tim morris
Member
- Location
- Kentucky
I am trying to determine if the situation I will describe constitutes a ?separately derived service? under the definition of art 250.20 and will therefore require the grounding electrode conductor, etc. called for in article 250.30.
The conditions are as follows: a factory assembled (UL listed) piece of mechanical equipment (typically a water to air heat pump) is designed to operate at 277 volts. Internal to the unit is a 277 to 120 volt transformer that provides power to both an internally mounted fan and a terminal strip in the wiring compartment of the unit. External to the unit is a small circulating pump that provides water to the unit when it is running. The power for the circulating pump is fed from the terminal strip in the heat pump unit to a separate disconnect for the circulating pump.
The questions are:
1. If the external pump operates at 110 volts does that make the internal transformer a separately derived service requiring it to comply with Art.250.30?
2. If the circulating pump was internal to the unit would that make any difference?
3. If the circulating pump had the same operating voltage as the heat pump and the power feed was still from an auxiliary terminal strip in the unit would that make any difference?
One reason I think that this is not a separately derived service is that the wiring internal to the heat pump does not fall under the definition of ?premises wiring? in article 100 as discussed in art 250.20 (B).
All discussion is welcomed.
The conditions are as follows: a factory assembled (UL listed) piece of mechanical equipment (typically a water to air heat pump) is designed to operate at 277 volts. Internal to the unit is a 277 to 120 volt transformer that provides power to both an internally mounted fan and a terminal strip in the wiring compartment of the unit. External to the unit is a small circulating pump that provides water to the unit when it is running. The power for the circulating pump is fed from the terminal strip in the heat pump unit to a separate disconnect for the circulating pump.
The questions are:
1. If the external pump operates at 110 volts does that make the internal transformer a separately derived service requiring it to comply with Art.250.30?
2. If the circulating pump was internal to the unit would that make any difference?
3. If the circulating pump had the same operating voltage as the heat pump and the power feed was still from an auxiliary terminal strip in the unit would that make any difference?
One reason I think that this is not a separately derived service is that the wiring internal to the heat pump does not fall under the definition of ?premises wiring? in article 100 as discussed in art 250.20 (B).
All discussion is welcomed.
