Chose this part of the forum as i'm not a sparky

[KenL]

My daughter asked me to look at the supply to her garage and the lights and sockets did not work. She has just moved into this property about a month ago.
I have worked on electrics in my job as an A/C engineer, wiring three phase between air handlers and condensers and connecting the supply into the air handler.

I removed the 13 amp socket and it is supplied by a four core cable the Live and neutral (red and black) show 124 volts, if i between the red and yellow i get 240 volts. The sockets are wired using the red and black (124volts)
At the dist board all the MCB's are marked up as you would expect, lights, sockets, Central heating. There is one with a question mark, but at the time i did not have enough time to switch this supply off. ( had to go somewhere else)

I am confused as to why i would get 124 volts on two cores.
I have said she should get an electrician in.

Any help appriciated.

 

[Andy™]

dodgy connection usually

 

[Phoenix]

It sounds like there is a very high resistance/open neutral connetion, it is floating upto half supply voltage through capactive coupling, and your high resistance volt meter does not put any load on it, so you see that voltage, if you used a moving coil type meter it would likely be far lower. If you plugged a load like a heater it, chances are it would disappear totally, with the neutral, pulled upto line potenial (so you'd then see 0v between red and black, 240v between black and yellow, and you'd still have 240v red to yellow)

I'm assuming its armoured comming into the garage, its likely twin and earth in the house, try and find the joint and inspect that and see what voltages you get there

 

[Geoff1946]

What were you testing with? If it's the typical DIY multimeter, or a professional meter aimed at servicing electronics, it will be a high impedance.
This can give totally misleading indications as it can show a reading induced onto an open circuit cable if that lies alongside a truly live one.

 

[Murdoch]

I think you need to do some basic dead tests to establish what is connected to what

 

[SPECIAL LOCATION]

I think you need to do some basic dead tests to establish what is connected to what

Wot he said!

Always do dead tests before live tests!

 

[KenL]

It sounds like there is a very high resistance/open neutral connetion, it is floating upto half supply voltage through capactive coupling, and your high resistance volt meter does not put any load on it, so you see that voltage, if you used a moving coil type meter it would likely be far lower. If you plugged a load like a heater it, chances are it would disappear totally, with the neutral, pulled upto line potenial (so you'd then see 0v between red and black, 240v between black and yellow, and you'd still have 240v red to yellow)

I'm assuming its armoured comming into the garage, its likely twin and earth in the house, try and find the joint and inspect that and see what voltages you get there

I'm assuming it SWA but i cant see a gland, it just appears from the floor.

 

[KenL]

What were you testing with? If it's the typical DIY multimeter, or a professional meter aimed at servicing electronics, it will be a high impedance.
This can give totally misleading indications as it can show a reading induced onto an open circuit cable if that lies alongside a truly live one.

I have a Fluke meter.

 

[KenL]

Thanks for the replies, i will get my Son-in-law to get a sparky in. I will drop the MCB with the question mark out and impress upon them that this needs looking at.