Random Voltage Drop from 236v to 120v

AngelLaHash · Apr 15, 2024

BIG place OK lots of electrical bits.
but one on a 3 phase Radial is tripping its RCCB
so i check the wiring making sure its tight and it has continuity
even trust the RCCB that it trips. All ok

but i noticed on phase for a short while it dropped to 120v on my meter.. just Random comes and goes.
as soon as it was back to 236v i did a RCD test on it and ok

any thing on that Phase could be drawing it down to that voltage, and because its getting dropped to that, i guess any singal phase motor on that phase would slow down a lot and any three phase motors would poop themselfs!

how do you track down what is doing this and note it is Random.
i am wondering about Electric Fork trucks being put on Charge

Rockingit · Apr 15, 2024

You’ve two contenders : either a large load kicking in and out but long enough for your meter to resolve - or - a cable fault (and I’d be looking at the neutral).

AngelLaHash · Apr 16, 2024

[ElectriciansForums.net] Random Voltage Drop from 236v to 120v

I've never come across some thing that does this before. I don't have much concept of time so it felt like a minute it was on 120v (and that was with the machine not doing any thing and hooked up), why I think some thing else on the phase is doing it (why isn't any thing else tripping over this)

Rockingit · Apr 16, 2024

AngelLaHash said:
View attachment 115955
I've never come across some thing that does this before. I don't have much concept of time so it felt like a minute it was on 120v (and that was with the machine not doing any thing and hooked up), why I think some thing else on the phase is doing it (why isn't any thing else tripping over this)

What's the earthing system?

westward10 · Apr 16, 2024

If your meter is measuring line to earth voltage it is likely to be an earth continuity fault which would have no effect on any equipment. A line drop to 120v is likely to have a significant affect.

Rockingit · Apr 17, 2024

westward10 said:
If your meter is measuring line to earth voltage it is likely to be an earth continuity fault which would have no effect on any equipment. A line drop to 120v is likely to have a significant affect.

That looks like a Metrel display (I have one), they have a permanent 3 wire display that measures the three combinations so I would say that’s a genuine drop on the L.