24 VDC I/O & 120/240 Power

We are replacing our canning machine with another newer one. The newer one has a larger electrical panel and thus cannot be installed near the machine as the the older one was.

Right now, it's looking like a 75ft wire run.

• 20 I/O wires (24VDC) [IN mostly Prox switches/Photo Eyes & Safety Door switches, OUTS air solenoids)
• 6 Motor leads (3 Phase 240VAC) {For a 1HP conveyor motor, and .5HP ~ 1HP lift motor, which will pretty much be set once and left.)
• 1 Switch (120VAC) {For a motor contacter)
• 1 Ground wire

My question is, if run into the same PVC 1.25" conduit, all wires same gauge (14 AWG THHN) {maybe a larger ground}, will I have any interference issues?


I've had issues before with other machines that had RTDs and they wouldn't read properly until I ground one end of the shielded cable. This isn't the same situation though, there is no analog output and as of now, the 24VDC wires are not shielded.

Thanks

Gappvembe,

If you put all the wires into the same conduit, and want to comply with the National Electrical Code, then all your wires would need to have 300 volt insulation.

Because you would have at least 6 current carrying conductors in the same raceway, you will have to de-rate the wires according to NEC Table 310.15(B)(2)(a) to 80% of their normal capacity. 0.8 X 15 Amps = 12 Amps.

I might worry some about getting some induced noise on the 24 VDC signal wires. At least consider using shielded 300-volt insulated cables for those. Of course, if you can afford to do that, then it might be cheaper just to run two smaller conduits, and put the 24 VDC unshielded stuff in the second conduit.

If you use #14 wire for the 1 HP motor, then make sure your motor branch circuit protection does not exceed 15 Amps, which is the NEC limit for #14 wire.

I might leave the outputs to the air solenoids as #14 wires, but consider reducing the wires for the Proximity switches, Photoelectric switches, and safety door switches to #16 or #18 A.W.G.

Lancie1 said:

gappvembe,

If you put all the wires into the same conduit, and want to comply with the National Electrical Code, then all your wires would need to have 300 volt insulation.

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The wires are rated for 600 VAC with PVC insulation

Lancie1 said:

I might worry some about getting some induced noise on the 24 VDC signal wires. At least consider using shielded 300-volt insulated cables for those. Of course, if you can afford to do that, then it might be cheaper just to run two smaller conduits, and put the 24 VDC unshielded stuff in the second conduit.

Click to expand...

There are other conduits in this plant where mutli-voltages are ran and haven't had an issue. I was curious if the length of run would contribute to any possible interference.

I would not run all wires in same conduit. Inductive and capacitive coupling are proportional to wire length.

Now is the time and opportunity to make maintenance easier. I realize you are food industry and all that but spend the money and time to do it right the first time.

Dan Bentler

Yes, the closer and farther wires are run, the more of the 240 volt voltage will appear as ghost voltage on your 24 vdc wires. You may be able to measure 60 to 80 volts AC on these 24 volt DC wires. That doesn't help the control system much.

Think of the runs running close together as the windings in a transformer. A transformer works by winding a bunch of wire into a coil and placing it next to another coil, where the second coil picks up some "induced" voltage and power from the first coil. Wires in conduits work the same way as 1-turn transformers. To minimize this effect, you have to shield the lower-voltage wires by putting a Faraday cage around the wires - usually referred to as shielded cables.

Like Dan reccommended, just add the second PVC conduit and the shielded cables. The initial cost is small compared to years of mysterious events, switch closures not seen, solenoids not activating, signals not getting through.

You may be trying to reduce the number of different types of wire that you have to buy, but you are going to need at least two rolls of #14 1/conductor black and 1 roll of #14 1/C green just for the motors, and if you make your 24 VDC wires #14 also, then it is going to be much more difficult keeping track of both ends of all these wires. Much better to have all but the 240 volt stuff as 2/c shielded cables.

I would strongly suggest putting your control wire in one conduit and your motor leads in another.

It is good pratice and can save you alot of trouble down the road. Noise is one of many issues you can have.

Also, you did not say if your Motors are on motor starters or VFD's. If VFD's then this distance can get you into some issues.


One other thing, since your motor leads length are increasing substantionally then they may need to be upsized as well.

One other thing, since your motor leads length are increasing substantionally then they may need to be upsized as well.

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Clay, Good point. According to my handy voltage-drop calculator, he can get by with #14 for a 1 HP 240 volt 3-phase motor. 4.2 Amps for 90 feet one way (adding 5 feet each end for termination) in a PVC raceway produces a 1.54% voltage drop, meaning that the motor voltage will be 236 volts [IF THE SUPPLY VOLTAGE IS ACTUALLY 240 VOLTS], and within the 3% rule.

What he can't do is use more than a 15 Amp breaker on either motor circuit, due to the 80% derating factor for more than 6 current-carrying conductors in the same conduit, and the normal 15 amp capacity of #14 wire.

Lancie1 said:

Clay, Good point. According to my handy voltage-drop calculator, he can get by with #14 for a 1 HP 240 volt 3-phase motor. 4.2 Amps for 90 feet one way (adding 5 feet each end for termination) in a PVC raceway produces a 1.54% voltage drop, meaning that the motor voltage will be 236 volts [IF THE SUPPLY VOLTAGE IS ACTUALLY 240 VOLTS], and within the 3% rule.

What he can't do is use more than a 15 Amp breaker on either motor circuit, due to the 80% derating factor for more than 6 current-carrying conductors in the same conduit, and the normal 15 amp capacity of #14 wire.

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One more reason to use seperate conduit. This is really one of my pet peves. Why risk shorting out 480 to a 24 VDC curcuit for the sake of saving conduit.

Thanks, I think I am going to go with a shielded cable for the I/O & a separate conduit for the power.

I forgot about the PLC communications an AB Panelview Plus 600 to Micrologix 1200 (I think). Will there be any problems running the communication wire (CAT5, RJ-45) in this conduit?

There really isn't that much of a current draw on any of the I/O [the solenoid valves would be the most, roughly .35 amps] so should I worry about the wire size? Going from 20 AWG (2 Amps) ($677)to 16 AWG (2 Amps)($1570).

Also out of the conduit, I plan on putting the wires in a junction box with a terminal strip and from there to the individual components, should there be two different junction boxes since I am separation the conduit?

Lancie1 said:

Clay, Good point. According to my handy voltage-drop calculator, he can get by with #14 for a 1 HP 240 volt 3-phase motor. 4.2 Amps for 90 feet one way (adding 5 feet each end for termination) in a PVC raceway produces a 1.54% voltage drop, meaning that the motor voltage will be 236 volts [IF THE SUPPLY VOLTAGE IS ACTUALLY 240 VOLTS], and within the 3% rule.

What he can't do is use more than a 15 Amp breaker on either motor circuit, due to the 80% derating factor for more than 6 current-carrying conductors in the same conduit, and the normal 15 amp capacity of #14 wire.

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Correct, each motor has it's own breaker, in fact the whole panel is rated at 10 AMPS

I forgot about the PLC communications an AB Panelview Plus 600 to Micrologix 1200 (I think). Will there be any problems running the communication wire (CAT5, RJ-45) in this conduit?

Click to expand...

No problems, run it in the conduit with the 24 VDC wires.

There really isn't that much of a current draw on any of the I/O [the solenoid valves would be the most, roughly .35 amps] so should I worry about the wire size? Going from 20 AWG (2 Amps) ($677)to 16 AWG (2 Amps)($1570).

Click to expand...

Life is a series of compromises. Solenoid coils are one of the devices that have in-rush current, which can be 1.5 to 2 times the normal current. Assuming a max current of 1 amp, then for #18 wire your voltage drop over 90 feet would be 1.43 volts DC.

Also out of the conduit, I plan on putting the wires in a junction box with a terminal strip and from there to the individual components, should there be two different junction boxes since I am separation the conduit?

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Two are best, one will work, but separate the voltages to different sides of the box.

I question your wire numbers.

6 motor leads - 2 motors.
20 wires for mostly i/o - what happened to the dc+, dc common?
1 120 vac sensor - 2 wires required.

The e-net cable needs to be placed in a conduit by itself and have a pull cord in there with it.

the low voltage wire should be placed in a conduit by itself as already pointed out. you need to look at whether the 24 volt wiring is class 1, 2, 3 in regards to low voltage wiring,
NFPA 70, 2008 ed, section 725.

the motor wires also should be put in a separate conduit.

please look into the safety circuit wiring. if the safety device is a 0 volt contact device, you should consider putting them in a separate conduit.

My co-workers fried a unit when a wire touched one of the safety circuits by accident.

regards,
james

We don't have time to do it right. Production needs the machine. Get it running and we will give you the time to do it right later.

I should be ashamed of myself

Dan Bentler