3-pole ATS solid neutral

[anbm]

for the 3-pole ats, do we have to run solid neutral wire from ats
back to its normal and generator panel? what is the purpose for this neutral wire if there is no load that needs neutral wire? we used to see this neutral wire land at 3-pole ats.

 

[ron]

If there are no 4W loads, then the neutral can be left at the utility disconnect and generator (bond the N-G at both utility disconnect and generator). No need to bring a neutral to the ATS or out of the ATS downstream.

 

[anbm]

What happens if there is a ground fault at downstream ats panel?
will this fault current travels through equipment ground to the either sources in lieu of going back through neutral wire?

 

[infinity]

Why would a downstream ground fault have current traveling on the neutral conductor?

 

[kwired]

If source has a grounded neutral, then during a ground fault the fault current ultimately returns to the neutral point of the source, but in properly installed setup, that neutral point is only bonded once and is bonded at source or at first disconnecting means, so any neutral conductor beyond that bonding point isn't going to see the fault current. So for properly installed setup ground fault current follows equipment grounding conductors, metal frames of bonded equipment, etc. until it reaches the bonding point, from there it follows the grounded conductor the rest of the way to the source, but should be a short distance from the source.

Of course utility power and MGN distribution can allow for faults when on utility supply to follow other unintended paths at times, but we are usually arranging things so that the EGC path back to the bonding point is usually the lowest path of resistance and the bulk of fault current will flow to that point then back to source on the grounded service conductor.

 

[anbm]

Can the facility have a mix of 3-pole (solid neutral) and 4-pole (switching neutral) ATSs? The generator is considered as desperate derived system. How does this work? i.e 4-pole ATS has switched neutral while 3-pole ATS has solid neutral... sounds conflicting here... Should contractor not run the neutral wire to 3-pole ATS at all? (Assuming 3-pole ATS only power panel with 3-phase load, no neutral needed).

 

[kwired]

Can the facility have a mix of 3-pole (solid neutral) and 4-pole (switching neutral) ATSs? The generator is considered as desperate derived system. How does this work? i.e 4-pole ATS has switched neutral while 3-pole ATS has solid neutral... sounds conflicting here... Should contractor not run the neutral wire to 3-pole ATS at all? (Assuming 3-pole ATS only power panel with 3-phase load, no neutral needed).

I don't see why not. Only reason for switching neutral is to prevent neutral current from traveling over EGC paths in SDS setups. Non SDS there is no second bonding jumper and therefore neutral current can't find alternate paths.

 

[anbm]

I don't see why not. Only reason for switching neutral is to prevent neutral current from traveling over EGC paths in SDS setups. Non SDS there is no second bonding jumper and therefore neutral current can't find alternate paths.

Will this be a code violation when we have both switched and unswitched neutral ATS in the job with generator is considered a separate derived system?

 

[kwired]

Will this be a code violation when we have both switched and unswitched neutral ATS in the job with generator is considered a separate derived system?

If setup is SDS and has multiple transfer switches, they all need to switch the neutral.

Switching neutral on non SDS isn't going to hurt anything just likely to cost more to have an additional pole in the switch if it is not needed.