Fuse sizing for load or coordination?
Fuse sizing for load or coordination?
(OP)
I'm looking for the most common philosophy on fuse sizing for distribution taps (12.5kV system). In general,are most utilities sizing fused taps according to load or for maximum coordination with upline devices. Example: A single phase overhead tap off the main feeder 10 spans from the sub. I'm hanging one 25kVA Xfmr fused with a 6T (minimal chance for expansion)...a 10T would be sufficient for that tap. However, a 65T will give me max coordination with the substation breaker. Is it more common to use the 10T or 65T for this tap? I know this example opens the door to many other variables but I'm just looking for a general philosophy. I'm looking to implement a standard for fuse sizing at my utility and am trying to get the pros and cons of both philosophies....Thanks for your response!






RE: Fuse sizing for load or coordination?
RE: Fuse sizing for load or coordination?
Using the 6T would be what my utility is using right now for your situation. I am presently studying using a Dual Slofast fuse which would follow the txf overload curve while still providing protection for the txf and ckt.
For the upstream (protected) fuse, I would probably go with the 10T. This should still co-ord with any upstream fuses or reclosers.
For general info, you should see about getting a copy of the "Electrical Distribution System Protection" book by Cooper Power Systems and also A.B.Chance company has some good literature.
RE: Fuse sizing for load or coordination?
Fuse manufacturers have "preferred" and "non-preferred" ratings. If you stick with the preferred ratings, using smaller sizes as you go downstream, coordination is generally assured. As mentioned by others, you need to factor in the reclosing philosophy and reclosing sequence.