Voltage Drop and Conductor Size - Contractor Talk - Professional Construction and Remodeling Forum

TinkerGA · 02-10-2009, 07:37 PM

I am new to this site,love the comments.Have a question because I have never had such a long pull. Customer wants 9 (3 lamp) (60 watt) 120volt outdoor lights on 1 switch. Power source to first light is 42ft then 70ft,70ft,70ft,30ft,30ft,70ft,70ft,70ft for a total of 522ft. What size wire do I run? Will a 10AWG on a 30amp breaker be enough.I figured the voltage drop by length and amps betwwen each light. first light 42ft at 13.5amps second 112ft at 12amps third 182ft at 11.5 and so on using 120volts as a base even though PoCO VOLTAGE varies. Would like some feed back or good way to calculate.Still trying to learn.

walkerj · 02-10-2009, 07:43 PM

If this is a house, the lights most likely can't be installed on a 30 amp circuit.

#10's and a 20 amp breaker would probably work fine, but you could use #8's to the first light if it made you feel warm and fuzzy.

Magnettica · 02-10-2009, 08:25 PM

Here's an online calculator for voltage drop: http://www.elec-toolbox.com/calculators/voltdrop.htm

Speedy Petey · 02-10-2009, 08:41 PM

The calculator Mag linked is the one I like to use.

Guess what, for 522', @ 120v, @ 13.5A it is calling for #3. I know the load is incremental, but you still have a 120v load at 522'.
I'd say at least #6.

Can he use CFLs to lessen the total wattage?

nap · 02-10-2009, 08:58 PM

Quote:

Originally Posted by Speedy Petey

The calculator Mag linked is the one I like to use.

Guess what, for 522', @ 120v, @ 13.5A it is calling for #3. I know the load is incremental, but you still have a 120v load at 522'.
I'd say at least #6.

Can he use CFLs to lessen the total wattage?

Petey, what's the rules for running 240 for lights in resi? any problems?

If not, if Tinker can get 240 rated lights/fixtures (I know, luminaires (God I hate the new terminology with 12mm conduit and luminaires and all)).

that would drop the current so the voltage drop would require a much smaller conductor increase.

What do ya think?

Magnettica · 02-10-2009, 09:36 PM

Quote:

Originally Posted by Speedy Petey

The calculator Mag linked is the one I like to use.

Guess what, for 522', @ 120v, @ 13.5A it is calling for #3. I know the load is incremental, but you still have a 120v load at 522'.
I'd say at least #6.

Can he use CFLs to lessen the total wattage?

I probably got the link from you!

Speedy Petey · 02-10-2009, 09:45 PM

240v lights would help VD, but if he wants to use standard lamps that becomes a real issue.
He could use a multi-wire circuit to help lessen VD.

nap · 02-10-2009, 10:17 PM

I didn't know if they even made such buggers or not.

maybe some small HID fixtures would serve the purpose.

Is Marc back from France yet? Maybe he could bring over some 240 rated 60 watt incandescents and voltage rated sockets.

or how about a nap special install;

2-120 volt lamps in series. and then each group of 2 paralleled as normal.

TinkerGA · 02-10-2009, 10:21 PM

Thanks for the comments. I tried to get the customer to get 240v lights but he likes the ones he's already bought.I done the voltage drop calculation at first with 13.5amps at 522ft and got a #3 but that seems to be over kill then in increments and really a #10 seems to small , maybe I will go with a #6 just to be on the safe side.

nap · 02-11-2009, 12:29 AM

I would either act according to the voltage drop calc's or you are going to be responsible for any problems that may arise.
alternative; letting the (untrained and therefore, ignorant) customer make the call.

The only problem should be dim lights but depending on the exact circuit it can vary.

mickeyco · 02-11-2009, 12:29 AM

Quote:

Originally Posted by Speedy Petey

240v lights would help VD, but if he wants to use standard lamps that becomes a real issue.
He could use a multi-wire circuit to help lessen VD.

Question, how about a double pole switch ("on 1 switch") on a multi-wire, alternating the lights?

.