help with interlocking overhead doors to commercial heater

[tufdog71]

Hello all. First let me say that I am an overhead door mechanic. I have a fair bit of electronics troubleshooting and wiring experience from years of door systems service and repairs. This request is a little outside my comfort zone, but I think it is do-able with a little help from you all.

One of my customers has asked me to interlock 2 overhead doors to his heater so that if the heater is on and either door is opened, the heater will shut off. I know the 2 interlock switches must be wired N.O. and wired in series so when both doors are closed the circuit is complete.

He told me that the control circuit for the heater is 120VAC. I don't want to mess with the heater since it's not my area of expertise. And I'm not en electrician, so I can't run 120V lines. I want to do something low-voltage.

I know I need to find out what kind of current the control circuit in the heater is drawing, but.......

Questions:

1. Can I use a 24VAC SPDT relay to do the shutting off? Omron LY2F is what I have in-stock. Rated for 10A switching @ 110VAC
2. Would a 24VAC, 40VA plug-in type transformer (also in-stock) do the trick for coil voltage through 2 interlock switches? About 100 ft from heater controls to furthest interlock.
3. Should the heater be considered an inductive load?

Any help is appreciated.

 

[Sceadwian]

You might want to rephrase 'electronics troubleshooting' to 'electrical troubleshooting' VERY VERY different.

Without knowing the current the heater draws there is no way to answer your question with a specific device recommendation, but from your ideas and reference, why bother with the 24AC in the first place? Use straight 120V relays and 120V rated limit switches on the doors to switch the heater element on and off. If you're uncomfortable around 120V electricity you shouldn't be messing with things on this scale at ALL in the first place.

The heater is likely both inductive and resistive, there's virtually guaranteed to be a fan behind the heating element, and if it's a decent unit the fans stall/starting current is going to be pretty high.

 

[ronsimpson]

There is likely a 24VAC control wire for a thermostat for the heaters. Switching the low voltage/ low current thermostat wires is easy.

 

[Sceadwian]

That's a pretty big stretch there ron, it's only 'a' heater, and no specifications of any kind have been presented for it, you're guessing at best, and based on the original post I'm guessing modification of the heater controller itself is probably outside of the scope of the posters experience regardless of voltage.

 

[ronsimpson]

That's a pretty big stretch there ron, it's only 'a' heater, and no specifications of any kind have been presented for it, you're guessing at best, and based on the original post I'm guessing modification of the heater controller itself is probably outside of the scope of the posters experience regardless of voltage.

"Outside of the posters experience" that is why 24VAC is better than 220VAC. 100mA better than 30A.
"No thermostat" that sounds right. The heater is on all the time. You open the doors to cool off.

 

[Reloadron]

After reading this:

He told me that the control circuit for the heater is 120VAC. I don't want to mess with the heater since it's not my area of expertise. And I'm not en electrician, so I can't run 120V lines. I want to do something low-voltage.

I believe what you really need to do is find out exactly what you are up against. Find out exactly what the heaters are and exactly what the control is. While the control circuit (thermostat or whatever) may be supplied by 120 VAC there is a very good possibility (as was mentioned) that in reality the actual control voltage might be 24 VAC. Until you actually know what you have, it's all speculation. Doing what your customer wishes likely will not be real difficult but you need to know exactly what they have and not what they may think they have.

Ron

 

[KeepItSimpleStupid]

You need to find out what your dealing with?

One word of caution: Oil and gas heaters don't shut down right away. The plenum generally has to cool or the system may wait a pre-determined amount of time.