Next Year's Christmas Lights

[pierhogunn]

This year I have reached a threshold of sorts with my Christmas Lights

I have tripled the number of Icicle Lights that I run on the 1st floor, (by zip-tying 3 strands together, and running al 3 strands in parallell)

I have doubled up on the lights on my bushes

wrapped all 3 columns in front of my house in lights, and I have outlined the window and door on my first floor in lights

These lights share a 15amp circuit with some of the lights downstairs, and on occasion this will trip the 15A breaker in my panel

When I built this house I had a 20A 220V circuit put in my garage / shop and would like to use this for next years Holiday Illumination

The outlet is a 4 prong dryer type plug and I would like to know how to safely split this to be 2 20A 110V connections, but do it after I run the 220V thing through a 40A 220V AC Water-heater timer so I can just run this thing w/out actually touching it after the initial programming.

Ideally, I would like to have all of this mounted on a board that I can hang next to the outlet on the wall, and run extension cords to the lights

My goal is to some day require the use of welding glasses to view my holiday extravaganza w/out causing permanent damage . . .

[crokett]

Hmm....

With a 4 wire plug what you have is 2 110V legs, 1 neutral and 1 ground. If you split the 120s then I think you've effectively created a shared-neutral circuit. As I understand it this is legal IF you balance the loads across the each of the 110v legs. So I think what you would have to do is come through the timer and then wire each of your 110 outlets so the hot leg goes to only 1 of the 110v coming from the timer. All the outlets would then share the neutral and ground. You'd have to do your best to balance the loads.

Or I could be way off-base.

[Hellrazor]

Splitting a 220 line like that is just asking for trouble.

[pierhogunn]

what happens when you don't balance the loads? the only reason I ask is that it is a simple matter to take the joiner bar off the top of the 20A 110V circuit breakers.

fire, shorting, something worse? wear and tear on the breakers, gound circuit, neutral line...

[Uncle Cracker]

What happens is that your insurance company will use it as an excuse to bail on you if you have a fire from any cause. You'd be amazed at what their investigators can dig up when they don't want to pay a claim.

Think about it... If this were entirely Kosher, every HD on the planet would have 4-prong plug adapters with 110v outlets on them. And that little "joiner bar" you refer to is exactly the reason most newer breaker styles now have but a single throw handle for a two-pole breaker.

[Tom Slick]

I think you could do it. the two 120v legs are out of phase so they don't have an issue sharing the neutral. in a normal 220v circuit the neutral isn't used and the neutral can be used to have a 120v circuit within the appliance.

I'm sure LCHIEN will be around soon to straighten us out.

[LarryG]

These lights share a 15amp circuit with some of the lights downstairs, and on occasion this will trip the 15A breaker in my panel

What's the wire size on your existing 15A circuit? If it's 14ga you're stuck, but if it's 12ga you can change the 15A breaker to a 20A.

[LCHIEN]

I think you could do it. the two 120v legs are out of phase so they don't have an issue sharing the neutral. in a normal 220v circuit the neutral isn't used and the neutral can be used to have a 120v circuit within the appliance.

I'm sure LCHIEN will be around soon to straighten us out.

I'm an electrical/electronics engineer so the underlying electrical principles are clear to me but I'll profess to not having a good knowledge of what the NEC says about household wiring.

But in a 4-wire 220V setup, it doesn't seem to me that there's a technical requirement to balance the load in the two legs.
In a three-wire setup (no neutral) it of course has to be balanced unless you have a ground fault.
In a four-wire setup wired two 120V circuits as the OP requests its really not much different from a two circuit setup except the common point for the two neutrals is at the load rather than at the breaker box. Since the loads are out of phase, balanced loads results in 0 current in the neutral (perfectly safe), and unbalanced loads result in the difference being carried in the neutral leg so it will always be 15A or less. Not dangerous provided of course the neutral leg is of adequate gauge wire, same as the two hot legs.

So technically, I think there's nothing wrong with it, should work fine, no balancing required. Basically I agree with Tom in a lot more words.

[LarryG]

I just put your question to our primary electrical consultant. He is a registered electrical engineer, in private practice, who specializes in designing all manner of building-type wiring (i.e., he literally makes his living with the NEC provisions for commercial and residential wiring close at hand).

Short version: there's absolutely no problem with what you want to do.

(This was actually a surprise to me; but I literally read your post to him over the phone, to be sure he understood all the parameters. I am fully confident that his understanding of the question is correct.)

He says there's no problem whatsoever with a shared neutral. It's unusual in a residence, but he does it all the time in commercial buildings.

There's no reason to worry about balancing the load.

You can split the breaker if you wish; at the moment, it doesn't matter if you do or don't. But he advises leaving it as-is since the 2008 version of the NEC, which is forthcoming, will require paired-up breakers on circuits that use a shared neutral.

There IS one caveat, and it's an important one: your shared neutral should be split into two pigtails, with one going to one of the silver screws on each of your two 120V receptacles. Connect the two pigtails to the shared neutral with a wire nut and then connect the two pigtails to the two receptacles (one pigtail to each receptacle). Do NOT connect the shared neutral conductor directly to either outlet, and do NOT use the second silver screw on one outlet to jumper over to the other outlet, as is commonly done in residential wiring. The reason is that if you disconnected the neutral from one of the two outlets, you could possibly end up with 240V on the remaining outlet.

He is guessing your existing 240V outlet uses a double-gang box. If it does, you can install the two 120V receptacles into this and do all your wiring changes right there.

Lastly, I specifically asked him if there is anything about this that is shady with respect to the code, anything that might later come back to bite you in the butt. He said, quite emphatically: Nope, no problem at all. The use of pigtails, so both circuits will be fully operational independently of the other, is the only special requirement. He is also assuming that the wiring is the correct gauge for a 20A breaker and that you have no plans to change the breaker to a larger size.

[eccentrictinkerer]

It would be much, much safer to use the dryer outlet wiring to power a sub-panel. You can get one at at the BORG for under $30.

Then use appropriate breakers 15 or 20 amp. If you wire directly to the dryer outlet you have the potential for 30 to 50 amps.

Recipe for disaster if I understand your proposal correctly.

[crokett]

Glad somebody else chimed in. I coulda sworn there was a requirement to balance the loads somewhere in residential wiring but apparently not.

I do like tinkerers suggestion about using the 220v outlet to power a subpanel and split the circuit from there. In addition to what he posted you also have the advantage of being able to shut off each circuit separately if you need to.

[LCHIEN]

I think tying the breakers together is optional in this scenario. While it won't hurt or harm either way, both breakers will be opened if one side trips. You then have to figure out which side tripped. It would be simple to unload one side at a time and reset the breakers... if it trips its that side, if not, its the other side.

[eccentrictinkerer]

If you plan to continue with this project as stated, PLEASE put a 15 amp fuse or breaker in series (a breaker-type plug-strip would work) with each line (preferably near the dryer outlet). If you develop a short in a light string or extension cord without a 15 amp fuse, it will seem more like the 4th of July than Christmas.

What you are doing is technically feasible, but totally not to code and very dangerous.

JMO, Good luck.

[Jeffrey Schronce]

What happens is that your insurance company will use it as an excuse to bail on you if you have a fire from any cause. You'd be amazed at what their investigators can dig up when they don't want to pay a claim.

Completely, totally, 100% incorrect. Stupidity is one of the main perils covered under a homeowners policy.

Fraud and/or arson is the only thing you are going to do to prevent coverage from being extended for a fire.

[Tom Slick]

What you are doing is technically feasible, but totally not to code and very dangerous.

I don't understand what part isn't to code or inherently dangerous.