Published: 2 May 2014
Category: Q&A
Manoj asks this question about inverter drive wiring when there are a number of the devices of various ratings. It has been answered by ABB (Theme – Electrical Control):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: I’m wiring up a number of inverter drives in a motor control panel – they range from 75kW to 1.5kW each.
How should I drop down in cable size?
?For the 75kW drive inverter, the cable size is 70mm and for the 1.5kW inverter, it is 2.5mm?.
The supply is switched through two contactors before going onto a set of fuses for both the 75kW inverter and the 1.5kW inverter.
Do I need to carry the 70mm cable to the fuses protecting the 1.5kW inverter?
Answer: Depending upon the way you are wiring to the two inverters, you will be able to reduce the cable size down once you are past the protection device for the smaller inverter.
The cables need to be protected against overload and short circuit by a suitably sized fuse or circuit breaker situated on the supply side of the cable, so it will depend upon where you fit the smaller inverter fuse.
It is difficult to advise further without a wiring diagram of your proposal, but if there is one contactor per inverter, you could put the smaller control fuse on the supply side of the contactor to the smaller inverter - this would allow you to use the smaller cable size from that contactor to the inverter.
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