Nec 700.9

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mastadon13

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Trying to clarify the application of NEC 700.9, any help is appreciated.

I am working on the electrical design to do a wholesale replacement of packaged air handling units on the roof of a facility (~25 of them). Per owner request and to match the existing installation, the supply fan of each unit is to be on generator backup power, but the rest of the unit (compressor, combustion, etc.) is to be on utility power. The existing installation has two seperate power feeds (one normal, one emergency) to seperate fused disconnects mounted on the unit, but once inside the unit I don't think there is any real seperation of the emergency wiring and the normal utility power. Is this in violation of NEC 700.9? Or is it OK because it is inside the unit?

I am asking because I was planning on essentially re-using the existing conduit path and having the same two disconnect system, but I am concerned about meeting code within the unit.
 
Unless these fans are used to control smoke during a fire, I don't think they are emergency loads. They are probably "optional loads". See Article 702. There is no requirement for separation of "optional" power from normal power.

However, if this generator also feeds emergency lighting, it gets a lot more complicated. See 700.6(D) for example. You basically need separate transfer switches. One would have all the emergency lighting. The other would have all the optional loads.

Steve
 
Thanks for the reply, Steve.

They are not for any kind of smoke evacuation. But, unfortunately, the generator supplies egress lighting throughout the facility (which is a jail). I see what you mean about 700.6(D). Pardon my inexperience, but is that recent to the code? The original units were installed with the supply fan on emergency and the rest of the unit on normal power back in 1991, and that seemed to pass code then (not to say the AHJ might not bring it up now). The fans would be providing outside air to the inmate housing, which could qualify as "required facilities". Guess I'd have to check the local codes.
 
I can't say how long the rules have have been in place.

It is worth a look at the scope of Article 700.

700.1 Scope.
The provisions of this article apply to the electrical safety of the installation, operation, and maintenance of emergency systems consisting of circuits and equipment intended to supply, distribute, and control electricity for illumination, power, or both, to required facilities when the normal electrical supply or system is interrupted.

Emergency systems are those systems legally required and classed as emergency by municipal, state, federal, or other codes, or by any governmental agency having jurisdiction. These systems are intended to automatically supply illumination, power, or both, to designated areas and equipment in the event of failure of the normal supply or in the event of accident to elements of a system intended to supply, distribute, and control power and illumination essential for safety to human life.
Click to expand...

If a local AHJ determines these fans are essential for safety to human life they can be supplied by the emergency system.

Perhaps in a prison environment ventilation would be essential.

I strongly suggest working this out before proceeding with the local AHJ.
 
I think he meant it like, "I strongly suggest working this out (before proceeding) with the local AHJ."

Unless you were trying to be funny, Larry, in which case I did grin a little. :D
 
I thought maybe he meant after he was through with the job he could procede to beat the h*** out of AHJ if he didn't go along!:p :p

I was trying to take a stab at humor.:)
 
Consider me thoroughly stabbed.

stabbed.jpg
 
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