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Uprating wiring for motor starting? - trip problems

Wivsi

Hi,

I have a customer who is having problems starting a 3ph fan. The fan is rated at 5.5kw, 10a run current. They're running from a 16a socket. The fan is DOL started. It is tripping a D16 breaker on their board. With a D32 breaker the motor will run, but is underperforming. The fan runs fine at another location, so something is not quite right locally. The supply voltage is 415 between each pair.

My uninformed thinking is that, while their 16a socket is fine for the motor run current, the start current which is up in the 80a range is potentially too high for their wiring so the motor is never getting enough power to get up to speed. I suspect that uprating their socket to a 32a with a 4mm run will solve the problem. But I would like to have a sensible (standards based) reason for suggesting this - rather than just suggesting changing it and hoping.

I'm hoping for some expert input to steer the customers electrician in the right direction.  I'm just providing some informal input to help them track down the issue (and am not a sparks) but no one seems to be able to solve the problem at the moment so thought I'd put it out here. Any advice appreciated.

TIA!

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  • 0

    "will run, but is underperforming" needs clarification

    Do we mean is very slow to start, or even after many mins never gets up to speed?

    (and I assume they do not mean it is turning backwards - if that is true then swap any 2 phases...)

    and is the 415V still true while the motor is under-performing or was that the 'off load' reading.

    It might be interesting to look at the three phase to ground voltages - while on load-  too.

    A high impedance supply may lead to a no-start or a very slow one but once at speed it should be OK. Unless backwards of course...

    Mike

Reply
  • 0

    "will run, but is underperforming" needs clarification

    Do we mean is very slow to start, or even after many mins never gets up to speed?

    (and I assume they do not mean it is turning backwards - if that is true then swap any 2 phases...)

    and is the 415V still true while the motor is under-performing or was that the 'off load' reading.

    It might be interesting to look at the three phase to ground voltages - while on load-  too.

    A high impedance supply may lead to a no-start or a very slow one but once at speed it should be OK. Unless backwards of course...

    Mike

Children
  • 0 in reply to mapj1

    Thanks Mike. It's running way below the pressure it should - meaning it's running slow (although I've not measured the RPM - but the only way a fan can generate less pressure than it should is by running slow).

    It's not running backwards - we even ran it backwards just to sanity check and things are the same!

    I don't think we have phase to ground voltages on load - that is worth a check.

    mapj1 said:
    A high impedance supply may lead to a no-start or a very slow one but once at speed it should be OK. Unless backwards of course...

    That was my thinking! I can't come up with a reason for a slow run...

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