Selection of Multiconductor Cable

[Lay95]

Hi Guys,

I am using micro850 PLC (Allen Bradley), the customer requested that all panels should be at one place. So now I have to run control cables to the field.

I have 3 Joysticks, 2 distance measuring Sensors as an Input and 4 Solenoid Valves & 4 LED's as an Output and all of them runs on 24VDC including PLC.

1) What cable gauge (AWG) should I used? ( The cable will be running 50-60 feet from PLC to the field and it will have total 3-4Amp load)

2) The other question is can I used a multiconductor cable (as customer wants to run single cable from panel to field) to control/wiring all the above mentioned devices?
I am thinking of running one multiconductor cable and have a small JB at the field and split that cable's conductors to respective device. Is it possible to do that?

Please let me know if you need additional information.

Thanks.

 

[Ken Moore]

Use twisted and shielded pairs.
My standard is nothing smaller than 18ga in the field, but if you calculate the voltage drop you may be able to go smaller. There are many tables on line that will help with that calculation.

 

[OkiePC]

You could use a multicore cable for the digitals with or without the shield and individual shielded two wire cables for the analogs. Did you say some of these are analog?

I have a time or two used a multiconductor cable with individually shielded twisted pairs to handle digital and analog signals all in one cable. Yes, you can definitely add a J-box to break out of the main cable into smaller ones for each sensor. You'll have to do that unless you have a home run cable for each sensor.

 

[Lay95]

Use twisted and shielded pairs.
My standard is nothing smaller than 18ga in the field, but if you calculate the voltage drop you may be able to go smaller. There are many tables on line that will help with that calculation.

Thanks Ken.
I was thinking to go for 18AWG 24C cable. I totally forgot about the twisted shielded pair cables.

https://www.solar-wind.co.uk/info/dc-cable-wire-sizing-tool-low-voltage-drop-calculator

(I just calculated the cable sizing from the above mentioned link but I am not sure how accurate or correct I am)

 

[Saffa]

I would personally keep the solenoids out of any multi core carrying analog signals (assuming the level sensors are analog).

You guys with your AWG over there... no idea what the equivalent is, but we use a lot of 0.5mm2 twisted pair, over all screened.

If it was me I'd run that for your analog and digital PLC inputs, then a heavier gauge for the solenoids, probably 1.5mm2 or 2.5mm2 depending on calculated volt drop. Remember these are an inductive load, and do have a bit of inrush current to handle, depending on solenoid rating.

 

[Lay95]

You could use a multicore cable for the digitals with or without the shield and individual shielded two wire cables for the analogs. Did you say some of these are analog?

I have a time or two used a multiconductor cable with individually shielded twisted pairs to handle digital and analog signals all in one cable. Yes, you can definitely add a J-box to break out of the main cable into smaller ones for each sensor. You'll have to do that unless you have a home run cable for each sensor.

Thanks OkiePC
My sensors are analog and solenoid valves are digital (But the customer is emphasizing to run only one cable from PLC panel to the field), so I was planning I can get a cable which will work for both analog and digital input devices.

And no, there is no home cable run for individual sensor. As I mentioned in my post, I am thinking to set a small JB with a terminal block in it(wiring all the control cables from all devices to this terminal block) and split that conductors to the respective terminals. Is it viable?

Thanks.

 

[I_Automation]

Another option for the solenoids is along with the multi-conductor cable run a heavier (14 or 16AWG) power cable for the 24VDC, then in the remote box put in interposing relays so your signal wire is only pulling in small relays. Let them power the solenoids from the 24V cable.

 

[Lay95]

I would personally keep the solenoids out of any multi core carrying analog signals (assuming the level sensors are analog).

You guys with your AWG over there... no idea what the equivalent is, but we use a lot of 0.5mm2 twisted pair, over all screened.

If it was me I'd run that for your analog and digital PLC inputs, then a heavier gauge for the solenoids, probably 1.5mm2 or 2.5mm2 depending on calculated volt drop. Remember these are an inductive load, and do have a bit of inrush current to handle, depending on solenoid rating.

Thanks Saffa.

I will keep in mind that not to used multi core cable for analog signals.
And does 0.5mm2 twisted pair, over all screened good enough for 24VDC {3-4 amp rating} with a run of 60 feet?

[If it was me I'd run that for your analog and digital PLC inputs, then a heavier gauge for the solenoids, probably 1.5mm2 or 2.5mm2 depending on calculated volt drop. Remember these are an inductive load, and do have a bit of inrush current to handle, depending on solenoid rating.] --- That is a good point.

I believe solenoid valve will have a rating of 600-800mA.

Thanks.

 

[OkiePC]

If you will have solenoids and analog signals in the same cable, do use individually shielded pairs for the analog signals. I am not sure if your joysticks are analog or digital. You may end up with something like this with 8 shielded twisted pairs:

https://www.automationdirect.com/ad...individual_-a-_overall_shields/pltc3-18-8ss-1

You might need more than 8 pairs, but I am not clear on the digital and analog signal count. If your LEDs share a common as do your solenoids, you need 6 conductors to cover those, leaving 5 pairs for the joysticks and measuring sensors.

 

[Lay95]

Another option for the solenoids is along with the multi-conductor cable run a heavier (14 or 16AWG) power cable for the 24VDC, then in the remote box put in interposing relays so your signal wire is only pulling in small relays. Let them power the solenoids from the 24V cable.

Thanks I_Automation

That is a very good idea.

As I will be using Digital Output module 2080-IQ4OB4 (Allen Bradley) which will be 24VDC sink/source and to power up the solenoid valve, a power cable from valve to the small JB/ remote box. (Another power cable running from PLC Panel to this small JB/remote box which will be used to power all the devices in the field)

Can you please suggest some interposing relays that I can used.

Thanks.

 

[I_Automation]

These from McMaster about $10 each, then add the sockets, are what I usually use.

EDIT: Also if these is power in the remote machine instead of running a power cable put a 24V power supply locally for the relays.

 

[Lay95]

If you will have solenoids and analog signals in the same cable, do use individually shielded pairs for the analog signals. I am not sure if your joysticks are analog or digital. You may end up with something like this with 8 shielded twisted pairs:

https://www.automationdirect.com/ad...individual_-a-_overall_shields/pltc3-18-8ss-1

You might need more than 8 pairs, but I am not clear on the digital and analog signal count. If your LEDs share a common as do your solenoids, you need 6 conductors to cover those, leaving 5 pairs for the joysticks and measuring sensors.

Thanks OkiePC

Yes, I think each pair for 4 solenoid valves (output), 2 sensors (input), 3 joysticks (input) & 4 LED's (output) so total 13pair with 2 spare make it 15pairs. (Regardless of the analog or digital input/output)
So I will use twisted individually shielded pairs(15) cable.

 

[Lay95]

These from McMaster about $10 each, then add the sockets, are what I usually use.

EDIT: Also if these is power in the remote machine instead of running a power cable put a 24V power supply locally for the relays.

Thanks I_Automation.

I will look into it.

[EDIT: Also if these is power in the remote machine instead of running a power cable put a 24V power supply locally for the relays.]
You mean separate power(24V) supply for relay?

 

[I_Automation]

[EDIT: Also if these is power in the remote machine instead of running a power cable put a 24V power supply locally for the relays.]
You mean separate power(24V) supply for relay?

Yes. If the machine has 120 or 240V in it instead of running a 50 to 60 foot cable for 24V just put a 2.5A 24V power supply in the local machine.

Automation Direct has them for less than $35 (I think) and that would end up being less than running a 50 foot cable. Plus if the solenoids need more amps you can go up to a 5A supply for not really a big jump in cost.

 

[Lay95]

Yes. If the machine has 120 or 240V in it instead of running a 50 to 60 foot cable for 24V just put a 2.5A 24V power supply in the local machine.

Automation Direct has them for less than $35 (I think) and that would end up being less than running a 50 foot cable. Plus if the solenoids need more amps you can go up to a 5A supply for not really a big jump in cost.

Thanks I_Automation

Your plan can make the work easy.
Actually the situation is somewhat like this -- We have 600VAC source available at the site. I am using step down transformer to bring it to 120VAC & then using AC to DC converter power supply to power up my PLC{24VDC}. (SO PLC Panel consists of AC to DC converter and PLC itself)
And all the control/signal cables from PLC will be running 60 feet to the field.(Where all the sensors, joysticks, solenoid valves are located).

And customer told to run only one cable from PLC panel to the field. So I am thinking to use 1 twisted individually shielded pairs(15) cable which will be ran to the field and a small JB/remote panel to split these pairs into the terminal block.
And one power cable (24VDC) from the PLC panel to this small JB which I can used to power up all the devices in the field.
Do you think this will work?
And if yes, can you please suggest the gauge/size of power cable for 24VDC, 60feet long and 3-5amp load.

Thanks.