Non fusible disconnect 2

[Noway2]

I have two questions regarding (non fusible) disconnects that I would like to ask:
1 - I have been told by a manufacturer that it is an NEC violation to add a fuse to a "non fusible" disconnect. Is this true?
2 - With a fused disconnect, for service entrance, do the fuses go up or down stream of the disconnect switch? From what I am reading, it looks like they go upstream of the disconnect, but then to replace a fuse you would either need to suit up and work live or disconnect the service at the transformer.

 

[jraef]

Being that you mention the NEC, I'm going to assume you are in the US.

1 - You can only "add fuses" to a non-fused disconnect switch if the switch and enclosure has been designed for that purpose. If not, adding the fuses may change the wire bending space, heat loading etc. So that statement is generally true if you buy a stand-alone NF disconnect in it's own box. But there may be a few mfrs out there who use the same box for a Fused or Non-fused disconnect and for fused, they just sell you the fuse holders to add in the field. However if you are building a control panel and you want to add fuses below a NF disconnect switch, have at it! If UL listing is important to you though, there is another concern. A lot of the new small inexpensive NF rotary disconnect switches are only listed under UL508 as "motor controllers", which means they can be used in a specific motor power circuit, but are NOT rated as "Branch Circuit" devices. For that, the disconnect switch must be labeled as UL98. Most of the inexpensive rotary NF disconnects are not rated UL98, so you cannot use them as Main Disconnects in a control panel and you cannot use them for SUSE (Suitable for Use as Service Equipment) applications even if it is one motor controller. Bottom line, RTFM.

2 - For service equipment, whatever you use MUST have a SUSE label on it. You will NOT find any device that has a SUSE label on it with the fuses on the line side. The only way you could accomplish this would be to use a UL98 rated NF disconnect in it's own box, then buy a box to put ahead of it that would hold the fuses. But nobody makes such a box, and if you made your own, YOU would have to submit it to UL for listing at SUSE, because at that point, IT become the service drop. Bottom line, maybe it is possible in theory but its a moot point, you cannot do it because there is no product combination that allows you to do it, not because it is "illegal".

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[jraef]

Wish we had an edit function....

Also, I have no idea what you are reading that says the fuses are supposed to go upstream of the disconnect, but whatever it is, it is incorrect. maybe what you are reading is the instruction manual for a UL508 listed NF disconnect, and you are misinterpreting their instructions about the fact that it is NOT rated as a Branch Circuit device, so you must use it in a circuit that DOES have a Branch Circuit Device upstream somewhere. They may be lazy in only showing that as fuses rather than a fused disconnect (or UL489 listed circuit breaker), but their point may just be that the NF UL508 listed motor disconnect switch must have something else ahead of it.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[Noway2]

Thank you for the clarifying answers. I really appreciate it!

Yes, the installation is in the US and is service entrance to a building with 400A service, 14KAIC. This will be feeding into an MDP. Normally, we would use the MDP as the service entrance device but because of physical constraints (including cable entry that is several feet above the MDP) the service entrance will go through a couple of pull boxes before the MDP. Consequently, the inspector wants a service disconnect, which will go on the outside upstream of the first pull box. We have on hand a NF disconnect (Square D HU365DS) and the phenolic back panel really looks like it has fuse mounts that are left non populated (the fused model is the H365DS). The box is labeled SUSE.

As far as the upstream fusing, it may be an interpretation issue on my end, in part from this thread:

http://www.eng-tips.com/viewthread.cfm?qid=197102,

in particular the post by tommom where he says "protected by an upstream dedicated fuse". This lead me to believe that the fuses would be upstream of the switch.

 

[LionelHutz]

That post is wrong assuming it's referring to a proper UL98 listed switch, which can have the fuses both be before or after the switch. If you look at UL98 listed non-fusibles, they are often the same switch mechanism as the fusible version just without the fuse clips.

As already mentioned, there are motor control switches and manual motor controllers that have stipulations on the upstream protection requirements to achieve their fault ratings. I just recently looked at a cute little manual motor starter that was 50kA rated as long as it had a circuit breaker or fuse that was 600A or smaller upstream of it.

 

[jraef]

If you download the drawings for that non-fused version, you will see it is the same enclosure used for the fused version, and also importantly, the fused 4 wire version because most likely your service will be a 4 wire and you will need to also add the neutral landing lug/pad. If you contact a Square-D distributor, they should be able to get you the fuse holders and neutral pad as replacement parts kits.

Convincing an AHJ that the unit is still valid with a nameplate on it that says it is Non-fused may be a challenge however. Good luck with that.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[Noway2]

Off hand, I am pretty sure the enclosures are the same but it is worth checking for self edification. The non fused one did have what looks like a neutral or ground pad just to the side of the switch (and as I mentioned, it had a set of mounting holes for the fuses. For just a disconnect, the cabinet was really over sized and should have plenty of bending space. It also had a good 3 point latch, which I would expect. Our sales rep did contact the factory and ask about getting the kit for the fuses and that is what started the whole, "it is a violation" thing.

You are right about the inspector. Undoubtedly, based upon past experience, I can guarantee that to be an issue. We had a lot of issues with a recent renovation job and even filed a protest (with letters signed by a PE) all the way up to the state inspections office. That was a mess. The issue was the need for motor disconnects within site of the motors. We claimed that there were two exceptions that applied (both straight from the NEC): 1) industrial location (actually industrial portion of mixed occupancy (a mech room)) with controlled access to only trained service people with LOTO, 2) this does not apply to refrigeration equipment and this was on a chiller condenser cooling tower. We won on some of the disconnects but not others. Then there was the issue with the valve actuators not having UL stickers on them, though they had been certified for use in nuclear facilities - levels beyond UL. We ended up spending a couple grand to have a lab come out and look at them. So, undoubtedly it will be at best a wash to buy a disconnect than to certify it.

Thank you again for your help. A thanks also goes to LionelHutz for pointing out the correction on that other post.

 

[jraef]

My experience with AHJs is that if you manage to win a battle, you will lose the war. They do not like to be challenged. That's an expensive stainless steel disconnect and I can understand your desire to find a home for it, but you have to pick your battles.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376