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Old 03-07-2014, 09:10 AM   #16
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Door sensors to turn off heater when doors open (wiring)


I am concerned that you have a proper strong quality switch/contacts. That one is rated for 3 W watts but I don't know the wattage of your circuit. Like iamr's method he used a actual switch which can carry some current w/o arcing etc. When you are using switches and components from alarm systems or garage door openers that are low voltage/low current that is not the same as what a furnace uses, there are safety issues. My system of using a R8222D relay (google it) uses a strong general purpose relay and I used it hundreds of times in the old days for millivolt systems to trigger them with modern 24 volt thermostats. You should be able to go to graingers and get that relay and a basic 120/24 volt 20 VA transformer and mount it in a box and screw the relay onto a beam beside it and run some wires. Use 18 gauge wire (LVT or bell wire and nothing smaller) HDepot has it.

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Old 03-07-2014, 09:16 AM   #17
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Door sensors to turn off heater when doors open (wiring)


Thanks for the feedback.

I'm not an expert so getting your input is helping me a lot.
I have a relay with a built-in transformer between the thermostat and the heater. This one: http://www.aubetech.com/products/pro...2&noProduit=42



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I am concerned that you have a proper strong quality switch/contacts. That one is rated for 3 W watts but I don't know the wattage of your circuit. Like iamr's method he used a actual switch which can carry some current w/o arcing etc. When you are using switches and components from alarm systems or garage door openers that are low voltage/low current that is not the same as what a furnace uses, there are safety issues. My system of using a R8222D relay (google it) uses a strong general purpose relay and I used it hundreds of times in the old days for millivolt systems to trigger them with modern 24 volt thermostats. You should be able to go to graingers and get that relay and a basic 120/24 volt 20 VA transformer and mount it in a box and screw the relay onto a beam beside it and run some wires. Use 18 gauge wire (LVT or bell wire and nothing smaller) HDepot has it.
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Old 03-07-2014, 09:31 AM   #18
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Door sensors to turn off heater when doors open (wiring)


That relay is a high current relay to handle the 220 volt high current heater element. You need a different/additional relay to do the 24 volt control side.
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Old 03-07-2014, 09:37 AM   #19
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Door sensors to turn off heater when doors open (wiring)


If I want a reliable solution and would like to avoid a relay on the low voltage side (for thermostat and door sensors) what are my options ?

Thanks again. Much appreciated.


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That relay is a high current relay to handle the 220 volt high current heater element. You need a different/additional relay to do the 24 volt control side.
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Old 03-07-2014, 09:41 AM   #20
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Door sensors to turn off heater when doors open (wiring)


None that I know.

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Old 03-07-2014, 10:11 AM   #21
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Door sensors to turn off heater when doors open (wiring)


What if I get a magnetic door switch rated for 24V ?
The thermostat is 0.5A at 24V (12w)
The door sensors are 0.41A at 24V (9.84w)

This sensor is rated for 24V: http://www.elementalled.com/magnetic-drawer-switch.html
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Old 03-07-2014, 12:03 PM   #22
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Door sensors to turn off heater when doors open (wiring)


Then they are 2-3 watts too small. If you go the cheap route then later damage some components you will be sorry. If you create a fire hazard you will even be more sorry. One of my customers had his garage catch on fire from a staple pinching a low voltage wire to a central vac system. Did a couple hundred thousand $$ in smoke damage to the house and he had to live in a hotel for 6 months. Safety comes first not saving a couple $$.
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Old 03-07-2014, 12:31 PM   #23
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Door sensors to turn off heater when doors open (wiring)


Thanks again.

I didn’t know that a minor difference in wattage could cause a serious risk.
I don’t have a budget and I’m looking for the best reliable option. Is there a compact 24v relay that could fit in a single gang box and work with two NC door magnetic sensors ?
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Old 03-07-2014, 12:53 PM   #24
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Door sensors to turn off heater when doors open (wiring)


The R8222D relay has been around for over 30 years and is bombproof reliable. It is easy to mount to a piece of metal or wood. Put some metal over the wood if you want to be safer. After that whatever relay you choose is up to you. You get what you pay for $$ wise. I have no others to recommend or other ideas.

https://customer.honeywell.com/en-US...d=R8222D1014/U
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Old 03-07-2014, 01:17 PM   #25
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Door sensors to turn off heater when doors open (wiring)


Thanks Yuri. I will read more about that relay and hopefully I will figure out how to wire the two doors sensors and thermostat into it.


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The R8222D relay has been around for over 30 years and is bombproof reliable. It is easy to mount to a piece of metal or wood. Put some metal over the wood if you want to be safer. After that whatever relay you choose is up to you. You get what you pay for $$ wise. I have no others to recommend or other ideas.

https://customer.honeywell.com/en-US...d=R8222D1014/U
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Old 03-07-2014, 04:19 PM   #26
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Door sensors to turn off heater when doors open (wiring)


Pretty easy. R which is 24 volts hot from the transformer goes to one side of the door sensor and thru it and into the other sensor and thru it and feeds the 24 volt coil of the R8222D and then goes back to C on the transformer. W from the thermostat goes thru a normally open NO set of contacts on the relay and then to the heater relay. The R8222D comes with a wiring diagram. This way if the door sensors fail and give off low voltage all that can happen is the R8222 gets damaged not your heater.
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Old 03-07-2014, 05:03 PM   #27
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Door sensors to turn off heater when doors open (wiring)


Put a 120 volt switch in line with the transformer and in the Summer shut it off when you don't need the heater and it will save wear and tear on the R8222.
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Old 03-07-2014, 07:01 PM   #28
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Door sensors to turn off heater when doors open (wiring)


Thanks for the help.

The difference I have from your diagram is that my heater has no W terminal so that's why I need the 24V relay (with a built-in transformer) to control it. See my diagram below:



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Put a 120 volt switch in line with the transformer and in the Summer shut it off when you don't need the heater and it will save wear and tear on the R8222.
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Old 03-08-2014, 07:32 AM   #29
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Door sensors to turn off heater when doors open (wiring)


You put the NO normally open contacts on the W wire between the heater and the relay. Red circle.
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Old 03-08-2014, 08:26 AM   #30
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Door sensors to turn off heater when doors open (wiring)


Thanks again Yuri. Much appreciated.

So if I understand correctly, based on your last post I could install the door sensors (in series) on the W wire between the relay and the thermostat ? I dont need the additional Honeywell R8222 Relay ?

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