Voltage Fluctuating between 170V and 330V

[Izak555]

Hi,

I`ve been to a site today and noticed some units I`ve got have huge voltage drops. Voltage was fluctuating between 170V and 280V and on some units, I`ve had 330V.
I went to the DB board:

• Between live and earth some circuits were showing 217V and other one were showing 270V.
• Between Neutral and Earth, some circuits were showing 60V. When isolating each all MCBs, I`ve had 240v between neutral and Earth.
• The main supply was ok.

It looks like the issues is on the floor and feedback this on the DB board.

There are about 15 circuits. Each of them is connected to two spurs and feeding some VAVs boxes.

What could be the reason of the voltage fluctuating like this?

Many thanks,

 

[UKMeterman]

It is the kind of problem where you turn the supply off, and don't even think of turning back on unless the fault is fixed or you have had a blunt chat with the site MD .

 

[Izak555]

No. It will be on the 3-phase supply before the first point at which abnormal voltages are found.

That`s right

 

[Izak555]

It is the kind of problem where you turn the supply off, and don't even think of turning back on unless the fault is fixed or you have had a blunt chat with the site MD .

Well, this is exactly what I`ve done.

 

[Izak555]

There was a loose neutral cable in the DB board. It did cost a lot of money to sort it out but the electrical company found it. thanks for your replies

 

[Petej999]

Faulty neutral is the obvious suspect.

why do you think that the supply is ok?

OP what are you measuring the voltage with?

 

[timhoward]

There was a loose neutral cable in the DB board. It did cost a lot of money to sort it out but the electrical company found it. thanks for your replies

Thanks for letting us know the outcome. Glad it's sorted.