# Genrac bonding question



## kb1jb1 (Nov 11, 2017)

My opinion only. 

Does the meter with disconnect have overcurrent protection such as a circuit breaker or is it just a disconnect without OCP? A 200 amp mounded case switch?. If it has OCP then that is your service and all grounding takes place there. Water ground and any other GEC. Everything down stream are feeders and panels requiring 4 wires. White and green has to be separate. You might have to remove the green bonding jumper in the ATS. If you switch the neutral with the ATS, then it is separately derived system. If the neutral is not switched then it is not separately derived. I think what you described is correct but the meter/disco to the ATS is what you have to watch. That might have to also be 4 wire.


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## H.M. electric (Apr 8, 2014)

kb1jb1 said:


> My opinion only.
> 
> Does the meter with disconnect have overcurrent protection such as a circuit breaker or is it just a disconnect without OCP? A 200 amp mounded case switch?. If it has OCP then that is your service and all grounding takes place there. Water ground and any other GEC. Everything down stream are feeders and panels requiring 4 wires. White and green has to be separate. You might have to remove the green bonding jumper in the ATS. If you switch the neutral with the ATS, then it is separately derived system. If the neutral is not switched then it is not separately derived. I think what you described is correct but the meter/disco to the ATS is what you have to watch. That might have to also be 4 wire.


thanks for the reply, the meter/disco does have a 200amp OCP breaker, and if done the way you describe I believe I would have to remove the bonding jumper in the ATS and run a 4 wire from the meter disco to the ATS. from the ATS documents the neutral is not switched. 

my only thought on this was when the generator is running, wouldn't that serve as the main "utility" and then you would have no bonding between grounding and grounded conductor? that is the way it is spec'd in the manual for a system that is not separately derived so likely I am just not understanding something completely about the function of the generator and/or the bonding process.


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## H.M. electric (Apr 8, 2014)

ok I think I may have it now (sorry for the crap drawing). my last question, is the 2 wire (purple) for the load side going to the panel and the blue and green taps from the 4wire (yellow "utiltiy" line side going to ATS) ok going to the main house panel?

essentially:
1.) 4 wire (yellow) from main/disco to ATS line side 
2.) 4 wire (orange) from genrac to ATS emergency line side
3.) 2-wire (purple) (L1 and L2) from ATS load side back into meter/disco, connecting to existing 4-wire (pink) L1 and L2, then tapping the neutral and ground for main panel in the meter disco? (all bonding done in the meter/disco)


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## hornetd (Oct 30, 2014)

There are two bonding schemes laid out in the US National Electric Code.The underlying issue is that the flow of neutral current on the exposed surfaces of the metallic parts of the electric system and the metal encased appliances which the electricity supplies MUST be avoided. Any current flowing through the equipment grounding conductor system will have a voltage drop associated with it. That voltage drop would leave some parts of the exposed conductive portions of the electrical system at a voltage above ground. That elevated voltage is called touch potential. That leaves the installations users exposed to electric shock by becoming the conductor between a surface with an elevated touch potential and another which has a negligible voltage on it relative to ground. 

This is the reason that the US NEC requires that the EGCs be bonded to the neutral at only one point that being in the premise's Service Disconnecting Means. As long as there is only that one connection between the two there will be no current from normal operation flowing over exposed metallic surfaces of the electrical system. To prevent the connection of 2 Main Bonding Jumpers on the electrical system's neutral conductors you must do one of two things. One is to transfer the neutral conductor of the electrical supply from the utility source to the alternate source along with the energized conductors and install the a Main Bonding Jumper at the generator between the neutral point of the generator's windings and the frame of the generator. The other is to transfer only the energized conductor/s from the utility supply to the alternate supply. Since the neutral remains bonded in the Service Disconnecting Means (SDM) enclosure you do not add a bonding jumper at the generator. Short version if neutral is not transferred then do not bond the generator frame to the generator neutral. If the neutral conductor is transferred with the energized conductors then you do bond the generators winding's neutral point to the generator frame. 

This code required practice comes down through the code from a past situation were backup generators were relatively rare and seldom served entire premise normal loads. To supply only a portions of the premises load the transfer switch would supply a feeder supplied panel were all of the essential loads received their supply. Wherever that is the case it becomes very important to not have an additional bonding jumper at the generator because that would create two cross connections between the Grounded Current Carrying Conductor (Neutral) and the Equipment Grounding Conductor (EGC). The connection of the Neutral conductor to ground at the generator would effectively bond it to ground at the feeder supplied panel and thus at 2 places which have a difference in potential caused by the voltage drop in the neutral conductor back to the Service Disconnecting Means. The neutral current flow would divide over both conductive pathways in proportion to the difference in the impedance of between them. 

In the case of any alternate supply of any nature supplying only a portion of the total load normally supplied by the utility service the need for keeping the two pathways free of any contact with each other is important because of the voltage drop that would always be present on the neutral and/or the possibility of an open occurring in the neutral thus causing all of the neutral current to flow over the Equipment Grounding Conductor with the highest possible voltage drop and the greatest rise in touch potential. Even when the supply conductors are both connected to the load at the same point the alternate source has an EGC while the utility source does not. As a consequence of that difference an open or high impedance on the neutral conductor of the alternate source would cause some or most of the neutral current from that alternate source to flow over the EGC thus energizing all of the exposed conductive surfaces connected to that EGC by the voltage drop over the EGC pathway between the alternate source and the main bonding jumper. 

Were that leaves us with a unique problem with the use of portable generators as the alternate source, especially when using a breaker interlock in the panel that the generator will supply. Interlocked breakers only transfer the energized conductors. The neutrals of both the alternate supply and the utility supply remain connected to each other. It seams to me unlikely that a portable generator would always and only used to standby for a power outage at a home. If it is ever going to be used as a stand alone power source it must have a bond between the neutral point of it's windings and the frame because the receptacles mounted on the generator have their EGC terminals also bonded to the frame. That connection arrangement will assure that any fault on a load that the generator is powering will cause current to flow back to it's source in the generator winding at a high enough rate to open the generator's Over Current Protective Device (OCPD) thus deenergizing the fault. When supplying the building it must not, in theory, have it's windings neutral point bonded to the frame. The challenge is then to provide a Bonding Jumper on the generator which can be rapidly connected and disconnected when changing the use of the generator from one situation to the other. 

Does anyone know of a 3 Ø panel that accommodates 2 of the 3 pole breakers side by side either vertically or horizontally? I suspect someone will scream with rage and pain when I suggest this but with such a panel and a rocker style breaker interlock I could assemble a transfer switch that would switch the neutral along with the 2 energized conductors. Ouch. That would require 1 three pole 200 ampere breaker. I'll bet those aren't cheap! The other breaker could be sized for the generator or any readily available rating which is higher than the largest likely generator's ampacity.

-- 
Tom Horne


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## Arsenal FC (10 mo ago)

kb1jb1 said:


> My opinion only.
> 
> Does the meter with disconnect have overcurrent protection such as a circuit breaker or is it just a disconnect without OCP? A 200 amp mounded case switch?. If it has OCP then that is your service and all grounding takes place there. Water ground and any other GEC. Everything down stream are feeders and panels requiring 4 wires. White and green has to be separate. You might have to remove the green bonding jumper in the ATS. If you switch the neutral with the ATS, then it is separately derived system. If the neutral is not switched then it is not separately derived. I think what you described is correct but the meter/disco to the ATS is what you have to watch. That might have to also be 4 wire.


Yes. Separately Derived system and Service Grounding and Bonding "once" are your two keywords... Nothing to your existing knowledge and the relatively small question you had given.... This book was shown to me before and it really puts a FULL understanding to Grounding and Bonding... It helped me understand G&B in depth.






youre


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