Wiring size for shop lights

[Alaska4Ever]

I have a 50 by 90 pole barn with the first 50 x 50 being the shop and the remaining cold storage/ animals / my wife's area... enough said.

I am in the process of putting up lights in the shop. The power comes into the shop in the back portion of the shop ... approximately 60 feet from where the light switches will be. When i run the romex to the front of the barn by the we are looking at 60 feet plus the rise of 10 feet on both ends making it a total of 80 feet. This just gets power to the switch then the power will have to continue through 4 lamps that will each pull about 2 amps each so a total of 8 amps. This is one circuit.

Question: normally I would have said run 14ga on 15 amp breaker or at the max 12ga on 20 amp breaker. When i run the voltage calculators for that distance with this amperage it says i need 10 ga wire. WHY! sound like overkill to me and the NEC says 14 or 12 should be enough.... can someone help... I DO NOT want to run 10 ga wire but also want to be safe.

NOTE: I am in a rual setting with no building codes but would like to do it correctly 1) for safety 2) I think it helps in adding confidence in a sale should that ever occur.

I have more questions on the specifics of how to wire but will save that for a different topic

Thanks in advance.

 

[AZ Garage]

This is what I'm getting:

"A maximum distance of 103.68 feet will limit the voltage drop to 3% or less with a 12 AWG Copper conductor delivering 10 amps on a 120 volt system."

I've assumed a few things, as you can see.

#10's would be fine if you were going long distance and needed to account for voltage drop.

Which VD Calculator are you using?

 

[zmaxmotorsports]

You could run it all with 12/2 and feed it on a 15a breaker if youre really worried about the voltage drop.

 

[Alaska4Ever]

AZ Garage-- I have used many some are not so helpful the one i am getting the information from is the

followinghttp://www.electricaltechnology.org/2014/04/electrical-wire-cable-size-calculator.html

Another question for lights can I use the 5% drop as this seems to help with the wire size... bottom line it looks like 14 gauge is out.

Second question-- stay with me here as I try to explain how I am calculating one way wire run to make sure i am doing it the right way.

1. 50 x 90 barn-- Front 50x50 is the shop--- Power comes in 10 feet beyond my shop boundary in my large 90 foot barn
2. I will run the conduit inside for all electrical but am using romex to get from the breaker box to the font of the barn to supply the switches to save money on conduit and wire.
3. I calculated the total one way run this way.
a. breaker box to ceiling -----------------------10'
b. over to the shop wall partition --------------10'
c. across the barn the attic to front wall--------50'
d. power down to switch -----------------------10'
e. outgoing power back to up wall to ceiling---10
f. across ceiling to 5 lights (2 amps each)------50

I was thinking about a three way switch on the back wall but may not do this for ease of installation and plus I would think this would add even more length

So with all the numbers added up it is 140 feet for one row and the subsequent other rows would be even longer as you transition further from the switch across the the ceiling in the 50' barn.

Does this sound right? With that info in the above calculator with 5 drop and only 10 amps at the end of the string the calculator is saying 12 ga --- with 3% it jumps to 10 ga --- that just seems unreal.

 

[Alaska4Ever]

on a different note I would think that the plugs could easily be done with 12 ga as they would not all be used at once like the lights so the amps draw would be OK at least that is my thought maybe I missing something there as well... sure hope not as I wanted to use only 12 ga-- but want to be safe as well.

Shop use is typical shop use for home owner-- some wood working and such but not on a commercial scale or homeowner production set up. The big barn is nice but is a curse sometimes as well... Large area in -40 temps creates other issues.

 

[woodzy]

This might be a reason to use low voltage and a relay - you run power to the light and then low voltage to all the switches - you will reduce the length of the wire by a bunch and also save you a lot of money.

So - run maybe 14 gauge to the center of the lights and it goes to a latching relay. Then you run some low voltage transformer off that circuit and run low voltage wires to everywhere you want a switch. When you turn on - it energizes the relay and send 120 volts to each light. At any switch you hit the off button and the lights goes out. You have just saved a boat load of money...

 

[Cmreschke]

Honestly I wouldn't sweat it. I would run the 14 for the lighting ckt. If you really want to run 12s then feel free but I would not put in 10s for this run.

 

[zcar751]

I calculated it to be a 12 guage requirement. What kind of light fixtures are you using that draw 2 amps each? The standard 8ft t8 4 bulb florecent light is less than 1 amp. Unless you have 14+ foot ceilings you don't want any type of highbay fixtures because of light defussion.

 

[Bigbandguy]

I think I would compromise and run #12 to the switch and then wire the light string with # 14 .. I assume that is legal. I am quite sure a sparky will issue a correction if one is needed.

 

[CJ7VFR]

I think I would compromise and run #12 to the switch and then wire the light string with # 14 .. I assume that is legal. I am quite sure a sparky will issue a correction if one is needed.

If you use a 15 amp breaker it would work. You can't use 14 AWG wire on a circuit that is using a 20 amp breaker.

Jim

 

[matt_i]

A T5HO fixture will be 54W/tube x 4 tubes (typically, can be more or less) = 216W.

Very close to 2A per fixture.

 

[Cmreschke]

Might consider running 14 to the switch and 12 to the lights from the switch. Then land it on the 15 amp breaker. There will be less confusion on any future owners part. If you run 12 to the switch and 14 to the lights someone down the road may just reland the wire on a 20 amp breaker not knowing there is 14 in the ckt.

 

[mbatarga]

It makes no sense to run the longest length of wire with the smaller gauge - in effect you are increasing voltage drop with that design. I'd suggest using 12 AWG the full run.

 

[Cmreschke]

You realize we are also talking about an issue that really isn't an issue at all. In houses all across America line length for 15 amp cks far exceed 150' easily. From panel to last receptacle can hit over 200 feet and it's never a problem or a concern. Lighting ckts in Comercial buildings do this as well for 20 amp ckts.

I don't condone running 2 different sizes of wire in the same ckt, but if it's going to be done put the smaller guage wire at the panel so someone doesn't hook 14 guage wire to a 20 amp breaker.

Running the whole ckt in 12 solves that sure, so he hooks it up to a 15 amp breaker and in 15 years someone puts it on a 20 cause they add more lights. I'll bet line length won't be a consideration then (shouldn't really be now either)

 

[tfalk]

Are you seriously considering running a 60 foot length of lights with only 1 switch? I'm thinking you might be better off running it using 3 wire with a switch on both ends. Panel to switch to daisy-chained lights to switch, 1 total run instead of a long run from panel to switch, then running backwards switch to lights...

 

[Alaska4Ever]

Are you seriously considering running a 60 foot length of lights with only 1 switch? I'm thinking you might be better off running it using 3 wire with a switch on both ends. Panel to switch to daisy-chained lights to switch, 1 total run instead of a long run from panel to switch, then running backwards switch to lights...

Yes that is the preferred method and was my original plan until I read about Volt drop and thought that the traveler wire just added to the problem. Basic question is does the increased voltage drop increase the chance of fire. I know it affects motor efficiency and life. Obviously a 3 way is what I want.

Cmreschke has a good point and one that I have thought about --- houses all across the country violate these calculators volt drops ALL THE TIME. When I talk to the the electrical engineer at work he listened but did not say anything and continued to help me design

 

[Alaska4Ever]

This might be a reason to use low voltage and a relay - you run power to the light and then low voltage to all the switches - you will reduce the length of the wire by a bunch and also save you a lot of money.

So - run maybe 14 gauge to the center of the lights and it goes to a latching relay. Then you run some low voltage transformer off that circuit and run low voltage wires to everywhere you want a switch. When you turn on - it energizes the relay and send 120 volts to each light. At any switch you hit the off button and the lights goes out. You have just saved a boat load of money...

The electrical engineer brought this up... he called it using a contractor... I understand the concept but do not really understand the how to wire up and such.

 

[woodzy]

I will ask a buddy of mine who entire house has low voltage wiring for all lights. I'm sure he can draw up a sketch and I will upload it. I believe this is your best solution.

 

[manwithtools]

Yes that is the preferred method and was my original plan until I read about Volt drop and thought that the traveler wire just added to the problem. Basic question is does the increased voltage drop increase the chance of fire. I know it affects motor efficiency and life. Obviously a 3 way is what I want.

No is the basic answer to the increased risk of fire. The circuit breaker protects the wire from overloading and becoming hot enough to cause a fire. Too long of a circuit's main effect is reduced available voltage to appliances that might be sensitive to it.

Consider that the common design practice is to limit voltage drop in a circuit to 3%, but most equipment will operate on plus or minus 10% in supply voltage. That is why most applications work just fine with longer circuits that mildly violate the 3% rule.

 

[manwithtools]

The electrical engineer brought this up... he called it using a contractor... I understand the concept but do not really understand the how to wire up and such.

Actually I'm sure he suggested using a "contactor" not a "contractor". A contactor is a relay, plain and simple. There are specific versions rated to use as lighting contactors.

 

[woodzy]

I think you look at the diagram here on page 7 it will show you how to wire it.

https://www.vikingelectric.com/Images/img/043180/GE%20RS2-37.pdf

You can purchase the switches / latching relay here

http://www.kyleswitchplates.com/ge-low-voltage-lighting/

You will need a 24 volt transformer which I think the same as a doorbell transformer 24 volts AC.

You can add as many on / off switches as you want - you just need to run three wire between switch and relay. You can use any small three conductor wire.

 

[ddawg16]

My take (for what little it's worth)

I'd be looking at different lights. The LED stuff has really come a long way. While it might be more expensive, It will draw less and last longer. A point you appreciate when your lights are up high.

NO way I'd have just a single light ckt. The ground floor of my garage is 20x25....and I have 3 zones (total of 8 6" cans). 75% of the time I'm only using the lights in one zone.

Instead of running that much wire, I'd be looking into smart switches. No reason your shop shouldn't be setup with wireless and some type of smart interconnect, like ZWave or one of the others. In the long run it means you can turn the lights on and off with your smart phone. Becomes really nice when your in the house and you decide you really don't want to go back out to the shop but the lights are still on.