Help on calculating Wire Gauge for outdoor screen

[federico muelas]

Hi Everyone,
I have a technical question regarding calculating the wire gauge needed for a large size custom made screen I’m working on.

This is the dilemma:
The screen uses a maximum of 9.2 amps @ 120 VAC, Single phase, the length of the cable will be 150 feet. If I calculate the gauge needed it calls for a #10.

But this is the catch, the screen is made of 28 panels that connect to the main power line every 6 feet, meaning the current falls progressively as it’s being used along the 150 feet. I.e. at 3 feet a maximum current of 9.2 amps, at 6 feet - 9.14 amps, at 12’ –8.85 amps, at 18’- 8.49 amps…. at 30’ 7.58 amps and so on. I’m including a drawing for reference.



Then If I recalculate the current based on these distances, i.e 9.2 amps @ 3’ or 0.05 amps @ 150’ I always get #14 AWG wire.

So this is my question, is it ok to use #14 awg wire for the whole screen?

Thanks everyone!

Federico

[dacflyer]

what is this screen ?? door screen ? bug zapper screen ? or electric fence ?
clarify for us please.

[jwax]

Appears to be a large display consisting of 28 panels, 120 VAC each, with different current draws for each.
You can use #14 gauge to feed the screen, and technically, use smaller and smaller wire between each panel because the current requirement, as you pointed out, decreases.
Much like you have large wire entering your house power panel, but smaller gauge wire distributing smaller currents throughout the house.
#14 gauge throughout is fine.

[haklesup]

Use #12 as the main power cord and if you want to save a few bucks, #14 between the panels. However, I would just buy a roll of #12 lamp cord or cut up some heavy duty extension cords and use that throughout. #10 is usually for 30A or50A loads like a dryer, stove or oven. Solid core like Romex or stranded wire depends on the J boxes and terminals you use as to which is better. SOlid core makes better terminations but stranded is far more flexible

Consider house wiring. I can use #12 wire for at least a hundred feet of 120V, 20A branch circuit. Use the electrical code tables rather than some formula, you're over engineering this.

Now if you were powering with low voltage, high current DC, you would need that thick wire.

You can also consider other connection patterns from that series daisy chain you have, some combination of series and parallel.

[federico muelas]

Hi haklesup , jwax and dacflyer,
Thanks a lot! This is for a custom made LCD outdoor display for a Public Art Project for the New School of Architecture at UNM, in Albuquerque. You can check the project at
www.federicomuelas.com/blue_flower

Stranded wire will be preferable since we need for the cable to have some flexibility, I think what I would do is to use #12 stranded wire for the first 9 panels, #14 for the following 9 and #16 for the last 10 panels.

what about outdoor 120VAC @15 amps with three prongs connectors?. I have been looking into the TYCO connectors but they are kind of bulky (and quite expensive, and I need 28 sets) , I was looking for some rubber connectors and then i could seal the connection with heat shrink tubing or self fusing tape.

Thanks again guys.
F

[haklesup]

You realize TYCO owns at least half the passive and connector market. Your description is a bit too vague about the connector.

In any case, make sure to plug it into a GFCI protected circuit

[federico muelas]

Hi haklesup,
I was thinking more in something like the rubber circular connectors from Amphenol (http://www.newark.com/jsp/search/produc ... B100000001) . They fit from #14 to #18 AWG wire.

They fit really well on the conduit we are using and once the pair is connected they seal quite well. The problem is that they only hold up to 8 amps. so I either find something similar at a higher amperage or use a 6 connector plug and pair them (would this work?)

Another possibility would be using the following sure seal connectors, I haven’t try them myself but they are rated for 15 amps
http://www.peigenesis.com/en/shop/part- ... 97680.html

you’re right on the GFCI protected circuit, we would talk about this to the electrical inspector at UNM that will help on the connection of the screen to the main power.

Thanks haklesup!
F