Suitability of IEC style fuses for supplementary motor branch protection.

[Ugly]

Didn't see this exact thing discussed in search results I found.

Considering similar to Littlefuse 477 series, a "5X20mm, time lag, ceramic body, 500VAC" at various ampacities. I can't see anything specific in the NEC preventing their use in this app as long as appropriate current rating per 430.52 is applied. Anybody have an opinion otherwise?

The application in this case is a couple chain hoist motors subcircuit which is on a stepped down (400VAC) 5 wire branch circuit, and we would like to run smaller gauge copper out to the hoists.

Howdy, I'm new. Nice place here.

 

[don_resqcapt19]

I would not see that as supplementary branch circuit protection. I would see it as the branch circuit OCPD. Are these fuses listed for supplementary protection or are they listed for branch circuit protection?

 

[Ugly]

On re-evaluation I'd have to agree with your point about this being branch OCPD instead of supplementary protection since we are reducing wire gauge at this OCPD and so must protect the wire.

Are these fuses listed for supplementary protection or are they listed for branch circuit protection?

I can't see that they are listed for either from reading the data sheet. If this trurns out a significant and relevant point please pardon this embedded electronics developers as yet underdeveloped intamacy with NEC and its interpretation. As I mentioned in my previous post, I'm new and not just to this forum as it turns out.

However, there are several quoted agency approvals such as PSE, VDE (Brazil), UL (recognised), CE and some other S symbol with a circle around it I'm not familiar with.

Is this lack of a "listing" significant? Again pardon my newbishness but what NEC article does one find the required fuse listings per intended application?

 

[don_resqcapt19]

UL recognized is only suitable for use as a part of a system. It looks like that fuse has an interrupting rating of only 100 amps. Most branch circuits can supply a lot more fault current than that. The fuse must have an interrupting rating that is greater than the available fault current.
The following is from the UL white book information that the fuse is classified under.

This category covers supplemental fuses, which are also described as miscellaneous, miniature, and micro fuses. These fuses provide supplemental protection in end-use equipment to provide protection for components or internal circuits. They are not suitable for branch or feeder circuit use. Physical dimensions are not specified, but dimensional limitations apply to prevent insertion of supplementary protection fuses into branch or feeder circuit fuseholders intended to accommodate branch or feeder circuit fuses of the Class CA, CB, CC, CD, G, H, J, K, L, R or T Type.

 

[Ugly]

Thank you. It seems this follows directly from 90.7. This is something I probably should have known considering that a careful read of the first two pages of my codebook would have revealed my answer.

 

[Ugly]

If anyone is interested and in the interest of making this a more useful thread for a search hit... I believe I've found the definition of what makes up a branch circuit listable fuse. Unfortunately I only found it in a manufacturer documentation. Obviously some official reference would be much more satisfying but the Bussman explanation seems logical and consistent with the rational I'd expect NEC to use. Any specific reference to this in code anyone could provide would be well appreciated. I still think both 90.7 and 110.3 (B) are a little vague for my tastes.

I dug up this Bussman fuse selection guide http://www.bussmann.com/library/docs/spd02/SPDSection03.pdf that lists four requirements of branch circuit fuse overcurrent protection.

The Littlefuse 477 series I was originally considering clearly doesn't meet all the requirements.

Requirements from Bussman paper:

1. Must have a minimum interrrupting rating of 10,000 amps.
2.must have a minimum voltage rating of 125V.
3. Must be size rejecting such that a fuse of lower voltage cannot be installed in the circuit.
4. Must be size rejecting such that a fuse with a current rating higher than the fuseholder rating cannot be installed.