100% Rated Breaker to Add Load?

W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
jim dungar said:
Almost all bolted pressure switches are 100% rated by design, but enclosure manufacturers may not provide enough ventilation.
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To expand on this, looks like to use a fuse at a continuous load of 100% of its rating, you need to use a UL 977 (Fused Power Circuit Devices) switch. That standard says "1.2 Fused power-circuit devices . . are considered to be either bolted pressure contact switches or high-pressure butt-type contact switches." Oddly, it doesn't discuss 100% rating that I could see on a quick perusal, but it also doesn't have the UL 98 language imposing an 80% continuous load limit across the board.

The standard also specifies that fused power circuit devices have provisions for mounting fuses larger than 600A. So I guess if you want to use a fuse of 600A or smaller with a continuous load of 100% of the fuse rating, you're out of luck?

Cheers, Wayne
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
wwhitney said:
Oddly, it doesn't discuss 100% rating
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Agreed there does not appear to be a special additional UL listing or rating of the 'assembly' (in the NEC's words) of a 100% rated knife switch or a bolted pressure switch with a 100% rated fuse. Although I see now how the NEC wording can be construed to imply that, as that would be the case for breakers.
wwhitney said:
So I guess if you want to use a fuse of 600A or smaller with a continuous load of 100% of the fuse rating, you're out of luck?
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Use a UL 363 knife switch, they are rated for continuous load.
 
W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
tortuga said:
Use a UL 363 knife switch, they are rated for continuous load.
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Can you point me to a fused product listed under UL 363 that is labeled as 100% rated for continuous loads as an assembly?

I looked through Eaton's catalog of "Safety Switches," and there was no mention of UL 363. The General Duty and Heavy Duty switches all seemed to be listed to UL 98. So as per post #40, they would all be limited to 80% of the fuse rating for continuous loads.

Cheers, Wayne
 
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