Essential Electrical System: Emergency system on same vertical switchboard section

[wyattlewis]

An old friend of mine is asking me a question about an EES system for a building he is constructing. He was asking if he was able to power his Critical ATS and his Life Safety ATS from the same vertical section of switchboard. Then, he would power separate ATS and so forth.

I have always thought that, from the generator, each EES branch required its own vertical section; however, ?700 states that the emergency system requires its own vertical section. ?517.30(B)(2) explicitly states that the Emergency system is composed of the LS and CR branch.

Am I crazy to believe that the critical and life safety branches of the EES can be powered by the same vertical section of switchgear?

I would appreciate any input you could provide! Thank you!

 

[wyattlewis]

is there no interest? do i need to clarify? or is this a head scratcher?

 

[steve66]

The problem is that the NEC never really says if the Critical system is an Emergency system (article 700), or a legally required system (article 701.)

If I read article 700.1 Scope, and 701.1 Scope, it doesn't help me. THey both sound the same. Article 700, FPN#3 doesn't help either.

701, handbook commentary says legally required systems don't need power restored for 60 seconds, instead of 10 seconds required for emergency systems. That makes me think the critical branch is an article 700 systems. Also, article 517 calls the combined critical branch and LS branch the "emergency system", and I think that means they are both article 700 "emergency systems". See figure 517.30 #1.

So I believe both the LS branch and critical branches can be powered from the same vertical section. I think that only the equipment branch and any optional branches would require a separate vertical sections.

However, there is one argument on the other side. NFPA 99 definition of the LS branch says it is an emergency branch per article 700 of the NEC. There is no similar comment on the definition of the critical branch.

So yes, the question is a little bit of a headache.

 

[wyattlewis]

The problem is that the NEC never really says if the Critical system is an Emergency system (article 700), or a legally required system (article 701.)

If I read article 700.1 Scope, and 701.1 Scope, it doesn't help me. THey both sound the same. Article 700, FPN#3 doesn't help either.

701, handbook commentary says legally required systems don't need power restored for 60 seconds, instead of 10 seconds required for emergency systems. That makes me think the critical branch is an article 700 systems. Also, article 517 calls the combined critical branch and LS branch the "emergency system", and I think that means they are both article 700 "emergency systems". See figure 517.30 #1.

So I believe both the LS branch and critical branches can be powered from the same vertical section. I think that only the equipment branch and any optional branches would require a separate vertical sections.

However, there is one argument on the other side. NFPA 99 definition of the LS branch says it is an emergency branch per article 700 of the NEC. There is no similar comment on the definition of the critical branch.

So yes, the question is a little bit of a headache.

I think what I'd like to hang my hat on would be Article 517.30(B)(2) Emergency Systems The emergency system shall be limited to circuits essential to life safety and critical patient care. These are designated the life safety branch and the critical branch AND Article 517.31 Emergency System: Those functions of patient care depending on lighting or appliances that are connected to the emergency system shall be divided into two mandatory branches: the life safety branch and the critical branch...

This makes me believe the Life safety branch and the critical branch may original at the same switchboard vertical section. I then believe most of the functions that were reserved for the legally required system now move to the equipment branch. Anything required on standby power that does not fall within the framework of the EES may have another ATS labelled optional per 517.30(A)(5).

 

[steve66]

I think what I'd like to hang my hat on would be Article 517.30(B)(2) Emergency Systems The emergency system shall be limited to circuits essential to life safety and critical patient care. These are designated the life safety branch and the critical branch AND Article 517.31 Emergency System: Those functions of patient care depending on lighting or appliances that are connected to the emergency system shall be divided into two mandatory branches: the life safety branch and the critical branch...

This makes me believe the Life safety branch and the critical branch may original at the same switchboard vertical section. I then believe most of the functions that were reserved for the legally required system now move to the equipment branch. Anything required on standby power that does not fall within the framework of the EES may have another ATS labelled optional per 517.30(A)(5).

I generally think you are right.

However, I'm not 100% sure "emergency systems" in 517 are necessarly the same as "emergency systems" in Article 700. Consider that the two articles are probably written by different Code Making Panels. Also consider that in 517, the emergency system is defined by the paragraphs you quoted. But in 700, emergency systems are defined by the Scope of the Article (in 700.1). If they were intended to be the same, they should have been defined in Article 100, at the front of the book. That's where definitions that are used in more than one article appear.

 

[wyattlewis]

I generally think you are right.

However, I'm not 100% sure "emergency systems" in 517 are necessarly the same as "emergency systems" in Article 700. Consider that the two articles are probably written by different Code Making Panels. Also consider that in 517, the emergency system is defined by the paragraphs you quoted. But in 700, emergency systems are defined by the Scope of the Article (in 700.1). If they were intended to be the same, they should have been defined in Article 100, at the front of the book. That's where definitions that are used in more than one article appear.

This is where I'm held up! Section 517.26 Application of Other Articles states The essential electrical system shall meet the requirements of Article 700, except as amended by Article 517. This is where I think the terms emergency systems are related. They are referenced in each section (517 and 700) and then called out in 517.26. Article 517 doesn't explicitly state where and when Article 700 is being modified, though.

I just find it strange that I always have seen Critical and Life Safety in separate vertical switchgear sections, and I'm only coming to this discovery now!

I would still appreciate your thoughts on the subject.

 

[wyattlewis]

Bump

Sent from my C6506 using Tapatalk 4

 

[steve66]

Like I said earlier, I tend to agree that the LS and Critical Branch can come from the same section.

But in the end, I think its a call the AHJ has to make.

Maybe the code left it vague intentionally so the AHJ can make the call as he sees fit. Hospitals have a lot of freedom to decide what is required to be on the critical branch. I could see a 100 amp critical branch that only serves bedside receptacles being treated differently than a 1200 amp critical branch that feeds the server room. But I'm just guessing here.