# Why would this be done?



## Wirenuting (Sep 12, 2010)

A6USMC said:


> I went to a customers house today to see why their roof heat tape was not working. I found this contactor under the panel that controls two 120v circuits for the heat tape. When I looked to see what was feeding the coil, one side had the nuetral and the other, the red wire, to what seems like another relay, that appears to have a 120v coil circuit as well. I traced the black wire that connects to a red one and goes up the conduit into the ceiling, to where I dont know. The former owner of the house told the new owner that the system was automatic, and I just worked on its own. The new owner said a pilot light switch would be fine to control the contactor, but before I bypass/remove the smaller relay/control from the larger contactors control circuit, I want to know what exactly I am bypassing. I sent a photo of the smaller control/relay to my supplier, and the only info I got back is he thought it was some kind of "sequencer" made by Klixon. I researched them and learned that they made a wide variaty of switches and controls that can be pressure, temp. and other means of sensing, and they seem to be out of business as far as I can tell. I just wonder if this control is temp. sensitive and was used to turn on the heat tape for the winter, when the temp in the unheated garage dropped. I just wish I or someone out there knew how to decode the numbers on it so I knew its intended purpose. Any help would be appreciated. Thanks


 Looks like a Klix on.. Was it outside on a non-south wall?

edit: here is a Klixon cross reference page. Hope it helps. 

http://www.sensata.com/download/klixon-circuit-breaker-thermal-catalog.pdf


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## Big John (May 23, 2010)

A sequencer relay is just a time-delay element that allows large loads to be staggered so they don't all draw inrush at the same time. That style uses a bimetallic switch which I believe is heated by the control power until it closes.

Seems like in this case there's something that's supposed to operate concurrently with your heat trace and they didn't want the heat-trace contactor to pull in at once.


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## Hmacanada (Jan 16, 2014)

Big John said:


> A sequencer relay is just a time-delay element that allows large loads to be staggered so they don't all draw inrush at the same time. That style uses a bimetallic switch which I believe is heated by the control power until it closes. Seems like in this case there's something that's supposed to operate concurrently with your heat trace and they didn't want the heat-trace contactor to pull in at once.


Big john is right , it's a heat sequencer, see them on electric furnaces so the banks of elements don't come on all at once.
From what I can see in the pic I bet there is a thermostat somewhere.


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## Hmacanada (Jan 16, 2014)

That would be the automatic part!


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## Big John (May 23, 2010)

Hmacanada said:


> Big john is right , it's a heat sequencer, see them on electric furnaces so the banks of elements don't come on all at once....


 Yeah, that's where I'm familiar with them. Only those are heated by the plenum temperature, which is why I'm assuming in OPs picture the control circuit is what's doing the heating.


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## A6USMC (Feb 7, 2014)

Thanks for the responses, heres what I dont get though, the bottom red wire on this device has 120 on it, and the terminal right across from it on the top goes to one side of the contactors 120v coil. Why would you use this device/relay, that apears to have its own 120v coil to control another 120v coil?
I will call Sensata Technologies tomorrow to see if they can shed some light on the numbers of this control and decode its operation.


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## A6USMC (Feb 7, 2014)

Got my last reply in a little slow:001_huh:


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## Big John (May 23, 2010)

A6USMC said:


> ...What I dont get though, the bottom red wire on this device has 120 on it, and the terminal right across from it on the top goes to one side of the contactors 120v coil. Why would you use this device/relay, that apears to have its own 120v coil to control another 120v coil...?


Because in this application you're not using a relay for pilot duty (where a low power controls a high power), you're using it for time-delay only.

EDIT: _Hma _could be right, this might actually be a jury-rig, I can't say for certain they're using it for time-delay, only that in theory that's how it's designed to be used.


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## Hmacanada (Jan 16, 2014)

A6USMC said:


> Thanks for the responses, heres what I dont get though, the bottom red wire on this device has 120 on it, and the terminal right across from it on the top goes to one side of the contactors 120v coil. Why would you use this device/relay, that apears to have its own 120v coil to control another 120v coil? I will call Sensata Technologies tomorrow to see if they can shed some light on the numbers of this control and decode its operation.


They are using 120 to operate the coil on the sequencer and after a few second it will close the contacts on the top to operate the large contactor. But your right I don't know why they would do it that way, unless you have a stat that isn't rated for the load of the contactor coil. Like a electronic stat.
That's my best guess.


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## 8V71 (Dec 23, 2011)

It's using the temperature of the unheated garage to actuate the contactor and I think one of the heat tape loads is going through the white and black to heat the Klixon up a little and turn it off. Like a self cycling thing maybe.


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## Hmacanada (Jan 16, 2014)

Probably a dumb question, but did you bypass the sequencer and go straight to the contactor? Or pull the leads off the top two contacts on the sequencer and ohm them out to see if they are closing when you apply 120 to the bottom coil terminals. It's just a bi-metallic strip that when you apply power to it ,heats up and expands forcing another disc to close above ,closing the top contacts. And they do go bad in time. I,ve changed many on elect furnaces.


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## 8V71 (Dec 23, 2011)

The bottom terminals are a switch. You wouldn't want to apply 120v to those.


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## Hmacanada (Jan 16, 2014)

8V71 said:


> The bottom terminals are a switch. You wouldn't want to apply 120v to those.


 No , it's not. Just a metallic strip that expands and changes position off a disc above it. I hit a few with a hammer after replacing them to see what makes them tick.
The top two are just dry contacts


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## 8V71 (Dec 23, 2011)

Maybe we are getting the top and bottom confused. The red wires going to the contactor coil is the switch part.


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## Hmacanada (Jan 16, 2014)

8V71 said:


> Maybe we are getting the top and bottom confused. The red wires going to the contactor coil is the switch part.


Sorry correct , the red wires are the sw part of it. (Top)


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## Hmacanada (Jan 16, 2014)

This one has a extra set of contacts but same idea


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## 8V71 (Dec 23, 2011)

I agree with you though. If the contactor is never closing the switch part of the Klixon is most likely bad.


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## 8V71 (Dec 23, 2011)

And the heat tape load, or something, should be heating up the Klixon on the other terminals (heater) and turning it back off.


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## Hmacanada (Jan 16, 2014)

8V71 said:


> I agree with you though. If the contactor is never closing the switch part of the Klixon is most likely bad.


I think if it's automatic , set up the way it is. I wouldn't change it if he can repair it. Kind of nice not to have to remember to turn it on/off all the time.


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## Hmacanada (Jan 16, 2014)

8V71 said:


> And the heat tape load, or something, should be heating up the Klixon on the other terminals (heater) and turning it back off.


I would almost bet there is a thermostat somewhere , to put power to that sequencer


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## Going_Commando (Oct 1, 2011)

Hmacanada said:


> I would almost bet there is a thermostat somewhere , to put power to that sequencer


There is probably a moisture sensor combined with a thermostat. At least that is what I am used to dealing with when messing with heat tape. Then again, I have only ever installed conventional contactors when dealing with said sensors, not some fancy "sequencer".


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## Hmacanada (Jan 16, 2014)

Going_Commando said:


> There is probably a moisture sensor combined with a thermostat. At least that is what I am used to dealing with when messing with heat tape. Then again, I have only ever installed conventional contactors when dealing with said sensors, not some fancy "sequencer".


 Never though about that , could be. I've never saw a hook up quite like this one , do you think that that contactor would draw more than that sequencer heater?
I don't think sequencers like that are meant to stay energized for hrs much less days. Would shorten the life of it considerably !
Might be better to use a relay instead or just get rid of it all together!


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## micromind (Aug 11, 2007)

One possibility is that whatever controls the contactor has a tendency to chatter and the time delay was installed to keep the contactor from chattering. 

With the time delay, the thermostat/moisture sensor has to be solidly on for a while in order to close in the contactor.


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## A6USMC (Feb 7, 2014)

I am loving all the input on this, I hope to have a call in to Klixon today and back to the customer this coming Monday. If they dont want to pursue the original design, I will just install a switch next to the contactor. If I find out that the Klixon is N/O and closes at a given temp. I will research replacing it. The only thing that would not make sense with that design is why would it need a neutral and that other wire going up to the attic? That seems to imply some other triggering device. Monday we will see if she wants to pay for further investigation. I will report on the outcome, Thanks


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## Hmacanada (Jan 16, 2014)

I don't know who carries this stuff there, but lots of different manufacturers available. Supply houses that sell furnace parts or your local heating probably has a few in his truck. Just have to make sure it has a 120v coil rating for the heater coil in the sequencer. Good luck!
Maybe ask if it is rated for continuous duty as well.


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## lefleuron (May 22, 2010)

Just stumbled on this.

I am thinking the old HO used this as some type of buffer.

Imagine the heat tape comes on at 32 degrees.

Now imagine the temp is actually 32 degrees and the heat tape is cycling on and off, on and off.

I am not sure how long a delay you can get out of that thing, but if it were mine I would want to see 32 degrees for at least 1 hour before it came on.

But for all I now, it could be 2 minutes in your case.


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## Big John (May 23, 2010)

lefleuron said:


> ...I am not sure how long a delay you can get out of that thing, but if it were mine I would want to see 32 degrees for at least 1 hour before it came on....


 Not long, there's not a whole lot of thermal mass in there to keep the bimetallic element warm. In my experience once at temperature the delay is only a few seconds.


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## A6USMC (Feb 7, 2014)

Well it is confirmed as a time delay, and it appears the H20-70 is the delay for heating up and closing the N/O and the C20-70 is the cooling delay for the reverse. I will include the ref. material they sent me in case others could use it, its in the pdf file

http://www.sensata.com/klixon/thermostat-hvac-600-tdr.htm


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## bostongtp (Apr 9, 2014)

A6USMC said:


> Thanks for the responses, heres what I dont get though, the bottom red wire on this device has 120 on it, and the terminal right across from it on the top goes to one side of the contactors 120v coil. Why would you use this device/relay, that apears to have its own 120v coil to control another 120v coil?
> I will call Sensata Technologies tomorrow to see if they can shed some light on the numbers of this control and decode its operation.


You would use this 120v sequencer because it staggers the load, you don't have to, just a nice feature from a thoughtful electrician. If that wasn't used, and it was an automatic system your black wire would go directly to your contactor coil. You should look for an outside t-stat, logically it makes sense. If it's automatic it would need to know when it gets below freezing I need to turn on, what would do that? A thermostat, thermocouple, probe, etc and it wouldn't be mounted inside....it would be outside, where? That's your problem my friend. Hope this helped


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