I have a customer who provided a 25KW standby generator with an automatic transfer switch and contracted with us to install and terminate. We have installed generators of several different manufacturers, types and styles but this one was different. Particularly at the neutral termination. Inside the termination compartment the manufacturer has a threaded stud installed through the cabinet with the threads on the inside. The manufacturer then terminated all of their grounds and XO (neutral) conductors onto the stud tightened down and marked with a strip of green paint. There is no other neutral termination point. I contacted the manufacturer and asked where they had intended the field installer to terminate the neutral conductor. The response was either to terminate on the ground stud I mentioned above, or to remove the XO (neutral) conductors from the stud and splice to my neutral and leave floating. My question is. Which of these is correct? The other end of my neutral terminates at the transfer switch which is tied to the service neutral which is bonded at the main to the grounding electrode conductor. Should it also be bonded at the generator side? Or should the generator XO neutrals be pulled off of the ground stud in the termination cabinet and just spliced to the field installed outbound neutral conductor?
Standby Generator Neutral Termination
- Thread starter DEC01
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
If the transfer switch does not switch the grounded conductor, then it must be left floated at the generator.
Don
Don
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
I don't have a codebook handy, but 250.6 is one section that applies to the installation described.
If the neutral comes in contact with the EGC downstream of the bond at the service, then unbalanced neutral current will travel along the EGC between the service and the incorrect bond.
When under generator power, a ground fault will travel along the EGCs to the utility service bonding point, and then backtrack to the generator neutral point, opening the overcurrent protective devices.
If the neutral were switched at the ATS, then bonding the neutral of the generator to it's EGC would be necessary; also, the generator would become a seperately derived system, and 250.30 would come into play.
If the neutral comes in contact with the EGC downstream of the bond at the service, then unbalanced neutral current will travel along the EGC between the service and the incorrect bond.
If the neutral is not switched, then a second bond at the generator will cause neutral current to flow on the generator's EGC back to the utility. Therefore, the neutral is left floating.
When under generator power, a ground fault will travel along the EGCs to the utility service bonding point, and then backtrack to the generator neutral point, opening the overcurrent protective devices.
If the neutral were switched at the ATS, then bonding the neutral of the generator to it's EGC would be necessary; also, the generator would become a seperately derived system, and 250.30 would come into play.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Try 250.24(A)(5).
stand by generator
stand by generator
since everything is grounded prorerly at the main service, and the neutral conductors dosent break through the ats switch. inside the generator on the stud you should pull off the neutral conductors and splice in with the building neutral, the on the ground stud install the grounding conductor on it, inside the ats switch the grounding conductor should be spliced in with the grounding conductors, or if mount a ground lug to the cabinet, making sure the neutral are isolated from the cabinet. Does all this seem okay?
stand by generator
since everything is grounded prorerly at the main service, and the neutral conductors dosent break through the ats switch. inside the generator on the stud you should pull off the neutral conductors and splice in with the building neutral, the on the ground stud install the grounding conductor on it, inside the ats switch the grounding conductor should be spliced in with the grounding conductors, or if mount a ground lug to the cabinet, making sure the neutral are isolated from the cabinet. Does all this seem okay?
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