three phase problem - supply/motors/board?

[yorvac]

Hi all, I'm new here so :flowers:

I have a small industrial unit with three phase and single phase installed. The single is obviously for lights, standard sockets, phone, computer etc and is working perfectly.

The three phase supplies a tyre changer (10A breaker) and an air compressor (20A breaker).

Friday night they both worked fine, and as always I turned off the isolators and went home. Saturday morning, I came in, turned on the air compressor isolator and instead of firing up, the motor buzzed for a few seconds and tripped its breaker. Turned on the tyre machine and tried the motor, it too just buzzed but would not move, it buzzes without tripping the breaker. All 240v stuff continues to work.

I reset the compressor breaker, same result - buzz and trip. Same time after time.

I looked into the board, all the 3 incoming tails measure 240v each. Across L1-L2 its 425v, across L2-L3 its 425v, across L1-L3 its 0v. Does this make sense? Surely if each live is working independently, then it should read 415v(ish) across any pair? We measured the voltage all over the system, before the fuses (and checked fuses), before the meters, on the board before master switch, after it, before and after breakers, before and after isolators and on machines. Its the same result everywhere. We tried swapping the breakers, using the 20A on the tyre machine, that still does the same buzz but no movement.

I find it almost impossible that both machines have gone together, they have worked perfectly for a long time and nothing has been touched or changed. The whole installation is only 9 months old, all new wiring, board, breakers etc.

If the compressor did break, could it cause a fault on the board besides the breaker, and if so could it then affect the other breaker or other machine? None of the 240v is affected.

We are at a loss! We have no other 3 phase gear to test, and the shops are currently closed so can't try new breakers. The main thing bothering me is the L1-L3 being 0v, could a substation have a fault? But each live is still 240v?

Please help! Lost out on a day of business saturday and due to re-open tomorrow with no working machines!

Many thanks, Rich.

p.s I have pics and videos of equipment working (or not) if it helps.

 

[Gage]

Hi all, I'm new here so :flowers:

I have a small industrial unit with three phase and single phase installed. The single is obviously for lights, standard sockets, phone, computer etc and is working perfectly.

The three phase supplies a tyre changer (10A breaker) and an air compressor (20A breaker).

Friday night they both worked fine, and as always I turned off the isolators and went home. Saturday morning, I came in, turned on the air compressor isolator and instead of firing up, the motor buzzed for a few seconds and tripped its breaker. Turned on the tyre machine and tried the motor, it too just buzzed but would not move, it buzzes without tripping the breaker. All 240v stuff continues to work.

I reset the compressor breaker, same result - buzz and trip. Same time after time.

I looked into the board, all the 3 incoming tails measure 240v each. Across L1-L2 its 425v, across L2-L3 its 425v, across L1-L3 its 0v. Does this make sense? Surely if each live is working independently, then it should read 415v(ish) across any pair? We measured the voltage all over the system, before the fuses (and checked fuses), before the meters, on the board before master switch, after it, before and after breakers, before and after isolators and on machines. Its the same result everywhere. We tried swapping the breakers, using the 20A on the tyre machine, that still does the same buzz but no movement.

I find it almost impossible that both machines have gone together, they have worked perfectly for a long time and nothing has been touched or changed. The whole installation is only 9 months old, all new wiring, board, breakers etc.

If the compressor did break, could it cause a fault on the board besides the breaker, and if so could it then affect the other breaker or other machine? None of the 240v is affected.

We are at a loss! We have no other 3 phase gear to test, and the shops are currently closed so can't try new breakers. The main thing bothering me is the L1-L3 being 0v, could a substation have a fault? But each live is still 240v?

Please help! Lost out on a day of business saturday and due to re-open tomorrow with no working machines!

Many thanks, Rich.

p.s I have pics and videos of equipment working (or not) if it helps.

Do these motors even have overloads fitted? And have you checked the windings of both motors to see if they've burned out/gone to earth?

 

[telectrix]

sounds like you've lost a phase. might be a DNO fuse blown.

 

[Gage]

sounds like you've lost a phase. might be a DNO fuse blown.

And if you have your motors could also be damaged from this. Worth checking the windings.

 

[GLENNSPARK]

sounds like you've lost a phase. might be a DNO fuse blown.

exactly Tel....

- - - Updated - - -

And if you have your motors could also be damaged from this. Worth checking the windings.

not over a short duration....
find which phase has dropped.....reconnect....a Zs....done....

 

[Gage]

exactly Tel....

- - - Updated - - -

not over a short duration....
find which phase has dropped.....reconnect....a Zs....done....

No harm in checking. I've seen it happen.

 

[GLENNSPARK]

No harm in checking. I've seen it happen.

like i says....re-connect lost phase....juice em up...
you`l soon know if its shaged

 

[Richard Burns]

From what you describe I would say that the symptoms indicate a lost phase, however your measurements seems to indicate that L1 and L3 have been joined together with either L1 or L3 having gone down.

The problem sounds very much like it is before your installation so I would recommend that you contact the DNO for your area who should be northern power grid, emergency number 0800 66 88 77 or 0330 123 0877.
They may get you to contact your supplier but it would be a start.

 

[yorvac]

exactly Tel....

- - - Updated - - -

not over a short duration....
find which phase has dropped.....reconnect....a Zs....done....

Many thanks for the replies. Really appreciate your time. When you say reconnect the phase, you mean replace the fuse?

We did test the fuses (the 60A on the tails?) and try swapping them with next doors (although next door has no 3 phase so not absolute confirmation) and the results were the same. If a fuse was down, wouldn't that line read 0v inside? All 3 lives read 240v individually, how can that happen with a fuse out?

I should say I'm not an electrician myself, I have a professional looking at this for me but he is (no disrespect) only a domestic sparky and I think a little out of his depth, so I'm trying to find extra info to help.

As for checking the motor windings.... Not sure how to do that? There is an electrical motor specialist over the road who I can ask, but obviously they're closed til tomorrow.

 

[Amp David]

As the measurements have been taken at the main switch, then it certainly an issue external to your installation.

 

[telectrix]

could even be main switch or MCB breaking down on 1 phase under load.

 

[snowhead]

There is a fault on the incoming cable or distribution fuse outside of your building.
As others have said contact the DNO.

Forget the 240, all that matters is the phase to phase voltage.
Who was using the test meter?
Check one reading isn't 240mV

 

[Darkwood]

I take it the OP turn the main switch off when testing the supply... any three phase loads connected will give feed back that may lead to confusing test results i.e.... if a motor was still inline or a coil on a contactor you would register voltage on a phase that has been cut.

 

[Knobhead]

Best advice
Get an electrician in that doesn’t spout the proverbial!

 

[GLENNSPARK]

Best advice
Get an electrician in that doesn’t spout the proverbial!

well im flattered ...i really am....
now....the O/P can go through the series of tests....
alternativley
see post #7

 

[Knobhead]

well im flattered ...i really am....
now....the O/P can go through the series of tests....
alternativley
see post #7

???what???

 

[yorvac]

Many thanks for all help.

All those who said the problem is external to my building, looks like you were right. I came in this morning and everything was working. The reading across L1-L3 is back to 425v so obviously there was a phase down somewhere.

Thanks again.

 

[44ALLAN]

Aye some clever fellas on here mate