# Relay Duty Cycle



## splatz (May 23, 2015)

From another thread....



vinister said:


> In my application it was a very safety critical situation, so I wired up the relays using the normally closed contacts such that if power was lost to the control system or a relay failed, the shunts were fired. That way it was impervious to the safety system being disconnected or any attempts to "fool it" by disconnecting sensors. Everything has to be connected and powered before the breaker can be set.


I do the same thing where I use the NC contacts so that if the relay or power fails, it fails to the safe position. 

So in an application like this, that relay is pulling in the contacts just about 24/7/365. I am wondering what kind of experience people have had with regular ice cube type magnetic coil relays used this way. 

I recently put in some from Automation Direct, they promised me they are rated for continuous duty, but said they might not last as long if they are used this way. For the price of them, I am just going to replace the ice cube annually as part of the routine maintenance.

Has anyone had trouble with these failing early and causing trouble?


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## trentonmakes (Mar 21, 2017)

splatz said:


> From another thread....
> 
> 
> 
> ...


The biggest issue ive had with them is people tend to take them out. Lol
It was rare one went bad and needed to be swapped out and many were along the coast by the ocean. Somewhat harsh environment.

These powered up a control panel FWIW, if it failed or was pulled there is no power to the panel.

Texting and Driving


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## chicken steve (Mar 22, 2011)

If memory serves, a definite purpose rating is desirable

~CS~


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## RePhase277 (Feb 5, 2008)

chicken steve said:


> If memory serves, a definite purpose rating is desirable
> 
> ~CS~


You can't use a definite purpose relay or contactor in anything other than a machine designed for, well, a definite purpose. In other words, you can use a definite purpose contactor in an A/C condensing unit, but you can't use it to control tennis court lights in a field-assembled box.


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## HackWork (Oct 2, 2009)

RePhase277 said:


> You can't use a definite purpose relay or contactor in anything other than a machine designed for, well, a definite purpose. In other words, you can use a definite purpose contactor in an A/C condensing unit, but you can't use it to control tennis court lights in a field-assembled box.


Why is that?


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## RePhase277 (Feb 5, 2008)

HackWork said:


> Why is that?


Definite purpose contactors are generally recognized components (cute backwards R), for use in a listed assembly, but not themselves listed to be used anywhere else....

I may or may not have used many of them for unspecified purposes:whistling2:


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## HackWork (Oct 2, 2009)

RePhase277 said:


> Definite purpose contactors are generally recognized components (cute backwards R), for use in a listed assembly, but not themselves listed to be used anywhere else....
> 
> I may or may not have used many of them for unspecified purposes:whistling2:


I see, thanks.


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## Cow (Jan 16, 2008)

splatz said:


> So in an application like this, that relay is pulling in the contacts just about 24/7/365. I am wondering what kind of experience people have had with regular ice cube type magnetic coil relays used this way.


Ice cube relays have often been used as a master control or e-stop relays for years. Relay energized=safe to run. They are on essentially 24-7-365. I haven't had an issue with the ones I've installed, but it never hurts to throw a spare relay in the bottom of the cabinet for later, just in case.


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## glen1971 (Oct 10, 2012)

splatz said:


> From another thread....
> 
> 
> 
> ...


Mainly I've used decent ice cube relays (ALB, Omron, P&B, etc) and never had an issue with them failing. The thought of a spare one in the panel is handy, especially if one fries at midnight. So long as it is replaced on the next trip out.. 
I'd have to see the control drawing, but if you use the NC contacts and the relay loses power that tells me that the circuit needs to see open status, no voltage, etc during normal operation.. I don't know that I've seen that configuration as failsafe..


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## Jlarson (Jun 28, 2009)

The white ADC cubes are sqd/schneider/magnecraft rebrands. Never had any issues with them. 

Have lots of panels with cubes that have sat energized for a decade or more except during ocassional power outages with very few failures.


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## oliquir (Jan 13, 2011)

never had issues with cube relays but did had some contactor coil burned when used that way


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## mitch65 (Mar 26, 2015)

Lots of ESD circuits all over using these relays energized 24/7


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## emtnut (Mar 1, 2015)

mitch65 said:


> Lots of ESD circuits all over using these relays energized 24/7


Like this ? ....


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## MechanicalDVR (Dec 29, 2007)

RePhase277 said:


> Definite purpose contactors are generally recognized components (cute backwards R), for use in a listed assembly, but not themselves listed to be used anywhere else....
> 
> I may or may not have used many of them for unspecified purposes:whistling2:


I humbly disagree. 

Many OEM contactors bought directly from manufacturers for RTUs and condensing units are definite purpose contactors.

I don't think I ever had any other type sent from Lennox or Carrier just to name a couple brands that come right to mind.


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## RePhase277 (Feb 5, 2008)

MechanicalDVR said:


> I humbly disagree.
> 
> Many OEM contactors bought directly from manufacturers for RTUs and condensing units are definite purpose contactors.
> 
> I don't think I ever had any other type sent from Lennox or Carrier just to name a couple brands that come right to mind.


Right. That's what I'm saying. They are definite purpose because they go inside the RTU or condensing unit. That is their "definite purpose".


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## MechanicalDVR (Dec 29, 2007)

RePhase277 said:


> Right. That's what I'm saying. They are definite purpose because they go inside the RTU or condensing unit. That is their "definite purpose".


Just went back and read post #4, I thought you said you can't put them in a condensing unit.


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## mitch65 (Mar 26, 2015)

emtnut said:


> Like this ? ....
> 
> https://www.youtube.com/watch?v=RtlYi1yLTVQ


hopefully not.


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## glen1971 (Oct 10, 2012)

emtnut said:


> Like this ? ....
> 
> https://www.youtube.com/watch?v=RtlYi1yLTVQ


I'll guess his reference to ESD, refers to "Emergency Shut Down"


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## HackWork (Oct 2, 2009)

RePhase277 said:


> Right. That's what I'm saying. They are definite purpose because they go inside the RTU or condensing unit. That is their "definite purpose".


 OK, so the definite purpose rating has nothing to do with being better than continuous duty rating? 

Thank you for clearing that up, since Steve will never be back to answer for his misinformation.


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## RePhase277 (Feb 5, 2008)

HackWork said:


> OK, so the definite purpose rating has nothing to do with being better than continuous duty rating?


No. Definite purpose is just a designation for recognized ized units that are part of a larger listed assembly. But they are pretty beefy because they are almost always designed to handle compressor startup loads in HVAC.



> Thank you for clearing that up, since Steve will never be back to answer for his misinformation.


Well he would have to remember his lies and his continual state of inebriation makes that difficult. It's much easier to piss your pants and not make eye contact with your wife due to your shame.


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## sparkiez (Aug 1, 2015)

You can use ice cubes, but I would worry more about the coil burning up than the contacts. What you should be using is a safety relay. These devices are fail safe and made for your purpose.


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