NEC 517.30 (B)(4)

[mrelectric]

I am new to the forum but I have learned quite a lot by just reading through different threads. I need your input on the intent of 517.30(B)(4) on this scenario.

If I have an essential load consisting of 50KVA Life Safety branch, 100KVA critical circuit branch, and 150KVA non delay equipment branch, will the code allow me to put 1-150KVA rated transfer switch (TS) to serve both the life safety and critical branch and 1-150 KVA rated TS for the equipment ( as opposed to 1-50KVA, 1-100KVA, 1-150KVA TS for each of the branches) ?

I am often faced with a scenario where I have limited space to put my transfer switch in the electrical room. If such configuration is allowed this could reduce my number of TS.

Thank you for your replies.

 

[BJC]

No.
You need 2 transfer switches. one for the 50 KVA load and one for the 250 remainder.

 

[mrelectric]

Thanks for the reply, BJC but I don't get what you mean. 517.30 (B)(4)allows combining the life safety with critical and equipment auto provided that the maximum demand in the essential system ( which is composed of life, critical, and equipment auto) is 150KVA. My question is this:

Can I subdivide the essential loads to several essential branches with a maximum of 150KVA to comply with 517.30(B)(4)?

Thanks for the input.

 

[BJC]

I tink I was wrong and your right. Thats what happens when I am traveling and didn't look at the codebook.
Sorry mrelectric. That would be my first mistake of 07 but I made it last year. I was confused by the passage that refers to section 700.

 

[rbulsara]

I would beg to differ with both of you above.

Single ATS is permitted only when total of the essential equipment, life safety and Critical branch is 150kVA or less for the "entire" facility. If the total of the load to be place on ATS is in excess of 150kVA, you will need one or more ATS for each branch of the Emergency System (life safety and critical patient care) and for the essential equipment. Read 517.30(B)- (1), (2), (3) and (4) carefully. Especially the (4).

You cannot subdivide the loads in chunks of 150kVA and mix and match the type of loads on ATS for hospitals, per NEC.

 

[mrelectric]

RBULSARA,
I am leaning towards your interpreatation because the NEC handbook' refers an example to a small hospital with a max capacity of 150 KVA. But how the NEC defines essential system does not convince me that it is referring to the 'total' essential load. I may be wrong but I could not convince myself that several essential system/s may not or never exist in one facility. Any input?

 

[rbulsara]

You can have mutilple ATS for essential loads (or any category of loads), but you can not mix and match the type of loads on one ATS if the total "emergency/essential load" is in excess of 150kVA.

So if you have 175kVA of essential, 25 kVA of Life safety and 20kVA of critical load. You need "at least" three ATSs, one for each of these categories. You can also have one or more ATS for any of the branches/categories.

For small facilities, NEC permits a singel ATS so long as total essential/emergecy load does not exceed 150kVA.

By the way, proper categorization of Hospital loads is defined by NFPA 99.

 

[EEJaime]

The 150 kVA maximum absolutely is for the entire facility. In my area, the California Office of Statewide Health Planning and Development, (OSHPD), enforces the codes for health care facilities, and we have been designing and adding to facilities for over 25 years. They will not allow a subdivided system in 150 kVA 'chunks' as rbulsara states. You will need three ATS' for larger systems. I know we always have to fight for floor space, but it is extremely important to get the space alloted up front. Shoe-horning switchgear into an electrical equipment room after the walls are up is no fun, and will get very expensive, very quickly.

Best of luck.