JDBrown
Senior Member
- Location
- California
- Occupation
- Electrical Engineer
Is there a technical reason (i.e. not a Code reason) why you can't run the 3 phases in one conduit and the neutral in a separate conduit (assuming underground PVC conduit)? I understand why you wouldn't want to do it with steel conduit (induced currents, heating, etc.), but if the conduits are plastic, with no steel elbows or fittings, is there any reason why this can't/shouldn't be done?
So, here's the background, in case you're interested. I work for a power utility, so I'm not constrained by the NEC (contrary to popular opinion, we do have a lot of rules we have to follow; it's just that the NEC doesn't number among them). We have a large section of a circuit that we are going to move from overhead poles to underground conduits. This is currently a 3-phase, 4-wire circuit, and is what power utilities refer to as an "isolated neutral" system, meaning that the neutral conductor is only grounded at the source, instead of being grounded every x number of feet as is typical for a 4-wire utility installation. This allows us to protect the circuit from faults with what is essentially a large GFP. However, there are plans to change over to some new protection scheme a few years later, which will make the fourth wire unnecessary. The field crews are asking if they can install the phase conductors in one conduit and the neutral in another, so they can remove the neutral when it's no longer needed and have a spare conduit. So, that's the long version.
So, here's the background, in case you're interested. I work for a power utility, so I'm not constrained by the NEC (contrary to popular opinion, we do have a lot of rules we have to follow; it's just that the NEC doesn't number among them). We have a large section of a circuit that we are going to move from overhead poles to underground conduits. This is currently a 3-phase, 4-wire circuit, and is what power utilities refer to as an "isolated neutral" system, meaning that the neutral conductor is only grounded at the source, instead of being grounded every x number of feet as is typical for a 4-wire utility installation. This allows us to protect the circuit from faults with what is essentially a large GFP. However, there are plans to change over to some new protection scheme a few years later, which will make the fourth wire unnecessary. The field crews are asking if they can install the phase conductors in one conduit and the neutral in another, so they can remove the neutral when it's no longer needed and have a spare conduit. So, that's the long version.