# Cabinet question



## sparkiez (Aug 1, 2015)

I am retrofitting a PLC cabinet and need quite a few control relay's that are no existent in the cabinet. I am curious as to what approach I should take with the neutral wires on the relays.

Should I create a bus of some sort (via connectors in the middle of terminal blocks) or should I daisy chain the relays. I will only have about 10 of them, so there isn't too much worry of a daisy chain causing issue as long as the wire is sized right, but they will be turning on a PLC output, so I could also see the outputs getting quite a bit of harmonics back up the line when the coils deenergize.

Am I wrong in that assumption? What is the best standard practice for neutrals on control relays in PLC cabinets?


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## HARRY304E (Sep 15, 2010)

sparkiez said:


> I am retrofitting a PLC cabinet and need quite a few control relay's that are no existent in the cabinet. I am curious as to what approach I should take with the neutral wires on the relays.
> 
> Should I create a bus of some sort (via connectors in the middle of terminal blocks) or should I daisy chain the relays. I will only have about 10 of them, so there isn't too much worry of a daisy chain causing issue as long as the wire is sized right, but they will be turning on a PLC output, so I could also see the outputs getting quite a bit of harmonics back up the line when the coils deenergize.
> 
> Am I wrong in that assumption? What is the best standard practice for neutrals on control relays in PLC cabinets?


Each circuit should have it's own neutral.........Welcome to the forum.:thumbup:


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## sparkiez (Aug 1, 2015)

just to paraphrase and make sure I got this right, each relay should have a separate neutral in the cabinet running back to the primary neutral?


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## JRaef (Mar 23, 2009)

Daisy chaining the neutrals is fine, it's done all the time. The risk however is that if one wire comes off, you don't just lose one relay, you lose ALL of the relays down stream of that loose wire. That however can also make troubleshooting it a little easier. For 10 relays, I'd do it that way. There is no "harmonics" issue here, unless they are solid state relays? In which case, why?

The down side of having a separate wire for each one is that is you have 100 relays, that's 99 more wires in the wiring channel. It can get ridiculous. You need to weigh your risks and benefits. 

I'm not sure what you were trying to say when you said they were going to control an output of the PLC, outputs of a PLC are controlled by the PLC. If what you meant was that these relays will BE controlled by the outputs of a PLC, that makes more sense. In that case, these relays will be what is called an "interposing relay". There are many relay and terminal block suppliers that now sell small narrow interposing relays that are basically the same size or just slightly wider than a terminal block and are DIN rail mounted just like them. They can be used with special fanning strips that jumper all of the neutrals together for you. They cost more than the cheap ice cube style relays, but more than make up for it in time and space savings. Check them out by searching on that term, "interposing relay".


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## MDShunk (Jan 7, 2007)

Depending on what variety of relays you are using, and what bases (if required), there are neutral busing kits available from many manufacturers. If you have the lead time to spare, you might think about that approach. Makes for a slick install.


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## MDShunk (Jan 7, 2007)

Another approach that I like is to crimp on either a fork terminal or wire ferrules rated for two conductors of the size you intend to use. Crimp both the "wire in" and "wire out" of each relay into a single terminal. Keeps the neutral in-tact if a relay is replaced.


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## John Valdes (May 17, 2007)

I always daisy chained the neutrals and used a terminal buss at the strip. 
I have worked with guys that would bring down every single wire (including short jumpers) to the terminal strip so they could do ALL the troubleshooting from the terminal strip itself.
To me thats overkill. But then I put a number on every single wire end regardless of color. Including neutrals.
I really don't like the term neutral in this application anyway. The potential is the same and I sometimes used all one color to make this point.


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## sparky970 (Mar 19, 2008)

Check out Phoenix Contact


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## sparkywannabee (Jan 29, 2013)

If by 'harmonics', you mean the spike caused by an inductive load, you can use a snubber across the coil of the relay, RC type for AC coils and diode kind for DC coils, that will smooth things out.


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## RIVETER (Sep 26, 2009)

sparkiez said:


> I am retrofitting a PLC cabinet and need quite a few control relay's that are no existent in the cabinet. I am curious as to what approach I should take with the neutral wires on the relays.
> 
> Should I create a bus of some sort (via connectors in the middle of terminal blocks) or should I daisy chain the relays. I will only have about 10 of them, so there isn't too much worry of a daisy chain causing issue as long as the wire is sized right, but they will be turning on a PLC output, so I could also see the outputs getting quite a bit of harmonics back up the line when the coils deenergize.
> 
> Am I wrong in that assumption? What is the best standard practice for neutrals on control relays in PLC cabinets?


You are overthinking it. As long as you use the neutral from the supplying transformer...all will be okay.


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## don_resqcapt19 (Jul 18, 2010)

I often see the neutrals daisy chained, but with both ends taken back to the main neutral bus.


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## sparkiez (Aug 1, 2015)

JRaef said:


> Daisy chaining the neutrals is fine, it's done all the time. The risk however is that if one wire comes off, you don't just lose one relay, you lose ALL of the relays down stream of that loose wire. That however can also make troubleshooting it a little easier. For 10 relays, I'd do it that way. There is no "harmonics" issue here, unless they are solid state relays? In which case, why?
> 
> The down side of having a separate wire for each one is that is you have 100 relays, that's 99 more wires in the wiring channel. It can get ridiculous. You need to weigh your risks and benefits.
> 
> I'm not sure what you were trying to say when you said they were going to control an output of the PLC, outputs of a PLC are controlled by the PLC. If what you meant was that these relays will BE controlled by the outputs of a PLC, that makes more sense. In that case, these relays will be what is called an "interposing relay". There are many relay and terminal block suppliers that now sell small narrow interposing relays that are basically the same size or just slightly wider than a terminal block and are DIN rail mounted just like them. They can be used with special fanning strips that jumper all of the neutrals together for you. They cost more than the cheap ice cube style relays, but more than make up for it in time and space savings. Check them out by searching on that term, "interposing relay".


Thanks for the detailed explanation, and yes I'm familiar with the term "interposing relay." I also happened to purchase that type of relay for this system to replace the old full-sized ice cube relays in the cabinet and save some space. I wasn't aware of the strips to jumper the neutrals though, that is pretty cool.

Seeing as there are only 10 relays, it was really my hope that it would be fine to daisy chain them, The cabinet is WAY over-sized for this purpose and used to serve as a remote rack, but seeing as that system is no longer there I moved the controller and necessary cards down and added a couple inputs so that we, well for a lack of better words, what you would call a "3-wire start/stop" system so that the E-Stops are in series to an input with 3-position (push-neutral-pull) AB actuators and contact blocks so that there is a true start/stop rather than just a stop (to prevent the conveyor's restarted in the case of a power outage). There is talk of later making this into a sortation system, so I'm (sort of) building ahead for that as well.

Anyway, my question has been answered, thanks guys!


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## RIVETER (Sep 26, 2009)

sparkiez said:


> I am retrofitting a PLC cabinet and need quite a few control relay's that are no existent in the cabinet. I am curious as to what approach I should take with the neutral wires on the relays.
> 
> Should I create a bus of some sort (via connectors in the middle of terminal blocks) or should I daisy chain the relays. I will only have about 10 of them, so there isn't too much worry of a daisy chain causing issue as long as the wire is sized right, but they will be turning on a PLC output, so I could also see the outputs getting quite a bit of harmonics back up the line when the coils deenergize.
> 
> Am I wrong in that assumption? What is the best standard practice for neutrals on control relays in PLC cabinets?


Never thought of it that way, but with only 10 relays why not set a buss and go to each relay. It is less labor than thinking about it and will accomplish the same thing.


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## DesignerMan (Jun 13, 2008)

MDShunk said:


> Another approach that I like is to crimp on either a fork terminal or wire ferrules rated for two conductors of the size you intend to use. Crimp both the "wire in" and "wire out" of each relay into a single terminal. Keeps the neutral in-tact if a relay is replaced.


I've always used the crimp on ferrules made for 2-wires.
They make a good clean install and you can remove a neutral (if necessary) without loosing everything down the line. :thumbsup:


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