Eng-Tips is the largest forum for Engineering Professionals on the Internet.

Members share and learn making Eng-Tips Forums the best source of engineering information on the Internet!

  • Congratulations dmapguru on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Mixing overcurrent devices

Status
Not open for further replies.

althomas49

Electrical
Joined
Mar 24, 2012
Messages
2
Location
US
When selecting motor feeder circuit short circuit and ground fault protection, the code states:

You must provide the feeder with a protective device with a rating or setting not greater than the largest rating or setting of the branch-circuit short-circuit and ground-fault protective device (plus the sum of the full-load currents of the other motors of the group)

So if I use dual element time delay fuses for the branch circuits, but an inverse time breaker for the feeder, do I still use largest fuse rating for the calculation, or do I need to size the breaker as if the branch circuits were protected by inverse time breakers as well?
 
No, you recalculate the branch circuit protection as breakers and use that information to size the feeder protection.
430.62(A)says: "...based on the maximum permitted value for the specific type of a protective device in accordance with 430.52..."
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Back
Top