I have an old 3 phase panel next to a separate single phase 100 amp panel that is being used by one residence. This space has been used as a carpenter shop and an office in the past. Now it is being divided into two residences and I want to use the 3 phase panel for one of the residences by installing a single phase 120/240 subpanel. The place that I will need to install the subpanel is in the same building but it is about 60 ft away from the three phase panel. The 3 phase panel is powered by three #6 wires from the pole and there is no main breaker in this panel. I believe the system is Delta and two legs are 120 and one is 208. The questions are:
- Since the wire coming from pole is #6, what is the maximum Amp that I put in the 3 phase panel in order to power the sub-panel. Can I use 70amp?
- Can I use an entrance service cable ALU#4 inside the building above the existing suspended ceiling with or without conduit?
- Is it better to connect the cable#4 to the 120 legs or 70Amp breaker?
- I will use a 60Amp breaker in the sub-panel because I want the 60 amp breaker to trip before the 75 Amp in the main panel.
- There is an existing three phase 60 amp breaker in the panel. Can I use the two connectors that give 120 Amps? Is it ok for me to put 60 Amps in the subpanel?
ThreePhaseEel has asked me a couple of questions. First, I want to thank him for the answer. As to the color of the 3 phase wires from the pole, all are green. I don't see any white either. The high leg is the first wire from left in the box that is 208v. The second and third are 120v. So I think instead of A-B-C I have B-A-C. In the box the color of Bus bar C has been painted red but the voltage of this bar is 120. The voltages that you are showing are correct.
What I don't understand is where the white wire from the pole is, although I see the white wire has entered the adjacent breaker box from the pole.
What should I do when I don’t see white neutral coming from pole to 3phase panel? Is it possible there is only one neutral for both single and 3 phase panels? Can I use the neutral in single phase to connect to the single-phase 60-amp panel that is from 3 phase panel? How can you distinguish #6 PE from XLPE?
What is this balancing issue warning that some people are talking about when you want to install a single phase sub-panel of a 3 phase panel? Is it OK to have 60 amp breaker as feeder and as main sub-panel? Which one will trip first if there is a short?
Finally a question about conduit. Can I use two 1.5” 90 degree elbows (like S shape) connected to each other?