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  1. #1
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    Electric heat contactor ?

    Hey folks. I am in the process of figuring a job that requires electric radiant quartz. I know I am going to need to start a timed on period of about ten minutes initiated by a push button switch. This is for spot heating outdoors at a train stop so they just want it on when the rider hits the button.

    Heres my question. Since I do not want to switch these on by adding another time delay electric heat relay is there any reason I can not use a heavy duty two pole contactor? I see that Honeywell sells a simple two pole contactor for electric heat but one pole is used for switching fan only. The reason I ask is that this heater company sells an enclosure for about three times the cost of the heater and it seems it is nothing more than a glorified enclosure with a contactor, terminals and some inline fuses.

  2. #2
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    Quote Originally Posted by Glennhvac View Post
    is there any reason I can not use a heavy duty two pole contactor?
    Not that I know of. You may want to derate the contacts for longer life or higher reliability.

    General search
    http://www.google.com/search?client=...UTF-8&oe=UTF-8

    Specific hit
    http://books.google.com/books?id=DM6...cts%22&f=false

    So, by NASA rules if the heater pulls 15A the contacts should be rated at up to 30A but NASA asks for very high reliability.

    Contactor contact life may be 1,000,000 switching cycles or less at rated current and this translates to some number of years in your particular (resistive load) application.

  3. #3
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    Quote Originally Posted by WhoIsThat? View Post
    Not that I know of. You may want to derate the contacts for longer life or higher reliability.

    General search
    http://www.google.com/search?client=...UTF-8&oe=UTF-8

    Specific hit
    http://books.google.com/books?id=DM6...cts%22&f=false

    So, by NASA rules if the heater pulls 15A the contacts should be rated at up to 30A but NASA asks for very high reliability.

    Contactor contact life may be 1,000,000 switching cycles or less at rated current and this translates to some number of years in your particular (resistive load) application.
    Wondering of let's say a 50 amp contactor is rated at 50 amps constant. I would guess so because the momentary start amps are often 100 or so.

  4. #4
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    I'm sure these heaters are pretty low amps and 120vac. Don't get overly concerned with the contractors. Just size them appropriately. This is a train stations comfort heating, not NASA.

    As far as control, it can easily done with an appropriately size sized contactor, a monetary button, ICM TUDR timer, and an NEMA 3R enclosure.

  5. #5
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    I'd love the timer link as I am only now getting a handle on what I think will work. Yes, a momentary push button switch outside in the waiting area. The heater is ceiling mounted, 240v about 35 amps.

    Quote Originally Posted by ascj View Post
    I'm sure these heaters are pretty low amps and 120vac. Don't get overly concerned with the contractors. Just size them appropriately. This is a train stations comfort heating, not NASA.

    As far as control, it can easily done with an appropriately size sized contactor, a monetary button, ICM TUDR timer, and an NEMA 3R enclosure.

  6. #6
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    Found a pdf on the timer. Much better info than other nmanufacturers. Yes this is the type I was thinking of that I ran across in Grainger but different company. Thanks!

  7. #7
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    I was thinking this http://www.icmcontrols.com/Multimode...-Prodview.html

    Setup for single shot.

  8. #8
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    Quote Originally Posted by ascj View Post
    I was thinking this http://www.icmcontrols.com/Multimode...-Prodview.html

    Setup for single shot.
    Thanks a ton. Not sure what the NC contacts do. I spose I only need to switch one leg to the heater. I was thinking of doing momentary swith with 24 v and also throwing a thermostat with an outdoor bulb to limit this operation to 20 degrees or less outsde or whatever the village wants.

  9. #9
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    Quote Originally Posted by Glennhvac View Post
    Thanks a ton. Not sure what the NC contacts do. I spose I only need to switch one leg to the heater. I was thinking of doing momentary swith with 24 v and also throwing a thermostat with an outdoor bulb to limit this operation to 20 degrees or less outsde or whatever the village wants.
    Why complicate it with a transformer........your ICM time delay will control your contactor with a momentary switch and an outdoor state in series. Use the 240v for the control voltage.

    Sent from my C771 using Tapatalk 2

  10. #10
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    Quote Originally Posted by ascj View Post
    I was thinking this http://www.icmcontrols.com/Multimode...-Prodview.html

    Setup for single shot.
    Except this relay only handles a 10A resistive load and at least 35A is necessary, if I understand the hookup correctly.

    With resistive loads there is no startup current surge. They are easier to switch than motor, inductive or capacitive loads.

    If you post your proposed wiring diagram we can all follow along.

  11. #11
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    I was going to use that relay to power a contactor. The contactor is doing the actual powering up of the 240v quartz lamps.
    Quote Originally Posted by WhoIsThat? View Post
    Except this relay only handles a 10A resistive load and at least 35A is necessary, if I understand the hookup correctly.

    With resistive loads there is no startup current surge. They are easier to switch than motor, inductive or capacitive loads.

    If you post your proposed wiring diagram we can all follow along.

  12. #12
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    Quote Originally Posted by Glennhvac View Post
    I was going to use that relay to power a contactor. The contactor is doing the actual powering up of the 240v quartz lamps.
    Sounds good. The contactor coil is an inductive load so make sure this relay doesn't mind switching a low-current inductive load, or that the contactor coil has a spike suppressor/Transorb wired across it.

    If I didn't screw up the arithmetic, pushing the button twice/hour, day in and day out, would have your contactor working for more than five years if it had a 100,000 cycle lifetime, and once/hour would give you more than 10 years.
    I should crunch the numbers before talking about 1 million cycles and space flight reliability.

    A quick search I did didn't come up with a 240v time delay contactor/relay that can handle the 35A, with the delay that you want. That way the time-delay electronics would be built-in to the contactor housing and there would only be the 240v source, the lamp load and a single relay/contactor.
    And I'm not sure how much time you should spend doing a Websearch for such a gadget.

  13. #13
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    That sounds like a great solution. I gave them a rough price today which is quite a bit more than their other option. They are thinking of putting the door locks to the empty ticket station on a timer so people can go in and keep warm while waiting for a ride. I reminded them of the liability issue that they already know. Does not sound good giving who knows who access to a vacant building in the early a/m hours!

    Quote Originally Posted by WhoIsThat? View Post
    Sounds good. The contactor coil is an inductive load so make sure this relay doesn't mind switching a low-current inductive load, or that the contactor coil has a spike suppressor/Transorb wired across it.

    If I didn't screw up the arithmetic, pushing the button twice/hour, day in and day out, would have your contactor working for more than five years if it had a 100,000 cycle lifetime, and once/hour would give you more than 10 years.
    I should crunch the numbers before talking about 1 million cycles and space flight reliability.

    A quick search I did didn't come up with a 240v time delay contactor/relay that can handle the 35A, with the delay that you want. That way the time-delay electronics would be built-in to the contactor housing and there would only be the 240v source, the lamp load and a single relay/contactor.
    And I'm not sure how much time you should spend doing a Websearch for such a gadget.

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