Bussmann KTN-R Eaton LIMITRON Fast-acting Fuse, Class RK1, 250V

Physically yes, electrically think twice. KTN-R is Class RK1 and shares the Class R rejection-feature dimensions, so it mounts in the same Class R blocks and switches at the same amp rating. But it is a fast-acting fuse with a single element, where RK5 time-delay types tolerate motor inrush. Swap to KTN-R on a motor circuit and you can get nuisance openings on start. It suits feeders, panelboards and non-inductive loads.

200,000 A interrupting at 250 Vac, and 100,000 A at 250 Vdc. That covers the available fault current at most service entrances, and it is the reason Class RK1 gets specified for series ratings and equipment short-circuit current rating documentation over Class H fuses.

The KTN-R is offered in 70, 90, 110, 125, 175, 300, 350 and 450 amps, ordered as KTN-R-70 through KTN-R-450. Pick the rating from your panel schedule or the equipment nameplate, not from the fuse currently in the clips, since a previously mis-sized fuse is common on service work.

Yes, a Class R fuse goes into plain non-rejection 250V clips of the same amp size, because the rejection notch only prevents the reverse: it stops a lower-interrupting Class H or K fuse from being installed in a Class R rejection block. If the switch has the rejection ring, only Class R fuses like the KTN-R will seat, which is the point of specifying it.

Yes. Class RK1 fuses are current-limiting, which is what lets them hold let-through energy down to protect downstream components and support series ratings. The KTN-R is the fast-acting LIMITRON version in that class at 250V, so it clears faults quickly rather than riding through overloads.

You can't by sight. The KTN-R is non-indicating, with no pop-out pin or window, so checking it means de-energizing and testing continuity across the fuse or verifying voltage downstream. Plan for that on troubleshooting calls where access is tight.

Standard packaging, sold by amp rating. For a facility stocking spares, the practical move is to carry the ratings that match your panel schedules, since all eight ratings from 70 A to 450 A share the same 250V Class RK1 fast-acting characteristic and the same part prefix, KTN-R, with the amperage as the suffix.