gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090318-1925 EST
To add to what Larry said.
If there is only a small unbalance, then it may not matter much what loads are added.
If you essentially have a completely open neutral, then add load that won't be damaged by large over voltage. Two 250 W bulbs in series will tolerate 240 V. So on one phase you could connect this series load. Hot at 240 V the resistance would be about 115 ohms. Cold much lower, maybe 7 ohms for the series. With an open neutral and no load on the other phase the lamps won't light, but will move the neutral to a high voltage relative to the other phase. Add a 1500 W heater with no fan to the other phase. This is about 10 ohms. Now the lights will be near normal brightness. The voltage across the lamps will be about 240*115/125 = 221 V and 19 V on the heater,
If there was just a high resistance in the neutral, then just putting the heater load on one phase would be sufficient to change the neutral voltage and not present harm to the heater.
The reason you do not want to use a heater with a motor is that low voltage might damage the fan motor.
.
To add to what Larry said.
If there is only a small unbalance, then it may not matter much what loads are added.
If you essentially have a completely open neutral, then add load that won't be damaged by large over voltage. Two 250 W bulbs in series will tolerate 240 V. So on one phase you could connect this series load. Hot at 240 V the resistance would be about 115 ohms. Cold much lower, maybe 7 ohms for the series. With an open neutral and no load on the other phase the lamps won't light, but will move the neutral to a high voltage relative to the other phase. Add a 1500 W heater with no fan to the other phase. This is about 10 ohms. Now the lights will be near normal brightness. The voltage across the lamps will be about 240*115/125 = 221 V and 19 V on the heater,
If there was just a high resistance in the neutral, then just putting the heater load on one phase would be sufficient to change the neutral voltage and not present harm to the heater.
The reason you do not want to use a heater with a motor is that low voltage might damage the fan motor.
.