Page 1 of 2 12 LastLast
Results 1 to 10 of 15

Thread: portable generator hookup questions

  1. #1
    Join Date
    Jun 2016
    Location
    Tampa, FL, USA
    Posts
    1,619

    portable generator hookup questions

    My son-in-law would like to use a portable generator to power his house in case of outage. Three questions:

    1) The neutral from the generator will not be switched. (Backfed breaker with interlock on main). Is there any danger if the generator neutral is connected while using utility power?

    2) Should he tie the generator frame to the same ground rod as the service?

    3) The generator inlet will be about 40 feet from the backfed breaker in the panel. Does there need to be a breaker closer to the generator inlet to protect the cable like there would be for a service entrance cable?

  2. #2
    Join Date
    Jul 2003
    Location
    New Jersey
    Posts
    25,618
    1) No.
    2) No, it is not a separately derived system.
    3) No, the output breaker in the generator will protect those conductors.

    When set up like this the generator neutral to ground bond must be lifted and the inlet and panel require signage.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  3. #3
    Join Date
    Feb 2003
    Location
    Bremerton, Washington
    Posts
    7,915
    Quote Originally Posted by infinity View Post
    1) No.
    2) No, it is not a separately derived system.
    3) No, the output breaker in the generator will protect those conductors.

    When set up like this the generator neutral to ground bond must be lifted and the inlet and panel require signage.
    Inlet signage is in Art 702.7(C)
    If you don't lift the neutral then generator GFCI will trip.
    With the neutral lifted generator can't be used on jobsite
    Moderator-Washington State
    Ancora Imparo

  4. #4
    Join Date
    Jun 2016
    Location
    Tampa, FL, USA
    Posts
    1,619
    Quote Originally Posted by infinity View Post
    1) No, it is not a separately derived system.
    Quote Originally Posted by tom baker View Post
    Inlet signage is in Art 702.7(C)
    So am I correct that the below sign is the one I need? What's the definition of "floating neutral" here? Does that mean it's not grounded? How would the system be a bonded neutral? Does it matter which system I use?

    WARNING:
    FOR CONNECTION OF A NONSEPARATELY DERIVED
    (FLOATING NEUTRAL) SYSTEM ONLY


  5. #5
    Join Date
    Jun 2016
    Location
    Tampa, FL, USA
    Posts
    1,619
    Quote Originally Posted by infinity View Post
    When set up like this the generator neutral to ground bond must be lifted and the inlet and panel require signage.
    I just re-read your post and saw this. I see there are three and four wire generator inlets. I'm assuming the four wire have a separated ground and neutral that are bonded at generator. When the cord is removed from the inlet, this would break that bond, correct? What happens if the generator is left connected while under utility power? (I don't know if his generator uses a three or four wire outlet.)

  6. #6
    Join Date
    Jul 2003
    Location
    New Jersey
    Posts
    25,618
    If you're using a 30 amp setup most generators use a 4-wire cord set to a 4-wire inlet. This is a non-SDS so the neutral/EGC bond in the generator is removed. The signage required is as you've mentioned.

    Click image for larger version. 

Name:	Inletsign.jpg 
Views:	86 
Size:	144.5 KB 
ID:	20483Click image for larger version. 

Name:	Generatorbond.jpg 
Views:	88 
Size:	141.3 KB 
ID:	20484
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  7. #7
    Join Date
    Feb 2003
    Location
    Bremerton, Washington
    Posts
    7,915
    Its not complicated but to understand this you need to understand SDS and non SDS generators
    Here is a great video clip from Mike Holt on generator grounding
    https://www.youtube.com/watch?v=M3lX4XtlYXk
    Moderator-Washington State
    Ancora Imparo

  8. #8
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    5,438
    Quote Originally Posted by Coppersmith View Post
    I just re-read your post and saw this. I see there are three and four wire generator inlets. I'm assuming the four wire have a separated ground and neutral that are bonded at generator. When the cord is removed from the inlet, this would break that bond, correct? What happens if the generator is left connected while under utility power? (I don't know if his generator uses a three or four wire outlet.)
    The interlock Kit only allows either the breaker that the generator is backfeeding or the main to be on, not both at the same time. The point of the interlock is twofold one so that you cannot parallel out of phase with the power company and blow up your generator (and/or loads)and two, you do not backfeed the grid while the generator is running. If the power company restores power while your generator is running, it is shut off by your main breaker and the power stops there, while you're generator breaker which is closed is feeding your panel and all your loads. You have to shut off the generator breaker before you can turn the main breaker back on. With a properly installed interlock and dead front, it is physically impossible for both Breakers to be on at the same time.

    Eta: if his panel does not have a main breaker, I am not sure that you can install a generator Inlet perhaps an ATS, but not an MTS, don't know what code it violates but it would be extremely dangerous to manually transfer generator and Poco power without an interlock
    Last edited by JFletcher; 06-05-18 at 10:19 AM.
    Electricians do it until it Hertz!

  9. #9
    Join Date
    Jun 2016
    Location
    Tampa, FL, USA
    Posts
    1,619
    Quote Originally Posted by JFletcher View Post
    The interlock Kit only allows either the breaker that the generator is backfeeding or the main to be on, not both at the same time. The point of the interlock is twofold one so that you cannot parallel out of phase with the power company and blow up your generator (and/or loads)and two, you do not backfeed the grid while the generator is running. If the power company restores power while your generator is running, it is shut off by your main breaker and the power stops there, while you're generator breaker which is closed is feeding your panel and all your loads. You have to shut off the generator breaker before you can turn the main breaker back on. With a properly installed interlock and dead front, it is physically impossible for both Breakers to be on at the same time.
    My concern was only that the generator neutral would remain connected when the breaker interlock was switched to the main.

    Quote Originally Posted by JFletcher View Post
    Eta: if his panel does not have a main breaker, I am not sure that you can install a generator Inlet perhaps an ATS, but not an MTS, don't know what code it violates but it would be extremely dangerous to manually transfer generator and Poco power without an interlock
    He has a convertible panel which currently does not have a main breaker. We will install one so we can use an interlock kit.

  10. #10
    Join Date
    Jul 2003
    Location
    New Jersey
    Posts
    25,618
    Quote Originally Posted by Coppersmith View Post
    My concern was only that the generator neutral would remain connected when the breaker interlock was switched to the main.
    I don't see that as a problem. The neutral is floating in the generator so it's not really doing anything.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •