Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 40

Thread: Relay controlled fans from furnace

  1. #21
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    32,558
    Quote Originally Posted by Mustwin351 View Post
    Excuse my ignorance but having never used a relay in a box I'm guessing there is not a need to install a barrier between the high and low voltages? Does that only apply to switches?
    If the control circuit is class 2 or 3, the nipple into the RIB is listed but whatever you supply it with needs to have separation between class 2/3 conductors and power conductors. It doesn't necessarily need to be a barrier that separates them though.
    Class 1 control circuit would not require any separation at all.

  2. #22
    Join Date
    Aug 2015
    Location
    Texas
    Posts
    65
    Quote Originally Posted by kwired View Post
    If the control circuit is class 2 or 3, the nipple into the RIB is listed but whatever you supply it with needs to have separation between class 2/3 conductors and power conductors. It doesn't necessarily need to be a barrier that separates them though.
    Class 1 control circuit would not require any separation at all.
    So is it allowable by code to mix a class 1 and class 2 circuit in the same box?

  3. #23
    Join Date
    Oct 2007
    Location
    New Jersey
    Posts
    4,278
    Quote Originally Posted by Mustwin351 View Post
    So is it allowable by code to mix a class 1 and class 2 circuit in the same box?
    Yes. See here for Functional Device's RIBT with integral barrier.

  4. #24
    Join Date
    Aug 2015
    Location
    Texas
    Posts
    65
    Quote Originally Posted by gadfly56 View Post
    Yes. See here for Functional Device's RIBT with integral barrier.
    Ahh...thank you.

    I am guessing a device like this relay:
    https://www.functionaldevices.com/do.../RIBHX24BA.pdf

    You could by code only use it for replacing the same relay in a listed piece of equipment being that there is not separation between the high and low voltage. Is that correct?

  5. #25
    Join Date
    Oct 2007
    Location
    New Jersey
    Posts
    4,278
    Quote Originally Posted by Mustwin351 View Post
    Ahh...thank you.

    I am guessing a device like this relay:
    https://www.functionaldevices.com/do.../RIBHX24BA.pdf

    You could by code only use it for replacing the same relay in a listed piece of equipment being that there is not separation between the high and low voltage. Is that correct?
    That is an interesting question. Equipment is not covered under the NEC, except that in some parts it talks about "listed for the intended use" or similar such language. If you are replacing like for like you probably don't have an issue. If you are replacing an internal component with an external component, now I'm not so sure.

  6. #26
    Join Date
    Aug 2015
    Location
    Texas
    Posts
    65
    Quote Originally Posted by gadfly56 View Post
    That is an interesting question. Equipment is not covered under the NEC, except that in some parts it talks about "listed for the intended use" or similar such language. If you are replacing like for like you probably don't have an issue. If you are replacing an internal component with an external component, now I'm not so sure.

    I was thinking the same. So with that particular RIB where there is no separation between high and low voltages.....what situation or place could you actually use it legally by code?

  7. #27
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    17,659
    Quote Originally Posted by Mustwin351 View Post
    I was thinking the same. So with that particular RIB where there is no separation between high and low voltages.....what situation or place could you actually use it legally by code?
    The high and low voltages are wired through the same hole, so no separation there. But the wires are properly insulated to allow the low voltage circuit to be classified as Class 1 and wired in the same raceway with functionally related power wiring. And the coil of a relay is very much functionally related to the relay output circuit!

    Just make sure that the circuit driving the relay does not have to be Class 2 and be sure to use Chapter 3 wiring throughout. (On further consideration, that may take away the attractiveness of LV control in the first place.)
    Last edited by GoldDigger; 08-09-17 at 04:54 PM.

  8. #28
    Join Date
    May 2014
    Location
    AZ
    Posts
    1,847
    Quote Originally Posted by Mustwin351 View Post
    Ahh...thank you.

    I am guessing a device like this relay:
    https://www.functionaldevices.com/do.../RIBHX24BA.pdf

    You could by code only use it for replacing the same relay in a listed piece of equipment being that there is not separation between the high and low voltage. Is that correct?
    so are you saying the UL "part" can only be used as a replacement part, and not allowed to be used for making your own relay system? that doesnt make much sense to me because the risk you describe is the same whether or not you add it to a 4x4 box to make a relay, or if is attached inside a hvac air handler. or am i missing something?

    how does one obtain isolation? isnt that just a transformer? so is the goal to use a 24vac isolation transformer between furnace and rib ?? maybe use two or 3 isolation xfrmers in series, waste a little power, but heck, it will be super-duper isolated in the event the rib coil shorts into one of the contacts

    its almost like xfrmers used for landscape lighting. if worried about using the UL rib that is by itself not in UL equipment, then use a gfi to protect both a short in the rib and the fans? now thats very very very very safe.

  9. #29
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    17,659
    The thread mounted RIB is not just a UL Recognized Component (backwards RU) but a Listed device. It can be used in the field as long as the restrictions in my earlier post are met.

  10. #30
    Join Date
    Sep 2008
    Location
    UK
    Posts
    9,583
    Quote Originally Posted by purduephotog View Post
    I have a number of booster fans I need to turn on and off from the furnace. My original thought was to use the aux 24v relay in the furnace to switch a second circuit (load would be about 400w).

    This would require running 14/2 everywhere.
    Jason
    Just out of interest, what decides when to turn the fan on or off? Is it a manual operation or is there some sensor?
    Si hoc legere scis nimium eruditionis habes.

Posting Permissions

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