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Cable loop


Denray
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What Jim said. A common 3 phase configuration for residential has 208 V on one leg. If the house originally had that kind of configuration but now has 120/240 single phase service then the voltage on the third leg would now be zero without the jumper or only 120 with the jumper installed. Of course, if everything was working fine at the time of the inspection then the necessary changes to any 208/240 circuits using that leg must have been made already. Any 3 phase loads would have been replaced with single phase loads.

This happens when the utility changes the service configuration but the electrician (or homeowner) decides to add the jumper and change a few circuits around rather than change the panel.

I doubt any AHJ would bless such a shortcut.

Marc

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Thanks all.

Any easy to understand 3 phase info out there?

Just to be clear, the panel in your picture doesn't have three phase power. It's just a three phase panel being fed with single phase power. You don't need to understand three-phase systems to understand the panel.

Or are you just asking because you're interested in learning about three-phase systems?

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Yep, would like to know how it works and how could residential work on it?

The only places you're likely to run into it in residential inspections is on a farm where the farm has 3-phase power and they run two phases to the house or in an apartment building where each apartment gets two phases of a three-phase system.

There are lots of good explanations of 3-phase systems on the net. I sugggest beginning by getting a handle on the difference between delta and wye systems. Try this site:

http://www.epuniversity.org/tech/w3.html

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The only places you're likely to run into it in residential inspections is on a farm where the farm has 3-phase power and they run two phases to the house or in an apartment building where each apartment gets two phases of a three-phase system.

Jim,

I will have to disagree with you. I have several older neighborhoods with three phase power in my area.

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Denny, thanks for the pic of the other half. It looks like the large breaker on the upper left is feeding power to the panel making this a backfed subpanel.

The power supply is single phase 240, a black and a red, going thru that main breaker to two of the bus bars in the panel. The jumper energizes the 3rd bar, so there could be an imbalance on one of those legs, having double the number of circuits on it. That would depend on what the individual loads are, and that is a job for an electrician to figure out.

That big missing knockout needs a plug.

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