# Control Relay Wiring Terminology



## swimmer (Mar 19, 2011)

What do you call the wiring technique when, for example:
A switch sends 24V to A1 of the relay coil.
A2 of the coil on the control relay is wired to a NC button and the other end of the button goes to an NC contact on another relay and on and on.

What is the term for that "on and on" business. Like "daisy chain" or something?


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## MDShunk (Jan 7, 2007)

I'd typically call it daisy chaining, but from having to service such installs, I'd also call it a pain in the ass to troubleshoot when a button fails on the machine somewhere. I'd rather see each point brought back to a terminal strip then back out to the device. Saves spending an hour opening up pushbutton boxes, remote relay panels, and remote junction boxes when I could just spend a couple minutes with the prints and a meter dancing down the terminal strip in the control panel.


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## Helmut (May 7, 2014)

MDShunk said:


> I'd typically call it daisy chaining, but from having to service such installs, I'd also call it a pain in the ass to troubleshoot when a button fails on the machine somewhere. I'd rather see each point brought back to a terminal strip then back out to the device. Saves spending an hour opening up pushbutton boxes, remote relay panels, and remote junction boxes when I could just spend a couple minutes with the prints and a meter dancing down the terminal strip in the control panel.



In a perfect world maybe.

Every TB takes up space on a din rail, and sometimes the cabinet ain't big enough to do what you suggest.


And you had prints? Lucky you.


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## bill39 (Sep 4, 2009)

If I’m understanding your description correctly then the PB and other contacts are all in “series”.


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## swimmer (Mar 19, 2011)

Yes Bill 39, one terminal of the relay control coil is in series with other stuff. But what do people call this? Series interrupts? daisy chain? I don't think daisy chain is very descriptive. Control interrupts? Series control interrupts? By the end of the second decade of the 21st century, there should be a very descriptive term that everyone uses.


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## oliquir (Jan 13, 2011)

if possible always wire the A2 terminal to DC common or neutral if AC relay, i hate when some circuits cut the A2 terminal, it is like cutting the neutral on a light circuit!


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## MDShunk (Jan 7, 2007)

oliquir said:


> if possible always wire the A2 terminal to DC common or neutral if AC relay, i hate when some circuits cut the A2 terminal, it is like cutting the neutral on a light circuit!


I suspect he might be dealing with a European machine. Seems like the popular thing to do there. Sort of along that same theme, PNP sensors are popular in north america while NPN sensors are more of euro/asia thing.


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## RePhase277 (Feb 5, 2008)

op 


Helmut said:


> In a perfect world maybe.
> 
> Every TB takes up space on a din rail, and sometimes the cabinet ain't big enough to do what you suggest.
> 
> ...


Every machine I go into varies from 5 to 100 years old. I can't think of many that had prints. The ones that did were wildly off after a few years.


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## RePhase277 (Feb 5, 2008)

oliquir said:


> if possible always wire the A2 terminal to DC common or neutral if AC relay, i hate when some circuits cut the A2 terminal, it is like cutting the neutral on a light circuit!


That's silly. It is nothing at all similar to opening a lighting neutral. Both break the circuit, but opening a grounded conductor in a lighting circuit can raise the screw shell of lamp sockets to line voltage. Two different worlds. It also gives you more than one interlock path besides just opening the hot. People going into control cadinets aren't Betty Sue Homemaker, standing on a chair changing a light bulb. Be aware that grounded conductors may be open by design. If you ever had to design a control circuit from scratch, you would appreciate the flexibility of opening a grounded conductor.


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## bill39 (Sep 4, 2009)

swimmer said:


> Yes Bill 39, one terminal of the relay control coil is in series with other stuff. But what do people call this? Series interrupts? daisy chain? I don't think daisy chain is very descriptive. Control interrupts? Series control interrupts? By the end of the second decade of the 21st century, there should be a very descriptive term that everyone uses.


The world is too big and there is too much slang out there for a standard term in a case like this. The only way to deal with it is by using an experienced ear or a print. I feel your pain.


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## swimmer (Mar 19, 2011)

I think I'll say "Series interrupt on a relay control circuit". Not too ambiguous. Daisy chain makes me think of the way I coil my extension cord.


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## RePhase277 (Feb 5, 2008)

I think the term you're looking for is "interlocked" . The start relay is interlocked with the oven door, for example.


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## John Valdes (May 17, 2007)

MDShunk said:


> I'd typically call it daisy chaining, but from having to service such installs, I'd also call it a pain in the ass to troubleshoot when a button fails on the machine somewhere. I'd rather see each point brought back to a terminal strip then back out to the device. Saves spending an hour opening up pushbutton boxes, remote relay panels, and remote junction boxes when I could just spend a couple minutes with the prints and a meter dancing down the terminal strip in the control panel.


I call it series because it is series. 



Helmut said:


> In a perfect world maybe.
> Every TB takes up space on a din rail, and sometimes the cabinet ain't big enough to do what you suggest.
> And you had prints? Lucky you.


I worked with a guy that always brought every point of connection to the terminal strip. And you are correct it takes up space and added terminal blocks. 
He even brought a wire to the terminal strip for jumpers. He was OCD about troubleshooting down the road and OCD about drawings.
I'm the same way.



swimmer said:


> Yes Bill 39, one terminal of the relay control coil is in series with other stuff. But what do people call this? Series interrupts? daisy chain? I don't think daisy chain is very descriptive. Control interrupts? Series control interrupts? By the end of the second decade of the 21st century, there should be a very descriptive term that everyone uses.


Look at any simple drawing. Its easy to see they are wired in series. Why use the word interrupt? Its connected in series. Nothing more. 



swimmer said:


> I think I'll say "Series interrupt on a relay control circuit". Not too ambiguous. Daisy chain makes me think of the way I coil my extension cord.


I would have to ask for an explanation if you used that term with me.
Have you ever even looked at a machine schematic?


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## paulengr (Oct 8, 2017)

European starter circuits start with a manual motor starter which has the disconnect, MCP, and overload as a single device. They add a contactor when/if you need control. This is different from the American layout which started as a disconnect, fuses, contactor, and overload as separate components right down to replaceable contactor tips and coils, and overload heaters. In Europe post WWII they had a severe electrician shortage so they tried to make everything easily replaceable whereas the American philosophy was to repair when possible since labor was cheap and readily available but components were expensive. So the control schemes are kind of polar opposites by design. But now US companies have learned how to properly use the cheap/low labor cost European methods and adopted a lot of it so we have a mix of both. Yes the European stuff is more complicated to work on and not as easy to repair (if it can be repaired at all). Europeans also love bureaucracy and paperwork so they would freak out at the idea that 99% of the time I can troubleshoot with no prints at all. All I can say is get used to it because it’s not going away.


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## MDShunk (Jan 7, 2007)

I remind myself all the time that "it was cheap" when I replace an IEC starter that I can hold in the palm of my hand that burned up in 5 years when the equivalent NEMA starter next to it from 1968, that would take a hand truck to wheel in, is still going. I remind myself "it was cheap" when the 22mm pushbutton panel gets a new button or two every few years when the 30.5mm pushbuttons on the next panel down are worn smooth from decades of use. Anyone else remember replacing christmas tree bulbs in photoswitches? Now you chuck the whole 300 dollar sensor in the bin. The first PLC's I worked on had replaceable ice cube relays in the output cards. I'm getting grouchy. I should make some lunch. :smile:


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## Helmut (May 7, 2014)

RePhase277 said:


> The ones that did were wildly off after a few years.


Or have been folded so many times that you can't tell where that wire #10 goes, or even it's a 10. Might be 18....


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## MDShunk (Jan 7, 2007)

I think there's an unwritten rule somewhere that the first thing you should do in a new control cabinet is rip off all the Panduit covers, throw the prints away, and put a bunch of crap in the bottom of the panel. Oh, and throw a few boxes of spare 15 amp glass fuses in there, because they're work in place of whatever size fuse blows.


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## just the cowboy (Sep 4, 2013)

*my plant*



MDShunk said:


> I think there's an unwritten rule somewhere that the first thing you should do in a new control cabinet is rip off all the Panduit covers, throw the prints away, and put a bunch of crap in the bottom of the panel. Oh, and throw a few boxes of spare 15 amp glass fuses in there, because they're work in place of whatever size fuse blows.


You must of been in my plant. And the glass fuses are not even used in that panel.

welcome back Marc


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## paulengr (Oct 8, 2017)

So if the IEC contactor is rated say 15 A, does that mean it’s rated for a motor that is 15 A? NO. You have to know the utilization category such as AC4 and the number of cycles in its life then look at the charts on the spec sheets to size it correctly which might mean you need the 35 A rated one...big difference! Might have to up it to say 50 A. If you don’t do this the contactor burns up.

With NEMA we need HP, voltage and that’s it.



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## Flyingsod (Jul 11, 2013)

MDShunk said:


> I think there's an unwritten rule somewhere that the first thing you should do in a new control cabinet is rip off all the Panduit covers, throw the prints away, and put a bunch of crap in the bottom of the panel. Oh, and throw a few boxes of spare 15 amp glass fuses in there, because they're work in place of whatever size fuse blows.




You forgot the blown fuses that must be placed there. That’s def a rule. 


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## John Valdes (May 17, 2007)

MDShunk said:


> I remind myself all the time that "it was cheap" when I replace an IEC starter that I can hold in the palm of my hand that burned up in 5 years when the equivalent NEMA starter next to it from 1968, that would take a hand truck to wheel in, is still going. I remind myself "it was cheap" when the 22mm pushbutton panel gets a new button or two every few years when the 30.5mm pushbuttons on the next panel down are worn smooth from decades of use. Anyone else remember replacing christmas tree bulbs in photoswitches? Now you chuck the whole 300 dollar sensor in the bin. The first PLC's I worked on had replaceable ice cube relays in the output cards. I'm getting grouchy. I should make some lunch. :smile:


I get the physical superiority of NEMA vs IEC when it comes to control devices.
And I also get the superiority, as far as pricing when it comes to IEC.

If I'm one the guys working in the plant, I want NEMA, unless I have a tight budget.
If I'm designing, pricing and building a control system for a customer and money is part of the equation, I sell IEC. (Money is always part of the equation) Of course I would include a quote to use NEMA.
Imagine the look on the customers face at the remarkable price difference.



paulengr said:


> So if the IEC contactor is rated say 15 A, does that mean it’s rated for a motor that is 15 A? NO. You have to know the utilization category such as AC4 and the number of cycles in its life then look at the charts on the spec sheets to size it correctly which might mean you need the 35 A rated one...big difference! Might have to up it to say 50 A. If you don’t do this the contactor burns up.
> With NEMA we need HP, voltage and that’s it.


All IEC contractors list the HP as well as the current.
When sizing one for a customer, I trusted the HP rating along with the other specs.
I hear so much about how bad IEC is compared to NEMA, yet I saw no more failures with IEC vs NEMA. Also most IEC is re-buildable, just like NEMA. 
For an example, I had several machines with IEC contactors on extruder barrel cooling fans. (on/off, on/off,on/off,) over and over again day and night for many years.
Anyone in the temperature business (heating and cooling processes) is aware of the abuse a contactor would see in this application.
I worked there for 5 years and I can count on both hands how many of those contactors had to be replaced.
For the record they were Allen Bradley IEC. Reliable. So reliable we only kept two on the shelf.



Flyingsod said:


> You forgot the blown fuses that must be placed there. That’s def a rule.


Time to think mini breakers, IEC, din rail mount.


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