700.12(D)

[charlie b]

Suppose I take two separate medium voltage utility sources (the two utility substations are miles apart), and connect them to a Main-Tie-Main switchgear. Each side "normally" supplies half the building. If one utility substation is lost, the switchgear automatically transfers the entire building to the other utility. The transfer takes less than 10 seconds, and I specify the switchgear to be "identified for emergency use," per 700.6. Am I done with all "emergency system" requirements of article 700? Do I even need to call one light an "egress light" and separate its circuitry from the nearby "non-emergency" light? Would the fact that the switchgear's transfer mechanism be serving all loads, normal and emergency, constitute a violation of 700.6(D)?

The client is trying to take credit for the second utility source, and wants to avoid having to buy a diesel generator.

By the way, before anyone asks what would happen if both utility sources were lost, let me pose the question of what would happen if the utility source were lost in some other building, and if that building's backup generator failed? Do we even have to design for the possibility that the backup source might fail?

 

[elec_eng]

Charlie,

How about UL1008 listing? Is a MTM switchgear listed for that?

 

[RUWired]

Charlie, i think you would be in violation of (2008) 700.6(A). during a utility failure, the normal and emergency would be tied together.

700.6 Transfer Equipment.
(A) General. Transfer equipment, including automatic transfer switches, shall be automatic, identified for emergency use, and approved by the authority having jurisdiction. Transfer equipment shall be designed and installed to prevent the inadvertent interconnection of normal and emergency sources of supply in any operation of the transfer equipment.

Rick

 

[charlie b]

How about UL1008 listing? Is a MTM switchgear listed for that?

I have passed that question to the equipment vendor who is assisting me with this project. Thanks.

 

[charlie b]

Charlie, i think you would be in violation of (2008) 700.6(A). during a utility failure, the normal and emergency would be tied together.

I get that part. What I am pondering is whether I need to have an emergency distribution system at all. That is, since I have two separate and independent utility sources, and since the entire building would be re-energized shortly after the loss of either utility, can I meet the building code's requirements for egress lighting (there would be no other "emergency" loads in this building), without installing an automatic transfer switch and an emergency lighting panel that serves every third light or so?

 

[jim dungar]

I believe the 2nd utility source is clearly an acceptable source of power.

I just can't get past 700.6(D).
But, who says you even need to have transfer equipment? 700.17(2), in 2005, allowed for two independent lighting sysems as part of general lighting without a transfer switch.

Depending on the size of your M-T-M, how do you plan to address Ground Fault protection vs. annunciation?

 

[charlie b]

I believe the 2nd utility source is clearly an acceptable source of power.

So do I.

I just can't get past 700.6(D).

I have the same issue. That is essentially the reason for my posting this question here.

But, who says you even need to have transfer equipment? 700.17(2), in 2005, allowed for two independent lighting systems as part of general lighting without a transfer switch.

This may very well be the answer to my problem. I will look into it more closely. Many thanks. :thumbsup:

Depending on the size of your M-T-M, how do you plan to address Ground Fault protection vs. annunciation?

The M-T-M is at 34.5 kV, so 230.95 does not come into play.