Input Card Wiring

I AM WANTING TO USE A MULTICONDUCTOR CABLE TO RUN FROM A PUSHBUTTON PANEL TO INPUT CARDS ON MY PLC.
120VAC
20 GA WIRE

WHAT WOULD BE THE SAFEST MAX DISTANCE THAT I COULD RUN THIS WITHOUT CREATING PROBLEMS??

20 AWG is 55 Ohms per mile, V=I x R, voltage drop should be less than 10%.

Having said that, I usually try to avoid anything less than 16 AWG with 120 Volts just because of mechanical strength and the potential for short circuits, loose connections, and the attendant safety issues.

I agree with Tom about not using anything smaller than #16 AWG, especially when leaving the panel.
I prefer to use #16 wiring from the I/O card to terminal block in panel, and then #14 or #12 from there to the field.
With some cards, like 16 point isolated inputs, which have 32 wires running to card, if you are using anything larger than #16 it does not make for a pretty sight.

Not really related

What would you say about running 50 meters (or less) for a 70 volt 2.8A 5 Phase stepping motor with 18 or 20 AWG multiconductor cable?

Put your pushbuttons far enough away on an AC control circuit and the contacts will appear to never open due to distributed capacitance.

Well, Ron, I reckon I'd say ya' do what ya gotta do. I don't know nuthin' 'bout steppers, and even though I try to avoid smaller wires sometimes ya cain't. I suspects that like anythin' else, for special applicahuns ya know special techniques thet ya kin use, and with multi-conductor cable ya wouldn't have some of the mechanical strength problems I mentioned. If ya kin stand the voltage drop I reckon it must be OK.

Gerry said:

Put your pushbuttons far enough away on an AC control circuit and the contacts will appear to never open due to distributed capacitance.

Click to expand...

I've had that problem before and had to install interface relays. Are there I/O cards which deal with it so one does not need interface relays?

Andy

I don't know of any I/O modules that deal specifically with this. I think the simplest way to eliminate the problem is to use DC.
For quantity, using remote I/O or devicenet may be a better choice than multicore cable.

If I understand the question correctly, I would recommend staying away from the DC option (Don't know of any 120V DC input cards), due to the voltage drop.

Gotta go with Tom and Gerry on this one

If your cable is subject to flexing, you may be better off with 16 or 18 GA wire for the mechanical strength.

Also, I would definitely stay away from 110VAC I/O when possible. 24VDC is much more forgiving to misplaced fingers when troubleshooting.

For inputs, voltage drop shouldn't be a problem. According to my Siemens catalog, a typical 24VDC digital input draws 6 mA. Using Tom's 55 ohms per mile, that works out to .385 volts per mile. 24 - 0.385 = 23.615V. Siemens digital inputs interpret anything from 13V to 30V on an input as being "on". Now I obviously wouldn't run a mile of multiconductor cable, I just wanted to show that voltage drop wouldn't be an issue.

Just how many inputs are we talking? How long of a distance do you want to run your cable? Like Gerry said, remote I/O might be an attractive option for you.

Good Luck-
Kevin

THANKS FOR THE INFO EVERYONE......I WOULD PREFER DC TOO, BUT THAT IS NOT AN OPTION IN THIS CASE.
AT THIS POINT I AM LOOKING AT A 15 CONDUCTOR CABLE WITH A MAX RUN OF 250 FT.
BASED ON THIS AND ALL THE POST, THE QUESTION I WOULD HAVE NOW IS

"SHEILDED OR UNSHEILDED" ??????

I ALWAYS SHIELD ANY DC CABLES BUT.....WOULD THERE BE ANY REASON TO SHIELD AC I/O??

( THERE ARE NO ENCODERS IN THESE CONTROLS )

another "beginner" answer but is it not best to be safe and not sorry. in which case i would say shielded

Use Shielded as you will have a 250 foot antenna