Working Space about an indoor 5KV Transformer

[MO EE]

I am trying to determine the working space required around a 4,160V to 480V, 1,000KVA, dry type, 3-phase, transformer. The transformer will be located in a chiller building and is not acting as the service entrance. The transformer will be in a enclosure with vent openings only. So, energized parts will not be exposed.

The 2005 NEC Handbook, Table 110.34 (A) Minimum Depth of Clear Working Space at Electrical Equipment Condition 1 would seem to cover this. To me, it seems that 3 ft is the minimum clear distance required about the enlcosure.

Is this correct for my application?

Thanks

[ January 06, 2006, 10:16 AM: Message edited by: MO EE ]

 

[charlie b]

Re: Working Space about an indoor 5KV Transformer

Originally posted by MO EE: . . . energized parts will not be exposed . . . Condition 1 would seem to cover this.

You need working clearance around equipment. Whether that equipment will have its own energized parts exposed is not how you determine if you are in Condition 1, 2, or 3. It is presumed that you have the equipment open for some work you intend to do, and that during your work the energized parts are exposed.

What matters is the space between the energized parts (or the case of the equipment) and the nearest obstacle. If that nearest obstacle itself has energized parts exposed, then you are in Condition 3. If that nearest obstacle is grounded (that includes concrete walls and any metal pipes, stairs, and conduits), then you are in Condition 2. If that nearest obstacle is isolated from ground, then you are in Condition 1. Most of the time, electrical installations will be Condition 2.

Also, your transformer's secondary voltage to ground is either 277 volts (i.e., a 480/277 WYE) or 480 volts, both of which are below 600 volts. So that part of the equipment is governed by 110.26, and not by 110.34. The primary side voltage to ground is probably 4160 (i.e., delta wound primary). So the minimum working clearance would be 5 feet from that side of the transformer (assuming Condition 2).

 

[MO EE]

Re: Working Space about an indoor 5KV Transformer

Charlie b-

Thanks for clearing that up for me.

 

[charlie b]

Re: Working Space about an indoor 5KV Transformer

Now perhaps someone can clear up something for me. Was I right about having different working clearances on different sides of the same equipment, given that the voltage accessible from one side is different than the voltage accessible from another side? Or would you need the higher value of working space to be available all around the equipment (or at least around the sides that have access panels)?