View Full Version : wire sizing

11-17-2001, 07:12 PM
I'm going to be starting a large commecial job on monday. My boss and I laid it out today and walked it over and we're gona have some pretty long wire runs. Rain-aid always specs the single strand 14 gague for commercial, but I hate that stuff with a passion. What's worse than keeping track of 30/ + different zones when you're using 2 colors? (well actually, troubleshooting a system that was installed that way)....I'd love to use the multistrand 18 gague direct burail on the whole job, but I know it won't work. My solution is to use the multistrand for the zone wires and a 14 gauge single strand for the common. I've read that 18 gauge is suitable for valves as far as 1000 feet away from the controller which would mean a total of 2000 feet of 18 gague wire. Using that rule of thumb, does anyone see a problem with me using an 18 gague zone wire / 14 gague common wire for a valve located 2000 / - feet from the controller?



11-18-2001, 10:51 AM
There are formulas for this and I've used 18 gauge for runs over 2000 ft without a problem.

I also rewired a mall done with heavy single that kept breaking. I actually had a wire company spool me some 15 strand I think and used 14 or 16 single for the common. Longest run was about 4500 feet. Yeh it worked and I did the math before pricing the project.

I hate single unless there is an engineering reason. I don't think designers and architects bother to do the calulations.

I'll look up the info and repost. I can also fax some stuff if you need it.

11-18-2001, 11:02 AM
Too much info to write out. I can fax if you in a hurry.

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11-18-2001, 11:12 AM
at what point does the voltage drop in a solenoid circut become unacceptable? I would not be suprised if the coils still opperated at half their specified voltage. I would also not be suprised if the life of the solenoid was dramatically shortened (my damn starter motor needed to be replaced every few months till i figured out the cable btwn the solenoid and motor was bad)....i've found several voltage drop calculators on the web. According to the calculators, If I have a 2000 foot long run of 18 gague control and 14 gague common with 24 volts coming out of the clock and a solenoid that is drawing .2 amps (that's what irritrol specs for the holding current on their solenoids), than I'll have a voltage drop of around 4.5 volts....is that acceptable? what is acceptable?


11-18-2001, 11:15 AM
check your private messages and call me on the phone

11-18-2001, 04:42 PM
I always use 14 guage when going over 750 feet or so, just the way I do it. I only do that because I feel it is better to be safe than sorry. But....I hate troubleshooting the 14 guage also. You can buy 14 guage in lots of other colors, just a pain if you only need 1000 and have to buy 2500 foot spool of purple. You may never use it again.
I didn't bother to do the math but if I had a voltage drop of 4.5 volts, it would be unacceptable to me. Just my .02

11-18-2001, 04:59 PM
I talked to Harold this morning and after hearing about his personal experiences and what his books had to say, plus what i've read on the web, assuming that there are no extenuating circumstances on the site (water pressure above ~90 psi or line voltage below 110 volts) I'll be totally safe for runs up to 4000 feet from the controller to the valve with 18 gauge zone wire and a 14 gague common. If the water pressure is in the 50 - 60 psi range or the line voltage is closer to 120 volts than I should be safer for even longer runs


11-18-2001, 05:15 PM
Never said you wouldn't be safe, just that I wouldn't do it.


Don't forget to put loops in wire at every turn, and not to stretch it AT ALL. The problem isn't always just voltage drop. I worry more about settling ground and the wire stretching and breaking within the insulation.

I have a question:

What if you push the limit to save yourself time and money and the pressure changes on the site in 5 years or the line voltage drops for some reason. Wouldn't you feel badly that the 14 gauge would have continued to work but not the 18?

My own personal rule: Always use 14 gauge on commercial and 18 on residential due to changes beyone your control on commercial sites. More control on residential.

11-18-2001, 06:20 PM

Good tip on the wire and stretching, it's of particular concern up here where we have frost cycles. I make a point of minimizing elbows and bends in my mainlines and always make sure to lay wire loosley in the trench.

As for the possiblity that the water pressure might go up or the line voltage go down, my guess is that they will both go down over time and just as I'll take the possibility of the pressure dropping as time goes on when deciding how may gpm to run in each zone, I'll take the possiblity of the line voltage dropping into account, but I still think that I'll have a system that is easier (and cheaper) to install and service with the 18 gague / 14 gague combo.

If the line voltage drops from 110 to 100 or 95 volts and the solenoids start burning out, than I'll tell the customer the same thing that I told the customer who's water main was kinked 2 yrs after the system was installed....I took reasonable precaution in designing the system but I did not nor should I have taken an extreme case like this into consideration.