Re: [PSES] Circuit Breakers

Thu, 31 Oct 2024 18:08:48 -0700

Hi, Steve.
The 489 breaker at the input to the PDU is to protect the branch circuit wiring from faults within the equipment. So long as there are no loads external to the equipment and the loads within the equipment are all known/controlled, other branch circuit protection isn't needed and supplementary protection is OK.
An exception could be if the PDU also provides power to external equipment that is also a known load and is an accessory to the main equipment AND doesn't use a connection system normally used for a branch circuit (e.g., custom cable). In this case, the system would require an evaluation.
Regards,
Peter Tarver
Date sent: Tue, 29 Oct 2024 21:32:24 -0400
Send reply to: Steve Brody <[email protected]>
From: Steve Brody <[email protected]>
Subject: [PSES] Circuit Breakers
To: [email protected]
Some clarification and/or education required.
 
A client has a product that has an PDU that has a UL 489 CB where the branch circuit enters the PDU.  All other CBs are UL 1077 supplementary protectors downstream from there. 
 
One of the downstream circuits with a UL 1077 supplementary protector is for internal servo motors, AC and DC.
 
My understanding was that as long as the motors are not external to the product,
that a 1077 device is OK for circuit protection in this scenario.
 
Is this correct or am I wrong?
 
Sorry I can't provide a circuit diagram.
 
Thanks,
 
Steve Brody
[email protected]
C - 603 617 9116
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