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Breaker sizing for a panel with 2 motors with VFDs and a PLC

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M

Mumbaigirl

Member
Location
USA
Occupation
Electrical Engineer
I have a treatment panel with 2 3-phase 480V 100HP motors (112A FLA) both on variable speed drives. The max. input current on the VSDs is 112.7.

The panel has a 400A disconnect available for us to connect to.

I am figuring out the breaker size and wondering if I am doing this correctly:

Per 430.52 (c) (1): Breaker size would be 175% of the Highest motor FLA + Second motor FLA + PLC + HMI = 1.75*112+112+ 20 (approx for the PLC+HMI) = 328A.

Am I doing this correctly? Will a 350A breaker suffice?

I appreciate your help on this.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
It depends on whether that breaker is going to be a feeder or the branch OCPD. If it is going to be the Branch, then you need to check on the specs for the VFDs to see if there is a maximum breaker size that can be used as the OCPD, or if breakers can be used at all and they need to have fuses.

If each VFD already has their own appropriate OCPD already, then it doesn't matter and the breaker is just a feeder, so you size it based on the size of conductors you will be using.
 
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