Generator bonded Neutral.

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  #1  
Old 11-01-12, 04:43 PM
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Generator bonded neutral (safety issue)

Hello:
I am trying to determine the safety issue when using a portable generator with bonded neutral and a transfer switch which does not switch the neutral. I found various explanations across the net but opinions vary. Thanks Bob
 

Last edited by bob_m; 11-01-12 at 05:56 PM.
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  #2  
Old 11-01-12, 07:34 PM
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While there are people that will vehemently disagree with me I do not see this as a huge safety factor as long as certain precautions are taken.

When a "neutral to equipment ground" bond is in place at both the generator and the service panel the "return path "(neutral currents) will return to the generator on BOTH the neutral AND the equipment grounding conductors of the generator interconnect cable. This is, by definition a code discrepancy as the equipment grounding conductor is to carry current ONLY under "fault" conditions.

Using a transfer switch (single circuit) or a transfer panel (multiple circuits) that switches the neutral-equipment ground bond from the utility service panel to the generator is one way to overcome this problem and it is the code compliant method. Unfortunately most transfer switches and panels installed and currently on the market do NOT switch the boding point.

My advice is NOT code compliant but it IS relatively safe, definitely safer than having the the parallel currents on the neutral and equipment grounds of the interconnect cable. All you need to do is NOT connect the generator equipment ground at the transfer switch/panel. What this will do is keep all the same ground fault protections offered by the service panel neutral-to-equipment ground bond in the house. You DO lose "line (hot lead) to ground fault protection ON THE INTERCONNECT CABLE between the transfer switch/panel and the generator but the actuality of a fault in this cable is very low PROVIDED you do nothing that may injure the cable such as laying it across a driveway and then running the car over it.
 
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Old 11-01-12, 09:52 PM
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Hi Furd:

>definitely safer than having the the parallel currents on the neutral and equipment grounds of the interconnect cable.<

Ok what is the major safety issue here? Considering <50’ run to the generator, no branch circuits like in the case of a sub pannel. I can see that ground will generally be undersized in standard 10-3 w/ground but I can’t see any other problem. I am probably missing something.

I also feel that generator manufactures are not helping. Like you said, most transfer switches do not switch neutral and most Generators do not make it easy to separate the bond, like mine.

Thanks Bob
 
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Old 11-01-12, 11:54 PM
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This all came about a year or two ago when OSHA issued new rules concerning the use of portable generators on job sites. The new rules mandated that any generator built after a certain date MUST have built-in GFCI (ground fault circuit interruption) protection. The National Electrical Code followed suit and now it is all but impossible for a portable generator to be connected to a residence without violating some code provision.

IN MY OPINION the hazard is small and I have no trouble in recommending the method I detailed. This method requires no changes with the generator (which might void a warranty) and it requires no changes with the regular wiring within the house. All the GFCI protected circuits within the house will still operate as they do on utility power. With the "hot" lines of the generator completely removed from the utility connections there is no chance for the generator to energize the incoming utility conductors. Even within the interconnect cable a fault from one of the "hot" leads to either the neutral or the equipment ground will trip the generator-mounted protective device (circuit breaker). The ONLY thing that is a hazard is if a hot lead in the interconnect were to somehow come to connect to a solidly earthed conductor (the ground rod and/or connecting conductor) at the main service then the possibility exists of a fault current going from the hot conductor through the ground to the neutral-equipment bond in the service and back to the generator. Such a current would likely NOT be enough to trip the generator's protective device but it COULD be hazardous to personnel in some way unknown to me.

As for the parallel currents on the neutral and equipment grounding conductors in the interconnect cable it is a code violation, pure and simple. Again, under some conditions unknown to me it could be hazardous.

If you like, I can detail several provisions of current code that make connection of portable generators to fixed wiring unacceptable. You have to make the decision as to whether or not to follow the code.
 
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Old 11-02-12, 06:55 AM
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>All you need to do is NOT connect the generator equipment ground at the transfer switch/panel. What this will do is keep all the same ground fault protections offered by the service panel neutral-to-equipment ground bond in the house. You DO lose "line (hot lead) to ground fault protection ON THE INTERCONNECT CABLE <

Interesting, thinking about this (non code compliant) solution, since most installations use an outside 30amp inlet box, I would imagine you would want to connect ground at least up to this point. That way the inlet can is grounded back to the main pannel. Then when you make up the Interconnect Cable, use 10-3 “without” ground. What do you think?

>I can detail several provisions of current code that make connection of portable generators to fixed wiring unacceptable<

Ok, if the generator is not bonded, what would be the code violation if using a transfer switch?

Thanks Bob
 
  #6  
Old 11-02-12, 11:16 AM
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Use a 10-4 interconnect cable with all conductors properly terminated. Connect the equipment ground from the service panel to the metal box of the inlet connector. Do NOT connect the equipment grounding terminal of the inlet connector to anything. This way you have an interconnect cable suitable for any installation and/or generator. The inlet connection metal box is grounded for safety. All you have done is broken the parallel path for return currents to the generator.

It's still early for me so I might miss something. Code violations for using a portable generator to feed a premises wiring system (code-speak for a building) is that the neutral-equipment ground bond must be made BEFORE any disconnects. That means before the generator's circuit breaker, before the generator's panel-mounted receptacle, before the inlet connection plug at the house, before the transfer switch and before any main or branch circuit breakers in the house. So far, so good with a generator that has a bonded neutral.

Now remember, I'm only firing on three cylinders right now so I might get this wrong. The code also mandates that there be no disconnects between the bonding point and the service panel. With the portable generator there are several disconnects, the generator's circuit breaker, the generator's output receptacle, the inlet connection at the house and the transfer switch itself. Code also prohibits any neutral-ground bonds downstream of the required bond so that makes the existing neutral-ground bond in the service panel a code violation when power is supplied from the generator.

Bottom line is that the only way a generator can be completely code compliant is to hard-wire it through a transfer switch that allows transferring the neutral-ground bond from the service panel to the generator. I suspect that there will be some changes in this particular code requirement in upcoming revisions.

Please don't ask me to cite the code paragraphs detailing these requirements. My brain is already fried.
 
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Old 11-02-12, 01:47 PM
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>Use a 10-4 interconnect cable with all conductors properly terminated. Connect the equipment ground from the service panel to the metal box of the inlet connector. Do NOT connect the equipment grounding terminal of the inlet connector to anything. This way you have an interconnect cable suitable for any installation and/or generator. The inlet connection metal box is grounded for safety.<

I see your point but since the inlet box is an installed fixture in the home, I would consider it better to wire that correctly. That way the next owner of the home has a properly wired fixture. The alterations can occur in the disposable cable which I can label and use for my own use. Just two ways of looking at it I guess.

Thanks for the information on the code, very interesting. When is the next revision due out?

Bob
 
  #8  
Old 11-02-12, 02:09 PM
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National Electrical Code is revised every three years. The latest revision is 2011 so 2014 will be the new code.

You can certainly wire it as you propose and your reasoning for doing so is sound. Although I have a generator that outputs 120 volts only I replaced the twist-lock output receptacle on it for a 240/120 volt model and wired my interconnect cable, power inlet box and transfer switch for 240/120 operation. This way if I ever get a 240/120 gennie, or I croak and the new owner of my house wants a 240/120 generator, everything is already set up for that purpose.
 
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Old 11-03-12, 05:48 AM
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Hello Furd, I have been reading a lot of your answers on this forum and appreciate all of it!

My question is; if you isolate and cap the Ground Wire in the main panel while hooking up your generator with a interlock kit, I understand that the generator GFCI would not work on the generator but wouldn't the generator still be grounded because the Neutral and Ground are bonded in the Main Panel? Meaning there would be some ground safety for the generator?

Thanks!
 
  #10  
Old 11-04-12, 11:00 AM
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Generator Bonded Neutral

Use a 10-4 interconnect cable with all conductors properly terminated. Connect the equipment ground from the service panel to the metal box of the inlet connector. Do NOT connect the equipment grounding terminal of the inlet connector to anything. This way you have an interconnect cable suitable for any installation and/or generator. The inlet connection metal box is grounded for safety. All you have done is broken the parallel path for return currents to the generator.

I thought all I have read on this subject lately gave me enough understanding to proceed with purchasing the equipment and installation. I was planning to simply NOT connect the ground leading from the inlet box to the service panel by capping it with a wire nut inside the CB panel. I don't grasp the above alternative and am confused. How can you "Connect the equipment ground from the service panel to the metal box of the inlet connector" but at the same time "NOT connect the equipment grounding terminal of the inlet connector to anything". Does this maybe mean run the ground inside the inlet box, along with the other wires, but just not connect it to the inlet grounding terminal? Or does it literally mean screw the ground wire into the inlet metal box itself. If so, why might this be a better route to go?

 
  #11  
Old 11-04-12, 08:43 PM
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The conduit (or cable if you use cable) between the transfer switch and the power inlet connection will have four wires for a 240/120 volt generator. The red and black will be "hot" leads, the white will be the "neutral" lead and the green (or bare) is the equipment grounding conductor. connect this green (or bare) to the metal BOX enclosing the inlet connector. There may or may not be a screw for this wire but if there is not use a 10-32 self-tapping machine screw (NOT a sheet-metal screw) in an appropriately sized hole.

The power inlet connector will have a green screw/terminal that connects to the equipment grounding conductor in the interconnect cable to the generator. Connect NOTHING to this terminal.

The reasoning? NEC REQUIRES all metallic junction and pull boxes along with any other metallic parts of an electrical system to be BONDED to the equipment grounding conductor. This is to provide a low impedance (low resistance) return path for electricity to flow during a fault condition. This in turn causes a high current to flow that will actuate the overcurrent protective device (OCPD) commonly a fuse or circuit breaker.

Not connecting the equipment ground from the power inlet isolates the equipment grounding conductor in the generator interconnect cable from the bonded neutral/equipment ground in the service panel, preventing a parallel path between the neutral and the equipment grounding conductors in that interconnect cable. NOTE THAT THIS ONLY APPLIES IF THE GENERATOR HAS A NEUTRAL/EQUIPMENT BOND AT THE GENERATOR. If the generator does NOT have a neutral/equipment bond then you DO connect the power inlet equipment ground to the green or bare wire in addition to the metallic case of the power inlet connector.
 
  #12  
Old 11-05-12, 06:54 PM
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Furd:

Thanks so much for the detailed explanation! Mt Generac 6500E is bonded neutral to ground (I have not been able to find out how to undo it). I will break the loop on the other end at the power inlet box as you described INSTEAD of leaving the 10-3g NM-B's equipment ground conductor disconnected/capped inside the CB panel (where I plan to install an interlock switch).

Also, good tip on the grounding screw type to use. I bought a whole pack of these green grounding screws last summer for another home electrical project after discovering the junction box I had didn't come with one.

Next I will try to figure out what type of conduit best to enclose the 10/3+g cable leading from the power inlet on the outside wall down through a hole in the concrete into my basement CB panel. I understand it is very important to physically protect the cabling with this type of set-up.
 
  #13  
Old 11-18-12, 09:50 AM
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I have the L-14-30 power inlet wired with the ground wire to the CB panel connected to the box itself (not the terminal screw on the inlet). My next question regards the wiring of the ground wire on main, and only, CB panel. After inserting the 2 pole 30 Amp circuit breaker in the 2-4 position for the Square D interlock switch, I see there is only one free bus slot for the neutral and ground wires. Most all of the other bus slots have both the neutral and ground in the same slot which I have read is not good for some reason (even though the neutral and ground currents are apparently shared via bus bar on the panel itself). Is it OK to attach the neutral and ground wires form the inlet box to the same bus slot? I don't want to needlessly separate the current neutral and ground arrangement and break up the consistency of how the panel is wired. Any ideas for how best to approach this?
 
  #14  
Old 11-18-12, 06:18 PM
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Typically you can have 2 ground wires to one hole and screw and one neutral wire to one hole and screw. Look at the panel label inside the panel door on Homeline panels and inside the panel box on QO panels for more information.
 
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Old 11-20-12, 01:33 PM
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So if you remove the bond on the generator, do you need to have a ground rod at the generator?
 
  #16  
Old 11-20-12, 03:00 PM
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No, but you DO need to carry the equipment grounding conductor (green wire) through the inlet connector and all the way to the neutral/equipment ground bus in the service (main) panel.

Read post #11 carefully.
 
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Old 11-23-12, 04:54 PM
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Thanks CasualJoe for your response (#14). I guess I opened up a can of worms (or more accurately wires). My CB panel (Square D QOB20M100 series G1, 100A) has the white neutrals and bare copper grounds going into the SAME screw holes on the neutral buses. I, as well as two contractor electricians, followed this wiring schema when adding the four breakers that have been installed to this panel since I bought the house in 1995 (The house itself was built in 1928). Now that I have added a two pole 30A breaker for an on order generator interlock switch, I would like to break the tradition and re-route all of the grounds to a panel specified ground bar kit also on order (Square D ground bar kit PK15GTA). My question is where/how do I install this 15 terminal ground bar? I have seen pictures of ground bar kits bolted to the middle of the panel below the circuit breakers and I have also read that they can be attached to factory pre-drilled locations on the panel meant for such purpose. Can someone please give me a good hint about how best to proceed? Does the ground bar require being connected to the panel main ground wire or does just attaching it to the box make the necessary ground to accept the equipment grounding wires?

Also, does the small bus where the main service neutral attaches also serve as a place to ground the equipment neutrals? It looks like there are three screw holes available on it but not sure if that is meant for the same purpose as the other two obvious neutral buses (please see attached pictures). Thanks.
 
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Old 11-24-12, 07:04 AM
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My question is where/how do I install this 15 terminal ground bar?
Your Square D QO loadcenter is not terribly old so I would first check the data information label inside the panel box, I am sure the illustration will show where the pre-drilled holes are located. This would be the easiest way to install the ground bar.

Does the ground bar require being connected to the panel main ground wire or does just attaching it to the box make the necessary ground to accept the equipment grounding wires?
The included mounting screws will tap their own threads in the pre-drilled mounting holes. This bonds your ground bar to the box which should be bonded to the grounded neutral bar through the neutral bonding screw. You should check the data information label once again to locate the neutral bonding screw hole and be sure the bonding screw was installed.

does the small bus where the main service neutral attaches also serve as a place to ground the equipment neutrals? It looks like there are three screw holes available on it but not sure if that is meant for the same purpose as the other two obvious neutral buses
Yes, that is also part of the neutral bus. As long as this is the main panel and there are no disconnects between this panel and the meter, the neutral bus is used for both neutral and ground conductors.
 
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Old 11-24-12, 07:33 AM
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Square D panels have typically up to 3 sets of raised bumps with pre-drilled holes for mounting the auxillary ground bars. Look in the gutter space under the wiring.
 
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Old 11-24-12, 10:22 AM
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The inside areas of the panel with the documentation labels are covered with extra lengths of looped wire and very difficult to see. I did not want to needlessly pull out the wires but now that I know there is possibly additional helpful information to be had will turn off the main switch and give it a closer examination.

I will attempt to determine the placement of the ground bar and locate the neutral bonding screw to make sure it was installed. I assumed there had to be a neutral bonding screw installed given the neutral and ground wires occupied the same bus screw holes but it sounds like it is important to confirm the configuration. Thanks for the advise!

 
  #21  
Old 11-24-12, 03:58 PM
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I opened up my CB panel again but only found information on the label regarding the ground bar catalog # to be used and nothing regarding where to install it. I did find two small bumps above the bottom panel gutter and am wondering if they are possibly meant to accept the screws that come with the grounding bar kit (photo attached).

I transferred the neutral #10 copper wire leading from the 2 pole 30 A breaker for the interlock switch over to one of the free screw holes on the bus where the main service neutral is attached. Now at least the 2 pole breaker does not share a bus screw hole with its ground wire (photo attached).

I found a label chart with information on the neutral bonding screw placement but unfortunately there are two screw holes to the right of the right side neutral bus. The one immediately to the right is empty and there is also one to the right of that which is occupied. It is not clear to me if this second screw is for grounding or simply for securing a component of the panel equipment (photos attached). Thanks.
 
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  #22  
Old 11-25-12, 12:08 PM
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For a transfer switch that switches the neutral, that disconnects the panel neutral from the service neutral. It des not necessarily unbond neutral and ground within the panel.

The bonding screw in the neutral bus of a panel is generally green colored to point out that it serves no other purpose than bonding neutral and the panel body.(; frame; can). A threaded hole in the neutral bus through which a screw, if long enough, does nothing besides dig into the panel back is a hole suitable for a bonding screw.

A whole house transfer switch, by definition, is a "main" disconnect upstream of the "main" panel. If you install one of those then you should separate grounds and neutral in the "main" panel that follows, adding a separate ground bus bar if needed.

For the panel pictured above, separating neutrals and grounds is not a trivial task. For that reason alone I actually recommend leaving the neutrals and grounds as is if you are installing an interlocked backfeed breaker for your generator or a transfer switch box containing a number of individual branch circuit transfer switches.

A short length of #6 copper wire from one of the neutral bus holes to a bolt and nut (they say not a wood screw or sheet metal screw) where the panel back was scraped bare of paint will also bond the panel to ground adequately.

Except for tripping a ground fault circuit interrupter built into the generator, you really don't have to worry about return current flowing on the equipment grounding conductor between the generator and the panel given that ground and neutral are bonded at the panel and also at the generator.

Because of ground-neutral bonding at the panel, all of the EGCs and grounded circuits throughout the house are safe. Because the detination of the return current is the generator and not the earth, there is no danger outside the house.
 

Last edited by AllanJ; 11-25-12 at 12:50 PM.
  #23  
Old 11-25-12, 07:09 PM
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Thanks for all of the detailed information AllenJ! I will certainly avoid any non-trivial alterations if at all possible. I guess it is safe to say my panel appears to be bonded to neutral even though there is no green screw.

Here is what I will go with when I hopefully receive the correct Square D interlock switch this coming week:

2 pole switch with #10 AWG ground wire in far left side neutral bus screw hole by itself and the #10 AWG neutral wire in neutral bus where the main neutral service attaches in screw hole by itself (holes rated on panel label for two #14 or #12).

leave other ground and neutral wires occupying same far left and far right neutral bus holes in place

wires from CB panel connected to outside power inlet 2 hots and neutral terminals with the ground connected to the box itself and not the inlet ground terminal

leave factory neutral bond of portable generator in place

save neutral ground bar on order for some other possible future use

try to figure out why my CB panel is wired with most all the neutral and ground wires connected in the same neutral bus screw holes (one neutral and one ground in one hole)

I have learned a lot about electrical wiring with this project but still have a ways to go with my understanding of everything involved. I sincerely appreciate all the advise and explanations.
 
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