thunder15j
Member
- Location
- Cali
We have been upgrading some existing electrical systems that are/ were 3 phase 3 wire systems that feed irrigation pumps for agricultural water pumping apllications (25hp to 250hp). Added load has neccessitated service upgrades from 100 amp to 200 amp or 200 to 400 amp services. All loads are motor load only. All new services are upgraded to 4 wire from existing 3 wire. Ground rods are driven and tied/bonded into the incoming grounded conductor at the main switch.
I've been noticing at some existing 480 volt installations that I'm picking up voltage to ground from the 3 ungrounded conductors at 277 volts. Most services are overhead so it is quite simple to look up the utility owned pole where the transformer(s) are mounted. On underground units we're in the dark. I'm seeing that the utility has run a ground wire down the side of their pole probably to a plate or ground rod. Also they run an overhead drop consisting of 3 hot (ungrounded) alum conductors wrapped around a bare wire (quad) to supply the customer. However the bare conductor is not connected at either end. At the customer end there is nothing to connect to since there are only 3 wires coming out of the weather head (this is a 3 phase 3 wire ungrounded system originally). Meter socket is a 5 jaw configuration.
The utility transformer usually looks kind of new. The utility probably changed it out due to either failure or distribution voltgage changes. The quad drop probably changed from original 3 wire open spool installations. The problem I see here is that an existing customer owned 3 phase/ 3 wire installation is now fed by a 3 phase 4 wire system utility modified installation. There is not an ungrounded conductor connecting the customer serive to the utility transformer. A ground fault would have to travel from ground rod to ground rod via the earth. Not a good scenario. Even if a low resistance ground rod (less than 25 ohms) and very conductive soil existed, there is no way of knowing that the utility ground rod and conductor is satisfactory.
Fortunatly, we are eliminating these potential problems with the 4 wire upgrades. What really surprises me is that a utiltiy would connect a newly reconfigured grounded transfomer to an existing ungrounded system, that was formerly fed by a transformer that was ungrounded. Also not installing a 4th wire from transformer to main switch or overhead riser. Is it possible that the readings are coming from the electrical meter connectins, which I kind of doubt?
Please provide your thoughts......
I've been noticing at some existing 480 volt installations that I'm picking up voltage to ground from the 3 ungrounded conductors at 277 volts. Most services are overhead so it is quite simple to look up the utility owned pole where the transformer(s) are mounted. On underground units we're in the dark. I'm seeing that the utility has run a ground wire down the side of their pole probably to a plate or ground rod. Also they run an overhead drop consisting of 3 hot (ungrounded) alum conductors wrapped around a bare wire (quad) to supply the customer. However the bare conductor is not connected at either end. At the customer end there is nothing to connect to since there are only 3 wires coming out of the weather head (this is a 3 phase 3 wire ungrounded system originally). Meter socket is a 5 jaw configuration.
The utility transformer usually looks kind of new. The utility probably changed it out due to either failure or distribution voltgage changes. The quad drop probably changed from original 3 wire open spool installations. The problem I see here is that an existing customer owned 3 phase/ 3 wire installation is now fed by a 3 phase 4 wire system utility modified installation. There is not an ungrounded conductor connecting the customer serive to the utility transformer. A ground fault would have to travel from ground rod to ground rod via the earth. Not a good scenario. Even if a low resistance ground rod (less than 25 ohms) and very conductive soil existed, there is no way of knowing that the utility ground rod and conductor is satisfactory.
Fortunatly, we are eliminating these potential problems with the 4 wire upgrades. What really surprises me is that a utiltiy would connect a newly reconfigured grounded transfomer to an existing ungrounded system, that was formerly fed by a transformer that was ungrounded. Also not installing a 4th wire from transformer to main switch or overhead riser. Is it possible that the readings are coming from the electrical meter connectins, which I kind of doubt?
Please provide your thoughts......