Fuses in Instrument Circuits in Class I Div. 2 Locations

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ajmajm

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12-10-12: The following message was posted 11/28/07 and the answers appear to be somewhat conflicting with regards to using glass type fuses in class I division II environment. If anyone can clarify that would be appreciated.

Fuses in Instrument Circuits in Class I Div. 2 Locations

From NEC 501.115(B)(3):
"For the protection of motors, appliances, and lamps...fuses shall be permitted if they are within general purpose enclosures, and if they are of a type in which the operating element is immersed in oil ..... or the fuse is a nonindicating, filled, current-limiting type."​
From NEC 501.105(B)(5):
"...fuses for overcurrent protection of instrument circuits not subject to overloading in normal use shall be permitted to be mounted in general purpose enclosures if each such fuse is preceded by a switch complying with 501.105(B)(1)."​

QUESTION:
I occassionally have people tell me that any fuse in a Class I, Div. 2 area must be per NEC 501.115(B)(3), or specifically, "nonindicating, filled, current-limiting" However, that section seems to apply to "motors, appliances, and lamps".

I'd appreciate any comments on using standard 5x20mm glass fuses in control panels based upon NEC 501.105(B)(5). I think that this section allows the use of fuses under certain conditions (instrument circuits not subject to overloading), with certain requirements (each such fuse is preceded by a switch...). I also think that this section does not restrict the type of fuse to use. One example is the Allen-Bradley SLC-500 PLC: The power supply for the SLC-500 has a glass fuse next to the power terminals (under an access door).

I see a lot of control panels with GMA-style fuses (5x20mm glass) used in Class I, Div. 2 areas, but I still hear people quote the NEC 501.115(B)(3) to say that this practice is not allowed.

What do others out there do?

If anyone has read this far, what about the use of indicating fuse terminals? I'm referring to the terminal blocks with fuse holders that also have an LED to indicate when the fuse is blown. I see these used all the time in control panels, too. The little LED circuit is not necessarily rated for a Class I, Div. 2 area, so is this okay or not? What do you think?​
 
ajmajm said:
12-10-12: The following message was posted 11/28/07 and the answers appear to be somewhat conflicting with regards to using glass type fuses in class I division II environment. If anyone can clarify that would be appreciated.

Fuses in Instrument Circuits in Class I Div. 2 Locations

From NEC 501.115(B)(3):
"For the protection of motors, appliances, and lamps...fuses shall be permitted if they are within general purpose enclosures, and if they are of a type in which the operating element is immersed in oil ..... or the fuse is a nonindicating, filled, current-limiting type."​
From NEC 501.105(B)(5):
"...fuses for overcurrent protection of instrument circuits not subject to overloading in normal use shall be permitted to be mounted in general purpose enclosures if each such fuse is preceded by a switch complying with 501.105(B)(1)."​

QUESTION:
I occassionally have people tell me that any fuse in a Class I, Div. 2 area must be per NEC 501.115(B)(3), or specifically, "nonindicating, filled, current-limiting" However, that section seems to apply to "motors, appliances, and lamps".

I'd appreciate any comments on using standard 5x20mm glass fuses in control panels based upon NEC 501.105(B)(5). I think that this section allows the use of fuses under certain conditions (instrument circuits not subject to overloading), with certain requirements (each such fuse is preceded by a switch...). I also think that this section does not restrict the type of fuse to use. One example is the Allen-Bradley SLC-500 PLC: The power supply for the SLC-500 has a glass fuse next to the power terminals (under an access door).

I see a lot of control panels with GMA-style fuses (5x20mm glass) used in Class I, Div. 2 areas, but I still hear people quote the NEC 501.115(B)(3) to say that this practice is not allowed.

What do others out there do?

If anyone has read this far, what about the use of indicating fuse terminals? I'm referring to the terminal blocks with fuse holders that also have an LED to indicate when the fuse is blown. I see these used all the time in control panels, too. The little LED circuit is not necessarily rated for a Class I, Div. 2 area, so is this okay or not? What do you think?​
Click to expand...

No fuses of any kind in ordinary enclosures without a compliant switch for instrumentaion circuits in Class I, Div. 2 areas. Period, end of sentence. Why would you think that indicating type fuse terminals would have an exception?
 
Weressl,

Let me clarify my question. I'm not concerned about the last paragraph in the original question which pertains to indicating fuses. My question is related to the section of the question which is repeated in the green text below, which was originally posted in 2007 by someone else. For Instrumentation circuits not subject to overloading, is it permitted to use a standard 5X20mm glass type fuse in a Nema 4 panel where the panel is located in a class 1 divsion 2 area, if each fuse is preceded by a class 1 division 2 rated circuit breaker? Thanks. Aaron.

I'd appreciate any comments on using standard 5x20mm glass fuses in control panels based upon NEC 501.105(B)(5). I think that this section allows the use of fuses under certain conditions (instrument circuits not subject to overloading), with certain requirements (each such fuse is preceded by a switch...). I also think that this section does not restrict the type of fuse to use. One example is the Allen-Bradley SLC-500 PLC: The power supply for the SLC-500 has a glass fuse next to the power terminals (under an access door).
 
ajmajm said:
Weressl,

Let me clarify my question. I'm not concerned about the last paragraph in the original question which pertains to indicating fuses. My question is related to the section of the question which is repeated in the green text below, which was originally posted in 2007 by someone else. For Instrumentation circuits not subject to overloading, is it permitted to use a standard 5X20mm glass type fuse in a Nema 4 panel where the panel is located in a class 1 divsion 2 area, if each fuse is preceded by a class 1 division 2 rated circuit breaker? Thanks. Aaron.

I'd appreciate any comments on using standard 5x20mm glass fuses in control panels based upon NEC 501.105(B)(5). I think that this section allows the use of fuses under certain conditions (instrument circuits not subject to overloading), with certain requirements (each such fuse is preceded by a switch...). I also think that this section does not restrict the type of fuse to use. One example is the Allen-Bradley SLC-500 PLC: The power supply for the SLC-500 has a glass fuse next to the power terminals (under an access door).
Click to expand...


...and I can't state my answer any clearer than I did. Period, end of sentence.
 
ajmajm said:
... For Instrumentation circuits not subject to overloading, is it permitted to use a standard 5X20mm glass type fuse in a Nema 4 panel where the panel is located in a class 1 divsion 2 area, if each fuse is preceded by a class 1 division 2 rated circuit breaker? ...
Click to expand...
IMO, yes.
 
My appologies, but I'm just a little confused and would like to come back for clarification. Your original answer said no fuses without a compliant switch. I do have a compliant switch and based on your original answer I was thinking that glass fuses are allowed if a compliant switch is used. Still no glass fuses, even if a compliant switch is used? Thanks. Aaron.
 
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