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Old 01-01-2012, 08:31 PM   #1
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Generator & Interlock Kit – Float the Neutral?


I had a Square D interlock kit (UL listed) installed by an electrician to my main service panel in October, along with an inlet box (240 Volts) to allow me to plug in an external generator. Not long after, I bought a portable generator.

The portable generator (6700 watts) has a bonded neutral and GFCI protection on the 120 V outlets, but no GFCI protection on the 240 V / 30 amp outlets.

I connect it to the inlet with a 40-foot, 30 Amp cord.

I have since been told two opposite things:

1) Some have said that I should unbond the neutral at the generator to avoid the risk of shock from a parallel path and for code compliance (I don’t need an inspection here).

2) I have also been told that unbonding the neutral at the generator creates a greater risk, in case the generator develops a fault caused by an internal component failure, and it is not at that time connected to the house inlet via the 40-foot, 30-amp cord. Those with the second opinion (all claiming to be electricians on internet boards) have said that the risk of a shock at the generator from a parallel path caused by bonding at the generator and at the service panel is miniscule.

I don’t plan to use the generator as a stand-alone unit, but instead for emergency power. However, you never know, so I’m reluctant to have the neutral unbonded. Even though it will be used primarily (or more likely exclusively) for emergency power, we will often start it without the 30-amp cord plugged in to the house, for monthly testing. The cord will only be plugged in when we need to connect to the house.

I have the generator set up so it is completely protected from the elements - it will never be exposed to rain or snow.

If I leave the neutral bonded, is there much of a risk of shock due to the double bonded neutral at the generator (which is upstream from the main panel)?

The power company has a bonded neutral upstream from my house when they are supplying potentially a zillion watts.

In tests, the generator powers everything I need it to run properly, and without tripping any GFCI’s.

Both my dryer and range have neutral bonds, due to the age of my house, by the way, although my main service panel is now brand new. We have never had a problem with shocks from these devices, or any electrical problems with our service, but a generator may not be the same animal.

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Old 01-01-2012, 08:40 PM   #2
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Generator & Interlock Kit – Float the Neutral?


Leave it alone. And the power company doesn't "supply" watts. Watts is a term of consumption, not supply. Your 6700 watt generator can handle a total usage of 6700 watts....it doesn't just throw it out there and hope it goes where it is supposed to go. If you have a 100 watt light bulb, it uses 100 watts....no more, no less. You had the proper interlock installed, good for you. Many homeowners try to shortcut this step and create a potentially dangerous situation. You will be fine leaving the generator as it is, and your interlock provides the required safety for you and any lineman working on the utility lines.

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Old 01-01-2012, 09:17 PM   #3
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Generator & Interlock Kit – Float the Neutral?


I say leave it alone as well.
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Old 01-01-2012, 09:55 PM   #4
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Generator & Interlock Kit – Float the Neutral?


Thanks, guys. That's what I would love to do. I'd rather not have my electrician or power equipment guy open up and mess with the generator's innards, even if it is simple and reversible.
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Old 01-01-2012, 11:16 PM   #5
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Generator & Interlock Kit – Float the Neutral?


Leave it alone x3.

Any portable generator that has receptacles is under 10kw and sits on the ground is intended by design to be a separately derived system for the operation of cord and plug tools and equipment. The nec requires any seperately derived system to have a main bonding means between neutral and ground.

Operating a portable generator as emergency power for single family dwellings has been a dilemma for manufacturers for years as the neutral to ground bond cannot exist at the generator when connected to premise wiring which also has a main bonding jumper with the utility. One or the other but not both. They have just recently been writing in their instructions on emergency power use about this issue of neutral and ground bonding.

Limit your exposure to the generator when operating the house wiring through your integrated interlock system. Stop it,fuel it, start it get away from it. I don't mean that as there is eminent danger , the possibility of electrical shock is there but it has to have nearly powerball win odds to happen.

Do not drive a ground rod and attach to the frame, this increases the odds of getting shocked. Do not operate hand tools from the generator receptacles just let the generator power the premise wiring.

To date I do not know of any manufacturer of a portable generator where in their instructions actually tells you what to do about the neutral and ground bonding. They just say contact a licensed electrician about it. By doing so they pass the liability to you and the electrician.

The manufacturers never meant for you to power your house with a portable but it was one heck of a selling point to say you could ....

This opened up a whole new market for portables to other than construction type consumers.
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Old 01-02-2012, 07:48 AM   #6
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Generator & Interlock Kit – Float the Neutral?


This is what I would do for a portable generator connected via cord and plug (not saying you should).

Unbond neutral and ground in the generator only if this can be done easily.

If not then plug in the generator "normally" allowing neutral and ground to be bonded both at main panel and at generator.

If generator GFCI keeps tripping then put generator on dry wood platform and unhook green wire somewhere between generator and house panel for example at the male receptacle on the side of the house. Also unhook generator from ground rod.
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The manufacturers never meant for you to power your house with a portable but it was one heck of a selling point to say you could
More preferable: Plug lights and appliances into generator using extension cords, not going through regular house receptacles and main panel. A male receptacle on the side of the house can still be used, going to a subpanel and then a nearby box with receptacles, in the house and not connected to the main panel.

Some household circuits such as for the furnace can be equipped with individual transfer switches. Use a 4x4 square junction box with a double pole double throw* switch (not a regular 3 way switch), and a small male receptacle for the extension cord to the generator. Switch commons is for the branch circuit hot and neutral conductor. One "traveler" terminal pair is for the panel feed hot and neutral. The other "traveler" terminal pair is for the male receptacle.

* DPDT switches can sometimes be used as 3 way switches but depending on the configuration you can get bizarre results, namely flip the switch one way and one light goes on and another goes off, and you have to go to the other switch location to synchronize the lights.
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Old 01-02-2012, 08:50 PM   #7
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Generator & Interlock Kit – Float the Neutral?


Thanks for all of the information - all of this helped me understand this concept better, and hopefully, some other readers. When I add it all up, I think I'll stick with the double-bonded neutral, and try to touch the machine as little as possible when it's running.

A few comments here. I read that 80% of portable generators are bought to provide backup/emergency power for homeowners.

When I mention that I bought a generator, I'm surprised at the number of friends, neighbors and even a small business who tell me they are backfeeding through a dryer outlet or other 240 outlet (and at least a couple have had these installations set up by electricians). Few seem to have a transfer switch or an interlock.

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Old 01-02-2012, 10:02 PM   #8
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Generator & Interlock Kit – Float the Neutral?


Yes it is very common among homeowners who listen to misinformation and simply do not understand the consequences to use portable generators in this manner. You are required to use some device, transfer switch, interlock etc..that prevents backfeeding the utility. You can be held liable both civil and criminal for any accident that may occur to a lineman or someone in your home or on your property. The NEC,NESC and local codes and others will be presented in a court of law in the event of a law suit.

Sleep at night and do it correctly.
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Old 10-24-2012, 08:33 AM   #9
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Generator & Interlock Kit – Float the Neutral?


RE: safety and accidentally backfeeding the grid>It also occurs to me that you could potentially injure your neighbor(s) by backfeeding the grid.

While we're at it, I have some very basic questions of my own on this subject. I own a portable 6700 watts generator. I just bought this transfer switch:
http://www.homedepot.com/webapp/wcs/...472&ci_gpa=pla
Before buying it, I went round and round trying to decide the best way to use the generator. This seemed the safest, easiest and cheapest way to do the job and use the equipment. The only downside is, I'm limited to 10 circuits. We don't lose power THAT often, so it should be fine.

While I'm not an electrician, I'm a handy person and I've done LOTS of electric over the last 25 years. While I feel very comfortable doing this job, I have a couple of questions:

1. Can someone explain how a portable generator is grounded when used as a standalone?
2. Can someone explain how I should treat the neutral and ground between the transfer switch and the main panel?
3. Can someone tell me the best sequence to follow when operating the generator in this manner?
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Old 10-24-2012, 10:14 AM   #10
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Generator & Interlock Kit – Float the Neutral?


I installed that same transfer switch a couple months ago. Just follow the excellent instructions that came with it. They show you exactly how to make all the necessary connections to your main panel.


Quote:
Originally Posted by TomJV View Post
RE: safety and accidentally backfeeding the grid>It also occurs to me that you could potentially injure your neighbor(s) by backfeeding the grid.

While we're at it, I have some very basic questions of my own on this subject. I own a portable 6700 watts generator. I just bought this transfer switch:
http://www.homedepot.com/webapp/wcs/...472&ci_gpa=pla
Before buying it, I went round and round trying to decide the best way to use the generator. This seemed the safest, easiest and cheapest way to do the job and use the equipment. The only downside is, I'm limited to 10 circuits. We don't lose power THAT often, so it should be fine.

While I'm not an electrician, I'm a handy person and I've done LOTS of electric over the last 25 years. While I feel very comfortable doing this job, I have a couple of questions:

1. Can someone explain how a portable generator is grounded when used as a standalone?
2. Can someone explain how I should treat the neutral and ground between the transfer switch and the main panel?
3. Can someone tell me the best sequence to follow when operating the generator in this manner?
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Old 01-13-2013, 01:35 PM   #11
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Generator & Interlock Kit – Float the Neutral?


If the transfer switch in the house does not switch the neutrals it is not a SDS. Yes, you want to remove the neutral/ground bond in your portable gen. After you do so, you must label the gen as "floating neutral" and "not OSHA compliant" It's ok to use the gen as a standalone purposes as long as you have GFCI protection for the 120 volt outlets and not use the 240 volt for standalone purpose as that particular outlet is not GFCI protected. The 240 outlet should then only be used for plugging into your transfer switch inlet. The neutral/ground is bonded at the service panel so any faults will trip gen breaker. I knew someone that got shocked because they failed to remove the ground/neutral bond in their gen when they hooked it up to their house non-SDS transfer switch. Yes, it maybe unlikely you get shocked off the gen frame, but the potential is there. Don't take the chance, especially if any kids walk around it and happen to touch the gen frame while barefoot on wet concrete or ground.
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Old 01-13-2013, 02:32 PM   #12
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Generator & Interlock Kit – Float the Neutral?


Does anyone know of a readily available, reasonably priced transfer switch that switches the neutral?

Sounds like that is the best solution...
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Old 01-13-2013, 05:28 PM   #13
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Generator & Interlock Kit – Float the Neutral?


Quote:
Originally Posted by TTW View Post
Does anyone know of a readily available, reasonably priced transfer switch that switches the neutral?

Sounds like that is the best solution...
A transfer switch that switches the neutral is neither cheap nor readily available.

They are expensive, and most have to be special ordered.

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