Commercial 3 Phase Question


Old 12-24-14, 03:34 PM
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Commercial 3 Phase Question

I don't even know enough to be dangerous, so forgive the rather vague question.....

We have leased a commercial space and we are planning the build out that needs to occur prior to getting the sub contractor quotes. We want to have a rough idea of what is practical before the quote stage. We are creating an area within the space that is going to be a kitchen area and will need all new circuits run for it. The main 600 AMP panel is quite a distance from where this needs to occur. Across the roof is (what was referred to by the owner as a 'bus'). It appears to have been a three phase supply with a series of boxes that machines were individually attached too with power drops. Is it possible to tap into this supply, convert it to single phase and power a sub panel from it? This would mean we wouldn't have to run significant amounts of wire to get power where we need it. I am assuming that IF it is possible, this would be a cheaper solution that wirig a supply line all the way to the sub panel location?

I know this is vague, but generally speaking does it make sense?

Thanks for humoring me!
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Old 12-24-14, 03:58 PM
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That would be three phase bus duct. Each one of those boxes is a disconnect. Most of those disconnects are fused and some are not.

If that was a machine shop then there is a good chance that the duct is solely three phase with no provisions for low voltage. No neutral. You would need to set a transformer near your kitchen to feed a new sub-panel. It would be a three phase high voltage to three phase low voltage with a neutral.

Definitely do-able if you could find a transformer at a reasonable price.
You would need to confirm the voltage of the duct. It's most likely 480vac.
Old 12-25-14, 11:52 AM
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I would not say it is most likely 480v. I have seen plenty of bus duct that is 208 or 240v with, and without a neutral.

I agree with PJ, You can pretty much make whatever voltage you need off the bus duct using a transformer. A 480 to 120/208 75 KVA transformer will run you about $2500 new. This will give you about 200 amps 3 phase available. I would not waste your time installing anything single phase if you have 3 phase available.

I would call an electrical contractor to come in and take a look at what you have. This can, and should, be done before you start any construction IMO as he can make suggestions and bring up things you may not think of, such as panel clearances, which are often overlooked by most people.
Old 12-25-14, 06:37 PM
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Across the roof is (what was referred to by the owner as a 'bus'). It appears to have been a three phase supply with a series of boxes that machines were individually attached too with power drops.
It would very unusual for this to be on the roof. It's probably hung from the bar joists. Typically the 600 amp busduct will accept 100, 200 or 400 amp fusible switches. It's also probably a 3-phase 4-wire busduct. Your design/build elctrical contractor can check it out for you and tell you exactly what needs to be done.

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