2 Different Supply Voltages??

I'm in the process of generating a wiring diagram and parts list for a machine that my company is designing. It is a semi-automated "parts" washing machine. Imagine a conveyor with parts on it running through a variety of spinning brushes and spray nozzles. Since some of the spray needs to be hot, we have found a circulation heater to run it through - it requires about 50A at 480v. This is the only component that needs 480v. I was planning on getting the VFDs to run on 480v and run controls on a step down transformer. It turns out that the client has specified a particular hot air drying machine to incorporate that only runs at 110v - they don't make any other version. This, of course, substantially increases my transformer requirement (from approx. .5kVA to 3kVA).

I would rather not go this route because of panel space requirements, heat, and cost. Would it be acceptable to bring two supply voltages into the machine (480v, 120v)?

I have read in the NFPA 79 section 5.1.1 that the supply circuit SHALL, as far as practicable, be derived from devices like a transformer. This seems a little vague to me - shall = must, as far as practicable = only if you can without too much trouble...

Any thoughts??

Thanks for all the help!

Chip

Yes you can do this. Each must be labeled and you must note power comes from more than one source on the door. Most panels I have seen doing this have the 480 disconnect to open the door and the 120 remains live. I would have the outside 120 vac land on a terminal strip and have a breaker/fusing disconnect capable in the panel.

Typically, 120 vac from another source ie; lighting panel, uses yellow wires to denote a seperate source from the 120 vac from the cpt in the panel.

Thanks Leadfoot! That was originally what I was thinking until I read that section of the NFPA.

Chip

I too have found most regulation/code books are as clear as mud.

Why not add an enclosed transformer, mounted outside the electrical panel?

bluebyu said:

Why not add an enclosed transformer, mounted outside the electrical panel?

Click to expand...

Well, the most simple reason is the tight budget. If the two supply circuits were not a good idea, then that's what I would do.

Like Leadfoot was saying, and NFPA 79 (5.3.1)--

"A supply circuit disconnecting means shall be provided for the following:

(1) Each incoming supply circuit to a machine"

We have yellow signs with black lettering on any panel built with more than one supply circuit saying " CAUTION--There is more than one source of electrical energy to/inside this Panel "