3 Phase High leg Delta breaker in single phase box



3 phase 240 volt 60 amp Square D QO breaker in a single phase box. The Highleg Red, Wildcat leg (208 volts to neutral) directly feeds the 3 phase 3 pole breaker via a wire from the watthour hour meter and NOT a bus bar, like the other two legs do. This config was legal for a new install before 1978 but is grandfathered for existing installs. **If you ever have to replace a breaker like this the input wire is un fused and come directly from the C phase of the 7 jaw watthour meter. Thus massive danger if you let the wire hit the metal case, ie nothing to limit the current except Impedance of the transformer and the wires from gooseneck to the transformer. ie several thousands of amps, maybe 5000 to 8000. The max current with a fault is determined by the wire gauge, length of wire and Impedance of the transformer. (which varies by kVA size of each transformer ).

The load is a single 5 ton 3 phase AC unit that uses the 240 volts line to line 3 phase. The two bus bars are 120 volts line to neutral, the wild cat red leg is 208 volts line to neutral.

There can be either 2 or 3 transformers on the power pole for this type of configuration. A High leg delta configuration is still used for new installs and legal but the circuit breaker panel has to be a 3 phase box with 3 bus bars and not a breaker fed by a wire like this one to a “Delta Breaker”.


Post time: Oct-15-2017
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