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Discuss Why are the contactors always closed/energized? in the American Professional Electrical Advice Forum area at ElectriciansForums.net

I just installed a brand new 36 kw electric boiler. 240v, 3 ph, works good, more expensive to operate than I had hoped...regardless when the power/circuit breakers are on, the contactors energize/close always. Why? That makes no sense to me. What’s their purpose if always energized. Why not bypass them and save the 24v transformer life and cost to power it. I checked the schematic, it is designed that way. Gladly I turn the breaker off in the non- heat season. To further explain, even when there is no demand, the contactors are closed, only the relays energize upon demand. I don’t understand - do you? If so, please explain. Peace n thx!
 
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PEG

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Mentor
Arms
Esteemed
Hi,i don't think the coil power will help that 36kW load😎
It's possible they are a 'fail safe' inclusion....can you post the drawings?
 

snowhead

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Mentor
If the contactors are always enegised then there must be some other control for the heaters otherwise you's have a steam generator and not a boiler. o_O

If there is other control for the heaters, maybe solid state, then the contactors may be for over temperature safety protection.
 

Megawatt

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Arms
I just installed a brand new 36 kw electric boiler. 240v, 3 ph, works good, more expensive to operate than I had hoped...regardless when the power/circuit breakers are on, the contactors energize/close always. Why? That makes no sense to me. What’s their purpose if always energized. Why not bypass them and save the 24v transformer life and cost to power it. I checked the schematic, it is designed that way. Gladly I turn the breaker off in the non- heat season. To further explain, even when there is no demand, the contactors are closed, only the relays energize upon demand. I don’t understand - do you? If so, please explain. Peace n thx!
What about the wiring by others, has it been done correctly
I just installed a brand new 36 kw electric boiler. 240v, 3 ph, works good, more expensive to operate than I had hoped...regardless when the power/circuit breakers are on, the contactors energize/close always. Why? That makes no sense to me. What’s their purpose if always energized. Why not bypass them and save the 24v transformer life and cost to power it. I checked the schematic, it is designed that way. Gladly I turn the breaker off in the non- heat season. To further explain, even when there is no demand, the contactors are closed, only the relays energize upon demand. I don’t understand - do you? If so, please explain. Peace n thx!
cprodgers who did the other wiring by customer was the heat demand thermostat wired correctly?
 

snowhead

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Mentor
As I'd suggested, the contactors are there for overtemperature protection.

On power up the contactors are powered on.
Then subject to demand, under control of the Ultra Smart, Relays 1,2,3,4,5,6 are individually enabled to power stages of heaters.

The contactors are a fail safe to ensure power is disconnected in an overheat situation, the contactors do not continually switch on and off as the relays do, so are more likely to disconnect.

This is a very common system of control.
 

PEG

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Mentor
Arms
Esteemed
As I'd suggested, the contactors are there for overtemperature protection.

On power up the contactors are powered on.
Then subject to demand, under control of the Ultra Smart, Relays 1,2,3,4,5,6 are individually enabled to power stages of heaters.

The contactors are a fail safe to ensure power is disconnected in an overheat situation, the contactors do not continually switch on and off as the relays do, so are more likely to disconnect.

This is a very common system of control.
Which makes it "safe" when it "fails" ,and reset automatically,when cleared.😍
 
  • Thread Starter Thread Starter
  • #9
As I'd suggested, the contactors are there for overtemperature protection.

On power up the contactors are powered on.
Then subject to demand, under control of the Ultra Smart, Relays 1,2,3,4,5,6 are individually enabled to power stages of heaters.

The contactors are a fail safe to ensure power is disconnected in an overheat situation, the contactors do not continually switch on and off as the relays do, so are more likely to disconnect.

This is a very common system of control.
Thank you, I understand. However, they could be energized upon demand, yet still be “a fail safe.” I don’t understand why it is not designed that way.
 

ElectroChem

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Arms
Using contactors to control large frequent switching currents degrades the contacts. I would suspect that 'R1' to 'R6' are solid state relays, which are better for repeated switching of elements.
 

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