R-Rated Motor & Soft-Starter Fuses
DENCO R-rated fuses provide short-circuit protection for medium-voltage motor starters and soft starters. They are current-limiting with a high interrupting rating and are supplied in single, double and triple barrel configurations.
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Specifications
| Parameter | Value |
|---|---|
| AC voltages | 2.5kV, 4.8kV, 7.2kV (AC) |
| Ampere range | 1R, 2R, 3R, 4R, 5R, 6R, 9R, 12R, 18R, 24R, 36R |
| Interrupting rating | RMS symmetrical 63kA and 65kA; RMS asymmetrical 100kA |
| 2.5kV range | 1R to 36R (35A-650A) |
| 4.8kV range | 2R to 36R (70A-650A) |
| 7.2kV range | 2R to 24R (70A-450A) |
| Configurations | Single, double and triple barrel |
| Melting characteristic | Melts in 15 to 35 seconds at 100x the R rating |
Applications
- Medium-voltage motor protection
- Motor starter and controller protection
- Motor circuit protection
Limits and boundaries
- Short-circuit protection only — not overload protection
- Coordination study required; see the selection guide
Standards and testing
- Designed to DIN 43625
- Designed to IEC 282-1
- Designed to BS 2692
Wording reflects the evidence DENCO holds. “Designed to” a standard is not the same as certified or listed to it; where a certification exists we publish the certificate number.
Technical documents
Data sheets, dimensional drawings and time-current curves for this family are available on request. Ask for the documents you need.
What we need to quote
Voltage and whether the system is AC or DC, continuous current, required interrupting rating, physical dimensions and mounting, any indicator requirement, and the standard or approval you must meet. A photograph or drawing of the existing part is usually the fastest route.
Common questions
What does an R rating mean, and is it an ampere rating?
It is not an ampere rating. Under ANSI/IEEE C37.46 an R-rated fuse must melt in 15 to 35 seconds at a current equal to 100 times the R number, so a 6R is defined by its behaviour at 600 A rather than by a 6 A continuous rating. The R number is a way of matching the fuse to a motor circuit, not a load current.
Do R-rated fuses provide overload protection?
No, and they are not intended to. R-rated fuses are back-up fuses in the ANSI C37.40 sense: they interrupt from their maximum interrupting rating down to a stated minimum interrupting current, and below that they cannot be relied on to clear. They are applied with a medium-voltage motor starter whose overload relay covers the low-current region. An R-rated fuse must never be the only protective device in a motor circuit.
Can an E-rated fuse be fitted where an R-rated fuse was?
No. The two are defined around different duties — E-rated fuses around transformer and feeder protection, R-rated fuses around motor short-circuit protection — and their melting criteria are different, so an equal ampere rating does not make them equivalent. If the original part is unreadable or obsolete, send us what you have and we will work back from the starter and the motor rather than from the fuse body alone.
Technical review
Specifications on this page are quoted from DENCO’s product catalog. Confirm any rating against DENCO engineering before specifying.