Cable trays in hospitals.

Status
Not open for further replies.
Re: Cable trays in hospitals.

Steve,
I wish there was something that made it a little clearer.
Click to expand...
you and I both. :)

Here is my reasoning; in that the Essential System makes up both the Equipment and Emergency Systems, I would still think the vertical brackets would cover all the way back to the generator. As I said in my earlier post this is just my opinion.

I would ask why would we mechanically protect any portion of this system less than another part?

We would want the chain to be of equal strength along it's entire length.

Roger
 
Re: Cable trays in hospitals.

Rodger:

If the emergency system begins at the generator, wouldn't you have to have a separate circuit breaker at the generator in order to meet the separation requirements of 517.30(C)(1)?
 
Re: Cable trays in hospitals.

Ron, I can see your point, but from the supply source to the transfer equipment there is no seperation of the two "Essential Systems". This would not mean that the "Emergency System" doesn't exist as part of the supply wiring.

Roger

[ February 04, 2005, 06:21 AM: Message edited by: roger ]
 
Re: Cable trays in hospitals.

Thanks Steve,
I know it's a good application but if you haven't seen something like this, and understand what the engineering behind it is, it looks scary.
The installing electrical contractor's leadman disavowed anything to do with the job- "I just did what I was told." This guy ran a job where 1000' of 4" RMC was bent and screwed together around existing switchgear, conduits and made it look simple and beautiful. He never ran any MI though; he knew what he could do with RMC and how it held up. I think he still wishes it was RMC.

MI is one of those rare applications that many very good electricians only hear about....in places like this but never actually get their hands on in real life.

That's what I was thinking concerning the comments.
Rick
 
Re: Cable trays in hospitals.

Posted by rb:

If the emergency system begins at the generator, wouldn't you have to have a separate circuit breaker at the generator in order to meet the separation requirements of 517.30(C)(1)?
Click to expand...
There are some members here who are of the opinion that is the case. Maybe they are right, or maybe not. I'm not qualified to say.

Roger posted:

I would ask why would we mechanically protect any portion of this system less than another part?
Click to expand...
Here is what I'm thinking might apply: The normal source to the transfer switch doesn't require protection because it is backed up by the generator. The generator source may not require protection because it is backed up by the normal source (at least 99% of the time).

So I can see how the wiring from the transfer switch on might require more protection.

Again this is just speculation on my part - I don't see anything in the code that says I'm right or I'm wrong.

Steve
 
Re: Cable trays in hospitals.

I have always thought that the emergency system began when the feeder conductors left alternate source distribution panel.
 
Re: Cable trays in hospitals.

Steve,
The generator source may not require protection because it is backed up by the normal source (at least 99% of the time).
Click to expand...
and the problem would be if a feeder or feeders from the Alternate Source(s) was / were damaged, it would not be apparent until needed.

This would make all the other protection a worthless effort.

Let me ask, when does a generator become an Emergency Generator?

I must point out that I hope some one can without a doubt, prove my opinion wrong. :)

I have installed almost all feeders from the generators to the transfer equipment in PVC, except for one facility where RMC was used on 4160 generators . This was only because the RMC was specifically called for in the specs.

Roger
 
Re: Cable trays in hospitals.

Well, I was thinking that monthly testing would find any problems with the generator feeder to the transfer switch. But after reading a little bit of NFPA 110, I see that a load bank could be used for the test. So the feeder wouldn't necessarily be tested.

Steve
 
Re: Cable trays in hospitals.

The devil is in the details...or definitions in this case.
Assuming we are talking about a large healthcare facility:
The "emergency system" are your Critical (bedside patient care, laboratory, diagnostic, etc. ) and Life Safety (Fire alarm, exit light, emergency communications, etc.) branch LOADS. It is here that separation is meant to be kept.
"Emergency generator" is not a good definition.
What the NEC requires is an "alternative power source" that will support selected and "emergency system" loads. That could be battery/inverter but mostly diesel generators are the choice for numerous reasons; the biggest being an energy supply can be stored on site.
The "alternative power source" output, distribution, transfer switches and Emergency system make up the Essential Electrical System.
 
Re: Cable trays in hospitals.

Roger
While I respect your opinion mine differs. If you look at the brackets for the essential power source you will notice they go all the way up to the alternate power source. This is where we differ. I think that from the gen set to the transfer switch and beyond are part of the epss. There for it should be wired in a non flexible metal raceway.
To answer another part of this post the normal part to the transfer equipment is not part of the epss so if you want to wire it with an extension cord :D haha go ahead.
When does a generator become an emergency generator, any times it feeds life saftey and critical life automatic transfer switches and loads. JMHO.
Jeff
 
Re: Cable trays in hospitals.

Hello Jeff, actually I am in agreement with you.


From my post of February 03, 2005 03:35 PM:
Rbb, IMO the Emergency System starts at the Alternate Source, pretty much as shown within the brackets of the "emergency system" in FPN Figures 517.30 No.1 and No.2.
Click to expand...
When I said I hoped some one could could prove me wrong it was because of the fact I feel that all the PVC we have run from the Generators to the transfer equipment is wrong. :)

Roger
 
Re: Cable trays in hospitals.

I believe the normal supply to the transfer switch IS part of the Emergency Supply since it is where the prime power originates for the Critical loads. To install them in a lesser manner than the load side of the transfer switch implies that the transfer switch has a magical power that increases dependability.
 
Re: Cable trays in hospitals.

Rick,
Originally posted by rick hart:
I believe the normal supply to the transfer switch IS part of the Emergency Supply since it is where the prime power originates for the Critical loads. To install them in a lesser manner than the load side of the transfer switch implies that the transfer switch has a magical power that increases dependability.
Click to expand...
now we will have to run the service conductors in a "Non flexible Metallic Raceway" back to the Utility source, not just to the MDP.

In the words of Willie P Richardson ain't this here a mess. ;)

Roger
 
Re: Cable trays in hospitals.

OK, so I'm the only one thinks the run from the transfer switch to the generator might not be part of the emergency system.

So I guess the safe thing to do is assume that it is part of the emergency system, and that it has to be in metal conduit.

Steve
 
Re: Cable trays in hospitals.

It is not magic Rick. It is called an alternate source. If you read in other NFPA documents like 99,101 and 110 " we must be prepared to defend in place" the reason, at least in my opionon that the emergency sysytem from the generator to the transfer switches to the last outlet is treated special is that is our last line of defense. Kind of like why do we have a way to laock a fire pump in the run postion and the OCPD sized for locked rotor. We want it to function no matter what.
I agree with roger when he says using your interpatation we have to go all the way to the utlity. i personally don't think that is the intention.
 
Re: Cable trays in hospitals.

I'm confused about this utility thing. I am under the impression that flexible conduit is not permitted for service entrances anyway. The wiring to a transfer switch is not required to be in rigid conduit but I have a problem with flex.

My point is that if a level of protection is made on the alternate supply, that level should be afforded on the prime/normal side. It makes no sense to reduce the protection on a feeder that has higher fault currents and can cause more damage if physically assaulted.
In my opinion, you do not bolster the emergency system in order to keep it up, you make BOTH sides hardened so that the emergency system is less likely to be needed; both sides are critical and should be constructed of similar characteristics.

The loads we are talking about are almost always connected to normal.
 
Re: Cable trays in hospitals.

230.43 Wiring Methods for 600 Volts, Nominal, or Less.
Service-entrance conductors shall be installed in accordance with the applicable requirements of this Code covering the type of wiring method used and shall be limited to the following methods: (15) Flexible metal conduit not over 1.8 m (6 ft) long or liquidtight flexible metal conduit not over 1.8 m (6 ft) long between raceways, or between raceway and service equipment, with equipment bonding jumper routed with the flexible metal conduit or the liquidtight flexible metal conduit according to the provisions of 250.102(A), (B), (C), and (E)
(16) Liquidtight flexible nonmetallic conduit

Charlie
 
Re: Cable trays in hospitals.

Rick, all loads are connected to normal until normal is lost, then the selected loads are connected to the EPSS through transfer switches or paralleling gear.

What brings flexible conduit for Service Entrance Conductors into the conversation?

My point is that if a level of protection is made on the alternate supply, that level should be afforded on the prime/normal side.
Click to expand...
Not a bad idea, but if the entrance is overhead how are we going to install a conduit to the pole? :D

It makes no sense to reduce the protection on a feeder that has higher fault currents and can cause more damage if physically assaulted.
Click to expand...
This has nothing to do with physical protection of the Emergency System, the normal source can fail for any reason, not necessarily damage to the immediate facility, take a look at the Power Grid Black Out, Hospitals all over the North East and Mid West needed Emergency Systems up and running (although, some, due to non compliance with testing requirements didn't fair so well) and protecting the Normal source would have made no difference.

When thinking of the EPSS, think run until it burns to the ground with the facility, the Normal Source wouldn't need to stay on line.

Rick you have been involved in Health care design, so what are you fishing for?

Roger
 
Re: Cable trays in hospitals.

Roger,
Here's my point- not fishing or enjoying re-reading what I write here- and you made it earlier in this string.

"I would ask why would we mechanically protect any portion of this system less than another part".

You made the comment above concerning the equipment branch and the emergency branch. I totally agree with your statement. I would extend the same reasoning to the normal feed to each ATS. That's all- Keep them similar in NEC compliant characteristics all the way back to each source- generator output and service entrance. Not all the way back to Hoover Dam. I would much rather keep my standby system, standing by. The best way to do that is to place the same importance on the entire system and be ready with a totally reliable emergency system for the problems outside my control for my most critical duties. That's not NEC necessarily but good practice that allows failure to adequate state.
 
Re: Cable trays in hospitals.

Rick, I would venture to say Normal Power failures occur much more in generation or delivery to the facility than the service entrance conductors actually being physically damaged.

So even if we did protect the Normal System conductors as strenuously as we do the Emergency system, I would say there would be very little difference in overall Normal failure occurrences.

Roger
 
Status
Not open for further replies.
Top