120 volt (3 Phase Delta) 3 wire

[spotted123]

We have 2 panels fed by the above service, 1 three pole breaker feeds the sub-panel, and 2 pole breakers feed Control cabinets of various duties. This equipment is on a marine vessel that is sensitive to grounding issues (Tanker). I have not been able to access the actual equip. but am trying to understand the engineering behind this type of service. Usually electronic equipment is very sensitive to "floating" neutrals but in this case the 2 wire 120 volt supply may serve to reduce that problem? Maybe there are power conditioners in the panels? I will attach the edited drawings to be clear.

 

[jim dungar]

It has been many years, but I remember often supplying equipment for 120V delta systems for shipboard systems.

 

[kwired]

We have 2 panels fed by the above service, 1 three pole breaker feeds the sub-panel, and 2 pole breakers feed Control cabinets of various duties. This equipment is on a marine vessel that is sensitive to grounding issues (Tanker). I have not been able to access the actual equip. but am trying to understand the engineering behind this type of service. Usually electronic equipment is very sensitive to "floating" neutrals but in this case the 2 wire 120 volt supply may serve to reduce that problem? Maybe there are power conditioners in the panels? I will attach the edited drawings to be clear.

You do not have a neutral to potentially "float" in your system.

If you "float" a phase conductor in this system, you will have reduced voltages across the connected loads, but will never have above 120 volts across any loads, unlike you will have with a 208/120 wye with a floating neutral.

In the wye system if you lose the neutral for loads connected A to B you get 208 volts from A to B in series with both loads. If the loads are equal impedance they operate just fine, if not one will have a higher voltage across it and the other will have a low voltage across it.

In the delta as described, if you have same two loads connected A to B and B to C and lost B phase you have both loads in series between A and C but total applied voltage is 120, so both loads will never see more than 120 no matter what.