PD across live and earth?

[Inthedark]

Hi, My downstairs ring main kept triping the 32A MCB.
I think I have found the fault, a cable from one socket to another was under a concrete floor and I noticed a low resistance between the live and earth.
I have disconnected the cable and all now seems fine.
I suspect the cable has been crushed under the floor?
I did also notice there is a PD of 182VAC between the earth and live, is this correct?
The PD between the live and neutral is also 182VAC, is this a little low??
Thanks for any help.

 

[ban-all-sheds]

Hi, My downstairs ring main kept triping the 32A MCB.
I think I have found the fault, a cable from one socket to another was under a concrete floor and I noticed a low resistance between the live and earth.
I have disconnected the cable and all now seems fine.

All is very much not fine as you no longer have a ring! You must replace the cable or reduce the MCB to 20A.

I suspect the cable has been crushed under the floor?

Damaged in some way, I agree. Difficult to actually "crush" T/E..

I did also notice there is a PD of 182VAC between the earth and live, is this correct?
The PD between the live and neutral is also 182VAC, is this a little low??
Thanks for any help.

Very low.

Should be 230V +10% -6%.

So low in fact that I doubt the readings - how were you measuring it?

 

[Inthedark]

Thanks for the help.
Yes, I will replace the 2.5mm2 cable that I have cut out of the ring.

I was measuring the voltage using a Wavetek HD115B meter. Wavetek are now owned by Fluke and I believe the meter is no longer made.

Should I get the local Electrical Co. to check this out?

I am concerned about the PD across the arth and live, is this normal?

 

[teachergeezer]

Hmmm, as mentioned they are very low readings. 230ish volts (PD) between live and earth is what you should expect, you should have the same live to neutral too.
As there is obviously something amiss, and you don't know where it is, it may be better to get someone in to check it through. There's a bit of fault finding needed. Piece of mind will be your reward!
Years ago I was on a job where T&E had been crushed sufficiently to thin the insulation, which had started a fire. Fortunately it had burnt itself out fairly quickly, charring the side of a joist as it did so, but the lights in a newly wired extension stopped working. The customer then left them not working for 20+ years until the flat roof needed replacing and the cause was discovered. Cheaper on bulbs, I guess...
However the flat roof could have easily caught light, which would have ended somewhat differently.

 

[ban-all-sheds]

Thanks for the help.
Yes, I will replace the 2.5mm2 cable that I have cut out of the ring.

Sooner rather than later....

I was measuring the voltage using a Wavetek HD115B meter. Wavetek are now owned by Fluke and I believe the meter is no longer made.

Should still work, though. Please don't be offended, but you did have it on AC didn't you?

Should I get the local Electrical Co. to check this out?

I doubt if they will.

If you really had such a low voltage you'd notice things like the lights being dim, the kettle taking for ever, the shower not getting hot...

I am concerned about the PD across the arth and live, is this normal?

Not just normal - highly desirable. If you have a PD between L & N and not L & E it means you haven't actually got an earth, which is a Bad Thing™....

 

[Inthedark]

Interesting story Teachergeezer, glad I checked the problem.
I assumed the fault was caused by the new set of Christmas lights!

Yes, of course if there is no PD across L&E then no E...sorry.

I will check the other circuits (upstairs ring and lights, cooker, kitchen, etc) to see if they are all the same low voltage.
I will ask a local friendly sparky if he will do a quick check also.
May I ask if any of you have come across a low domestic voltage like this before? If so, what was the cause?

If the sparky's results are the same as mine, what then?

 

[ltfc]

Makes me wonder if the earth is any good

 

[ban-all-sheds]

Then you get on the horn to your supplier and raise merry hell.

 

[Inthedark]

Sorry I sent of the previous reply without seeing this.

"Should still work, though. Please don't be offended, but you did have it on AC didn't you?"

No offence taken, yes, it was on AC.

I do not have a shower fitted, yet.. but I haven't noticed any problems with any other electrical devices.

 

[Inthedark]

"Makes me wonder if the earth is any good"

Can I check this?

I have had a quick look into my "Meter cupboard" and the input seems to be via a single cable coming up through the ground.
This goes into three fuses, I assume this is three phase?
The only earth I can see seems to be attached to the outer armour sheath of the incoming cable.
This E then connects to a terminal block of three other E's.
One to my consumer unit and two smaller ones which disappear behind the wooden backing on which the meter, "Horstmann" night/day clock, and other fuse?/connector? block, but not my consumer unit are mounted.
My consumer unit is mounted away from my "Meter cupboard".

 

[Adam_151]

Do you have a fresh battery in your mulimeter, mine tried telling me that the mains voltage was 280v before I changed the battery...

 

[andy]

Do you have a fresh battery in your mulimeter, mine tried telling me that the mains voltage was 280v before I changed the battery...

mine once told me that a dead cable was 620VAC, and that a 9VDC battery had 200VDC in it....


and it once told me a live cable was dead... fortuntly i doubted the meter in question and tried another meter

 

[Inthedark]

Ahh...a low battery, yes this could be the problem.

Thanks very much for all the help. I will get a new battery tomorrow and check again.
Cheers