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Electrical noise created by 3ph machine

Steve Phillips

Hello all

Life long sparky... semi-retired now, but working at a local workshop

The company had a local (rather shoddy) electrical company come in and re-supply a 3ph, 35A per phase painting/spray machine.    It was fed before and created flickering in the office fluorescent lights.

But, it still does it.  The fluorescent lights in the offices on the mezzanine nearby flicker when the machine pulls a high load.

It's fed from a sub DB that has a 125A, 25mm 3ph SWA supply (This run is considerable from the incomer - probably somewhere like 70M+.   

Machine MCB is 32A

They used 6mm 5 core SY cable (I would have gone 10mm) over a 25M run.  But they laid it on top of (not in) a 4" galv trunking with T&E inside.  Entirely possible the lighting feeds run within this trunking.

I may unstitch the cable and move it away from the trunking, but I am not entirely convinced that is the issue.

Any ideas on what to try?  

Personally, I would rewire the machine directly back to the incoming mains cupboard, but that is no easy task.

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  • 0

    If it's VSD driven, the problem could well be protective conductor currents ... although radiated emissions may also be an issue.

    The SY braiding and trunking will only be effective barriers to radiated emissions, if they are properly earthed, and provide complete 360-degree coverage (including with the SY, use of proper glands). Poorly fastened lids, and corrosion, of the trunking, may also affect things. Physical separation, of say 1m, may help.

    If the problem is protective conductor currents, then additional earthing and bonding is a good solution - see BS EN 50310 - but over such long distances a good solution may be costly to implement.

    Another possibility is conducted EMI through mains - this can be more problematic, and might require dedicated noise filters to address.

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  • 0

    If it's VSD driven, the problem could well be protective conductor currents ... although radiated emissions may also be an issue.

    The SY braiding and trunking will only be effective barriers to radiated emissions, if they are properly earthed, and provide complete 360-degree coverage (including with the SY, use of proper glands). Poorly fastened lids, and corrosion, of the trunking, may also affect things. Physical separation, of say 1m, may help.

    If the problem is protective conductor currents, then additional earthing and bonding is a good solution - see BS EN 50310 - but over such long distances a good solution may be costly to implement.

    Another possibility is conducted EMI through mains - this can be more problematic, and might require dedicated noise filters to address.

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