Strange voltage readings - broken earth

[gazdkw82]

Was fixing a broken twin florescent fitting today and came across something I couldn't work out.

First thing I did was measure the incoming voltage. At the fitting I measured L-E =190, N-E = 90v.

Scratched my head for a minute until I realized the Earth's coming in from the numerous (4) twin and Earth's didn't look right.

3 cpcs we're in a terminal block and the other cpc was direct into the fitting. I decided to try L-E at the terminal block and got 240v.

I sorted the wiring out so all the Earth's were in the fitting properly and all is good. However, I can't seem to grasp why the off readings. I was effectively measuring L-E (just the single cpc from a single t+e) when I got the odd readings but 240 when measured with the other Earth's.

Only thing I can think is either the single cpc was not connected to earth properly (poor connection) ??

Thoughts

 

[Gakure]

Most probably

 

[jay sean]

Some times a loose neutral gives voltage across neutral and earth

 

[gazdkw82]

Some times a loose neutral gives voltage across neutral and earth

I thought that but once all cpcs we're connected together the readings we're normal

 

[*-jester-*]

Only thing I can think is either the single cpc was not connected to earth properly (poor connection) ??

Yes that CPC could've been the one going to the switch so only connected to the back box therefore not direct to earth.

 

[multimick]

an earth is only an earth when it's connected to earth

 

[Richard Burns]

So long as the cpc on its own was not connected to earth then you would be measuring a floating voltage. The value would not really mean anything as there is no reference point for it.

 

[dmxtothemax]

If the earth wire you were testing was not connectted to ground,
Then you were measuring "Ghost voltage".