Page 1 of 3 123 LastLast
Results 1 to 10 of 25

Thread: Generator Control Wiring

  1. #1
    Join Date
    Jun 2005
    Location
    Massachusetts
    Posts
    1,188

    Generator Control Wiring

    I'm wiring up a Generac 20 KW. The fourth one in the last month. Every one of them has had a very long run to the ATS and much of it is outside the house. The runs have been about 100 feet long with lots of changes in direction. Conduit and multiple JB's would be way too much work so I have been running #1 Aluminim SER for the power and switching over to copper in a JB with Carflex and #3 copper for the final connection.

    The control wiring consists of three low voltage (12 volts) wires and three line voltage wires for voltage sensing of the normal and generator power. The minimum size wire is #18. I have been running 18-3 sunlight/weather resistant for the low voltage and 14-3 UF for the line voltage. I have run these cables to a WP JB and switched over to 1/2" with THHN and carflex for the last few feet The cost of the UF and running a seperate 18-3 seems like more work and cost than it should be.

    If the runs were much shorter I would run conduit for everything. The changeover from AL to CU would be eliminated and I could run all the control wires in one conduit (6 # 18 thhn in 1/2 inch). I'm looking for suggestions on how to combine the control wiring into one cable. As far as I know I can't buy 18-6 UF cable. Is there anything I'm missing?

  2. #2
    Join Date
    Jul 2003
    Location
    New Jersey
    Posts
    19,256
    What is the Class of the 12v, low voltage wiring? If it's Class 2 it must be seperate from the line voltage conductors so a hybrid cable or single raceway won't help much.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  3. #3
    Join Date
    Jul 2007
    Posts
    3,100
    Has Generac changed their control scheme? The last 20 kw I hooked up has been a few years ago, but they had only two 12 Vdc wires to control the transfer switch, two 240 volt wires for utility sense, and two 240 volt wires for the charger. You had to do a separate 120 volt circuit for the block heater. Onan uses three 12 volt wires from the generator to the transfer switch to power the switch electronics and start function, Generac must be doing the same thing now.

  4. #4
    Join Date
    Jun 2005
    Location
    Massachusetts
    Posts
    1,188
    Quote Originally Posted by infinity View Post
    What is the Class of the 12v, low voltage wiring? If it's Class 2 it must be seperate from the line voltage conductors so a hybrid cable or single raceway won't help much.
    I don't know the class of the 12v wires and I'm not sure how to figure it out. The instructions (Generac) show all the controls wires in the same conduit and they specifically say to keep them seperate from the generator output wires.

  5. #5
    Join Date
    Jun 2005
    Location
    Massachusetts
    Posts
    1,188
    Quote Originally Posted by hillbilly1 View Post
    Has Generac changed their control scheme? The last 20 kw I hooked up has been a few years ago, but they had only two 12 Vdc wires to control the transfer switch, two 240 volt wires for utility sense, and two 240 volt wires for the charger. You had to do a separate 120 volt circuit for the block heater. Onan uses three 12 volt wires from the generator to the transfer switch to power the switch electronics and start function, Generac must be doing the same thing now.
    Yes the control scheme is different in the new models. Not sure when they made the switch.

  6. #6
    Join Date
    Jan 2008
    Location
    Raeford, NC
    Posts
    3,494
    Quote Originally Posted by hillbilly1 View Post
    Has Generac changed their control scheme? The last 20 kw I hooked up has been a few years ago, but they had only two 12 Vdc wires to control the transfer switch, two 240 volt wires for utility sense, and two 240 volt wires for the charger. You had to do a separate 120 volt circuit for the block heater. Onan uses three 12 volt wires from the generator to the transfer switch to power the switch electronics and start function, Generac must be doing the same thing now.
    They are using n1 n2 as the utility sensing and the other is T1 it is the ungrounded wire for the batt. charger you pick up the neutral in the generator to complete the circuit

    Quote Originally Posted by mkgrady View Post
    I don't know the class of the 12v wires and I'm not sure how to figure it out. The instructions (Generac) show all the controls wires in the same conduit and they specifically say to keep them seperate from the generator output wires.
    Most of Generac's instructions state if you go over the 30ft factory whip or do not use it then they must be separated. As long as the insulation rating is over the voltage being produced then they can go in the same conduit. I know that you must follow the Mfg's instructions but there is no real reason the wiring must be separated. The control wires are running 240v utility voltage. If utility drops out a set of contacts close and the gen. starts. The ATS and gen are not "talking" to each other so EMFs wouldn't bother any thing.
    Organized people are people that are just too lazy to look for their stuff

  7. #7
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    8,766
    Quote Originally Posted by ceb58 View Post
    I know that you must follow the Mfg's instructions but there is no real reason the wiring must be separated. The control wires are running 240v utility voltage.
    On long runs, there may be a problem with capacitive coupling between the conductors, resulting in 'incorrect signals' to the sensing equipment.
    Just because you can, doesn't mean you should.

  8. #8
    Join Date
    Jun 2005
    Location
    Massachusetts
    Posts
    1,188
    Quote Originally Posted by ceb58 View Post
    They are using n1 n2 as the utility sensing and the other is T1 it is the ungrounded wire for the batt. charger you pick up the neutral in the generator to complete the circuit



    Most of Generac's instructions state if you go over the 30ft factory whip or do not use it then they must be separated. As long as the insulation rating is over the voltage being produced then they can go in the same conduit. I know that you must follow the Mfg's instructions but there is no real reason the wiring must be separated. The control wires are running 240v utility voltage. If utility drops out a set of contacts close and the gen. starts. The ATS and gen are not "talking" to each other so EMFs wouldn't bother any thing.
    These generators have not been supplied with a factory whip. The runs from the gen to the ATS is about 100 feet.

    I don't think I am going to find a cable that has 5-#18 rated for 240 volts and suitable for outdoor installation. If I could I would save a lot of time and expense

  9. #9
    Join Date
    Jun 2005
    Location
    Massachusetts
    Posts
    1,188
    Quote Originally Posted by jim dungar View Post
    On long runs, there may be a problem with capacitive coupling between the conductors, resulting in 'incorrect signals' to the sensing equipment.
    I know next to nothing about capacitive coupling but is it likely in this case? I assume the control wires in question carry next to nothing in actual current. CEB's post above describes what each wire is used for.

  10. #10
    Join Date
    Feb 2003
    Location
    Boston, MA
    Posts
    6,856
    I've been running two 14/3's for the control wiring. To a jbox with nonmetallic liquid tight and from there to the gen.
    There are two kinds of people - those smart enough to know they don’t know, and those dumb enough to insist they do.-----Margery Eagan

    Open shop since 1988

Posting Permissions

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