Neutral bonding and generator

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  #1  
Old 04-17-10, 06:52 PM
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Neutral bonding and generator

I recently setup my house with an interlock kit and generator inlet.

I have a Coleman Powermate 3,500 watt generator. The system works well, I was surprised at how much the little generator was able to power.

One issue I have is the bonding of neutral and ground at the generator. Since my interlock kit does not switch the neutral, neutral is bonded to ground in my main panel and therefore should not be bonded to ground in the generator as well. This is common and usually you would disconnect the bond at the generator when the generator needs to be connected to the house.

My problem is that the instructions for my generator don't mention this at all, so I am not sure where the proper bond is and how to disconnect it. Second, on the panel of the generator near the receptacles it says "Neutral floating" which seems to mean that the neutral is not bonded to ground at all. Is that possible? If neutral was not bonded to ground at the generator, how would the ground prong on the generator's receptacles work properly when a device was connected directly to the generator?

Any insight?
 
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Old 04-17-10, 10:54 PM
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My generator (a Yamaha EF 3000iSE) also has the floating neutral although it isn't mentioned. What it means is that the circuit breaker on the generator only responds to overloads and not to faults to ground. Unless you have a power cable between the gennie and the house that is subject to damage, like someone repeatedly driving over it, I wouldn't worry. Faults to ground WILL be "seen" by the circuit breakers in the service panel and they WILL respond (trip) on such faults.
 
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Old 04-17-10, 11:05 PM
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Most small generators when they have floating netual set up the reason why they want to keep it seperated due one reason is RCD { GFCI } function properly and also in the majorty of jobsite the OSHA is very strict on this { kinda long winded situation with generators I am pretty sure Furd and others are famuair with this one }

most case the netural we just don't float it at all with between the generator and shore power { uility or POCO }unless there is specal situation then we will do the switching netural that is useally found on larger units but for grounding conductor and bonding we never float it at all this is key issue for safety.

Merci,Marc
 
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Old 04-18-10, 05:31 AM
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Thanks for the replies guys.

So basically, the ground prong on the generator serves no purpose whatsoever?
 
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Old 04-18-10, 09:28 PM
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Originally Posted by VoltageHz View Post
Thanks for the replies guys.

So basically, the ground prong on the generator serves no purpose whatsoever?

It do for if the electrical circuit decied to short out it will trip the generator breaker but not always the case so I really recomened that make sure you have GFCI working on the generator otherwise buy inline GFCI cord pigtail device both will work fine.

Merci,Marc
 
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Old 04-18-10, 09:35 PM
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Originally Posted by french277V View Post
It do for if the electrical circuit decied to short out it will trip the generator breaker but not always the case so I really recomened that make sure you have GFCI working on the generator otherwise buy inline GFCI cord pigtail device both will work fine.

Merci,Marc
A short would be the hot to neutral so I assume you mean a ground fault. If the neutral was not bonded to ground on the generator, how would a ground fault trip the breaker? Hell, how would a GFCI even work if there was no neutral/ground bond? There would be nowhere for that stray current to flow so the GFCI would be worthless, correct?
 
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Old 04-18-10, 09:51 PM
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Woah,.. woah.,, let back up a min please.,, Merci { thanks }


To be fair with you the GFCI do work with ground or not and they will sense unblance between the hot and netural conductor it will trip due it have small current transfomer inside the GFCI so it will work with ground or not even no ground present it still read the netural and hot unblance.

I will find a photo how the inside of GFCI work so you will get the idea with it and understand it more clear.

Thanks for being understanding here

Merci,Marc
 
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Old 04-18-10, 09:57 PM
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Originally Posted by french277V View Post

To be fair with you the GFCI do work with ground or not and they will sense unblance between the hot and netural conductor
In a house, sure, because even if there is no ground going to the receptacle, there is still a neutral/ground bond at the main disconnect, so the current has somewhere else to flow to get back to the source (let's say a cold water pipe, for instance).

But in a generator, if neutral is not bonded to ground, how could the current take any other path except the neutral? Knowing that, what purpose would a GFCI serve?

I understand how a GFCI works, but I don't understand how it would work with a generator (a SDS) that doesn't have it's neutral bonded to ground.

Thanks for talking this out.
 
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Old 04-19-10, 01:45 PM
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any leakage which which you would get unless the generator was sitting on a cement slab...would trip the gfci..

If you had the neutral bonded at the generator then your gfci would trip instantly because the neutral is bonded in the main service. Some current would try to flow back to the generator from the bond in the main service thru green/bare back to the genny half bypassing the neutral of the gfci in a way. If you were just running tools straight of the genny it would be fine.
 
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Old 04-19-10, 01:59 PM
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Originally Posted by braether3 View Post
any leakage which which you would get unless the generator was sitting on a cement slab...would trip the gfci..
How would you have leakage if neutral was not bonded to ground? We are talking about a standalone generator with a GFCI and device connected to it. Please explain the alternate path that current could flow, and therefore trip the GFCI, if neutral is not bonded to ground.

How could you possibly have a "ground fault" if the "ground" is not bonded to neutral at any point?
 
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Old 04-19-10, 02:09 PM
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the leakage would could flow into the earth as i said unless it was on a cement slab

IF BIG IF you grabbed onto the hot lead coming out of the genny your going to get a shock.. thats leakage now if you were standing on a 3 inch rubber mat it likly wouldnt trip the gfi but if you were standing in a swimming pool it most definitely would because more power is leaving the hot than is coming back on common neutral.
 

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Old 04-19-10, 02:13 PM
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Originally Posted by braether3 View Post
the leakage would could flow into the earth as i said unless it was on a cement slab
It would flow into Earth? Where would it go from there? How would it get back to it's source (the generator's alternator)?


Additional question, why would it flow into Earth UNLESS it was on a concrete slab?
 
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Old 04-19-10, 02:21 PM
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Originally Posted by VoltageHz View Post

Additional question, why would it flow into Earth UNLESS it was on a concrete slab?
that was just an example of a insulator....

it would TRY to get back to the generator but it would not be very successful

it would work the same way as a ground fault works on a gfi run in a house with NO ground wire...

one of the pros will explain better than I can
 
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Old 04-19-10, 02:52 PM
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Originally Posted by braether3 View Post
that was just an example of a insulator....
I only ask because concrete could be a decent conductor (which is why the UFER ground is being pushed so much now).
it would TRY to get back to the generator but it would not be very successful
Exactly, and since if can not flow, it would never trip the GFCI.
it would work the same way as a ground fault works on a gfi run in a house with NO ground wire...
That is completely different. Altho there might not be a ground wire going to the GFCI, there is still a neutral/ground bond. Because of that, there are many paths back to the source. The cold water pipe is an example, as is a puddle of water outside. If you touch a hot wire with one hand and the water faucet with another, current will flow thru the water pipe, thru the ground wire back to the panel and to the neutral bar, completing the circuit. In that case, the GFCI will trip because current had an outside path.

Now if you never had that path, if neutral was not bonded to ground, the current can't flow.

So my contention is this: If neutral isn't bonded to ground, you can't have a ground fault. If you can't have a ground fault, a GFCI is worthless. Or, I am completely wrong and missing the big picture here. If so, this is a great lesson to learn and a very interesting topic.
 
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Old 04-19-10, 08:19 PM
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Very interesting topic indeed. Electrical Engineeringing 101 I think.

VoltageHz? Can I chime in and ask a question or 2?

1) Should a portable generator be on a cement slab or rubber mat?

2) My portable genny has a lug to use a ground bare wire. Is this useless because of the ground wire (4 wire) going back to the panel? So there is no need to install a ground rod and ground the genny frame? If there is a fault to the frame, and the genny is on cement, the fault will be carried back to the panel via ground wire and trip the genny breaker?
 
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Old 04-19-10, 08:31 PM
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Originally Posted by Thonati View Post
1) Should a portable generator be on a cement slab or rubber mat?

2) My portable genny has a lug to use a ground bare wire. Is this useless because of the ground wire (4 wire) going back to the panel? So there is no need to install a ground rod and ground the genny frame? If there is a fault to the frame, and the genny is on cement, the fault will be carried back to the panel via ground wire and trip the genny breaker?
that was kind of my point...UNLESS it was in those situations then it might not trip...just about all generators have a ground lug on them that should be connected, but realistically doesn't get connected because of portability.

I don't agree that they the Gfci's without ground and a generator gfci are TOTALLY different
 
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Old 04-20-10, 12:23 AM
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Where is Bruto when we need him?

Several things are being discussed and they have different answers. There are portable generators where the "neutral" terminal is bonded to the equipment ground terminal, portable generators where the "neutral" terminal is NOT bonded to the equipment ground terminal, portable generators that have internal GFCIs and portable generators that do NOT have GFCIs.

Then there are questions of having a portable generator connected to a residential service and questions where the portable generator is used as a source of power for portable power tools.

Let's start with the generator that does not have a GFCI and also does not have any leads connected to the earth ground terminal or the equipment grounding terminal of the power out receptacle. I will also limit the discussion to a generator with a single voltage two-wire output although the principles are the same for three-wire dual voltage units.

With such a generator there IS NO "NEUTRAL" TERMINAL! A single fault from one of the power leads to either earth ground or any metallic surface, (conduit or equipment enclosure) does nothing, no shock hazard or tripping of the generator's circuit breaker. HOWEVER, if another unintentional fault occurs between the other power lead and "ground" (either earth or equipment)there WILL be a current flow and depending on the resistance of the faults there could be sufficient current flowing to either trip the circuit breaker or if the second fault passes through a person the person will be shocked.

If this generator is used for supplying power to a single "tool" (consumer of electric power) an external GFCI will have no effect even if a fault to "ground" occurs because there is still no return path to the source (generator) other than the original two wires. Electricity DOES NOT "naturally" travel to the earth as some people may believe, it ONLY returns to the source. Now let's assume that there IS a "fault to ground" of one wire between the generator and the external GFCI. in this case an second fault to ground in the same generator lead but after the GFCI WILL cause the GFCI to trip because there are now TWO "return paths" and therefore the current through the GFCI is no longer balanced between the two generator wires. Without the GFCI such a pair of faults could become a shock hazard if the second fault was through a person although the normal resistance of a person and whatever amount of earth was between the person and the first fault would likely limit the current to an amount so low as to not be detectable by that person.


A generator with a built-in GFCI would always have one lead connected to the equipment ground terminal and that lead would then be the "neutral" as it is commonly defined. In this scenario the "ground" terminal on the generator should normally be connected to to not only the earth but also to any metallic surface that could under fault conditions be energized. Under these conditions a GFCI and the generator's circuit breaker would be effective under most fault conditions just as the circuit breakers and GFCIs in a residence supplied by utility power.

(Next post to detail generators connected to a residence for emergency usage.)
 
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Old 04-20-10, 12:53 AM
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(For this part I am going to use the North American system of a utility serving a residence with a three-wire, dual voltage system.)

There are two ways that a portable generator could be connected to a residential system although only one method is used. The method NOT used would be where all three utility wires AND THE NEUTRAL TO GROUND CONNECTION are broken with the generator neutral being connected to the house without also being connected to the earth OR the equipment grounding conductors in the service panel. This would be called (NEC definition) a "separately derived system". What IS used is a connection that breaks only the "ungrounded" (AKA "hot" leads) utility wires and leaves the "grounded neutral" connection and the connection of this wire to the equipment grounds and earth ground.

Using a generator with no internal connection of any lead to the equipment ground or earth ground terminal would still be considered a "grounded supply" because the neutral lead IS "grounded" in the house's service panel through both the generator's "neutral" and equipment grounding conductors being connected together at the service panel. HOWEVER, the "ground" lead in the generator-to-house cable is NOT (and cannot be) a "current carrying conductor UNLESS the "ground" terminal at the generator is actually connected to earth ground and even then the current that might flow on this connection will be minuscule UNLESS the earth connection is made to (or close to) the earth-embedded grounding connection of the house service panel. Under this scenario the grounding of the generator's "ground" terminal is of little importance. The action is pretty much the same if the generator DOES have the "neutral" lead connected to both equipment and earth grounds. The biggest difference is that under some conditions the equipment grounding conductor of the generator-to-house cable will be a current carrying conductor under ground fault conditions.

Finally, in the case of a generator with internal GFCI the equipment grounding conductor in the generator-to-house cable WILL become a parallel return (parallel with the neutral) allowing the return current to divide and therefore trip the GFCI because of the neutral / ground bond in the service panel. Generators with internal GFCI are NOT suitable for use as an emergency source when connected to a service panel that has a neutral-to ground connection.

I hope this clears up some of the questions.
 
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Old 04-20-10, 05:37 AM
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Originally Posted by furd View Post

With such a generator there IS NO "NEUTRAL" TERMINAL! A single fault from one of the power leads to either earth ground or any metallic surface, (conduit or equipment enclosure) does nothing, no shock hazard or tripping of the generator's circuit breaker. HOWEVER, if another unintentional fault occurs between the other power lead and "ground" (either earth or equipment)there WILL be a current flow and depending on the resistance of the faults there could be sufficient current flowing to either trip the circuit breaker or if the second fault passes through a person the person will be shocked.
agreed and point well made

Originally Posted by furd View Post
Electricity DOES NOT "naturally" travel to the earth as some people may believe, it ONLY returns to the source. .
as I said it would try to get back to the source THROUGH the ground.
 
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Old 04-20-10, 01:56 PM
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There has to be a difference in potential for electricity to flow. Without having one side of the source connected to the earth there would be no differential and therefore no reason to expect any flow "through the earth" back to the source.
 
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Old 04-20-10, 02:05 PM
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Originally Posted by furd View Post
There has to be a difference in potential for electricity to flow. Without having one side of the source connected to the earth there would be no differential and therefore no reason to expect any flow "through the earth" back to the source.
That was my whole theory behind why a GFCI would be worthless is neutral wasn't bonded to ground.

But you brought up the possibility of two simultaneous ground faults so that changes it.
 
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Old 11-12-11, 03:32 PM
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hi guys-i bought a homelite generator-5000 watts with neutral bonded to ground.theres an article if you GOOGLE -HOME GENERATOR INSTALATION-This guy really does a great job of making sence in thoery and in practice-actually for home back-up applications a floating neutral is prefferable and easier to wire through a transfer switch-If you have a neutral bonded to ground,you must have a transfer switch(switch neutral kit) $100 @ Gentran website-to properly have only one ground at any given point in time which facilatates the correct usage of the GFIC used on these OSHA compliant generators
 
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