Hospital Ground Fault

[brother]

Im trying to understand 517.17 NEC 2005. Had a situation where the ground fault at a hospital trip, and when it switch to emergency power, it also tripped. Of course later they found the problem. But here is my question,

When reading 517.17(B)Feeders (1) "additional levels of ground fault protection shall NOT be installed as follows: on the load sid side of an essential electrical system transfer switch."

Was it wrong to have a ground fault trip when the emergency power came on?? Im not quiet sure i fully understand this here. thanks for your help.

 

[M. D.]

A bit of a mess, but I hope it helps ....

The Less Obvious ?Not Needed? List
Because of their life safety issues, health care facilities and emergency power generators represent
special applications, which have evolved with some unique requirements. With regard to EGFP in
health care facilities, article 517.17B stipulates that, where required by articles 215.10 or 230.95,
EGFP must also be incorporated in the feeder disconnecting means one additional step
downstream of the first device. This is a requirement regardless of the rating of the second
downstream feeder, be it 1000A or 100A, because its purpose is selectivity. However, this
additional level of EGFP may not be installed on:
1. The load side of essential electrical system transfer switches.
2. Between the essential system generator(s) (ref 517.35B) and the essential system transfer
switches.
3. On electrical systems other than solidly grounded wye between 260 to 600VAC, inclusive.
The intent of the first two restrictions would seem to be the prohibition of inserting EGFP into an
essential electrical power system. Item 1, however, only prohibits locating the additional step of
EGFP on the secondary side of that transfer switch, not the first. The same is true for item 2 with
respect the installation of the additional level of EGFP between the essential system?s generator
and transfer switch.
In fact, the code permits the addition of EGFP to the emergency electrical system. Article 700.26,
only states that the alternate source of power for an emergency system ?shall not be required? to
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have automatic EGFP. This is quite different than a clear prohibition. It is left to the commentary of
the 2005 NEC Handbook, article 700.7D, to provide necessary clarity, which is not included in the
basic code publication. That commentary states that locating any EGFP in such an application is
?not appropriate.? The code?s intent in these applications is clear and no level of automatic EGFP
should be applied to the alternate emergency power source. But ?ground faults can occur in such
systems, and they can result in equipment burndown.? So states the handbook commentary to

http://64.233.169.104/search?q=cache:aaHgR_QT78QJ:www.geindustrial.com/Newsletter/Spring05Ground.pdf+517.17+(B)+NEC&hl=en&ct=clnk&cd=1&gl=us

 

[jim dungar]

Im trying to understand 517.17 NEC 2005. Had a situation where the ground fault at a hospital trip, and when it switch to emergency power, it also tripped. Of course later they found the problem. But here is my question,

When reading 517.17(B)Feeders (1) "additional levels of ground fault protection shall NOT be installed as follows: on the load sid side of an essential electrical system transfer switch."

Was it wrong to have a ground fault trip when the emergency power came on?? Im not quiet sure i fully understand this here. thanks for your help.

517.17(B) says ground fault tripping should not be installed after a transfer switch. If the GFI opens the emergency circuit what good is it having the emergency supply?

Where was the GFI that tripped located?

 

[benaround]

Remember this is under FEEDERS not branch circuits.

 

[brother]

It looks like what they got going on here is when the transfer switch switches over to the 'emergency power' , the GFP is between that source and the transfer switch.

I suppose this is 'legal' then since its BEFORE the transfer switch if i interpet the code correctly. It just looks like this would be forbidden. correct me if im wrong.

 

[brian john]

How many levels of GFP does this facility have?
Is the GFP on the Main CB in the generator?
Does the hospital have Zone Selective GFP?
Have the systems be set per a coordination study and tested?
What Faulted to result in the GFP operation?

 

[RB1]

The shouldn't be GFP on the generator. Only GF annunciation is permitted on a generator supplying an essential electrical system (700.7(d)).

 

[brother]

How many levels of GFP does this facility have??

Im not 100%sure, but i think on this particular run its 2. this is something worth looking into, but it is a HUGE hospital.

Is the GFP on the Main CB in the generator???

Its not on the generator it self, the generator is at another location and GFP (when it switches to emergency power) is at another location. The thing with this hospital is that it has more than one service, so its not just a 'generator' that steps in when they need emergency power. I think it only comes in if something happens to the other back up service in this location. However they CAN just go to generator power in this emergency hook up. The main ISSUE i have with this set up is in NEC 2005 517.17 (B)(2)

"The additonal levels of ground fault protection shall NOT be installed as follows: (2) Between the on-site generating unit(s) described in 517.35(B) and the essential electrical system transfer switch (es)"

Does the hospital have Zone Selective GFP??

Again, im not sure, I think they do.

Have the systems be set per a coordination study and tested??

All these questions i wish i could give definite answers, but im new here and so i can only ASSUME that it was when they had it installed. then again you know what they say when you 'ASSUME' something.

What Faulted to result in the GFP operation?

there was a line to ground fault (we meggered it) that we found on some equipment that it supplied. we have taken it offline to get it fixed. It has to be on the emergency /essential power panel for the hospital. It supplys some type of ventilation or suction or something.

Im still new to this stuff, and maybe an engineer can explain this thing, but it really sounds like they are NOT suppose to have a GFP on the emergency side going to this equipment via the transfer switch.