the garage CPC isn't connected to the MET.

 

[Essex1]

Can't see how that will make any difference when the garage CPC isn't connected to the MET.

Really?