plc wire size

sujinvipin

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Join Date
Jan 2011
Location
Ottapalam
Posts
17
my PLC Input contains only push buttons , limit switches, scanner signal etc, for which the PLC doesn't consumes much current.So if i use a 18AWG(0.75mm sqr) of 1.5m having 7A ampacity is it ok? or should i have to go for for 20AWG, 22AWG ETC.I have seen that for control signals PLC consumes apprxmtly 3mA or around it, please clear my doubt.....
 
Where is the wiring going and how long of a run is it?

For most of what I do, the field wiring (from control panel to the end device) is usually done with #16 AWG wire. At the end device, I use an FS box where I splice in the quick connect cable that is used to connect to the sensor. This quick connect cable is usually #20AWG but I've seen anywhere from #18AWG to #22AWG.

There are as many configurations as there are people designing and wiring the systems. You need to understand voltage drop for long runs and physical strength for pulling wires in conduit and cable trays. ou will also need to understand insulation types depending on how and where you run the wires.
 
Any wire size will work, i'd just use whatever you feel comfortable with. I generally just grab #18 or #16 600V insulated wire for short runs. Sometimes its hard to fit smaller wire snugly behind the connection screws on some pushbuttons. On longer runs, i use #14.
 
As i have referenced about cables ampacity, i have seen 20AWG cables have 4A ampacity. But our PLC digital inputs consumes typically 3mA, say 15mA peak. So is 20AWG a good option.I know you have already given you opinion, but please consider this too and suggest if i m wrong.
 
As i have referenced about cables ampacity, i have seen 20AWG cables have 4A ampacity. But our PLC digital inputs consumes typically 3mA, say 15mA peak. So is 20AWG a good option.I know you have already given you opinion, but please consider this too and suggest if i m wrong.

The Amperage capacity of wire is its maximum. Anything above what the inputs require will be OK.

So your 20AWG cable (with 4A rating) will be OK with your (peak) 15mA (0.015A) inputs.

You can go a lot smaller with your cable amps rating, but bear in mind all that has been said about robustness and Voltage drop on long runs.
 
Smaller wire may be cheaper but the strands will be more likely to break if you do much of anything. 16 is a good balance if the runs are short. But yeah if you are only going 1.5 meters then you can almost use whatever scraps you may have handy. The amperes wire can handle shouldn't be the deciding factor in this case. I would go with the 16AWG you are putting too much work into a extremely simple and insignificant decision.
 
In our Power Utility power stations all instrumentation wiring to PLC’s is only 0.5mm2 multi-strand. We run cables of over 100m in length.

Your biggest concern is the shielding of these signal cables as not to have heavy electrical equipment cause any induced electromagnetic interference in your signal cables.

I assume you know about installation rules (routing and racking) of electrical vs. instrumentation cables?
 
Use shield cable on devices that spec it or if noise is an issue and only ground one end of the shield. Also, when running the wire, all the wires in the conduit/etc should be insulated to the highest voltage contained inside the conduit. Please don't run small signal wire in the same conduit as 480V motor leads!
 

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