thermostat vs contactor

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e150club

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just curious about boiler wiring some circulators are switched from the thermostat. some run to contactors . is it prefrance or code of course it depends on the load of the motor and the rating of the therm. if the therm. can handle the load why install a contactor.
 
e150club said:
if the therm. can handle the load why install a contactor.
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To reduce costs.

The wire size needed to operate a t-stat can be very small....that same small wire can energize a coil.
 
e150club said:
. . . it depends on the load of the motor and the rating of the therm. if the therm. can handle the load why install a contactor.
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You've answered your own question: if the T-stat is rated for the voltage and current both, there's no reason against it, as long as you can terminate your connections properly.
 
I've never seen a thermostat control just a circulator pump. I suppose it would work if boiler control maintained boiler temperature at all times.
 
Contactors usually have overcurrent protection. Or they can be added to the contactor. I would rather have my thermostat tell my contactor to close than have my thermostat start my motor. What size are these motors????
 
Pierre C Belarge said:
Are you stating this does or does not require a Chapter 3 wiring method?
What is the voltage?
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My take was that he would use a line voltage thermostat and romex, mc, etc. I may have misunderstood. If that's the case, I don't know why you would want to.

Most boilers have a control with an aquastat for high and low limit. This control has TT terminals which pull in the relay. This relay will usually energize the circ. pump. Along with the burner motor, etc.

I suppose that if you had a boiler which maintains temperature, you could run the circulator pump(s) through a 120v t-stat. There are reasons you wouldn't want to, though. Such as if domestic water is from a tankless on the boiler.
 
i may have posted a dumb question there is no job im doing just that ive seen boilers wired with contactors that are large and expensive looking and boilers using the aquastat as the control ,or zone valves w/ an end switch as the control to a relay in the boiler why use the expensive contactors rather then small push in relays with a fused com. if ocp is needed.
 
"why use the expensive contactors" If your buying Square D, Telemech, or AB, I can see your point....LOL
Note: You can buy IEC contactors very cheap now. VERY CHEAP and great quality.

If these motors start and stop alot, you will be changing thermostats alot, at least the contacts.
 
I've seen thermostats that couldn't even drive a regular motor contactor. The motor contactors had to be replaced with definate purpose contactors. It was either that, or use a thermostat to switch a relay to switch the contactor to switch on the heat.

I don't think you will have much luck driving even a small load from the thermostat.

I also wonder how much heat a 1 amp current would create in the thermostat. That might throw it off.

Steve
 
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