3 phase supply issues

paul-k · Sep 21, 2010

Hi I'm having some problems with a 2 phase supply and any help would be appreciated.
I got a breakdown last week on a machine with a 3 phase motor, the contactor was burnt out and the motor windings also. The main contactors and overload have been replaced and the motor rewind completed and tested, but i've got issues with the incomming supply.
On testing each between each phase (red -yellow, red -blue, yellow - blue) i only get 415v on 2 readings indicating a phase down. If i test each individual phase to earth i get 230v so i know i've got voltage on all phases.
The supply cable has been checked and the distribution pannel. I beleive the fault is on the mains supply, but can anyone advise on what it may be?

Thanks,

Paul

johnboy6083 · Sep 21, 2010

are two of the phases the same phase? in oher worsd you only get 415v due to each phase being 120o out of sync with eachother. if two of your "phases" are the same phase, then it will register a potential difference to earth of 230v but ther will be no potential difference between 230v to 230v.

malcolmsanford · Sep 21, 2010

Had this once before, check the MCB at the board, I had an old crabtree 3 phase breaker where the Yellow(Balck) phase on the MCB had broken internally and only supply 2 of the phase Red (Brown) and Blue (Grey) to the isolator switch worth a check.

silva.foxx · Sep 21, 2010

Where exactly are you testing the supply?

ie. Incoming supply side of main isolator at machine with the switch open (off), at the motor contactor or elsewhere?

.

paul-k · Sep 21, 2010

Thanks for replying. I've just been back to site and the fault is on the supply comming from the sub station. The electric company where having problems so they converted the supply 415v to 230v. Hence 230v showing on 3 phases but phases out of sync.
Nice to know they make mistakes too!