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The inter-system bonding termination (IBT) is where other services like telephone and cable TV get their ground bonds from the house's grounding electrode system (ground rods).

2014 NEC (NJ) 250.94 seems to say that an IBT must be placed in proximity to the house service. My home currently has a main panel with main breaker as the service disconnect. I am in the process of installing a whole-house transfer switch for a generator, which then becomes the service entrance equipment. My understanding is that the wire between the transfer switch and main panel becomes a feeder in that case (and necessitates isolating neutral and ground, etc.)

Am I required to relocate the IBT to near the new transfer switch, which is about 60 ft away on a different location on the house closer by the generator? (There was no additional room in the utility room for the transfer switch, so it is being mounted in a protected location outdoors.) All of the communications wires for the house already terminate by the existing IBT, so this would result in a rats nest of 5-6 wires having to be spliced and then traveling over to the new IBT location. For all practical purposes, this seems like a bad idea.

David Pfeffer
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    Are you moving the service drop and electric meter to the generator shack? Is this being wired by the generator company? – Harper - Reinstate Monica Jun 16 '19 at 12:40
  • Why are you going with whole-house transfer BTW? Is having a standby subpanel not an option for you for some reason? – ThreePhaseEel Jun 16 '19 at 13:25
  • @Harper The service is moving underground and next to the new transfer switch, which is in a different area of the house from the old OH meter. There's no generator shack, its a freestanding exterior generator. I'm doing the generator myself. – David Pfeffer Jun 16 '19 at 20:49
  • @ThreePhaseEel Nearly every load in the house is something we'd possibly want to have during a long term power outage. I work from home, and we're in the country and have well/septic/etc. Overall, it wasn't worth it. – David Pfeffer Jun 16 '19 at 20:51
  • @DavidPfeffer -- *nods* are your heavy appliances (water heater, range, dryer, central heat) electric or gas? – ThreePhaseEel Jun 16 '19 at 20:57
  • @ThreePhaseEel Propane range, electric dryer. We also have an electric oven that will lock out when transfer switch is on generator. Heat/hot water is geothermal with propane emergency heat; while the generator is sufficiently large to run the heat pumps and we will use it for that during the cooling months, a call for heating will go directly to propane backup during heating and skip the heat pumps. It makes little sense to me to tax the generator to inefficiently generate electricity just to convert it back to heat instead of running the 99% efficient propane boiler to make heat directly. – David Pfeffer Jun 16 '19 at 21:24
  • @DavidPfeffer -- ah, I think you're in an OKish position then...although, while you are correct on your generator-power vs. propane argument re: resistance heat, you're a bit off-base for heat-pump heat, as that doesn't take into account the COP of the heat pump. – ThreePhaseEel Jun 17 '19 at 00:13
  • The fact that you want to power every load in the house *does not preclude a subpanel*. Putting every load in a subpanel is perfectly reasonable and often justified, especially if generators are involved. At the end of the day, do it most expedient/cheapest. – Harper - Reinstate Monica Jun 20 '19 at 00:34
  • Also ThreePhaseEel is correct on heat pumps. Those *are* worth running on generator since they are *over-unity machines* - they may pump 3-4 watts of heat for every watt of electricity they consume. It's not magic, they are simply pumping heat instead of creating it. Also if the generator is liquid cooled, there's a whole bunch of free heat to grab. – Harper - Reinstate Monica Jun 20 '19 at 00:37
  • @DavidPfeffer -- what wiring method is being used to connect the panel to the transfer switch? – ThreePhaseEel Jun 20 '19 at 02:38
  • @Harper I'm not sure what the distinction is between the formerly main service entrance panel that is now being fed from the transfer switch, and a subpanel with every load in it. – David Pfeffer Jun 20 '19 at 11:59
  • @Harper The COP is around 3.5 for my unit on average. But, just doing some rough fuzzy math: My generator uses 217500 BTU/hr for half load according to its spec sheet, which is equivalent to 63,742 W. Half load of the generator is 10,000 W. So, that's about 15% efficient. Even with a 3.5 COP boost, I'm still around 50% efficiency. The propane boiler on the other hand is 99.5% efficient. – David Pfeffer Jun 20 '19 at 12:05
  • @ThreePhaseEel I'm not exactly sure what you're asking, sorry. What do you mean by wiring method? – David Pfeffer Jun 20 '19 at 12:08
  • @DavidPfeffer -- as in, what sort of cabling/wiring is used to connect the two locations together – ThreePhaseEel Jun 20 '19 at 22:18
  • @ThreePhaseEel Ah! Its USE running from the generator to the transfer switch and from the pole to the transfer switch. SER running from the transfer switch to the main panel. – David Pfeffer Jun 21 '19 at 23:16
  • @DavidPfeffer -- I take it a 4-wire (mobile home feeder or quadruplex) USE is being used for the generator-to-transfer-switch run? or does your ATS switch the neutral? – ThreePhaseEel Jun 22 '19 at 00:25
  • @ThreePhaseEel Actually, come to think of it, I think I ran XHHW for the generator-to-transfer-switch run. I think it ended up being a bit cheaper than the mobile home feeder USE wire. Or at least, XHHW is what I indicated on my permit application. :) Its been a while since I started this. – David Pfeffer Jun 22 '19 at 02:41
  • @DavidPfeffer -- as individual wires in conduit I take it? As long as it's a 4-wire run, we're cool here... – ThreePhaseEel Jun 22 '19 at 03:12
  • @ThreePhaseEel Yup! – David Pfeffer Jun 23 '19 at 11:59

2 Answers2

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Leave the ground rods. Install a second set at the new service location.

The IBT only needs to go to ground rods. It doesn't need to go to particular ones.

This plan depends on there being a ground wire between the old and new rods; it's a rare time when metal conduit shell, water pipe, etc. won't do.

There is no penalty for more ground rods than the house requires.

Harper - Reinstate Monica
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    That only works if there's a wire-type EGC between the two locations (not conduit or such), otherwise it violates NEC 250.121... – ThreePhaseEel Jun 20 '19 at 00:55
  • @ThreePhaseEel well there would need to be, wouldn’t there, if the service point was being moved there? – Harper - Reinstate Monica Jun 20 '19 at 02:31
  • Well, it could be the case that the wiring was done using a method that supplies the EGC some other way. I agree that in residential, it's likely that the EGC is a wire... – ThreePhaseEel Jun 20 '19 at 02:38
  • 250.94 states, "... at the service equipment or metering equipment enclosure..." I do already have a new ground rod at the new service location, and then am reusing one of the original ground rods via a wire that runs into and back out of the house to get to it. I'm concerned only with the physical location aspect of the code. From a practical perspective, the bonding is completely fine. – David Pfeffer Jun 20 '19 at 12:12
  • @ThreePhaseEel fixed. – Harper - Reinstate Monica Jun 22 '19 at 01:10
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I would say you are fine. And it should be outside near the meter location. I keep reading 250.94 and can not find any violation. The only thing i see is if you add ,phone or cable out to the other building. You may have to add a ground bar or IBT. But there are exceptions on existing saying not required.

  • I'm not sure if this impacts your answer, but, there's no "other building." Its just my residence and a generator. – David Pfeffer Jun 16 '19 at 20:52
  • The new meter location is not near the old IBT. – David Pfeffer Jun 16 '19 at 20:53
  • I thought it was in a shed.. Will look at it more. Still think your ok . –  Jun 16 '19 at 21:13
  • So you are adding a new service. New meter,transfer switch, and disconnect. At new location ? And making existing panel a sup- panel. You have to bring water bonds out to new service,,gas bond if gas ect. –  Jun 16 '19 at 21:24
  • All plastic water piping. The gas is bonded directly to the wires going to the ground rods, and I've connected into that wire wand extended it along with the service wires to the transfer switch. The IBT is on one of those wires too, its just not in proximity to the new meter, service disconnect, etc. – David Pfeffer Jun 16 '19 at 21:28
  • Are your phone and cable wires going to new service or staying where the are and are still on the wire to the ground rods. See no reason to run wire if splice on. already, –  Jun 16 '19 at 21:44
  • Phone/cable wires are staying where they are. I agree logically it shouldn't need to move since it still is a single point grounding, but, as we both know code doesn't always follow what's logical/practical. :) – David Pfeffer Jun 16 '19 at 21:48
  • Doing home work found. 800.1 exception were you just add own ground rod for communications. You should be fine as long as IBT is on the grounding electrode. If phone cable go to new service install another IBT. –  Jun 16 '19 at 21:54