Generator Hookup to House ?

[panjumbie]

The mechanical (sliding plate) interlock mentioned by several here and pictured in one of the posts would appear to be absent when the cover to the breaker panel is removed.

For that reason and others, it has not been permitted in some jurisdictions and by many utilities.

Backfeeding the utility can be fatal to a utility worker restoring service. The transformer feeding your property works in both directions. It will step up the 120/240 volts from your generator to the thousands of volts on the primary side. And if the outage is local and there is little other load on the primary side of the transformer, it is quite possible that the external load will be insufficient to trip the breaker on the generator.

I'm interested in whether that interlock is UL (or other listing agency) approved for that application.

John Schmidt, PE (retired)

[MAXUM]

Originally Posted by panjumbie

The mechanical (sliding plate) interlock mentioned by several here and pictured in one of the posts would appear to be absent when the cover to the breaker panel is removed.

For that reason and others, it has not been permitted in some jurisdictions and by many utilities.

I just installed one of these for generator isolation for a new subpanel I put in. The mechanical interlock is actually built into the breaker itself not part of the cover. You'd have to literally destroy the breaker to get it off and I would venture a guess this is by design. The interlock I put in is UL listed and was manufactured by Square D.

[8gv]

Originally Posted by panjumbie

The mechanical (sliding plate) interlock mentioned by several here and pictured in one of the posts would appear to be absent when the cover to the breaker panel is removed.

For that reason and others, it has not been permitted in some jurisdictions and by many utilities.

Backfeeding the utility can be fatal to a utility worker restoring service. The transformer feeding your property works in both directions. It will step up the 120/240 volts from your generator to the thousands of volts on the primary side. And if the outage is local and there is little other load on the primary side of the transformer, it is quite possible that the external load will be insufficient to trip the breaker on the generator.

I'm interested in whether that interlock is UL (or other listing agency) approved for that application.

John Schmidt, PE (retired)

Here’s the MET certification for the Square D kit:

https://www.geninterlock.com/wp-cont...ass-letter.pdf

Mine was installed by a licensed electrician with a permit from the town. The town then inspected and approved the work. Yes, removing the panel cover could defeat the system. I do not have any plans to do that.

[Rusty]

Originally Posted by panjumbie

The mechanical (sliding plate) interlock mentioned by several here and pictured in one of the posts would appear to be absent when the cover to the breaker panel is removed.

For that reason and others, it has not been permitted in some jurisdictions and by many utilities.

Backfeeding the utility can be fatal to a utility worker restoring service. The transformer feeding your property works in both directions. It will step up the 120/240 volts from your generator to the thousands of volts on the primary side. And if the outage is local and there is little other load on the primary side of the transformer, it is quite possible that the external load will be insufficient to trip the breaker on the generator.

I'm interested in whether that interlock is UL (or other listing agency) approved for that application.

John Schmidt, PE (retired)

Could you give me the "jurisdictions" and "utilities" that don't allow an interlock on the panel cover. Also do you know of any cases where someone removed the panel cover and caused damage to anything while operating a portable generator.

I do agree that an interlock that is under the cover is better and real easy to put on.

[WINNOCTURN]

Not only did we setup a (Portable) Backup Generator but 2 “SPRINGS” We finally (after16 years built THE GARAGE on the Foundation we poured back then. At that time we decide to put in the Emergency Lighting to back up our Emergency Generating System.

Having trouble loading complete Word file. Too many JPEG Files????

[panjumbie]

Originally Posted by Rusty

Could you give me the "jurisdictions" and "utilities" that don't allow an interlock on the panel cover. Also do you know of any cases where someone removed the panel cover and caused damage to anything while operating a portable generator.

I do agree that an interlock that is under the cover is better and real easy to put on.

Well, read the link at the bottom, all the way to the end. A hot topic among electricians. Typically disallowed in northern NJ, apparently. These have come up in informal discussion before and the understanding of the PE's I was talking with was that there were numerous locations that disallowed them.

In my mind any device that only works with the panel cover installed is unsatisfactory. Homeowners and even some lazy electricians leave covers off of panelboards all too often, either for a period while rewiring or for good.

I would be suspicious of any "third party" device, not manufactured by the panelboard/breaker manufacturer. The panelboards must be listed by UL or another listing agency, to be installed in compliance with the NEC, and quite likely (unless your jurisdiction has exempted the listing requirement) to be compliant in your jurisdiction. There is a significant question whether the panelboard listing, obtained by its manufacturer, is still valid (or would be considered to be valid by the manufacturer or the AHJ) if someone, licensed or not, modifies that panelboard with a third party device, particularly since the modification in this case requires drilling holes in the cover and putting a plastic wire tie around the circuit breakers (Yes, read the instructions provided!) The "kits" sold by the panelboard manufacturer itself would more likely be complaint with the listing.

Also note that the obtained listing for that product is for panelboards, not transfer switches, and the UL description for UL 67 specifically says it is not for transfer devices.

Additionally, if you check the listing restrictions on small portable generators, the article below says that the listing of the generator requires any transfer switch used with the generator to switch the neutral as well as the "hot" conductors. Circuit breaker interlocks can't do that. The NEC section on ground bonding limits most electrical systems to a single bond between the neutral and the safety ground, typically at or near the service disconnect. I think you'll find small portable generators have the neutral tied to the ground connections on the outlets (so that a ground fault can trip the breaker or GCFI) and probably also the frame of the generator. The NEC requires the portable generator ground to be tied to the building ground, and without a transfer switch that switches the neutral you will have a second bond between the neutral and the safety ground, which can cause stray currents in your system. If your portable generator has GCFI's, these stray currents may possibly cause tripping of the GCFI's. Since I don't have copies of the listing requirements (I do have a current copy of the NEC), I can't comment on the listing issues beyond what I've mentioned here.

Regarding people being injured or killed by backfeeds, Google "Lineman injuries from backfeeds". There are hundreds, maybe thousands, of links.

Beyond that, it is up to the owner and/or the electrician (or a Professional Engineer hired by the owner) to verify what your AHJ (Authority having Jurisdiction) and utility will permit. You might want to read your utilitiy's terms of service. They do have the right, (and under OSHA the requirement) to disconnect you if they find your installation presents a safety hazard to their employees.

I personally would not consider any "interlock" that would be inoperative if a cover were removed, or that required plastic cable ties around breakers to assure operation to be safe, but I'm not the AHJ or the utility safety engineer. Of course I (or anyone else) could file a request for a change of the NEC in the next (2020) edition of the code to add language to the code requiring the interlock not be defeated by removing a cover.

Do read the following: http://forums.mikeholt.com/showthread.php?t=152263

[Rusty]

Originally Posted by panjumbie

Well, read the link at the bottom, all the way to the end. A hot topic among electricians. Typically disallowed in northern NJ, apparently. These have come up in informal discussion before and the understanding of the PE's I was talking with was that there were numerous locations that disallowed them.

In my mind any device that only works with the panel cover installed is unsatisfactory. Homeowners and even some lazy electricians leave covers off of panelboards all too often, either for a period while rewiring or for good.

I would be suspicious of any "third party" device, not manufactured by the panelboard/breaker manufacturer. The panelboards must be listed by UL or another listing agency, to be installed in compliance with the NEC, and quite likely (unless your jurisdiction has exempted the listing requirement) to be compliant in your jurisdiction. There is a significant question whether the panelboard listing, obtained by its manufacturer, is still valid (or would be considered to be valid by the manufacturer or the AHJ) if someone, licensed or not, modifies that panelboard with a third party device, particularly since the modification in this case requires drilling holes in the cover and putting a plastic wire tie around the circuit breakers (Yes, read the instructions provided!) The "kits" sold by the panelboard manufacturer itself would more likely be complaint with the listing.

Also note that the obtained listing for that product is for panelboards, not transfer switches, and the UL description for UL 67 specifically says it is not for transfer devices.

Additionally, if you check the listing restrictions on small portable generators, the article below says that the listing of the generator requires any transfer switch used with the generator to switch the neutral as well as the "hot" conductors. Circuit breaker interlocks can't do that. The NEC section on ground bonding limits most electrical systems to a single bond between the neutral and the safety ground, typically at or near the service disconnect. I think you'll find small portable generators have the neutral tied to the ground connections on the outlets (so that a ground fault can trip the breaker or GCFI) and probably also the frame of the generator. The NEC requires the portable generator ground to be tied to the building ground, and without a transfer switch that switches the neutral you will have a second bond between the neutral and the safety ground, which can cause stray currents in your system. If your portable generator has GCFI's, these stray currents may possibly cause tripping of the GCFI's. Since I don't have copies of the listing requirements (I do have a current copy of the NEC), I can't comment on the listing issues beyond what I've mentioned here.

Regarding people being injured or killed by backfeeds, Google "Lineman injuries from backfeeds". There are hundreds, maybe thousands, of links.

Beyond that, it is up to the owner and/or the electrician (or a Professional Engineer hired by the owner) to verify what your AHJ (Authority having Jurisdiction) and utility will permit. You might want to read your utilitiy's terms of service. They do have the right, (and under OSHA the requirement) to disconnect you if they find your installation presents a safety hazard to their employees.

I personally would not consider any "interlock" that would be inoperative if a cover were removed, or that required plastic cable ties around breakers to assure operation to be safe, but I'm not the AHJ or the utility safety engineer. Of course I (or anyone else) could file a request for a change of the NEC in the next (2020) edition of the code to add language to the code requiring the interlock not be defeated by removing a cover.

Do read the following: http://forums.mikeholt.com/showthread.php?t=152263

Thank you for the info, a lot to digest but IMO and experience with interlocks they are safe and accepted by most code inspectors and utilities.

[Rusty]

Originally Posted by panjumbie

Additionally, if you check the listing restrictions on small portable generators, the article below says that the listing of the generator requires any transfer switch used with the generator to switch the neutral as well as the "hot" conductors. Circuit breaker interlocks can't do that. The NEC section on ground bonding limits most electrical systems to a single bond between the neutral and the safety ground, typically at or near the service disconnect. I think you'll find small portable generators have the neutral tied to the ground connections on the outlets (so that a ground fault can trip the breaker or GCFI) and probably also the frame of the generator. The NEC requires the portable generator ground to be tied to the building ground, and without a transfer switch that switches the neutral you will have a second bond between the neutral and the safety ground, which can cause stray currents in your system. If your portable generator has GCFI's, these stray currents may possibly cause tripping of the GCFI's. Since I don't have copies of the listing requirements (I do have a current copy of the NEC), I can't comment on the listing issues beyond what I've mentioned here.

Regarding people being injured or killed by backfeeds, Google "Lineman injuries from backfeeds". There are hundreds, maybe thousands, of links.

This is my generator setup and have been using it for 15 years..does it look OK?

7000 EXL Generac generator..neutral and ground are bonded.
Protran 6 circuit transfer switch which does not switch bonded neutral to floating neutral before going into circuit panel.
Seimens 200amp panel with neutral bonded to ground.

Would this pass inspection by the code cop?

[panjumbie]

Hi, I will not and cannot legally give you specific recommendations on your installation, only general information. My PE license is in NY, you are in NH. Furthermore, I'm retired and my license is set as "inactive". I'd have to pay to reactivate it. Finally, if I were legally able and willing to be your consultant, I'd have to take you on as a client.

In any event, the only people who can actually pass on your installation are the utility and the AHJ, Authority having Jurisdiction. usually your local electrical inspector or their managers.

As I explained before, the NEC is a recommendation, it has no legal standing on its own. Different jurisdictions have different laws. Some states have a state electrical code, which is most commonly based on one or another version of the NEC. New York, where I live, does not. Each locality has its own code and rules. The code in NYC is different than the one in Hempstead Village, where I live, and different again from the unincorporated areas of Hempstead Town.

And the inspection requirements are different. My village has an inspector, a Village employee. Many places use one or more private inspection/certification companies. The last time I looked, NYC had a self certification process for small projects, the contractor (licensed by the city) certified the work complied with the NYC electric code. But Con Ed also inspected services before making connections, particularly for underground services to residences, where Con Ed provided and owned the feeders running into your service and their employees made the final connection. Finally, for large businesses, their insurance company sent "loss prevention" inspectors from time to time. That was the case with my employer.

PE's can consult on code matters but the AHJ/Utility/Insurance inspector has the final word. If the owner feels strongly enough that the AHJ or utility is wrong, the owner can take them to court, where the PE may testify as an expert witness. Then the court decides. Needless to say, most such matters get settled before the court (either a judge or a jury) ends up having to rule.

Another issue, OSHA has adopted much of the NEC as a part of their rules, so if employees are protected by OSHA, their employer must comply with those parts of the code adopted by OSHA.

I will tell you that it appears your generator may tie the neutral to the safety ground internally, so you might have a compliance issue there, at least when the generator is plugged in. Whether the AHJ or utility cares, not for me to guess.

[Rusty]

Thank you for the well written response.

My generator does have an internal bonded-neutral but does not have any GFCI protected outlets which would trip once I plug it into the transfer switch. I could unbond the neutral in the generator but I use it at construction sites which could be dangerous to me and my help. I guess I could buy a generator where the neutral isn't bonded to the ground and use it just for my house but I don't think it is necessary. For the amount of time I use it to power my house I think I'll take a chance with this setup..

[panjumbie]

Originally Posted by Rusty

Thank you for the well written response.

My generator does have an internal bonded-neutral but does not have any GFCI protected outlets which would trip once I plug it into the transfer switch. I could unbond the neutral in the generator but I use it at construction sites which could be dangerous to me and my help. I guess I could buy a generator where the neutral isn't bonded to the ground and use it just for my house but I don't think it is necessary. For the amount of time I use it to power my house I think I'll take a chance with this setup..

I am not sure, and this is not professional consultation, but you may likely find that OSHA requires generators on construction sites to now have GCFI. At the minimum you should consider using portable cords that have GCFI included for all portable connections to the generator.

I suspect there have been more electrocutions on construction sites than from backfed utility services.

I would also think twice before modifying the wiring in the generator. The cure could be worse than the disease, particularly once the generator is unplugged from your house. If you modified the wiring, and then someone got hurt using the generator, even though it had nothing to do with the modification, you might be in a bad position.

One thing you might consider at home is to leave the generator unplugged from the transfer switch except when it is switched to generator. That does limit the possibility of issues from the parallel bonding to only when the generator is running. Since the generator is "small" and doesn't have GCFI's, you are less likely to have (non-regulatory) issues. Since I assume your transfer switch is manual, this doesn't add much effort to switching sources.

You should probably verify that the safety ground for the generator is at least as heavy as the neutral, because some or all of the neutral current is probably flowing through the safety ground when the generator is powering your house.