I am currently working on a hospital and I need some guidance on my design. Currently, this hospital has has 3 transfer switches. One each for the equipment system, life safety branch and critical branch. Upon normal source failure, the nonessential loads of the hospital are shed. During my site visit, I was told that the generator can handle approximately half of the entire hospital's load. The client has requsted that he would like the generator to handle the entire hospital. As an estimation and looking at the kilo watt hour meter log for the last couple months, I have ROUGLY sized the generator as 500 kw ( it was 200 kW). Load calculations will follow. Looking at article 517.30 in the 2005 NEC, I see that for 150 kVA or less a minimum of 1 transfer switch is required. This however, is not entirely my case as non of the hospital's load is shed during utility failure. Can I replace the 3 transfer switches with one for my case? Can someone please explain why three transfer switches are required for loads greater than 150kVA? Any references would also be appreciated. Thanks and sorry for the long read. patrick
Hospital Transfer Switch
- Thread starter pdemapan
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chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
That sounds small to me. 800A hospital? Will be looking foward to seeing the load calcs.pdemapan said:
patrick,
It takes years to understand how to properly set up a system like this in a
hospital. I would recomend finding a co-worker who has been through this
type of design already to answer the questions you don't know to ask at this
time. Please don't feel offended, I offer this in good intentions.
Good Luck,
It takes years to understand how to properly set up a system like this in a
hospital. I would recomend finding a co-worker who has been through this
type of design already to answer the questions you don't know to ask at this
time. Please don't feel offended, I offer this in good intentions.
Good Luck,
I don't see where you said the essential load is under 150KW?? If its not, you can['t combine the transfer switches.
Even if it is under 150KVA, I wouldn't eliminate the 3 transfer switches. The additional switches provide added safety. For example, it makes it less likely that an AC unit will lock up, trip a breaker, and plunge the surgery dept. into darkness.
That said, you will also have to put all the other hospital loads on a 4th transfer switch. See 517.30, (B)(5). The other hospital loads are optional, and must be served by a separate transfer switch.
Steve
Even if it is under 150KVA, I wouldn't eliminate the 3 transfer switches. The additional switches provide added safety. For example, it makes it less likely that an AC unit will lock up, trip a breaker, and plunge the surgery dept. into darkness.
That said, you will also have to put all the other hospital loads on a 4th transfer switch. See 517.30, (B)(5). The other hospital loads are optional, and must be served by a separate transfer switch.
Steve
hbendillo
Senior Member
- Location
- South carolina
You cannot get rid of the other transfer switches. My advice would be to set up a separate transfer switch for the remaining load. Since it is non-essential you could make it a maual transfer switch to save money and guard against overloading the system if the hospital is expanded in the future. A manual transfer would allow you to manually shed loads before tranferring if the load grows beyond capacity in the future.
hbendillo said:
I don't think that would comply with the requirements for automatic load shedding in 517.30(B)(5).
On the other hand, I have always wondered if load shedding is still required if the generator is designed large enough that overloading will never happen.
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