Complex voltage drop question?

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bclumen

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I am bidding on a res. site ltg. project with some really long runs to parts of the yard for fixtures and gfi's. I plan on exiting the house with 2 conduits w/ 1-20amp and 2-20a swd. ckts. underground to a j-box 150+/-' away. Then splice the outlet ckt. and 2 swd. ckts. each to 3 other longer runs 250', 260', 380' away. For the outlet ckt. should I size my wire on the longest run, 530+', @ 20 amps or is there something else here I should consider?
 
Man that is a LONG run... for a 20a 120 circuit... And a really long trench!

Under what type of load are they to run. Size the lighting for the actual load IMO. A low load you would hope....

The outlets what are they for, or are they just GP? Do they need to be operational all the time? 'Cause I might suggest a small transformer to bump up to 240 on #6 - then back down to 120 at the outlet. Otherwise you might be looking at 1000' of #1 to give it 120 at a full 20a at that length... Thats a really expensive outlet for the gardner.... (If thats what its for? Might be cheaper to buy him a generator to drive around... ;) )

Could they be fed from a second service on the property? I've done one where we had one service at a gate, and another for the house 1/4 mile up the driveway... :rolleyes: You could switch with LV or photo or clocks...
 
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bclumen said:
I am bidding on a res. site ltg. project with some really long runs to parts of the yard for fixtures and gfi's. I plan on exiting the house with 2 conduits w/ 1-20amp and 2-20a swd. ckts. underground to a j-box 150+/-' away. Then splice the outlet ckt. and 2 swd. ckts. each to 3 other longer runs 250', 260', 380' away. For the outlet ckt. should I size my wire on the longest run, 530+', @ 20 amps or is there something else here I should consider?
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GP at 530'+? Geesh. Although, I have met a few I wouldn't mind sticking that task to:grin:
 
You also need to remember whatever size you increase the circuit conductors to 250.122(B) requires you to increase the EGC to as well.

If you run 6 AWG for hot and neutral on a 20 amp circuit the EGC will also have to be 6 AWG.
 
dummy me

dummy me

bclumen said:
I am bidding on a res. site ltg. project with some really long runs to parts of the yard for fixtures and gfi's. I plan on exiting the house with 2 conduits w/ 1-20amp and 2-20a swd. ckts. underground to a j-box 150+/-' away. Then splice the outlet ckt. and 2 swd. ckts. each to 3 other longer runs 250', 260', 380' away. For the outlet ckt. should I size my wire on the longest run, 530+', @ 20 amps or is there something else here I should consider?
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What is a "swd" circuit?
 
As others have said, what are the loads? Are they going to be used simultaneously? If they are, then you add the loads to get the amount of amperage from the panel to the junction box. Calculate the voltage drop to the junction box. Then figure the individual loads from the junction box to the end of the circuit. Calculate the voltage drop from the junction box to the outlet using the reduced voltage (from the previous voltage drop calculation) at the junction box.

If the loads are not going to be used simultaneously, then I'd figure the longest run. You can figure the shorter runs using the larger conductor to the junction box then the proper sized conductor for the rest of the circuit.

Like Bob said, don't forget to upsize your ground.
 
Thanks for all the input! The power is for Christmas lights and i guess party's too. This will not be the first time I have run big wire to outlets.
 
If it is for Christmas lights, voltage drop is not too much of a consideration. Incandescent lights do not care too much the voltage with which they are supplied. Just remember that as the voltage drops the light output will be slightly less (and bulb life will be increased). Motor loads are a different story, since motors will try to supply their rated horsepower even with reduced voltage, which will increase the amperage draw. As others have said, base your voltage drop calculation on the load you would reasonably expect, not the amperage of the circuit breaker.
 
Have they though about using an inverter and solar battery charger? Or at least a trickle charger that you can downsize the conductors for? Christmas lights are usually night only, so they could recover the charge on the batteries slowly throughout the day, either with solar or a 2-5A trickle charger. That'd be only 0.6A on the 120V side +- inefficiencies. (5A * 14V = 70W; 0.6A = 70W / 120V)


Another thought - If you have an charger with an international-compatible input, could you run 240V and ignore voltage drop? The placard will say something like (90-240VAC 50/60 Hz), so anything between 90V and 240V is ok. Is that legit according to the NEC?
 
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I doubt the homeowner is going to want some rigged up way to get the power out there. Obviously, if he has a run that is 530' away, then he has a pretty large yard, and I imagine a large house and large wallet to go with it.

Things to remember, the large wire at 120V is probably not going to fit on the terminations, and additional splicing will be required. At 120V I think your asking for trouble.

Use three - 2pole breakers out of the panel and feed three 2-pole switches at Owner desired location (even though only two need to be switched, it makes it cleaner to have switches on all three). Run two 3/4" or even 1" conduits (conduits cheap after trench is dug) out to the 150' j-box location from the switches. Out of the J-box take the 240V SWD circuit out to each location. At each location set a 2KVA single phase, 240V primary - 120V secondary outdoor encapsulated transformer. You can even use the transformer taps to help keep the 240V circuit wire size down to a minimum out of the panel.

Looks like you could use #10AWG on the 530ft run, and #12 on the 400 and 410ft run. Using the taps on the transformer you might even be able to use #12AWG on all three circuits.

The smaller size conductor is certainly going to offset the cost of oversized wire, larger conduit, larger j-boxes, etc.
 
bclumen said:
I am bidding on a res. site ltg. project with some really long runs to parts of the yard for fixtures and gfi's. I plan on exiting the house with 2 conduits w/ 1-20amp and 2-20a swd. ckts. underground to a j-box 150+/-' away. Then splice the outlet ckt. and 2 swd. ckts. each to 3 other longer runs 250', 260', 380' away. For the outlet ckt. should I size my wire on the longest run, 530+', @ 20 amps or is there something else here I should consider?
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Yes, you could calculate the voltage drop to the actual current of the load. If you have loads at the j-box, then you can subtract those from the calculation of the remainder of the run only and calculate a separate voltage drop from that point on with the reduced current. Make sure that you take into account that the voltage at the junction point is already reduced, so subtract the result of your separate VD from that voltage to make sure you still have sufficient voltage at the service point.
 
If the "lay of the land" permits, I'd consider a remotely-located sub-panel, requiring a smaller quantity of large conductors, and branch out from there. Lighting can be remotely controlled if necessary.
 
haskindm said:
If it is for Christmas lights, voltage drop is not too much of a consideration.
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I would have to respectfully disagree. I've seen cases where a #14 was run from a panel to multiple receptacles for Christmas lights on a residence. Lights were run from a receptacle near the panel and from a receptacle at the far end of the house so that the tails of the light strings met in the middle. The lights plugged in close to the panel were noticeably brighter than lights plugged in at the far end of the house.

Martin
 
hmspe said:
I would have to respectfully disagree. I've seen cases where a #14 was run from a panel to multiple receptacles for Christmas lights on a residence. Lights were run from a receptacle near the panel and from a receptacle at the far end of the house so that the tails of the light strings met in the middle. The lights plugged in close to the panel were noticeably brighter than lights plugged in at the far end of the house.

Martin
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Wll, so what?
Some of are brighter, and some of us are dimmer but we still manage to have a conversation:D
 
My point was, other than being a little dimmer, there is no real problem with incandescent lighting and voltage drop, unlike a motor load which may be damaged by excessive voltage drop. If this is for Christmas lights only, "the juice may not be worth the squeezing" to make sure that voltage drop is kept to a minimum. Of course you will also need to take the voltage drop of the actual lighting string (and any strings into which it is plugged) to have accurate calculations.
 
haskindm said:
My point was, other than being a little dimmer, there is no real problem with incandescent lighting and voltage drop, unlike a motor load which may be damaged by excessive voltage drop. If this is for Christmas lights only, "the juice may not be worth the squeezing" to make sure that voltage drop is kept to a minimum. Of course you will also need to take the voltage drop of the actual lighting string (and any strings into which it is plugged) to have accurate calculations.
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Not to mention that those christmas lights will last FOREVER and EVER:)
 
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