# On delay circuit



## tim465 (Oct 24, 2011)

I am wanting to wire a 5 sec. Warning siren before conveyor starts. The motor is a 120v 1HP 12.7A. I have a square d 9050 ft-12 relay timer I want to use. It states it is rated 3600va on make and 360va on break. I am not exactly sure what that means on make and break but it looks
pretty duty, please enlighten me. I want to use 1- 120v 20a circuit to feed my controls and my motor. I am also adding in 2 emergency rope pull stops, my weakest link. My question is this, will this circuit work as long as i put a in line fuse on my e-stop controls? Is my relay timer adequate to carry the load of the motor. I open for any suggestions or other ways to do this.
Thanks,
Tim


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## don_resqcapt19 (Jul 18, 2010)

The relay is not suitable for controlling that motor directly. You would be braking a load of 1524 va with a set of contacts rated for a maximum of 360 va. You will need to add a contactor to control the motor and let the TD relay control the coil of the contactor.


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## tim465 (Oct 24, 2011)

don_resqcapt19 said:


> The relay is not suitable for controlling that motor directly. You would be braking a load of 1524 va with a set of contacts rated for a maximum of 360 va. You will need to add a contactor to control the motor and let the TD relay control the coil of the contactor.


So what is my best options for a a contactor for this 120v single phase monitor. I know most definite purpose relays are only for 1/2 hp motors. What do you suggest for something that is not too expensive. Trying to keep the cost down.
Thanks.


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## tim465 (Oct 24, 2011)

don_resqcapt19 said:


> The relay is not suitable for controlling that motor directly. You would be braking a load of 1524 va with a set of contacts rated for a maximum of 360 va. You will need to add a contactor to control the motor and let the TD relay control the coil of the contactor.


So the 3600VA on make is only for the on delay only? And the 360va on break is after the delay? Huh, It just looks pretty heavy duty. Would it not make for 5 seconds then <break> then it makes again. So my horn, which is rated only about 1 amp or less, would be on the NC - timed open and then my 120 volt conveyor would be on the NO contacts and would make after the 5 sec delay. This contactor is rated for 3600 va on make. The conveyor would not be connected to a break, right?

Here is the PDF for more info on this contactor. Take a look at let me know that you think..

http://www.stevenengineering.com/Tech_Support/PDFs/45RSST.pdf

Thanks!


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## dronai (Apr 11, 2011)

How much is the Time delay ? If you need two contactors, may be it's cheaper by using a cheap PLC ?


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## McClary’s Electrical (Feb 21, 2009)

dronai said:


> How much is the Time delay ? If you need two contactors, may be it's cheaper by using a cheap PLC ?


So you run motor loads through a plc??


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## dronai (Apr 11, 2011)

mcclary's electrical said:


> So you run motor loads through a plc??


 
Plc has the TON timer in it. Wire the conveyor on switch, to the input with on delay, output to contactor coil to motor. Eliminates heavy duty Time Delay, if the cost justifies it. Click PLC is about $100.00


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## McClary’s Electrical (Feb 21, 2009)

dronai said:


> Plc has the TON timer in it. Wire the conveyor on switch, to the input with on delay, output to contactor coil to motor. Eliminates heavy duty Time Delay, if the cost justifies it. Click PLC is about $100.00


You still need a contactor, which your first post sounded like a plc would eliminate. Yes, you could eliminate the timer.


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## JRaef (Mar 23, 2009)

tim465 said:


> So the 3600VA on make is only for the on delay only? And the 360va on break is after the delay? Huh, It just looks pretty heavy duty. Would it not make for 5 seconds then <break> then it makes again.


OK, you seem a bit confused on the terminology here. Let's see if we can clear that up. It's important to know this if you are doing any control system work, which it appears you are.

This has absolutely nothing to do with the timer portion of your device. In a set of contacts, you are either opening a circuit, meaning "breaking" the flow of electricity, or you are closing a circuit, meaning "making" the circuit complete. The effect that these actions have on the contacts themselves is very different. ALL contacts have a "make" and "break" rating, as well as a HP rating (or lack of one).

*Making:* When you "make" a circuit complete, we assume there is a load of some sort, like a light or a coil on another device such as the electromagnetic in your buzzer. But also things like motors, transformers and power supplies have coils as well. The nature of the different types loads presents different challenges for making the circuit with a set of contacts. When you make a circuit complete into a AC coil, the coil is just like a short circuit for a brief moment until the electromagnetic field is created and interacts with the coil itself to limit the current flow. So for that brief moment, there is an "inrush" of current that the contacts, which are "making" the circuit complete, will need to handle. So in your spec above, it is saying that these contacts can be used to "make" a circuit that will have an inrush of 3600VA. This is based on a thermal damage curve of the contacts themselves. If you exceed this, you are risking damage to the contacts and melting the points so that they either burn away or worse yet, weld together permanently so that they can no longer open.

*Breaking:* When the contacts are used to "break" a circuit, there is a different challenge. When the contacts begin to open, there is an arc formed between them as the current continues to TRY to keep flowing. Fully breaking the circuit means that your contacts have opened far enough apart that the dielectric strength of the air, the properties of air that resist the flow of electricity, is high enough to interrupt it and extinguish that arc. As the contacts open, the arc, which is the same temperature as the surface of the sun, is melting the contact material. This does some serious damage to those contacts, much worse than anything they see when making a circuit. But they cool off almost immediately and the material is ready for the next operation. However, the damage is real and the larger the current is to start with, the more damage takes place. Hence in your situation, those contacts may be able to handle 3600VA under the "making" process, but because the damage is so much more severe, only 360VA when they have to "break" a circuit. 

*HP rating:* You will also notice that in most cases, the "breaking" capacity does not always correlate to the Motor HP rating of the contacts, to the point of in some cases, there is NO horsepower rating on them at all. The reason is that again, things with coils such as other relays, contactors, transformers and motors, will have another different effect on extending the brief life of that arc, called "inductive kickback, which makes matters worse. But with motors, the motor actually REGENERATES power back for a brief moment, making them the hardest kind of common load to break (capacitors are actually a little harder, but more rare). So often times you will see a spec that says a contact is rated to make 30A, break 6A, 3A continuous (NEMA B300 rating, which is what your timer is) but has no motor HP rating at all, even though technically something like a 1/16HP 120V motor is rated 2.2A. The duty of turning a motor off is too much for those little contacts to handle. 

Did that clear it up for you?


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## tim465 (Oct 24, 2011)

JRaef said:


> OK, you seem a bit confused on the terminology here. Let's see if we can clear that up. It's important to know this if you are doing any control system work, which it appears you are.
> 
> This has absolutely nothing to do with the timer portion of your device. In a set of contacts, you are either opening a circuit, meaning "breaking" the flow of electricity, or you are closing a circuit, meaning "making" the circuit complete. The effect that these actions have on the contacts themselves is very different. ALL contacts have a "make" and "break" rating, as well as a HP rating (or lack of one).
> 
> ...


So in other words my solid state timing relay is not adequate to handle my load of the conveyor. So I will need take this time delayed output to feed the coil on a definite purpose contactor for my motor load so not weld or melt my contacts in the timer relay. correct?


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## tim465 (Oct 24, 2011)

dronai said:


> How much is the Time delay ? If you need two contactors, may be it's cheaper by using a cheap PLC ?


Time delay is 5 seconds, just long enough to sound warning siren before conveyor start. What if I use a DPDT on delay timing relay (8 pin relay), then have the output of this feed a definite purpose contactor rated for 1 hp or more? Will that be fine? I can always set a fuse block to protect my controls.
Tim


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## JRaef (Mar 23, 2009)

tim465 said:


> So in other words my solid state timing relay is not adequate to handle my load of the conveyor. So I will need take this time delayed output to feed the coil on a definite purpose contactor for my motor load so not weld or melt my contacts in the timer relay. correct?


Exactly, although we didn't discuss the issue of having an Overload Relay. 

A lot of 120V motors have built-in thermal protection and therefore don't need it, but there's an issue with that on a conveyor. Let's say it does, and the conveyor overloads, so the motor thermal switch trips. Most of those are automatic reset, so while it's tripped, let's say you are troubleshooting that conveyor to figure out the problem, and you have your fingers in a dangerous pich point. Then the motor thermal protector cools off enough to reset, does so, and because yoru contactor is still on, it starts up again. Yopu lose your fingers. If you had an Overload Relay attached to the motor contactor, which the proer interlock contact in the control circuit, an overload would bean you have to go an manually push the reset buttong to re-start it, which means (hopefully) nobody is still working on the conveyor. A contactor + and Overload Relay is called a Motor Starter. That's what I would use.

I also personally hate "Definite Purpose" contactors. The DP should stand for "Don't Purchase" because they are junk from the outset. They are not meant to be used in anything other than a highly engineered OEM system, and even then only because the OEM knows in advance *exactly* how long they want it to last, which is the Warranty Period plus one day. I would rather see you buy an IEC contactor/starter for that motor, even if it costs you a bit more.

But really, that last part's just an opinion. As long as you have a different switching device.


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## tim465 (Oct 24, 2011)

Thanks so much JRaef for your reply. This conveyor is lightly used through out the day. It rarely stays on for a long period of time. I believe the DP contactor will be fine for this situation. It's just plugged into a receptacle right now and they want to keep it that way so they could move it around as needed. If it was a main conveyor that ran all day I would definitely be putting an motor starter with overloads protection for sure. Thanks again!


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## dronai (Apr 11, 2011)

tim465 said:


> Time delay is 5 seconds, just long enough to sound warning siren before conveyor start. What if I use a DPDT on delay timing relay (8 pin relay), then have the output of this feed a definite purpose contactor rated for 1 hp or more? Will that be fine? I can always set a fuse block to protect my controls.
> Tim


I meant, How much money is the TD, because you said heavy duty SQ blah blah

Horn -Sounds like you have that part figured out. 

What about your E-stop pull cords ? Is this the type 
http://www.bannerengineering.com/en-US/products/sub/107


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## Jlarson (Jun 28, 2009)

JRaef said:


> I would rather see you buy an IEC contactor/starter for that motor, even if it costs you a bit more.


Really the run of the mill small 20 and 30 amp DP contactors are like the same price as similar sized IEC contactors.


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## tim465 (Oct 24, 2011)

dronai said:


> I meant, How much money is the TD, because you said heavy duty SQ blah blah
> 
> Horn -Sounds like you have that part figured out.
> 
> ...


I got a good deal on it. $33.50. It is what it is, but it work great to pull in my motor contactor.


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## tim465 (Oct 24, 2011)

Jlarson said:


> Really the run of the mill small 20 and 30 amp DP contactors are like the same price as similar sized IEC contactors.


I got my contactors for 35.00 ea. and they are rated 2 hp. (sq d)


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## John Valdes (May 17, 2007)

Since you guys are talking pricing, check these guys out. http://www.weg.net/us/Products-Services/Controls/Motor-Protection-and-Starters

You cannot buy direct, but your motor and control vendor can.


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## fjl810 (Jul 20, 2011)

This is one way to wire it.


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## McClary’s Electrical (Feb 21, 2009)

fjl810 said:


> This is one way to wire it.


 
LAcking some details but it will work. Remove that ground symbol uptop. That's a grounded conductor, not grounding conductor.


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## JRaef (Mar 23, 2009)

Nice and simple.

I'd probably put the motor circuit on it's own fuse though.


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## Tsmil (Jul 17, 2011)

Are you using the horn as a conveyor start warning because the conveyor is out of sight of the panel? If so, you may want to place that o/l contact in the same line as the e-stops. Where you have it in the diagram, the conveyor will start immediately when it is reset. Have to be careful with remotely started equipment.


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