Health Care EES (less than 150kVA) - Article 700.10(B) & 517.31(B)

[wyattlewis]

hello everyone!

I am trying to understand a Type 1 EES system with continuous load of switch of 150kVA or less. My previous jurisdiction had a very strict interpretation of these code sections and my new jurisdiction leaves this entirely to the engineer of record. I am hoping for some clarification and discussion to bring me to a place of comfort! Relevant code sections have been added to the bottom of this post for reference and discussion purposes.

So the distribution in question is as such.

[150kVA or less generator with single output breaker] --feeder1--> [Single ATS] --feeder2--> [single panelboard distribution EDP]

EDP is a standard (i-line or equal) distribution board containing distribution circuit breakers for the life safety branch, the critical branch, and the equipment branch.

My interpretation of the code for this installation says this is not code compliant.

• The generator is the emergency source.
• feeder1 may be used to power the ATS per 700.10(B)(5)d.
• The use of the single ATS is allowed per 517.31(B)(2).
• feeder2 is again allowed per 700.10(B)(5)d.
• Panel EDP is not allowed by code to contain the life safety circuit breaker (emergency) with the critical and equipment branch circuit breakers (nonemergency) per 700.10(B)(5)c.

The life safety circuit breaker in EDP is a creating a mixed load situation where an emergency circuit and a nonemergency circuit are originating from the same panelboard enclosure.

Am I wrong in this line of thinking?

If you disagree, can you please provide me with a code reference that can show me the error of my ways?

THANK YOU in advance for taking the time to read this and to help me in my struggles!

- W



Relevant code sections:
(this will be based on NEC 2020, though I can find no major code changes to the relevant sections back to NEC 2014)

517.26 - The life safety branch of the essential electrical system shall meet the requirements of Article 700, except amended by Article 517.

517.31(B)(2) - One transfer switch shall be permitted to serve one or more branches in a facility with a continuous load on the switch of 150 kVA (120 kW) or less.

700.10(B) Wiring. Wiring from an emergency source or emergency source distribution overcurrent protection to emergency loads shall be kept entirely independent of all other wiring and equipment unless otherwise permitted in 700.10(B)(1) through 700.10(B)(5):

(1) Wiring from the normal power source located in transfer equipment enclosures​

(2) Wiring supplied from two sources in exit or emergency luminaires​

(3) Wiring from two sources in a listed load control relay supplying exit or emergency luminaires, or in a common junction box, attached to exit or emergency luminaires​

(4) Wiring within a common junction box attached to unit equipment, containing only the branch circuit supplying the unit equipment and the emergency circuit supplied by the unit equipment​

(5) Wiring from an emergency source to supply emergency and other (nonemergency) loads in accordance with 700.10(B)5a., (B)b., (B)c., and (B)5d. as follows:​

a. Separate vertical switchgear section or separate vertical switchboard sections, with or without a common bus, or individual disconnects mounted in separate enclosures shall be used to separate emergency loads from all other loads.​

b. The common bus of separate sections of the switchgear, separate sections of the switchboards, or the individual enclosures shall be either of the following:​

(i) Supplied by single or multiple feeders without overcurrent protection at the source​

(ii) Supplied by a single or multiple feeders with overcurrent protection, provided that the overcurrent protection that is common to an emergency system and any nonemergency system(s) is selectively coordinated with the next downstream overcurrent protective device in the nonemergency system(s).​

c. Emergency Circuits shall no originate from the same vertical switchgear section, vertical switchboard section, panelboard enclosure, or individual diisconnect enclosure as other circuits.​

d. It shall be permissible to utilize single or multiple feeders to supply distribution equipment between an emergency source and the point where the emergency loads are separated from all other loads.​

I have omitted some of the 517.26 exceptions as they did not apply here, but i can keep this updated and edited as new information comes to light!

 

[gh0st]

Hi. The ESS (LS, Crit., Eq.) can be powered via single ATS if the load is 150kVA or less. See figure 517.31(b) of the 2017 NEC for sample SLD. The mixing of loads is acceptable in a healthcare application only and not others (office, school, etc). Note, this does not include optional standby loads.

 

[wyattlewis]

Do you have a clarification anywhere that says the diagram for 517.31 supercedes the code written in 700?

There are also some pretty sketchy schematics that are definitely not code compliant in the transformers section of the code.

Also, a common bus described in the 517.31 figure is not inherently against the code so long as the bus complies with the rules clearly laid out in 700.10(B).

 

[steve66]

To me it doesn't seem clear if the intent was for the LS breaker to be separated from the critical and equipment branch breakers. The diagram in 517.31 shows the 3 branches separating without any breakers (like they are all tapped off a bus duct or something similar), so I think you could be right.

However, since you are at less than 150 KVA, all the breakers will probably be 400A or less. With small breakers like that, I find it much less likely that a arc will occur, or that it would affect the other breakers and wiring if it does.

If you are concerned about it, put feed-through lugs in the Iline panel and run tap conductors to a separate disconnect for the Life Safety branch.

 

[wyattlewis]

To me it doesn't seem clear if the intent was for the LS breaker to be separated from the critical and equipment branch breakers. The diagram in 517.31 shows the 3 branches separating without any breakers (like they are all tapped off a bus duct or something similar), so I think you could be right.

However, since you are at less than 150 KVA, all the breakers will probably be 400A or less. With small breakers like that, I find it much less likely that a arc will occur, or that it would affect the other breakers and wiring if it does.

If you are concerned about it, put feed-through lugs in the Iline panel and run tap conductors to a separate disconnect for the Life Safety branch.

So in this case, I've been told by AHJ's to provide an arrangement after the ATS that is similar to this distribution from the generator.

https://imgur.com/a/l0hnmBb

 

[steve66]

I was wondering why you separated the Legally required breaker from the optional breaker. But I see that's how its shown in figures 700.10B a and b.

It doesn't seem like the authors of article 700 talked to anyone about article 701, because 701 allows the wiring for the legally required loads to occupy the same raceways and enclosures as other general wiring. So the figures in 700.10 seem to be showing an requirement that doesn't exist.

I don't even see anything that requires the the legally required ATS to be dedicated to LR loads. So in your diagram, the normal loads and the legally required loads should be able to come from the same ATS.

But I don't think you even have a "legally required" branch anyway, and you didn't mention an optional branch. From what I see, the LS branch is the only one that needs a separate breaker.

 

[wyattlewis]

I was wondering why you separated the Legally required breaker from the optional breaker. But I see that's how its shown in figures 700.10B a and b.

It doesn't seem like the authors of article 700 talked to anyone about article 701, because 701 allows the wiring for the legally required loads to occupy the same raceways and enclosures as other general wiring. So the figures in 700.10 seem to be showing an requirement that doesn't exist.

I don't even see anything that requires the the legally required ATS to be dedicated to LR loads. So in your diagram, the normal loads and the legally required loads should be able to come from the same ATS.

But I don't think you even have a "legally required" branch anyway, and you didn't mention an optional branch. From what I see, the LS branch is the only one that needs a separate breaker.

This is a provided detail by the NEC. I believe the intent here to simply show that you must separate out the Art. 700 loads. I do not look further into it because it is a visual aid meant for 700 and not 701/702 which those sections cover nicely.

For the purposes of this discussion legally required and option standby loads are secondary to the separation of a a 700 load and in this case the life safety branch.

Critical and Equipment branches eventually do become legally required (again a different discussion), but those requirements of 701 are never referenced due to the completeness of Art 517 and NFPA 99.