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Powering Christmas Lights - Calculating Amps and Circuit Requirements

Powering Christmas Lights - Calculating Amps and Circuit Requirements


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Old 12-12-16, 05:11 PM
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Powering Christmas Lights - Calculating Amps and Circuit Requirements

I put up a pretty large amount of Christmas lights. I think that this year is the most I've done. I had wanted to use LEDs, but they are still very expensive. A couple of seasons ago, I had two 20 amp outdoor outlets installed. Even with the additional circuits, it appears that I don't have enough capacity. I was hoping to get some help figuring out what I need in terms of circuits/amps. I don't think that my present configuration is sufficient.

I am not sure of the exact number of lights that I have installed, but I calculated an approximate figure:

1 tree with ~20,000 lights
1 tree with ~18,000 lights
Front shrubs with ~4,500 lights
Icicle lights ~600 icicle lights

Total lights: ~43,100

I use sets of 100, and they apparently draw 0.32 amps per set. If my calculation is correct, that means that my lights are drawing ~138 amps. That seems high to me, so maybe I'm calculating incorrectly. I have 200 amp service. If that is accurate, is it concerning that I am drawing that many amps?

As it stands right now, I am powering the lights with the following circuits:

Dedicated to Outside:
2 - 20 amp receptacles
2 - 15 amp receptacles (1 of these receptacles is fed from my swimming pool subpanel - 40 amps)

Shared (These outlets are not dedicated to the outside. They were installed when the house was built in the 80s and are branched from indoor circuits.):
3 - 15 amp receptacles
1 - 20 amp circuit w/ 15 amp receptacle

To power the trees satisfactorily, I have to use 4 different circuits for each one. I have noticed that when the circuit is near capacity, the lights start to look dim/yellow. I assume that means I am drawing more than 80%, which I know is not good. When I've see that happen, I've shifted lights to other receptacles. Would it be wise to get a clamp meter and measure the draw on each circuit? Can someone help me make sense of the numbers (amps/circuit requirements)?

I wanted to add another 20 amp circuit. I thought that it would be easy to install one in my pool sub panel, but it is only 40 amps. Since there is already a 15 amp receptacle there, I assume that I only have room for an additional 15 amps. Is that correct? Is there a better way for me to power everything? I wish I had given this more thought, but I never realized that the lights drew this much current.
 
  #2  
Old 12-12-16, 05:20 PM
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A 100-count string of incandescent mini lights runs at 40 watts which is .33A
So your calculation of 138 amps is very close.

That means roughly $1.90 per hour to run all your lights.... based on .11/kwh.

Is your pool panel 40A at 240vac ?
If yes.... you can install two 20A receptacles. One on each leg.



You're too far south for me or I'd stop by and check out the display.
 
  #3  
Old 12-12-16, 05:26 PM
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Wow. Just Wow.

You must post a pic or two.

Your calculation is correct; but I suspect the .32 amp figure may be a max and typical may be less.

With 200 Amp service you can actually draw up to 400 amps at 120 volts (since the 200 figure is at 240), but that assumes perfect balance between legs. Nevertheless it means you have more headroom than perhaps you thought.

Likewise, if the pool subpanel is 240 volt you would actually be able to draw up to 80 amps at 120, again assuming perfect split between the two legs.

In any case, even if subpanel is 120 volt, you can add another 20 amp circuit assuming the pool isn't operating. The individual circuits in a panel can add up to more than the capacity of a panel since most circuits don't operate anywhere near full load most of the time. Your lights are an exception. But if the breakers don't trip, you are not overloading anything.

I suspect your dimming may have to do with your extension cords. You need 12 gauge cords if they are short and 10 gauge or heavier if they are longer.

A clamp meter would be instructive and help you evenly distribute the loads across circuits, but you could even use a Kill-a-watt meter, it's cheaper than a decent clamp on. Note, if you go with a clamp on, you need the adapter that splits the line into separate wires for measurement, since if you just go around an extension cord, it will read zero due to offsetting current flows. The adapter often comes with the meters.

Please do post some pics...and give us a hint as to what your electric bill for December is!

http://www.doityourself.com/forum/el...-pictures.html
 
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Old 12-13-16, 09:32 AM
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Thanks for the replies. That is very helpful. My pool is on a double-pole 40A breaker, so if I understand correctly, that means it's 240 vac. I have 2 spaces left at the subpanel. Am I able to add two 20A outlets in addition to the 15A one that is already there, or do I only have enough capacity for an additional 20A? That's where I get confused. If the receptacles are 120v, do I technically have 40A capacity on each leg? My pool is closed, so the receptacles will be the only active circuits.

What should I use to mount the receptacles? I saw that Arlington makes some type of stake, but it's intended for an underground feed. With how close I am to the subpanel, I don't think I would need to bury it. I can use LFNC.

I've posted a picture of my pool sub panel for reference. I've also included one of my main panel. I would install the outlets there, but I've actually never worked on a live panel. I'm confident that I would know what to do, and what not to touch, but I've been apprehensive about it. I'll have to do it eventually, and I don't know why I'm nervous. At least with the sub, I can cut power at the breaker.

As soon as I get everything situated, I will post some pictures! I'll let you know what my electric bill looks like!

Subpanel (Pool Sub is on Bottom Left - Click Image to Enlarge)


Main Panel
 
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Old 12-13-16, 11:55 AM
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That means roughly $1.90 per hour to run all your lights.... based on .11/kwh.
That's low for power these days, surely power in NJ isn't that cheap?
 
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Old 12-13-16, 01:16 PM
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Electrically you can add two 20 amp circuits to the pool subpanel. What I don't know is if there are special code provisions around pool panels and especially if the receptacles would be anywhere near the pool) Others here will know....

Since we can't see the area around the panel, it's hard to advise how to mount receptacles, but they need to be in weather tight boxes with in-use covers, and of course need to be GFCI protected.
 
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Old 12-13-16, 05:41 PM
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Electrically you can add two 20 amp circuits to the pool subpanel. What I don't know is if there are special code provisions around pool panels and especially if the receptacles would be anywhere near the pool) Others here will know....

Since we can't see the area around the panel, it's hard to advise how to mount receptacles, but they need to be in weather tight boxes with in-use covers, and of course need to be GFCI protected.
Can I add the two 20A circuits in addition to the 15A that is already there? I don't think it would be easy to convert the existing 15A to 20A, because there is 14 AWG running to the pool lights. I am a pretty good distance from the pool, but I am not familiar with the applicable code. The subpanel is mounted to a pine post, but there is no room for any other receptacles. It already has my low voltage lighting transformer, filter control, and salt water generator mounted to it. I wasn't sure if there was some type of stake that they sell for that purpose. I don't even care if it's a temporary install. I'd be willing to remove/reinstall each season.
 
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Old 12-13-16, 06:04 PM
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Yes you can install 2 20 amp circuits in addition to the 15 amp.

If there is no room on the pole, the easiest thing would probably be to sink another post close by, like a pressure treated 4x4 and mount the receptacles to that. Just don't hit any buried lines. You could run Liquid tight from the panel to the weather tight box or boxes if they are close.

Or remove some of your other gear, install a piece of pressure treated plywood, and remount the gear plus the receptacles on the plywood.
 
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Old 12-14-16, 06:26 PM
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I am going to add the two 20A receptacles tomorrow at my pool subpanel. I have a few questions, and I just wanted to get clarification:

1. My understanding is that it's okay for two circuits to share one box. I wanted to use a 2-gang box with both receptacles. Is that permitted?

2. I assume that I need to run a separate ground wire for both circuits. Should the ground wires be left separate in the box, or do they need to be tied together? I was under the impression that they should be left apart, but I just wanted to make sure.

3. Can I run 6 12 AWG THHN/THWN connectors (2 hots, 2 neutrals, 2 grounds) in one 1/2" LFNC, or do they need separate conduit? I can buy 3/4" if that is required. Am I allowed to run 2 circuits in the same conduit?

Thanks in advance for any input.
 
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Old 12-14-16, 06:47 PM
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Two circuits can share same box. Both need to be GFCI. I'd get a deep box if you can as the GFCIs take up a lot of room. Box needs to be at least 21 cubic inches.

You only need one ground wire. Tie it to both receptacles.

You can have up to 9 #12 in 1/2 inch LFNC.

Yes you can run multiple circuits in one conduit.
 
 

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