# Generator Bonded Neutral

Asked Jan 18, 2007, 03:07 AM — 12 Answers
I'm certainly not an electrician but maybe someone who is can help me with this. I recently bought a new generator for home backup, camping, and remote powering of tools. The generator had a bonded neutral (the neutral is connected to the ground circuit). The neutral needs to be "floating" when connected to my home for back-up power but should be "bonded" when used as a remote power supply. My question is... Why would you want the neutral connected to the ground for any application? I always thought that the current ran (normally) through the hot (black) wire to the load then returned via the white (neutral) wire and that the ground was just and alternate path to get rid of the voltage in case of a short. Wouldn't connecting the neutral to the ground create current in the ground circuit? Apparently that isn't the case as the neutral and ground are tied together at the main box in a home electrical system. And finally why would two bondings in one circuit create a problem? It seems like if bonding the neutral to the ground in the home is a good thing that bonding the neutral to ground in the generator or anywhere else would be good as well. As I said, I'm not an electrician but I have done many electrical hobbies and have done many home circuits (mostly lighting and outlets) and I do know the right way to make the connections but I don't understand the why and am hoping someone can make sense of it for me. I've spent over 7 hours researching this online and the only responses that I've been able to find are "Because that's the way the code says to do it." OK, I get that but being able to understand why makes it a lot easier to remember.

 tkrussell Posts: 9,673, Reputation: 3698 Senior Electrical & Lighting Expert #2 Jan 18, 2007, 06:02 PM

Ok, you have some good questions, and it is difficult to find something on the web to help explain or illustrate exactly what you are asking.This can be a complicated topic to understand, and explain to someone that may or may not understand grounding, theory, etc. So I will do the best I can.

First, keep in mind, a portable genset is called a Separately Derived System, and is treated just like a service. The neutral (grounded conductor) and equipment ground are connected, and grounded to earth.

This is to insure the first breaker, at the power source will trip. This lowers the impedance of the grounding wires.You can think it as allowing the fault current (short) to return to the source.

A genset connected to a home will normally be a Non- separately Derived System, and the neutral and grounding is separated, same as a sub panel.

This method is dictated by the transfer switch , not by the generator or the purpose.

If the transfer switch does not switch the neutral from the genset, the neutral of the genset and the service is connected permanently, and this system is now called the Non-Separately Derived system,

If the transfer switch switches, or opens, the neutral at the same time as the ungrounded conductors (hots), then the genset is treated as a separate service, and the neutral and ground is connected, and grounded the same as the main service, with it's own grounding electrodes (ground rods).

The main purpose is that any electrical system should be grounded at one point, again, to insure the main breaker will trip, and to eliminate ground loops, which can occur if there were more than one grounding point beyond the main service. If there were a short circuit, the fault currents can, and will seek out each ground rod, and basically get divided to each ground rod, and not necessarily evenly, due to the impedance of each ground path.

This can result in fault currents flowing but not get to a high enough threshold to trip the main, or any breaker for that matter.

Did this make any sense?
 tckitt13 Posts: 3, Reputation: 1 New Member #3 Jan 23, 2007, 03:36 PM
tkrussell,

You did a good job of explaining the rules and to some degree the two separate grounds producing a "ground loop". Could you explain a ground loop to me? It seems like the idea is to get any "stray" current into the earth and dispersed as quickly as possible. So, it seems like the more grounding the better. I know that's not true because of the possibility of ground loops but I don't really understand what a ground loop is.

Also, my generator has rubber wheels and rubber pads under the front stand so no metal on this unit touches the ground. So it seems to me that the generator isn't grounded unless I pound a grounding rod 8 feet into the ground and connect it to the frame (not likely that I'll go to that much trouble... kinda takes the "portable" out of a potable generator). Doen't the ground wire that runs to the grounding plugs on all the outlets of the generator also connect to the framework? And how about the neutral wiring... isn't that connected to the frame at some point as well? If not, the generator portion of the unit is metal and it is bolted to the frame so wouldn't that suffice?

Finally, what if I just remove the wire from the neutral plug to the ground plug in the outlet of my generator effectively "floating" the neutral. What is the real danger if I float the neutral and leave it that way for all aplications?

I appreciate your expertise on this subject and very much appreciate you help. Many of the electricians that I have talked to are lost when it comes to generators.

Thanks,
TK
 tkrussell Posts: 9,673, Reputation: 3698 Senior Electrical & Lighting Expert #4 Jan 24, 2007, 03:51 PM

The issue is not so much with generators but with grounding.

A ground loop is just that, current that can flow in a circle because the path has been created.

The quantity of grounding electrodes is not the issue. Yes the more the better, The issue is where the grounding electrode is connected to the neutral (grounded conductor) to ground the neutral.

Grounding a portable generator with a rod may not be necessary because it is a separately derived system, if the genset is used for portable use. You need to follow the manufacturer's instructions for this purpose.I believe the neutral and ground in a portable genset are connected together, which is correct.

If you disconnect the connection between a neutral and ground, any fault current from a short may not trip a breaker.

Once a portable genset is connected to a permanent system, such as a building, the feed needs to go through some sort of transfer switch, and then the grounding is dictated by the transfer switch.

I am trying to keep my answers short but meaningful without getting too into the gory details. Too much more explanation is getting beyond the scope of this forum and I can direct you to find a copy of "Soares Grounding Book", and take the chance of giving you the impression of the typical "just because".

Proper grounding is needed because it relates to grounding the neutral, and keeping the impedance low so that breakers operate, so you can see how one subject blends into another. Not trying to out of answering, but I am only here to answer a few questions and not get into an electrical course.
 truckerx Posts: 4, Reputation: 10 Junior Member #5 Nov 10, 2011, 08:03 PM
Hi every-one just bought a Homelite generator with a bonded neutral system- watched an electrician on Youtube hook up generator by back-feeding it through an approved outdoor connector and small section of added conduit in the house into the main panel and using an interlock device to prevent tripping both sources by accident.

Said it conforms to all codes and is safe, cheap and legal-would seem if the generator was fed with a four wire twist connector at the generator and the wiring from the inlet adapter to the main service panel included the neutral and ground being attached to the same busses as the main service panel the system would only form one ground loop and would be good to go so to speak.

It a nice generator and kind of hate to bring it back because it has a unique neutral circuit- adding a new circuit shouldn't be a big deal.

Wondering what you think so far?
 tkrussell Posts: 9,673, Reputation: 3698 Senior Electrical & Lighting Expert #6 Nov 11, 2011, 03:38 AM

I deleted your other posted questions, as they are duplicates of what you have here.

Leave the neutral-bond connection as is. Drive a ground rod for the genset only if the manufacturer recommends it.

Here is a manual for a 5000 watt Homelite unit, it states to ground the frame to a "suitable ground source".

If generators do not have wheels or rubber feet, usually it does not need a ground rod as the frame sits on the ground, and is sufficient.
 truckerx Posts: 4, Reputation: 10 Junior Member #7 Nov 11, 2011, 06:21 PM
Hey TKRUSSEL- thanks for the feed-back-sounds like Id be OK to wire in my generator as I described - interlock switch, feed into the main panel with neutral and ground going to their busses and a new breaker top right hand corner just below the main for interlock-I've stumbled into some pretty decent web sites that really shed some light on grounding and bonding AC generators and explained code definitons and how they apply to this application-cummings.com has a tech article that sounds exactly as you did in your replys-you obviously know your stuff-at a much higher level- us dummies really appreciate you help!If you Google"generator neutral ground bond" you'll see a cummings website-article 6606 I believe-took a lot to follow and understand but sure did help my overall grasp of how and why-your friend Chuck-thanks again
 truckerx Posts: 4, Reputation: 10 Junior Member #8 Nov 11, 2011, 06:35 PM
Actually it was power topic #6006 GROUNDING OF AC GENERATORS AND SWITCHING THE NEUTRAL IN EMERGENCY AND STANDBY POWER SYSTEMS' TYPED IN 'GENERATOR NEUTRAL GROUND BOND' with Google to find it- hope this will help others too-
 truckerx Posts: 4, Reputation: 10 Junior Member #9 Nov 12, 2011, 12:23 PM
For those of us who bought a "neutral bonded to frame" portable generator- iI,ve found some good clear easy to understand and "use today" web pages and info. To help learn what we need to know to do the job ourselves and understand what we're doing and why.#1 in my mind is *PORTABLE GENERATORS AND OSHA CONSTRUCTION REGULATIONS'-JOHN 'GRIZZY'* nice easy and fun look at why and how these generators became neutral grounded in the first place-#2 HOME GENERATOR INSTALATION-members.rennlist.com/warren/generator.com This guy really has an excellent section on neutral/grounded generator and transfer switch applications- also like his "do it right or dont do it mind-set"#3 Reliance TRANSFER SWITCH VIDEO-gives a nice step by step look at how the systems are put together-good chance to see if its really something your able to do yourself realisticaly-#4 Gentran TRANSFER SWITCH-(SWITCHED NEUTRAL KIT)- cost \$100, allows transfer switch to properly (switch) generator neutral to allow proper GFIC circuit protection to function as it was designed for your protection-HAVE FUN AND ALWAYS-BE SAFE! ALMOST FORGOT! THE WAY TO FIND THESE WEB PAGES IS TO TYPE INTO GOOGLE-EXAMPLE-"HOME GENERATOR INSTALATION" GOOD LUCK!
 richb_online Posts: 1, Reputation: 10 Junior Member #10 Feb 12, 2012, 09:14 PM
If your portable generator is new enough it likely has GFCI (ground fault) protection on its outlets. HERE'S THE ISSUE with Bonded-Neutral: A GFCI functions by comparing the outgoing current on the HOT to the current coming back on the NEUTRAL. A difference of as little as 6/1000 of an amp will trip it out. If you have the NEUTRAL and GROUND bonded at 2 points (also called a loop), the current will SHARE the return path to the generator between the GROUND wire and the NEUTRAL wire. Since the GFCI sees less current on the NEUTRAL than on the HOT, it will trip out, rendering your generator useless for household backup. So, do NOT attach the generators ground wire to the transfer switch at all, but DO use a ground rod to attach to the generators frame. Hope that helps, Richard. (journeyman electrician).

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