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Hi, we are having some odd electrical behavior where half of our power in the building is not working.

The way the electrician explained our system to me is, the Utility company supplied us with 3 Phase, however we are only utilizing 2 Phases.

BOX 1 which gets 3-phase supply from the Utility company, then passes the 2 wires (labeled PURPLE and ORANGE) to BOX 2. As you can see, BOX 2 is a 2-phase setup.

I noticed that in BOX 2, the GREEN line is HOT, but the RED line is DEAD.

So I traced it back to BOX 1, and noticed a few things. First of all, the PURPLE line coming out of the breaker is HOT, but the ORANGE line is DEAD. So I thought maybe the breaker was bad. However, I then noticed that the LINES 1, 2, and 3 which come from the Utility company --- Line 1 and 2 are HOT, but line 3 is DEAD.

If line 3 is DEAD, will this system not work, despite the fact that I'm only using 2 Phase? I wanted the electrician to come out, but he said I should first call the Utility company to check their connection on Line 3. Once they fix that connection, he says my 2 Phase system should be up and running? You don't think it could just be that the breaker in Box 1 with the Purple/Orange line is bad?


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Discussion Starter · #3 ·
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Building maintenance (commerical). Wondering if I should get an electrician to try swapping the breaker, or if all three legs really should be hot if we're utilizing two phases. My usual electrician is not available, but told me what I mentioned above.
 

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We've had outside connections by electric supplier go bad outside on just one phase. It can reak havoc with motors, contactors, & breakers by causing huge amp draws. On rare accasions, their transformers go bad.
 

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The fact you refer to two legs of a three-phase system as two-phase means you're in over your head.
 
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Goin' Down in Flames....
Highwayman
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There’s no such thing as “2-phase” anymore. I guarantee that no two legs in that panel are 90 degrees apart, hence, no two phase.

If one of the incoming 3 phase lines are dead, then yes, it’s quite possible that the sub panel will be dead on one side.

I have no idea from that picture if the 100A breaker feeding the sub panel is on AB phase, BC phase, or CA phase.

The electrician should trace it back to the service point, and if it’s still dead at that point, it’s a POCO issue. 👍
 

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Of course, you should get an electrician. I hate it to call for an electrician every time something is minor to fix around the house, cable-related. That's why I went through an electrician course at How to Become an Electrician so that I am capable of facing small challenges around the house. Some might find it ridiculous, but you'll be fascinated as to how simple it is to learn how to install a socket.
 

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Give the guy a break. You know darn well what he meant. Using 2 phases of the 3 easily translates into using 2 of the 3 wires of the three phase panel.
 

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You have a dead phase or a bad breaker that is feeding that panel. Everything on that phase will not work and any 3 phase equipment may be single phasing. If that is the main panel- no breaker ahead of it then the power company has an issue either in the meter base or out at the trany
 
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