No Neutral when the main switch was, 240Volts between neutral bar and earth???

[Kev2632]

I was called to a job today where the Main switch was faulty it was switching the Live but not the neutral, so when i measured between the neutral bar and earth, i was getting 240v, why would this be happening? once the switch was changed over to a new one, everything was ok, measured neutral to earth and i get 0Volts as expected.

Could somebody explain why i was getting 240v on neutral to earth when there was no neutral present to circuits?

 

[J&M Electrical]

faulty main switch maybe?

 

[Kev2632]

faulty main switch maybe?

Yea it was a faulty switch like and is now replaced and everything is working ok, but im what asking is, when there was no neutral present to the circuits and the MCB were all on, and i measured between neutral and earth i was getting 240v why would that be happening?

 

[plugsandsparks]

Would have thought that the neutral would rise to 240 through the load, nothing would work of course but this would lift the neutral voltage.

 

[Kev2632]

Would have thought that the neutral would rise to 240 through the load, nothing would work of course but this would lift the neutral voltage.

Yea thats what was happening like,nothing was working at all, but what i couldnt get my head around was, why was i getting 240volts on neutral to earth at the consumer unit then? could you explain the reasoning for me getting 240volts between N-E at the time of the main switch being faulty??

 

[telectrix]

because, with a disconnected neutral the 240v will be present on the neutral via the loads on the circuits. think.. no current flow due to the missing N, therefore no volt drop across loads.

 

[Kev2632]

because, with a disconnected neutral the 240v will be present on the neutral via the loads on the circuits. think.. no current flow due to the missing N, therefore no volt drop across loads.

ahh right yea, so there was no potential there for the current to flow anywhere is that right? there needs to be a potential difference between neutral and live for current to flow is that correct?

 

[Silly Sausage]

ahh right yea, so there was no potential there for the current to flow anywhere is that right? there needs to be a potential difference between neutral and live for current to flow is that correct?

Almost, you need a complete circuit for current to flow and a potential difference across the load.

In your case, with a break in the Neutral, you've got an incomplete circuit, so every point up to the break is at 230V. This is why you don't have a protective device on the Neutral. An apparently dead circuit is in fact live...danger!

 

[Deleted member 26818]

What voltage if any would you have expected to measure between the two neutral terminals of the defunct main switch?

 

[kingeri]

This is why we must never presume anything is dead in our line of work. Always check and double check before doing anything else!!

 

[snowhead]

What voltage if any would you have expected to measure between the two neutral terminals of the defunct main switch?

240v same as live to true neutral.

 

[adamh]

everything would of worked if you grabbed hold of the neutral bar if that helps lol

 

[oldtimer]

You probably had a faulty main switch with the neutral bar burnt out so when you switched it on the neutral had no return path hence when you measured between neutral and earth you got 240vac.

But what you did not add was what type od DB how old was it and what it was supplying ie was it a kitchen with high loads and why would that matter well any hi load will agrivate either a poor connection or a manufacturing fault on a switch in your case a DB main switch but it could easly have been cooker or a shower switch. The letting agent I do work for said the domestic appliance guy got a shock from a cooker he had switched off in this case the live contacts had welded on so when he switched it off the neon went off but the cooker was still live plus he should have tested it to make sure but he just took it for granted that the switch worked

 

[telectrix]

this is why, when tasting for dead, you not only put your tester across L and N, but across L and E as well.

 

[oldtimer]

Also just to add you need to have a procedure for testing. ie first thing when you have a problem like this you need to establish the fault so if it was me then if the customer says I have no electricity before I climb up to the DB I check a local socket with either my socket tester or my 1553 so when I get no neutral I go to the DB and switch it off then test the live side if you did this you would have recorded a live and neutral on the live side of the switch plus while you are their test for Ze PFC PSSC ect why because if you have a 1553 in your hands then its no big deal.

I did the same thing but traced the fault straight away to no neutral at the live side of the switch that is now a DNO fault plus the neutral part of the head end was hot so I got the customer to call their supplier and they then asked to speak to me I then confirmed my finding with them and they came out 3 hours later to repair .

 

[truckster]

this is why, when tasting for dead, you not only put your tester across L and N, but across L and E as well.

Is that licking the live wire?

 

[Guest111]

and a word of advice re testing,put probe on N or E first then other probe on L that way if you drop the probe its not live,or like me many years ago working on a fault and had 1 probe in live and then proceeded to scratch my head with other probe whilst deep in thought,then wondered why test lamp was buzzing and why my head hurt.

 

[telectrix]

and a word of advice re testing,put probe on N or E first then other probe on L that way if you drop the probe its not live,or like me many years ago working on a fault and had 1 probe in live and then proceeded to scratch my head with other probe whilst deep in thought,then wondered why test lamp was buzzing and why my head hurt.

so that's where the hair went.

 

[Guest111]

so that's where the hair went.

no that was the was and go,I washed it and it went lol