1 Leg Sub Panel Question

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djw2112

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Hi, i am adding a electrical sub panel off my main panel. I only want to use one leg not both. Meaning that there are two black wires, one common wire, and one ground wire comming from the main panel, i only want to use 1 black, 1 common, 1 ground.

Question - does it matter which lug in the sub panel i conntect to right or left when using only 1 leg?

This is the exact box i have in the pic (the one that will be the sub panel), i got this pic off the net showing the full hookup with both legs hooked up as an example of a full subpanel install using both legs. I only want one leg (black).

subpanel2.jpg


Thanks :)
 
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Mark_K5LXP

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The two legs are 120V opposite phase. Across them is 240VAC. Connecting them together would empirically test the main breaker.

Edit: unless you mean just use one leg and jumper the breaker slots together in the sub panel.

Mark B.
Albuquerque, NM
 
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Wizard46

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I would go ahead and run the other wire. Running two is the same as running one, same work and cost will be a just a couple of $ for wire. Later you will probably want the other wire and would be a lot of trouble to re do the job.
 

Pedro Dog

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Look at the main panel loads for the 120V CBs and determine which ones run the most. If you have leg 1 running more often, then use leg 2 to power the sub panel to balance the load. It really doesn't matter but balancing the load on the two legs reduces the total current flowing through the neutral.
 

Gary RV_Wizard

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Choice of L1 or l2 is a load-balancing thing. As Pedro Dog suggests, try to determine which leg has the lowest usage, both typical & peak, and borrow your subpanel power from that.
 

djw2112

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Thanks everyone, great info from all, really appreciate it. Yeah i think i will run both afterall, it makes sense in case i need to use more slots on the sub panel later.

It actually works out pretty good (i think) When i first hooked this up i ran the service wire from the meter to the bottom of the main breaker rather than the main lugs, works the same i believe.

So now i can use the original main lugs to run my jumper out the top of the one panel and into the top of the other panel and use the other panels lugs. I will have to get a two barrel adapter for the common wire but thats ok.

So am i right does that work out the same, the bus is still hot with the main breaker regardless if the service is connected to the main breaker or the lugs, is that correct? This box has a dedicated bar for the breaker so it cant go anywhere else. Its been this way for 4 years and no issues.

So something like this..

subpanel4.jpg
 

The Wanderer

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If I'm reading this correctly, do not come straight off the lugs in the main panel. The wiring to the sub panel needs to be protected with an appropriate sized circuit breaker in the main panel.
 

Jim18655

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Besides a sub-feed breaker you also need a ground wire to the sub panel and separate the neutral/common from the grounding conductors.
 

John From Detroit

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The two legs are 120V opposite phase. Across them is 240VAC. Connecting them together would empirically test the main breaker.

Edit: unless you mean just use one leg and jumper the breaker slots together in the sub panel.

Mark B.
Albuquerque, NM

Exactly And you are correct I should have been more specific.
Jumper the SINGLE LEG to both terminals in the Sub panel is what I meant.
You don't even run the 2nd leg.. Or just buy a 120 volt sub panel. either method works but if you already have the dual leg box.. Jumper IN THE SUB PANEL.
 

djw2112

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Thanks everyone, again great stuff, alot to consider here.

There will be a 100 amp circut breaker in the sub panel i already have one. Also i am aware that the sub panel needs to be grounded by using a add on ground bar which i also already have.

However, i found out today that even if there is no code enforcement out here in the country, if something should happen my insurance company wont cover the loss. So just to be safe i called and made an appointment for next week for an electrician to come look at what i have.

Meanwhile i can mount the sub panel and let him do the wireing from one to the other, then i can take it from there and run the circut out to the outlets. As long as both panels are fed correctly i can do the rest. Or he can tell me what to do exactly as part of his call out fee. Plus he can do the quick disconnect and reconnect of service if we need that. I think that is probably the best move for me at this point. :)
 

Gary RV_Wizard

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However, i found out today that even if there is no code enforcement out here in the country, if something should happen my insurance company wont cover the loss.
Just to be clear, only if that "something" is somehow related to a panel wiring fault. Your policy fine print defines reasons for denial of coverage and faulty DIY work is not typically listed.
 

djw2112

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The sub panel does not need or require a separate ground rod.
Thanks, correct just a small mini bus bar in the sub panel which i have. The ground wire should come from the main panel so there is one point of ground as i understand it.

Just to be clear, only if that "something" is somehow related to a panel wiring fault. Your policy fine print defines reasons for denial of coverage and faulty DIY work is not typically listed.

Thanks for the clearification, good to know... ill check the policy. :)
 

Gary RV_Wizard

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If you filed a claim for a loss, the insurance adjuster is not going to immediately ask for all prior building permits and inspection records. The issue only comes up if there is reason to believe faulty workmanship caused a problem and your insurer is considering suing the installer's insurance for damages (called subrogation). Obviously he cannot sue you, his policy holder. Questions of who did what come up in liability lawsuits, but not in routine loss claims. Even then, you are almost always covered unless you violated some explicit clause in your policy. The insurer may, however, refuse to renew your policy. So read the fine print clauses about denial of claims and act accordingly.
 
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