We install stationary, residential, backup power systems. The neutral is not switched in the transfer switch therefore I would understand that these installations are not "separately derived systems." For whole house applications, I've been advised that some of my competitors are coming from the meter socket, into a disconnect, and into the pre-existing service panel using 3 wire. At the service panel they leave in place the bond between the grounded conductor "neutral" and the grounding conductor so they don't have to separate the neutrals and grounds in the panel. They run 3 wire from generator to the transfer switch and a ground rod at the generator. This would really cut my costs if I could do this BUT I've been schooled that the code (2005 NEC) rqrmt in 250.24 (1)means the bonding of "neutral" and "ground" conductors needs to be at the first disconnect on the load side of the utility meter and that there needs to be 4 wire running from this first disconnecting means on. This means I must separate the grounds and neutrals at the existing svc panel which now becomes a sub-panel. I would like some input from this forum as to what is rqrd. Thank you.
Generator, Emergency Standby - Wiring
- Thread starter rwatt
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lawelectric
Member
Re: Generator, Emergency Standby - Wiring
"the first disconnect on the load side of the utility meter"...
Sounds like they are on the line side of the utility meter and the bonding remains on the load side of the utility meter.
"the first disconnect on the load side of the utility meter"...
Sounds like they are on the line side of the utility meter and the bonding remains on the load side of the utility meter.
ramdiesel3500
Senior Member
- Location
- Bloomington IN
Re: Generator, Emergency Standby - Wiring
In my personal opinion, your competitors are bending the rules a bit. 250.24(B) is pretty clear about this! The local authority may be letting it pass. If this is causing you to lose work, I would ask the local AHJ for a clarification on what they will accept. They may be considering the existing bonded assembly in the service panel as being "at" the location of the first disconnecting means even though it is not physically in the same enclosure. Some folks consider "at" to mean within 10' or something like that. But it still seems to me that your competitors are violating rule 250.24(B)
In my personal opinion, your competitors are bending the rules a bit. 250.24(B) is pretty clear about this! The local authority may be letting it pass. If this is causing you to lose work, I would ask the local AHJ for a clarification on what they will accept. They may be considering the existing bonded assembly in the service panel as being "at" the location of the first disconnecting means even though it is not physically in the same enclosure. Some folks consider "at" to mean within 10' or something like that. But it still seems to me that your competitors are violating rule 250.24(B)
ramdiesel3500
Senior Member
- Location
- Bloomington IN
Re: Generator, Emergency Standby - Wiring
Oh, by the way! Your competitors may be getting past this by trying to utilize 250.32(B)(2). This rule effectively allows you to feed an outbuilding without a grounding conductor so long as you bond at the panel. Its a stretch, but they may be getting by with it that way! I hope we get some more opinions on this. I am eagerly watching this post because I have been dealing with similar issues too.
Oh, by the way! Your competitors may be getting past this by trying to utilize 250.32(B)(2). This rule effectively allows you to feed an outbuilding without a grounding conductor so long as you bond at the panel. Its a stretch, but they may be getting by with it that way! I hope we get some more opinions on this. I am eagerly watching this post because I have been dealing with similar issues too.
Re: Generator, Emergency Standby - Wiring
This question relates to work on load side of the meter (thanks lawelectric) and I left out the transfer switch in describing the 3-wire pathway used by some competitors: from meter socket, into disconnect, into transfer switch, into pre-existing panel where the grounded conductor is bonded to the grounding conductor. The comment about "at" (thanks ramdiesel3500) is interesting but I agree with the need to have a disconnect ahead of the transfer switch and so still see the need to have my bonding of "neutral" and "ground" at this first disconnecting means and run 4 wire from that point. Any other observations/comments are greatly appreciated.
This question relates to work on load side of the meter (thanks lawelectric) and I left out the transfer switch in describing the 3-wire pathway used by some competitors: from meter socket, into disconnect, into transfer switch, into pre-existing panel where the grounded conductor is bonded to the grounding conductor. The comment about "at" (thanks ramdiesel3500) is interesting but I agree with the need to have a disconnect ahead of the transfer switch and so still see the need to have my bonding of "neutral" and "ground" at this first disconnecting means and run 4 wire from that point. Any other observations/comments are greatly appreciated.
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