Disappearing voltage under load

[Kyleb2210]

Hi all, quick one that I’m guessing one of you guys will solve quickly! Currently been doing some work on an old wartime building and trying to get power back onto some son floodlights after some demolition work internally, I’ve got 240v across line and neutral at the junction box (that’s presumed went to the old outside lights as a perminant supply as the lights have built in photocells) but as soon as I connect L+N of the load onto the supply the voltage disappears when I put the test meter on it then when I remove the load the voltage comes back! Any ideas? Apologies if the answer is stating me right in the face

 

[snowhead]

Loose connection /faulty mcb /isolator upstream

 

[PEG]

Hi,what test instrument are you using?

Using the correct AVI would assist in having a true indication of what voltage,is actually present.

You could have the live/line,coming through a component,or you may have lost a neutral,or a few other possibilities.

As strange as it sounds,if you are using the wrong instrument to measure this voltage,you could have a switch upstream,which is open...but full of water

 

[Richard Burns]

If you were to measure line to earth when under load and had line voltage then this would indicate a high resistance neutral.
If there is a low voltage line to earth when under load this would indicate a failing connection on the line side.
However both of these also require that the earth is sound!
Essentially it sounds as if all the voltage is being dropped over a high resistance (poor connection, failed switch, dirty contacts, etc.) elsewhere in the circuit and this is not seen when the voltage is measured with the near infinite resistance of a voltage tester.

 

[Kyleb2210]

Hi,what test instrument are you using?

Using the correct AVI would assist in having a true indication of what voltage,is actually present.

You could have the live/line,coming through a component,or you may have lost a neutral,or a few other possibilities.

As strange as it sounds,if you are using the wrong instrument to measure this voltage,you could have a switch upstream,which is open...but full of water

I’m using a fluke multimeter, I’ll get the megger on it in the morning and see if I get a more accurate voltage reading