E Rated Fuse
E Rated Fuse
(OP)
Why are E rated fuses rated 400E but when observing the TCC, the curve starts melting at like 900A?
If the purpose of E rated fuses is to clear inrush and meant only for short circuit protection, why is it called a 400A fuse?
This applies to almost all medium voltage fuses that I've seen. Is this because fuses are not meant for overload protection? And are exclusively for short circuit protection only?
If the purpose of E rated fuses is to clear inrush and meant only for short circuit protection, why is it called a 400A fuse?
This applies to almost all medium voltage fuses that I've seen. Is this because fuses are not meant for overload protection? And are exclusively for short circuit protection only?






RE: E Rated Fuse
"Fuses with an E-rating larger than 100E must open within 600 seconds (10 minutes) when subjected to an rms current of 220-240% of the fuse's continuous current rating."
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: E Rated Fuse
Fuse amp rating is the current they can carry without damage. The faster they trip, the more sensitive they can be to damage from transient overcurrent, and E fuses can be very fast, so the load current stays well under the trip TCC. If you want overload protection at medium voltage, you need relays. Then they will tell you to set the relay so high it is not good overload protection either.
J. Horak, P-R Engineering, Colorado
RE: E Rated Fuse
Thanks.
It still doesn't completely satisfy my curiosity about the amperage ratings.
So if a 400E fuse curve starts meltiing/clearing somewhere in the 800A region, can the relay safely handle currents only upto 400A? What about 500A? 600A?
RE: E Rated Fuse
If you wanted to precisely choose a fuse for your specific application, get a TCC curve from the fuse manufacturer and compare with your expected load amperes. If your time-current plot falls below and to the left of the fuse TCC, you're choice is good.
RE: E Rated Fuse
But thats what I'm saying. When I look up the TCC of a 400E rated fuse, which is advertised as good for 400A, the melting current portion of the curve starts at ~800A.
So yes, I personally think that the fuse is good for 500A, why is it advertised/marketed as a 400A fuse....
RE: E Rated Fuse
Mersen says their E-rated fuses are general purpose. Their text says something along the lines of the fuse can interrupt all currents between the current that causes melting in 1-hour up to it's interrupt rating. So, the curves would have to go to 3600 seconds as a minimum to show the lowest level.
Still, it's not a great idea to use E-rated fuses without a protection relay.
RE: E Rated Fuse