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Thread: stand-alone generators

  1. #1
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    stand-alone generators

    As most of you I receive via email newsletters from the Holt site. One tilted; Electrical Safety What you should know about backup power systems

    I made a comment to the newsletter and Mike posted a response that had a link to a very old thread on the discussion forum as well as making a statement that Honda had worked this out with UL 30 years ago.


    Looking for more clarification I sent an email to the Holt offices to wit I made the statement that 30 years ago in the 1982 code cycle the scope of 250 also said on page 84 that;“Systems and circuit conductors are solidly grounded to facilitate overcurrent device operation in case of ground faults.” I made this statement to show that a lot of things change over a 30 year period.

    I also pointed out that NEC Plus has a link to UL FTCN in 702.10 of the 2008 and 702.11 of the 2011 code cycles and ask for clarification to just what role UL FTCN has to play in the installation of stand-alone generators. The reply I got from Sean Hutchings was;

    "I am sorry, but there isn't anyone qualified to answer a technical question in our office. However, we do offer a free resource via our website, www.MikeHolt.com . Our Code Forum is 100% free and is a wonderful way to resolve any technical questions you may need answered. Not only do we have 1000’s of members that share information on the site, we also have several moderators that help out. Our Code Forum Moderators are experts in the electrical field and industry leaders that have been involved with the electrical industry for many years. You can register for free at the link included below. Please let me know if there is anything else I can help you with. Have a wonderful day."

    On the advice I received from the Holt office I now ask these expert moderators what role does 110.3(B) and UL FTCN have to play in the connection of a stand-alone generator to premises wiring system. Why does NFPA have a link to UL FTCN in NEC Plus concerning Optional Standby Systems in 702?

    702.11 Portable Generator Grounding. (A) Separately Derived System. Where a portable optional standby source is used as a separately derived system, it shall be grounded to a grounding electrode in accordance with 250.30. See related UL

    (B) Nonseparately Derived System. Where a portable optional standby source is used as a nonseparately derived system, the equipment grounding conductor shall be bonded to the system grounding electrode. See related UL



    I can’t find anywhere in the installation instructions outlined by UL where it is permissible to disconnect the neutral from the generator frame in order to connect it as a non-SDS. I do see where they make the statement in “1” that the generator is considered a SDS by both ANSI and NFPA.

    From UL FTCN
    This category covers internal-combustion-engine-driven generators rated 15 kW or less, 250 V or less, which are provided only with receptacle outlets for the ac output circuits. The generators may incorporate alternating- or direct-current generator sections for supplying energy to battery-charging circuits.
    When a portable generator is used to supply a building or structure wiring system:
    1. The generator is considered a separately derived system in accordance with ANSI/NFPA 70, "National Electrical Code" (NEC).
    2. The generator is intended to be connected through permanently installed Listed transfer equipment that switches all conductors other than the equipment grounding conductor.
    3. The frame of a Listed generator is connected to the equipment-grounding conductor and the grounded (neutral) conductor of the generator. When properly connected to a premises or structure wiring system, the portable generator will be connected to the premises or structure grounding electrode for its ground reference.
    4. Portable generators used other than to power building or structure wiring systems are intended to be connected to ground if required by the NEC.


    I am of the opinion that these stand-alone generators (the ones which have receptacles) are designed as temp power as outlined in 590.6(A)(3) and when used as a 702 installation must be connected as a SDS as outlined in UL FTCN.
    Mike Whitt
    God answers Knee-Mail.

  2. #2
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    There are a number of issues at play here. First the information from UL is correct where the generator has a neutral to frame bond, but the information only applies in that case. There are many portable generators that do not have such a bond and would not be connected as SDS. There are also generators that have a switch to remove or connect the neutral bond and generators where the manufacture has instructions on removing the bond. These may not be listed generators, but there is nothing that requires the use of a listed generator in the NEC.
    I guess it boils down to this...if the generator neutral is bonded at the generator, you need to connect it to the building via transfer equipment that switches both the ungrounded and grounded conductors, and if the neutral is not bonded the transfer switch should not switch the neutral.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  3. #3
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    I agree that the term “portable generator” is a broad term but I am not addressing all portable generators. I am addressing a stand-alone generator or one that has the receptacles mounted on the frame of the generator for supplying the equipment being used.

    There is a big difference between a portable generator and a stand-alone generator and this difference in mentioned not only in 250.34 but again in 590.6(A)(3)

    I am asking why NEC Plus references UL FTCN if these stand-alone generators are allowed to be installed as a non-SDS. I do not see where it makes reference that if it is not listed it does not apply.
    Why does 590.6(A)(3) exist if the stand-alone generator can come equipped without a neutral to frame bond.

    By the way, here in NC it can’t be installed if it does not have a third party label except in a few cases.
    Mike Whitt
    God answers Knee-Mail.

  4. #4
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    Quote Originally Posted by jwelectric View Post
    I agree that the term “portable generator” is a broad term but I am not addressing all portable generators. I am addressing a stand-alone generator or one that has the receptacles mounted on the frame of the generator for supplying the equipment being used.
    So am I.

    There is a big difference between a portable generator and a stand-alone generator and this difference in mentioned not only in 250.34 but again in 590.6(A)(3)
    Can you expand on that? I don't know what you are asking about.

    I am asking why NEC Plus references UL FTCN if these stand-alone generators are allowed to be installed as a non-SDS. I do not see where it makes reference that if it is not listed it does not apply.
    You would have to ask the authors of NEC plus that question. I have no idea what they say.
    Why does 590.6(A)(3) exist if the stand-alone generator can come equipped without a neutral to frame bond.
    The fact that the system is not bonded does not prevent the GFCI from doing its job. Even on an unbonded system if the current on the two wires of the circuit differs by more than ~5mA the GFCI will trip. In general this would take two faults.

    By the way, here in NC it can’t be installed if it does not have a third party label except in a few cases.
    Install or used? I don't see a portable generator being used to supply power to a building as being "installed". The transfer equipment would be installed but not the generator.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  5. #5
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    I have a generator that connects to the PTO of my tractor. It is a portable generator but does not have receptacles on it anywhere. I can rent a generator that will connect to the ball of my truck that is portable and it will not have receptacles.

    A stand-alone generator will have only receptacle outlets to take power from and they are required by 590.6(A)(3) to have all receptacles protected by GFCI. Should one of these be connected to the premises wiring as a non-SDS it will not work.

    Now look at the definition of premises wiring and see if it says anything about a temporary and power source installation.

    The authors of the NEC Plus are the same ones that publish the NEC therefore I would take it that their reference to UL means just what it says.
    Mike Whitt
    God answers Knee-Mail.

  6. #6
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    Quote Originally Posted by jwelectric View Post
    I have a generator that connects to the PTO of my tractor. It is a portable generator but does not have receptacles on it anywhere. I can rent a generator that will connect to the ball of my truck that is portable and it will not have receptacles.
    Yes, and that will likely not have a neutral bond at the generator.

    A stand-alone generator will have only receptacle outlets to take power from and they are required by 590.6(A)(3) to have all receptacles protected by GFCI. Should one of these be connected to the premises wiring as a non-SDS it will not work.
    Only the 30 amp and lower rated receptacles require GFCI protection. These generators likely have a neutral bond and should be connected as SDS. If you are supplying the building via a GFCI protected receptacle and you have connected it as a non-SDS, the GFCI should trip. At least on manufacturer is on record with a statement as to the method of removing the neutral bond so that it can be connected as non-SDS.

    Now look at the definition of premises wiring and see if it says anything about a temporary and power source installation.
    It is very broad, but it still uses the word "installed". I have a very hard time seeing a stand alone generator that is pushed or carried to the site and connected by a plug in cord as being installed. The code rules as to the type of connection would still apply and even a "non-installed" cord connection would create a code violation if it results in multiple points of bonding for the grounded conductor.

    The authors of the NEC Plus are the same ones that publish the NEC therefore I would take it that their reference to UL means just what it says.
    While they all work for the NFPA, the are not code making panel members and have no more standing in the interpretation of the code than you or I do. However if the generator in question is covered by FTCN, then there is no question that the code, via 110.3(B), requires the connection to be SDS.

    If the generator is not a listed product I don't see the information in FTCN as applying. That doesn't really change anything as the code rules do not permit the grounded conductor to be bonded at multiple locations and if the generartor has a neutral bond, then the transfer equipment would have to switch the neutral to be code compliant.

    I believe that there are listed generators that have only receptacles as outlets that do not have the neutral bonded.


    If you are really only asking if the code requires the building connection from a generator to be SDS where the generator has a bonded neutral....of course it does.

    However, I don't see any real world hazards if a stand alone generator is connected to the building without switching the neutral at the transfer equipment...I just see a code violation.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  7. #7
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    I think what jwelectric is saying is that, yes, he gets the NEC requirements. Don, by your comments, you do to. But I don't think that's the point. The point is that the rules are not clearly understood and do not directly address the real world installs out there.The average homeowner that has, say, a manual xfer switch with a power inlet installed would logically think that any port. generator with a matching recep. would be acceptable. The vast majority of small portables out there have the neutral bonded which would require a xfer switch with a switched neutral. How many switched neutral resi. grade xfer switches have you seen? I've never seen one. The idea that UL, NEC and the electrical industry don't get together and get this resolved in a clear and concise manner is just dumb. The reality is even many electricians and inspectors don't understand the rules. Then add to the mix GFCI on 30 amp or less receps and all the other possible situations (like JW's PTO generator) and things get messy. This situation IMHO is poor policy on the NEC's part and leads to non-compliant installations.

  8. #8
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    Quote Originally Posted by texie View Post
    The idea that UL, NEC and the electrical industry don't get together and get this resolved in a clear and concise manner is just dumb.
    It sure appears so, but I would bet there are conflicting intere$t$ at the root of it,

    This situation IMHO is poor policy on the NEC's part and leads to non-compliant installations.
    The NFPA is a private entity, UL is a private entity, the manufactures are all separate.


    What leverage do you see the NFPA having to get UL or the manufacturers to do what is needed to mesh with the NEC?

  9. #9
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    I just don't see this as a real world issue. I don't see a safety issue or other type of hazard when a stand alone generator is used to power a building and the neutral is bonded at more than one location. I is just a code compliance issue...not a real issue.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  10. #10
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    Quote Originally Posted by don_resqcapt19 View Post
    I just don't see this as a real world issue. I don't see a safety issue or other type of hazard when a stand alone generator is used to power a building and the neutral is bonded at more than one location. I is just a code compliance issue...not a real issue.
    Well, in a lawsuit... is compliance important?
    My position is that poorly written code and poorly coordinated with other agencies leads to non-compliant installs.

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