250.30 For 3-Phase / 3-Wire systems Seperately Derived Systems

[mull982]

I know that with 3-Phase 4-Wire separately derived systems you carry the neutral (or grounded conductor) between the transformer and first disconnect as well as a Supply Side Bonding Jumper (SSBJ). The system then has a System Bonding Jumper (SBJ located at either the transformer or first disconnecting means.

What a 3-Wire system where the neutral is not required for any of the system loads? Do you still need to carry a neutral between the transformer and first disconnecting means or can you omit the neutral and just run the SSBJ? I am thinking that you can omit the neutral and just run the SSBJ with the SBJ being located at the transformer. In the disconnecting means the SSBJ would connect to the ground bus and there would be no neutral bus.

Do I have this right?

What about an Impedance grounded system? I would think this would be the same as the 3-wire system I mentioned above with no neutral and SSBJ running between load side of resistor and first disconnecting means?

 

[Smart $]

First, you do not have to run the neutral in your first setting. The SBJ must be located in the transformer enclosure to do it this way. Running a neutral to the disconnecting means is only required of a service.

Your first setting becomes your second setting when you don't run a neutral. It is still *technically* a 4-wire system.

In an impedance-grounded system, the impedance device serves similar to the SBJ in a solidly-grounded system... but the neutral is not connected to either 'earth' or equipment ground. The Equipment Bonding Jumper, which serves similar to an SSBJ in a solidly-grounded system, is connected to the ground side of the impedance.

 

[publicgood]

You would only “have to run” the neutral for the purposes of properly providing ground fault protection and if this is a service and the utility required you at least have it brought to the meter.

 

[kwired]

You would only “have to run” the neutral for the purposes of properly providing ground fault protection and if this is a service and the utility required you at least have it brought to the meter.

Grounded conductor must be run to service disconnecting means. Beyond service disconnect grounded conductor only needs to be present if there is a load utilizing the grounded conductor.

 

[publicgood]

Grounded conductor must be run to service disconnecting means. Beyond service disconnect grounded conductor only needs to be present if there is a load utilizing the grounded conductor.

This has not been my experience. Do you have articles to support this?

 

[kwired]

This has not been my experience. Do you have articles to support this?

250.24(C) requires the grounded conductor to be brought to the service equipment. Lack of similar wording elsewhere makes it optional beyond the service equipment - may be a specific situation here and there but no general rule to do so.

If your load doesn't utilize a neutral conductor why would you need to run a neutral conductor?

You must have equipment grounding conductors beyond the service disconnecting means, even for ungrounded systems.

 

[Smart $]

This has not been my experience. Do you have articles to support this?

250.24(C) Grounded Conductor Brought to Service Equipment.


There are no sections which state you do not have to run a grounded conductor which is not a circuit conductor. 250.20(B) even hints that you do not even have to ground a system where the neutral is not used as a circuit conductor.