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Got a 3 phase panel (yes, with a burnt wire) that's only got a couple slots for 3 phase breakers. The rest of the breaker slots are only grab one or two bus.

Pictures of the main, and a couple bus shots.

What would this be called? Anything in particular?

Overview

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Close up disconnect

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110/240 slots

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3 phase slot; see the little tab sticking out from behind the barrier?

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Assuming someone used red tape on the middle SE conductor because they were out of orange, I'd say it's a typical 120/240v, 3 phase, unbalanced neutral configuration.

The unbalanced config gives you the 240v, 3 phase plus you can get 120 and 240 single phase via a center-tap on one of the legs. The center-tap is the neutral and since it isn't equidistant between all three legs (just between two of them), that makes the neutral unbalanced.

The less common (in residential, apartments and condos) balanced config gives you 208v, 3 phase plus three legs of 120v. No 240v. If you drawn a triangle on paper and put a dot in the middle, that dot is the neutral. Each corner is a leg and they're all 120V from neutral. Between any two corners is 208v. Most resid 240 appliances also work on 208. They're labeled '240/208'.

You'd have to check the voltage between any two SE conductors to be sure what you've got there.

Looks like a 3 phase bus all the way from top to bottom. 3rd bus is mostly hidden behind plastic.

Marc

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I'd measure the voltages between the phases and between each phase and the neutral and then just describe it as a xxx amp, xxx/xxx volt three-phase load center.

The schematic would tell the story of the bus configuration, but I suspect that Marc is right about the three phases alternating all the way down the bus.

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110 v between se and neutral, 220 between se's. 200 amp disconnect. No schematic.

The guy wants to put a small cabinet shop into the place. No big shakes, a couple table saws, spray booth, the usual revolving stationary power tool setup. 3-4 guys working at a time.

Seems like it would handle it ok. I've had shops that work fine with less.

Thanx for the lesson.

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120/240v, 3 phase can furnish 83,000 watts but to use that extra 35,000 watts (a 120/240 single phase standard resid service is 48,000 watts) from an unbalanced config, you need extra transformation to get the 240 from the other 2 legs down to 120v.

If it's 120/208 balanced config, there's an extra 24kw and it's readily available. Just install breakers in groups of three, balanced them between the legs and run it to the shop. If there are 208 v loads, install a small 3 phase panel and run whatever amps you need with a single 3 phase breaker on the main.

3 phase service is wonderful to have but it's hard to get from the utilities these days.

Marc

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I'm going to cut and paste that and send it to my client. What's it mean? When he asks, I want to be able to tell him.

Kidding aside, I think I get it. I'm going to let the electricians figure it out though.

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3rd bus is mostly hidden behind plastic.

Marc

Yeah, exactly. It only had a tab at a couple places.

No, it had a "3rd buss" every third or second place.

A 3-phase panel like that typically has the center buss running down the center mostly hidden by plastic. The outer two busses usually look like typical busses from a single-phase panel, only with different spacing.

Also, do NOT use "220" as your voltage. It's either 120/240, or 120/208 volt. A 120/240V 3-phase panel will have a high leg of 208V, typically in the center. This panel has so many single-pole breakers in it that it has to be a 120/208V feed.

In a 120/240V 3-phase panel with a lot of SP breakers you usually see a lot of empty spaces at every third position.

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Chad's photo shows a 3-phase, main-lug panel back-fed with single phase power via a 2 pole 100 A breaker (leads are numbered #1 and #2).

A 70 amp, 2 pole breaker below the 100 A breaker energizes the 3rd leg with power from the 1st leg.

The genius who wired it up could be a sparky with some familiarity in industrial/commercial wiring as numbers 1 and 2 are common choices for incoming power on wiring diagrams. Maybe he even stole the panel from the plant where he worked.

Marc

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