Replacing a Magnetically Locked Breaker (Mag-Loclk) with a Fused Disconnect - NEC 695

[jar546]

This is a good one. Actually, a nice change of pace around here from all the boring residential crap. Here is the scenario I am looking to create a discussion on.

I have an older high-rise built in the early 80s that has a POCO vault inside the building, and on the other side of the wall is a Mag-Lock service disconnect for the fire-pump inside the generator room. This is a separate service for the fire-pump is CT metered inside the POCO vault with the meter inside the generator room. Just trying to paint a picture. Here is how this breaks down.

The Mag-Lock 400A breaker/service disconnect feeds the normal power to the emergency generator ATS. The ATS is not service-rated. The ATS then goes on to feed the Fire Pump Control Panel (FPCP). The Mag-Lock breaker is its own disconnect and needs to be replaced. The electrician wants to replace it with a 400A fused disconnect because it is cheaper than a Mag-Lock breaker and easier to get.

My first thought was that they don't need a separate service disconnect, and they can just go right to the existing ATS, but it is not service-rated. Since this is off of a generator, they can't just go directly to the FPCP. If they install a service-rated fusible disconnect, it has to be capable of being locked in the closed (on) position and it has to be monitored by the fire alarm control panel (FACP). I don't believe the current service disconnect is monitored by the FACP.

What are your thoughts on this?

 

[wwhitney]

Is the question whether there is some reason a fused disconnect can't comply with the requirements for fire pump disconnects given in NEC 695.4(B)(3)?

As long as it is lockable closed, nothing jumps out at me as precluding a fused disconnect, but this is my first time reading that section. Locking it closed would suffice for compliance with 695.4(B)(3)(e), it wouldn't need to be monitored by the FACP for compliance with that section.

Cheers, Wayne

 

[jar546]

Is the question whether there is some reason a fused disconnect can't comply with the requirements for fire pump disconnects given in NEC 695.4(B)(3)?

As long as it is lockable closed, nothing jumps out at me as precluding a fused disconnect, but this is my first time reading that section. Locking it closed would suffice for compliance with 695.4(B)(3)(e), it wouldn't need to be monitored by the FACP for compliance with that section.

Cheers, Wayne

I believe the fused service-disconnect will have to be capable of being locked in the closed/on position. Not all are.

 

[wwhitney]

I believe the fused service-disconnect will have to be capable of being locked in the closed/on position.

Yes, that what I said and that's what 695.4(B)(3) says.

A related question is suppose you have a disconnect that looks like the one pictured below (random picture chosen; this exact disconnect may not be large enough for the application, and may not be service rated.) It is lockable open because a hole in the handle (which you can't see in the picture) will line up the hole in the bottom of that semicircular projection on the right when the handle is in the off position. Is it acceptable to make the disconnect lockable closed by simply drilling an additional hole in the top of that semicircular projection that lines up with the hole in the handle in the "on" position?

I would say yes. That semicircular piece is obviously designed so the manufacturer has the option to do exactly that. Doesn't matter who drills the hole.

Cheers, Wayne

 

[jar546]

Yes, that what I said and that's what 695.4(B)(3) says.

A related question is suppose you have a disconnect that looks like the one pictured below (random picture chosen; this exact disconnect may not be large enough for the application, and may not be service rated.) It is lockable open because a hole in the handle (which you can't see in the picture) will line up the hole in the bottom of that semicircular projection on the right when the handle is in the off position. Is it acceptable to make the disconnect lockable closed by simply drilling an additional hole in the top of that semicircular projection that lines up with the hole in the handle in the "on" position?

I would say yes. That semicircular piece is obviously designed so the manufacturer has the option to do exactly that. Doesn't matter who drills the hole.

Cheers, Wayne

I would not approve simply drilling a hole in this case because it is a fire pump service disconnect and would violate the UL listing of the product by modifying it. They already asked about that, and I said no. It also has to be service-rated. If the ATS were service-rated, they could simply eliminate the service disconnect, but it is not. They were trying to save money by not buying a mag-lock breaker.

 

[wwhitney]

I would not approve simply drilling a hole in this case because it is a fire pump service disconnect and would violate the UL listing of the product by modifying it. They already asked about that, and I said no.

Well, for the particular product pictured, that seems excessive. The question of lockability for it is evidently simple enough that you can see that an extra hole will be effective and without detriment. And the inspector certainly has the authority to approve it.

For an option that comes standard from the factory with lock on provisions, Square D's catalog says:

Lock OFF / Lock ON
Optional Lock-OFF Guard Kit Installed
Lock off provisions are standard on Heavy Duty Switches
Lock-on is also available as a factory modification on Type 12 and 304 Stainless Steel
Type 4X enclosures. Obtain by selecting on product configurator.

So certainly 400A 1 or 3 phase fusible disconnects with lock on provisions are commercially available.

Cheers, Wayne

 

[jar546]

Well, for the particular product pictured, that seems excessive. The question of lockability for it is evidently simple enough that you can see that an extra hole will be effective and without detriment. And the inspector certainly has the authority to approve it.

For an option that comes standard from the factory with lock on provisions, Square D's catalog says:



So certainly 400A 1 or 3 phase fusible disconnects with lock on provisions are commercially available.

Cheers, Wayne

I do believe that to be the case.

 

[jar546]

What is also interesting is that the contractor told me the original design from 1981 showed a 300A disconnect. He does not know why it was changed to a 400A so I recommended he check the LRC of the fire-pump and jockey pump motors to make sure that he has the correct-sized disconnect.