Switch Sizes
- Thread starter rheydel1
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barbeer
Senior Member
- Location
- Pinellas County, FL
I have never seen it in there. Other than standard fuse sizes, which is in the NEC, I believe it to be just trade standard or even manufacturer standard.
I thought that the N.E.C. said something about switches being sizes 30Amp (meaning 0-30 amps fuses would fit them), 60 amp (meaning 31-60 amp fuses would fit them), 100 amp (meanig 61-100 amp fuses would fit them etc). These were switch devise sizes though I thought and it was in the code somewhere. I think they may have taken that out though.These sizes I have memorized but I'm not sure of the larger sizes. Any info?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The NEC only lists the amp ratings of overcurrent devices, it does not care about their physical size.
In the US the fuse "cartridge" sizes are 30, 60, 100, 200, 400, 600A therefore the switch manufacturers make comparable sized switches.
I have no knowledge as to why the US standardized on these cartridge sizes.
In the US the fuse "cartridge" sizes are 30, 60, 100, 200, 400, 600A therefore the switch manufacturers make comparable sized switches.
I have no knowledge as to why the US standardized on these cartridge sizes.
lpelectric
Senior Member
Lots of info at 240.40 thru 240.61 in the '05 code. Perhaps you were thinking of the over-current sizes mentioned in 240.6
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Well, that's not exactly true. Both fuses and breakers are divided into classes where physical size is a parameter. To wit:jim dungar said:
You do know that those are the max ratings in each size, and there are others between, I take it. "Up to 30, up to 60, etc."
To a large extent, greater currents resuire larger contact area between fuses and their holders, they make bigger sparks when they open, and it helps reduce the magnitude of overfusing.
These are my guesses; it was not something I read or was told. (Disclaimer: if I am wrong, please disregard the above text.)
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
LarryFine said:
The NEC does not detail the physical size of fuses nor circuit breakers.
The NEC does not detail which range of ampacities of a device must have the same dimensions.
My guess is that NEMA created the fuse catridge sizes, UL eventually incorporated these cartridge sizes into its standards. Different classes of fuses (i.e. J, R, T) have different physical dimensions even though their ampacity break points remain the same.
There is no standard at all for circuit breaker frame sizes (not even ampacitiy ranges). In the old days there were some references to E-frame breakers but that really just meant that all ampacities from 15-100A from a single manufacturer were the same physical size. Conformance to E-frame construction did not provide interchangeability among manufacturers as is found in fuses.
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