The guys just replaced a single phase air handler in a resturant with a new 3 phase AH.
The 3 phase panel doesn't have a seperate bond ground buss bar although the old single phase AH was grounded to the existing ground buss bar in the panel.
To look inside this old 3 phase panel you would think it's a regular single phase type because all the breakers are double pole. The only way to tell is by checking the voltage because it has no 120 volts, both hot legs are 240 to ground. The new 3 phase Ah is supposed to have 4 wires but there is only 3 coming from the panel.
I haven't seen one of theses 3 wire - 3 phase panels since many years ago when one of my x-partners connected up a vacuum pump on the roof of a resturant with a cheater cord and found out 120 volt vacuum pump motors don't last very long on 240 volts.
Anyway, what would be the proper way to connect a case ground in this situation, just run another wire back to the panel and connect it to the ground buss?
Also, I know I'm showing my ignorance but it's been over 40 years since electrical school plus you just don't see these panels around here anymore (mostly we work with 208/120) but what is this type of 3 phase called?
How is the corner "hot as hell" if it is the only grounded conductor. "Hot" in reference to what? The only thing that makes this hotter than 3p wye is 2 phases are 240 above ground instead of 3 being 208 above ground. (or one phase being 208 above ground and 2 being 120 in "red leg")
Re: No ground buss#55104 08/16/0507:08 PM08/16/0507:08 PM
The third leg is grounded, if I remember corretly it was "B" center leg because like I said everything looks just like any single phase residential panel. The only voltage reading you can get is 240 volts.
Re: No ground buss#55106 08/16/0507:20 PM08/16/0507:20 PM
[q]"To look inside this old 3 phase panel you would think it's a regular single phase type because all the breakers are double pole. The only way to tell is by checking the voltage because it has no 120 volts, both hot legs are 240 to ground."[/q]
That sure sounds like corner delta to me
Re: No ground buss#55108 08/16/0507:41 PM08/16/0507:41 PM
You really treat corner delta like it was 240/0/240 single phase. The neutral is white and isolated from the Equipment Ground. This is a 4 wire branch circuit and feeder. If you did want to address the "hot" concern from Reno you would point out the neutral always carries the same current as the phases, not unbalanced current. That is why it is not regrounded after the service disconnect.
Re: No ground buss#55109 08/16/0509:24 PM08/16/0509:24 PM