chaoakax
Member
- Location
- Los Angeles
- Occupation
- Electrician
Hi everyone, I've been doing 99% residential electrical work, and recently decided to take upon a commercial job, which seemed like should have been easy enough but here comes:
So its an old office building that has 200A 1ph, 120/240v main for the offices, and a separate 100A 3ph 3 wire 240V meter with a square D 3 phase disconnect right below it. Before using it, i measure the voltage and get:
A to ground 240v
B to ground 240V
C to ground 0
A to B 240V
A to C 240v
B to C 240v
never before having heard about corner grounded delta systems, i automatically assumed the C phase is dead from utility and called for them to check on it and proceeded to installing a 3PH sub panel with breaker main to feed single phase AC units. Clients wanted all mini splits and they are all single phase 30A units. So to picture the overall system, it is a Meter, with the 3ph disconnect at the bottom, feeding a 3ph 100 subpanel with a straight shot of 30ft of EMT conduit. Then from subpanel we fed the AC units with 30A breakers. Edison rep calls tells me that its a normal system and that is how it is supposed to be and it works fine. AC guy turns on 2 of the units and tries firing them up. Nothing happens. Checks at the subpanel on the 100A main breaker at the sub, says gets absolutely no voltages there, and cant get to the Square D 3ph disconnect to check on the fuses because they are locked. So i have to go there to check on it but i am out of ideas what could have gone wrong. On a side note, when i first opened the old 3 ph disconnect, i noticed that only A and B phases had fuses installed and C had nothing. Now, what could have gone wrong? Could it be that the C phase was tapped as neutral at the utility transformer? How should i proceed when troubleshooting this?
I appreciate all the help i can get
So its an old office building that has 200A 1ph, 120/240v main for the offices, and a separate 100A 3ph 3 wire 240V meter with a square D 3 phase disconnect right below it. Before using it, i measure the voltage and get:
A to ground 240v
B to ground 240V
C to ground 0
A to B 240V
A to C 240v
B to C 240v
never before having heard about corner grounded delta systems, i automatically assumed the C phase is dead from utility and called for them to check on it and proceeded to installing a 3PH sub panel with breaker main to feed single phase AC units. Clients wanted all mini splits and they are all single phase 30A units. So to picture the overall system, it is a Meter, with the 3ph disconnect at the bottom, feeding a 3ph 100 subpanel with a straight shot of 30ft of EMT conduit. Then from subpanel we fed the AC units with 30A breakers. Edison rep calls tells me that its a normal system and that is how it is supposed to be and it works fine. AC guy turns on 2 of the units and tries firing them up. Nothing happens. Checks at the subpanel on the 100A main breaker at the sub, says gets absolutely no voltages there, and cant get to the Square D 3ph disconnect to check on the fuses because they are locked. So i have to go there to check on it but i am out of ideas what could have gone wrong. On a side note, when i first opened the old 3 ph disconnect, i noticed that only A and B phases had fuses installed and C had nothing. Now, what could have gone wrong? Could it be that the C phase was tapped as neutral at the utility transformer? How should i proceed when troubleshooting this?
I appreciate all the help i can get