240 between phases AND Ground, dead phase

Discussion in 'General Electronics Chat' started by Cheyne, Jan 10, 2011.

  1. Cheyne

    Thread Starter New Member

    Jan 10, 2011
    Hoping for clarity. Working in a commercial building with a 600A sub panel feeding the building's main air conditioning condenser and exhaust fans. This panel is labeled 240v 3ph 3 wire. The breakers are 3 pole breakers. The large motor running the air conditioning says 3ph on it. However, there is no voltage present on one of the legs in the panel. The voltage readings are 240V phase A to Phase B, 0V Phase A to C and B to C, 240V Phase A to ground and Phase B to ground, 0V Phase C to ground. There is no neutral in the panel. The motors are running happily away, and apparently have been doing so for some time. Is this normal? Particularly the 240V to ground issue and the 0V on one of the phase buss bars? I went to the main electrical room and checked the voltage on the meter side of the main breaker, and the situation was the same - only 2 legs had power/240V and the 3rd leg was dead, so apparently this is how power comes into the building. Thank you!
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    my guess is you have a corner grounded 3phase, with C being the grounded phase. Your phase to phase measurements don't jive with your phase to C measuremens. I'd check them again.