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Three phase HVAC equipment, single phase panel

Chad Fabry

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Yesterday, I needed help. I was on a roof of a small commercial building and inspected the HVAC equipment. It was all 208-230v three phase stuff typical for smallish commercial spaces. There was a (full of yellow jackets) Fed Pac,  three phase disconnect on the equipment.

In the basement, there were three single phase 100 amp disconnects that served panels in the building, and one service panel all fed from a gutter. There was one single-phase disconnect fed from another source with a back-fed 100 amp breaker, two, 2-pole 20-amp breakers and a 2-pole 60 amp breaker.

The 60 amp breaker was identified as the breaker for the HVAC equipment. My head started hurting. I then noticed that all the *neutral* wires had been re-identified with black tape. I metered L1 to L2 and got 240v. Then I metered L1 to ground and L2 to ground and each produced  240 v. 

I called Douglas Hansen; his caller ID must not work and he answered. After I explained the situation, he identified the system as  corner grounded three phase.

I've read about the configuration- I believe that the breakers used must be rated @ 240v or higher (not 120/240), they must also be rated for 3 phase. §240.85

Is there anything else I should discuss? Clearly, the panel in question is a complete do-over- I see the stuff wrong in this panel, but if I run into another one of these things  what should be discussed?  Since folks won't be able to resist- the panel and breakers are water damaged, breakers in use not rated for the panel, HVAC breaker should be 50 amps, not 60 and no hold-down kit on the back-fed main. 

Douglas- thank you for your help, I sincerely appreciate you taking the time to answer my call.


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I suspect the two-pole disconnects in the basement were actually supplying three phase power.  The third pole is actually the grounded conductor so it doesn't need, and shouldn't be, either switched or fused.  The 120/240 single-phase breaker panel nearby must have been fed by a single-phase, isolation-type, center-tapped, 1:1 transformer feeding off 2 legs of the corner-grounded service since a corner grounded 3-phase service cannot deliver a 120 volt supply.  This would be a large and very heavy transformer.

Adding to the confusion is the three-phase disconnect on the rooftop outdoor section.  As stated above, the third pole is actually a grounded conductor and should not have been switched.

Must have been fun.  Wish I could have been there.

Edited by Marc
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7 minutes ago, Marc said:

Must have been fun.  Wish I could have been there.


Four 50-year-old Wadsworth load centers that should have been wired as subs (not) that were significantly overcrowded. Two of the panels were about 7 feet high over stairs. One panel had a line splice using a weaver split bolt that was taped for insulation crammed up against the back of the dead-front. I went and bought rubber gloves to re-install the dead-front and left a big note in black sharpie on the panel.  Also on site was an exterior, live meter pan with no cover, cracked SE cables about 30 inches over the entire span of the flat roof (too high to hop, I had to limbo).

Fun? maybe not as much as time-consuming, profit-sucking and dangerous. Three hours just on electrical.  


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1 hour ago, Chad Fabry said:

Three hours just on electrical.

Feel free to text me under such circumstances.  You can attach photos to a text these days.  I'll PM my text number.  Don't call, I haven't met a phone that works since 1960.  I dunno what's causing it.

Edited by Marc
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