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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

    Have a look at the stated inrush current and compare it to the tripping curve of the breaker.  Worth looking at the cable calculation and volt drop as well from source of instalation as this may go through Db1 then DB2 then DB3

  • 0 in reply to Sergio Fernandez

    That is also worth a look. It's close to the local DB but could be quite a way from the main DB and if that is not on a decent cable size...

  • 0 in reply to Wivsi

    And do not overlook the obvious mechanical factors-  at the other location where it works is the mounting different (gravity the same way up, frame twisted by un-even supports, ducting sizes - does it have a duct ?)

    Mike.

Reply
  • 0 in reply to Wivsi

    And do not overlook the obvious mechanical factors-  at the other location where it works is the mounting different (gravity the same way up, frame twisted by un-even supports, ducting sizes - does it have a duct ?)

    Mike.

Children
  • 0 in reply to mapj1

    yep 100% the same. No duct, all in one unit - even built the same room around it just in case!

  • 0 in reply to Wivsi

    Hmm how odd.

    Let us know what the voltage tests find.  And if you can find a clamp meter, does it draw the same current on all 3 phases.

    M.

  • 0 in reply to mapj1

    Yep will do. Will put the clamp on as well...

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