Article 701 - Separate Transfer switches

[Npstewart]

Isn't there an exception somewhere in article 701 that allows you to use a single transfer switch that feeds the (3) different load types when the load is under a certain kW/kVA ? Application is a surgery suite with office loads.

 

[charlie b]

701 is not going to give you any requirements related to emergency systems. I had thought that article 701 would not allow the transfer switch that supplies legally required standby loads to also supply optional standby loads. But now I don't see those words anywhere in the article. Can someone show me what I am missing? :?

 

[david luchini]

Isn't there an exception somewhere in article 701 that allows you to use a single transfer switch that feeds the (3) different load types when the load is under a certain kW/kVA ? Application is a surgery suite with office loads.

You are thinking of the Essential Electrical Systems requirements in Article 517.

 

[Npstewart]

You are thinking of the Essential Electrical Systems requirements in Article 517.

Thanks Dave, you are right, thats exactly what I was thinking of.

So im thinking 517.30 diagrams would apply to this installation. Not Article 700/701.

 

[steve66]

Thanks Dave, you are right, thats exactly what I was thinking of.

So im thinking 517.30 diagrams would apply to this installation. Not Article 700/701.

My understanding is that article 700 and 701 would still apply to the respective branches. However, 517.30 does allow all three branches to be supplied from a single transfer switch if you meet the conditions noted.

However, I believe there must still be separation between the branches after the transfer switch. For example, the transfer switch might supply 3 different feeders to 3 different panelboards.

Also, I don't believe there is anything in 517 that would allow non-required (optional) loads to be supplied from the same ATS.

Charlie: I think you are looking for 700.5 (D).

 

[charlie b]

Charlie: I think you are looking for 700.5 (D).

Not quite. I had missed the connection with the hospital for this question. So let's set that (i.e., 517) aside for a moment and talk about your basic residential, commercial, or industrial facility. 700.5(D) tells me that I can't use one transfer switch to serve emergency loads and also to serve either legally required or optional standby loads. However, what tells me I can't use one transfer switch to serve both legally required and optional standby loads? I have always used separate ATSs for these two systems, but what tells me I must?

 

[Npstewart]

Currently we are planning on a single generator with a single transfer switch that feeds (3) separate panels; Life Safety (emergency lights), Critical (Operating Room Circuits), and standard loads (misc. lights/receptacles). This is only for a 35 kVA generator. Had the load been 150+ kVA than we would have had 3 separate transfer switches for the 3 different panels. As far as I know, this is code compliant.

 

[steve66]

Currently we are planning on a single generator with a single transfer switch that feeds (3) separate panels; Life Safety (emergency lights), Critical (Operating Room Circuits), and standard loads (misc. lights/receptacles). This is only for a 35 kVA generator. Had the load been 150+ kVA than we would have had 3 separate transfer switches for the 3 different panels. As far as I know, this is code compliant.

I'm not sure the putting the "standard loads" on the ATS is compliant. I think those loads need to be designated as Critical loads, or Equipment Loads.

However, a health care facility has a lot of freedom to designate what is on the Critical and Equipment Branches. I believe critical loads can include "selected loads necessary for efficient operation of the facility", which is basically a catch all. And I believe you can be even more liberal about what is put on the equipment branch.

So it may be more a mater of what you call those loads than anything else.

 

[steve66]

Not quite. I had missed the connection with the hospital for this question. So let's set that (i.e., 517) aside for a moment and talk about your basic residential, commercial, or industrial facility. 700.5(D) tells me that I can't use one transfer switch to serve emergency loads and also to serve either legally required or optional standby loads. However, what tells me I can't use one transfer switch to serve both legally required and optional standby loads? I have always used separate ATSs for these two systems, but what tells me I must?

Yes, now I'm having Deja-vu. I also thought that was a requirement, but then realized its not in 701 or 702. So it doesn't apply to legally required or optional standby systems. However, it does apply to COPS, which seems odd to me.

I have a hard time trying to decipher which loads are 700, and which are 701.

 

[charlie b]

I have a hard time trying to decipher which loads are 700, and which are 701.

And the NEC is not going to help you figure that out. The NEC defers that decision to other authorities.

 

[Maders]

My understanding is that article 700 and 701 would still apply to the respective branches.

Hi. Quick (and late question), why do articles 700 and 701 apply to the respective branches outlined in article 517 (life safety, critical and equipment)?

 

[don_resqcapt19]

Hi. Quick (and late question), why do articles 700 and 701 apply to the respective branches outlined in article 517 (life safety, critical and equipment)?

Per 517.26, Article 700 only applies to the life safety branch, and 701 does not apply to Article 517 installations.

 

[Maders]

Thank you for the reply. That is my understating as well. Just making sure that I was not missing anything.

 

[Pharon]

However, what tells me I can't use one transfer switch to serve both legally required and optional standby loads? I have always used separate ATSs for these two systems, but what tells me I must?

You can use the same ATS for both, under either of these two circumstances:

701.4 Capacity and Rating
A legally required standby system shall have adequate capacity
and rating for the supply of all equipment intended to be operated
at one time. Legally required standby system equipment shall be
suitable for the maximum available fault current at its terminals.
The legally required standby alternate power source shall be
permitted to supply both legally required standby and optional
standby system loads under either of the following conditions:
(1) Where the alternate source has adequate capacity to handle
all connected loads
(2) Where automatic selective load pickup and load shedding
is provided that will ensure adequate power to the legally
required standby circuits

 

[lielec11]

Yes, now I'm having Deja-vu. I also thought that was a requirement, but then realized its not in 701 or 702. So it doesn't apply to legally required or optional standby systems. However, it does apply to COPS, which seems odd to me.

I have a hard time trying to decipher which loads are 700, and which are 701.

Right, typically the AHJ makes the call on what falls under 701. However, I feel 700 is fairly straight forward. Egress lighting, fire alarm system, etc. I almost equate NEC 517 life safety systems to NEC 700.

 

[iwire]

In my world of retail and office buildings article 701 never seems to come into play. It all article 700 or 702.

Fire alarm, egress lighting, exit signs, sometimes door operators are pretty much the only 700 loads all other generator supplied loads are 702.