Keep Me From Burning Down My Shop - HaHa

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Forum topic by Matt posted 03-30-2009 10:21 PM 1620 views 0 times favorited 35 replies Add to Favorites Watch
View Matt's profile


181 posts in 3396 days

03-30-2009 10:21 PM

Ok, here is what I have going on. I am putting electrical outlets back into my shop after the drywall and insulation was installed. I found out there were two 20 amp breakers for my shop.

After investigating:
1. I see there is a single 12/3 with ground (black, red, white, green) running to the shop. (Two hots, neutral, ground) right?
2. I have a red wire running out of one breaker and a black running out of the other.
3. It looks like they used the (red, white, green) for one circuit, and (black, white, green) for the other.
4. I left the garage door wired to the (red, white, green) and also installed a flourescent light fixture (got three more to do) on this circuit as well.
5. I installed a single wall outlet on the (black, white, green).
6. I noticed when I turn on the circuit ON (black, white, green) and leave the (red, white, green) OFF it behaves accordingly.
7. When I turn the (red, white, green) ON, and the other OFF, the (black, white, green) circuit also has power.

What could I have possibly done wrong? I put my multi-meter to everything and I’m pulling 124v from black to ground, red to ground, and also on the wall outlet 124v from black to white. (My house has always read 124v ‘ish since we moved in)

I disconnected the opener and lights from the (red, white, green) circuit and they both still read ‘hot’ when the one circuit is turned off. I measured this from the first splice in my shop where is enters the structure from the house feed. Argh! I keep the breakers to the shop turned off unless I’m in there working, for fear of burning it down. I only started wiring the lights yesterday.

-- Matt - My Websites - - Hand Tools :: - Small Shops

35 replies so far

View Karson's profile


35125 posts in 4424 days

#1 posted 03-30-2009 10:30 PM

On 220 circuits. The red and black are hot leads. if you only use one with the common then you get 110V across the red and black you have 220 V

Your OK on what you found. You have two 124V circuits using 1/2 of the red/black pairing.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware soon moving to Virginia †

View Matt's profile


181 posts in 3396 days

#2 posted 03-30-2009 10:36 PM

So, it’s ok that when one circuit is turned on both of them are hot? But when switched oppositely one of them is not hot? I’m just making sure this is OK.

Thanks guys. Wow, I actually have 20amp 220 out there. Hahahaha, what is that good for? Not much, I suspect!

-- Matt - My Websites - - Hand Tools :: - Small Shops

View John Gray's profile

John Gray

2370 posts in 3909 days

#3 posted 03-30-2009 11:03 PM

My 2 cents, if I were you I would contact a licensed electrician.

-- Only the Shadow knows....................

View marcb's profile


768 posts in 3697 days

#4 posted 03-30-2009 11:07 PM

Sounds like the breaker is bad and won’t shut off. I’d try to swap the breaker.

View Matt's profile


181 posts in 3396 days

#5 posted 03-30-2009 11:09 PM

When I turn them both off, all the power is off in the shop.

-- Matt - My Websites - - Hand Tools :: - Small Shops

View Brad_Nailor's profile


2539 posts in 3981 days

#6 posted 03-30-2009 11:18 PM

I have the same config in my garage shop I think. There is a feed from my panel that is 220 Romex (red, black white and green). At the panel the red and black are on separate 20 amp 110 breakers and on the shop side the red and black (green and white) are separated on two duplex outlets giving me two separate 110 20 amp circuits on one wire. This works out pretty nicely for me so I can run my dust collection on one side and the power tool on the other. Be careful my friend…electricity bites…I have allot of contractor friends and I always call my electrician buddy whenever I do anything more dangerous than changing an outlet or a switch!


View wdkits1's profile


215 posts in 3376 days

#7 posted 03-30-2009 11:28 PM

Hi Matt
1 Check to see that the hots from the panel (black and red) are on different legs ( one breaker above the other ).
If they are then you do have 220 out in the shop.Check this with a meter at the first j box.

2 If you don’t have 220 between the red and black that means that both circuits are on the same leg which will put double the load on the neutral which is not a good thing.

3 If you do have 220 then what you have to look for is a loose or broken neutral which would cause a backfeed from one circuit to the other when one circuit is off.

-- Mike --

View sIKE's profile


1271 posts in 3777 days

#8 posted 03-31-2009 12:12 AM

Sounds like you got the neutral hooked up wrong on one of the two circuts.

-- //FC - Round Rock, TX - "Experience is what you get just after you need it"

View sandhill's profile


2128 posts in 3947 days

#9 posted 03-31-2009 01:33 AM

Matt, Check the green to a ground like a water pipe or a metal box that is hooked to true ground and let me know if you get ANY voltage at all. Measuring from red to black you will mot likely get 220 it they are coming from two different lugs. If they are the same circuit you will measure “0” or real close to it. It sound like you have looped the hot leg back to the same source some how, or a loose or broken ground.

View Matt's profile


181 posts in 3396 days

#10 posted 03-31-2009 03:06 AM

I have disconnected things all the way back to the house. With the lines disconnected at the box (about 3 feet from my panel), I checked for voltage in the red and black about 1 foot from the breakers. When the breaker with the black wire is on I get power only to the black circuit. when I turn it off and turn on the breaker with the red wire, I get voltage in both circuits. Strange. They aren’t hooked to anything at this point. That stuff was installed that way when I bought the place 18 months ago. Nothing is looped that I can see. That is unless they did it on purpose. Looks like they used lots of 12/3 and shared the wire all over my house to save some money or time or both or something.

I’m really close to having someone pull both 20 amp breakers, install a 60 amp breaker and fishing a 6 gauge out to the shop. Argh!

-- Matt - My Websites - - Hand Tools :: - Small Shops

View dusty2's profile


323 posts in 3452 days

#11 posted 03-31-2009 03:26 AM

If I was there, I would jump in with both feet and you and I would fix this. But since I am not there, I am going to wait, watch and listen for the outcome.

Be careful, this is a situation where you can get bit real well.

-- Making Sawdust Safely

View Woodchuck1957's profile


944 posts in 3787 days

#12 posted 03-31-2009 03:45 AM

My detached garage/shop was wired similarly. I decided to have a breaker panel put in, and split the circuits there. If I remember correctly the power from the house going to the shop was two 20 amp breakers on a red, black, white, and ground. We were able to replace those with a 30 amp dual pole breaker ( 240V ) An electrician did the job. Glad I had it done. Now I have three 240V circuits ( Contractors’s saw, dust collector, air compressor and , or an edge sander ) and three 120V circuits in the shop. I’m a firm believer in a dedicated 120V or 240V circuit for table saws.

View sandhill's profile


2128 posts in 3947 days

#13 posted 03-31-2009 04:11 AM

Bingo, Disconnect both red and black from the breaker and check for continuity from black to red going away from the panel if you read a closed ckt you have them touching somewhere in which case I would not recommend using that ckt at all just run a new line using the old 12 gage wire to pull the #6 gage and use plenty of lube.. If you do go with a 60 amp and a 60 am box don’t forget you really have 120AMP capacity.

View ajosephg's profile


1880 posts in 3584 days

#14 posted 03-31-2009 04:18 AM

Give us a reality check.

1. ou disconnected The red and black wires three feet from the CB. In other words the only place this piece of 12/3 goes is from the CBs to a point 3 feet away and they are open circuited at that point.

2. With black CB on and red CB off you have voltage on the black wire and no voltage on the red wire.
With the black CB off and red CB on you have voltage on both the black and red wires.

If that is true then:

With both CB breakers off do you have voltage on either wire? If you do it sounds like a defective black CB.

Verify by moving the black wire to a different breaker on the same side of the panel and see what you get.

-- Joe

View Matt's profile


181 posts in 3396 days

#15 posted 03-31-2009 05:00 AM

1. True

2. True

I’ve got a spare breaker in my panel I can hook it to and check it when I get home tomorrow evening. I’ve been making sure to turn off both breakers when I’m not out there for safety until I get this sorted out.

Sandhill. Hmmm, 120 amps out there. Tempting!

Thanks guys. Keep the ideas. Coming!

-- Matt - My Websites - - Hand Tools :: - Small Shops

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