Soft starts on 200 Hp Motors
Soft starts on 200 Hp Motors
(OP)
We have some large 200Hp motors that are presently started across the line on some fan motors. We're thinking of putting in some soft starters in place of these.
1) Does the size of the load wires affect the soft start? I understand there is impedance there...but does this make any difference to what soft starter we purchase?
2) The existing motors are fed with 1000kcmil AL cable, which we want to re-use. However the soft start we are looking has a maximum wire size of 500 kcmil. I'm guessing there is a way to lug this down, but I'm not familiar how to do it...any suggestions?
3) Any other issues with soft starts? BTW the motors do feed fans that are moving air and don't require lots of starting torque.
1) Does the size of the load wires affect the soft start? I understand there is impedance there...but does this make any difference to what soft starter we purchase?
2) The existing motors are fed with 1000kcmil AL cable, which we want to re-use. However the soft start we are looking has a maximum wire size of 500 kcmil. I'm guessing there is a way to lug this down, but I'm not familiar how to do it...any suggestions?
3) Any other issues with soft starts? BTW the motors do feed fans that are moving air and don't require lots of starting torque.






RE: Soft starts on 200 Hp Motors
2) Similar ampacity can be obtained from 2-350kcmil copper cable, but it probably can't fit your 500 kcmil lugs either. It throws a red flag that the soft starter may be undersized if it can't handle the cable size. You can also check if your desired soft start supplier offers other connection options, if not you may want to look at other suppliers.
3) Follow the mfg.'s installation instructions carefully. Some soft start designs include bypass contactors, overload protections, while others need external parts. Some designs pass-through one leg of three-phase and only control the other two legs, this can surprise you with voltage at the motor when you think it's unpowered.
Good Luck!
Sean
RE: Soft starts on 200 Hp Motors
2) The cable ampacity was derated because it runs outside and it is in a covered cable tray, thus the 1000kcmil size.
I'm asking can you lug this down legally...in some way legally. The current is no higher at this point, certainly seems you could. Maybe I need to go to the NEC forum.
RE: Soft starts on 200 Hp Motors
Can you find something that works in the terminal space of the soft starter? Probably not.
RE: Soft starts on 200 Hp Motors
Jim T
RE: Soft starts on 200 Hp Motors
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