Voltage difference

[jq1805]

I've recently installed a stud wall and extended the existing wiring for two double sockets by using a block connector and single cable. Does anyone know why one socket would show 240v and the other show 208v please?

Thanks.

 

[endecotp]

I've recently installed a stud wall and extended the existing wiring for two double sockets by using a block connector and single cable. Does anyone know why one socket would show 240v and the other show 208v please?

Thanks.

How are you measuring that?

Do the sockets seem to work?

 

[jq1805]

With a multimeter.

The 240v socket does, the 208v socket doesn't.

 

[plugwash]

You most likely have a bad connection somewhere.

 

[JohnW2]

With a multimeter. .... The 240v socket does, the 208v socket doesn't. {work}

What is the voltage between L and earth on the "208V socket"?

Kind Regards, John

 

[jq1805]

Thanks John.

It's 241v

 

[terryplumb]

Is the circuit a ring final ? If so how have you connected the two sockets with a single cable ?

 

[JohnW2]

Thanks John. It's 241v

Thanks. That strongly suggests that plugwash was right, and that there is a loose/poor connection on the NEUTRAL at that socket.

Kind Regards, John

 

[SimonH2]

Sounds like you have a bad connection - it's got a high, but not "infinite", resistance. So when testing with your high impedance voltmeter, you get a reading, but as soon as you apply a load, all the voltage disappears across the high resistance joint. This is the reason why we do certain tests to check work, using equipment that puts a reasonable amount of current through a circuit.
From the way your original post is worded, it sounds like you have done a non-compliant alteration, and quite possibly created a dangerous situation.

 

[jq1805]

Thanks very much John, very much appreciated. I'll have a look in the morning.

Regards.

John.

 

[JohnW2]

Sounds like you have a bad connection - it's got a high, but not "infinite", resistance. So when testing with your high impedance voltmeter, you get a reading, but as soon as you apply a load, all the voltage disappears across the high resistance joint. This is the reason why we do certain tests to check work, using equipment that puts a reasonable amount of current through a circuit.

I agree with your conclusion (as I said, it sounds like a poor connection of the neutral at the one socket).

However, as for testing, I suspect that even if someone had just installed an entire sockets circuit, they would probably not "...do certain tests to check work, using equipment that puts a reasonable amount of current through a circuit" at every socket on the circuit, would they? (and, if they didn't, they probably wouldn't detect a problem such as we are postulating in the OP's case at just one socket)

Kind Regards, John

 

[SimonH2]

You would as a minimum do L-N and L-E loop tests either around the ring or to every end of a radial (i.e. every branch). If not then you have not adequately tested the circuit. In addition, you would do polarity checks at every socket/outlet - otherwise you risk missing a miswire of the kind that comes up regularly (Birakos Enterprises Limited). And the loop tests would be done with something more than the micro amps a multimeter would put through the circuit.
So while a bad neutral connection could be missed, it would be unlikely - you would need the terminal of a socket to be loose, but the wires to be in good contact.

 

[ericmark]

My guess one reading line - neutral the other reading line - earth, lets see if right.

 

[JohnW2]

My guess one reading line - neutral the other reading line - earth, lets see if right.

That's not my understand - which is that one was reading 240V L-N (and 'working') and the other reading 208V L-N (and 'not working) but (following my question) the latter reading 240 L-E ...

... from which I concluded that it's probably a dodgy N connection at the second (208V L-N, with high impedance meter, 'not working') socket.

Kind Regards, John

 

[ericmark]

Easy to check, measure L - N and L - E at both sockets.