[mschumacker]

I have a free breaker in my panel and can fit a tandem 20 amp breaker so that I can run two bigger circuits in my garage. The plan was to have about 4 double gang boxes with two outlets, one from each circuit so that I can space out the need. Anyhow, I shutoff my main house panel from the actual main panel that is outside so that I can connect the circuits. I ran two 12 gauge wires through one knockout into the box, the connected each ground to the ground bar, each neutral to the neutral bar, and finally, each black wire to the tandem breaker which was off. All good.

I ran the wires into a metal surface box where I'm going to run PVC conduit from there to the new gang boxes. As I was moving the wires to install the PVC connector, I got a spark. I quickly grabbed my tester and using the black and white wires, no circuit. As I moved the wires again, big spark and burnt the ground.

Why? The ground is what got me. Is this because its in a metal box? Should I connect the ground to somewhere on the box?

 

[betelgeuse]

I quickly grabbed my tester and using the black and white wires, no circuit. As I moved the wires again, big spark and burnt the ground.

Did you test the tester beforehand on a known live circuit?
Did you check the black wire to ground?
Maybe you had a bad tester

 

[seharper]

Photos would be helpful. I'm not sure what you're referring to.

 

[mschumacker]

I'll check my tester again, but it's always worked. Is there a way that ground can pick up a charge from another circuit and when it came near the metal box is arc-ed? It burnt the little bit of the paper insulation that was around it.

I took everything out and closed it up for now. I'll open up the panel and show pictured tomorrow. I appreciate the help.

 

[MTN REMODEL LLC]

I have a free breaker in my panel and can fit a tandem 20 amp breaker so that I can run two bigger circuits in my garage. The plan was to have about 4 double gang boxes with two outlets, one from each circuit so that I can space out the need. Anyhow, I shutoff my main house panel from the actual main panel that is outside so that I can connect the circuits. I ran two 12 gauge wires through one knockout into the box, the connected each ground to the ground bar, each neutral to the neutral bar, and finally, each black wire to the tandem breaker which was off. All good.Was the main off or on

I ran the wires into a metal surface box where I'm going to run PVC conduit from there to the new gang boxes. As I was moving the wires to install the PVC connector, I got a spark. I quickly grabbed my tester and using the black and white wires, no circuit. As I moved the wires again, big spark and burnt the ground.

Why? The ground is what got me. Is this because its in a metal box? Should I connect the ground to somewhere on the box?

??????Above

 

[MTN REMODEL LLC]

Maybe we ought to see a pic of your panel wiring also......

 

[betelgeuse]

I'll check my tester again, but it's always worked.

Famous last words.
ALWAYS check the tester on a live circuit before declaring that you don't have power. Did you check from both wires to ground?

 

[surferdude2]

Let that be a lesson to you. Create the circuit and connect the receptacles or loads and disconnects before landing the branch circuit feeders in the panel. No point in challenging fate if it's not necessary.

Not knowing what your metal box was mounted on, I can't imagine why a ground wire touching it would make a big spark. Perhaps you have it mounted on something that is ground faulted and had no ground until you gave it one??? Very odd... Are you sure you landed the wires properly in the panel and that the breakers are off and measuring no output voltage?

 

[Datawise]

It is life saving to use proper testing techniques on any piece of equipment before using it; nothing is more critical then an electrical tester. An electrical tester is both a tool and a piece of safety equipment and should be treated the same as safety glasses, respirator or harness.

Your family relies on you being safe and knowing what you are doing; unlike something like painting, this can kill you pretty easy.

Cheers
John

 

[mschumacker]

Ok. Point taken, but just so you know, I've never done anything that would harm anyone in my family. I simply didn't test the wire, but as soon as I saw something amiss, I dismantled the whole thing until I figured it out.

So, I'm including pictures. In the close up picture, you can see the empty slot for my tandem 20 amp breaker (yellow arrow), the punched out knockout (blue) and the metal junction box where I plan to run the two 12 gauge wires, each with its own neutral, but not sure about the ground.

Question 1 - Since these are both 20 amp, and I'm using 12 gauge, shouldn't I only need one ground wire?

Of course the metal junction box I bought does not have a ground screw, so I'm planning on picking that one up tonight. Here's my wiring thoughts:

Circuit 1 - black wire hot from C1 of tandem breaker to black THHN
Circuit 1 - white wire neutral from neutral bar to white only THHN
Circuit 1 - bare copper ground from ground bar, so screw on metal box, and pigtailed to green THHN

Circuit 2 - red wire hot from C2 of tandem breaker to red THHN
Circuit 2 - white wire neutral from neutral bar to white (blue tape marked)
Circuit 2 -no ground from box.

I ran PVC from the junction box (to the left) that contains (black/white and red/white(blue tape) plus the green to a double gang box. Here I plan to install two GFCI's (20 amp) each with its own line/neutral, but common ground.

For now, that ends Circuit 2, but will be using the LOAD terminal to go to 2-3 more receptables, in series.

For Circuit 1, my plan was to come off the LOAD and pigtail to 2 outlets, one single one on the right side, and then go to the left with the Circuit2 outlets.

Thoughts?

 

[surferdude2]

Before going any further, you need to resolve how you intend to feed from the panel to this box. You may have to remove the work you have in the way in order to do that.

Then you need to use a pvc LR (or use a standard pvc ell) to replace that pull fitting in the corner that won't pass inspection.

Then plumb that single gang box up and provide a support clamp on the conduit (suggest placing clamp where stud is that supports panel).

One ground wire is all you need in the conduits... GFCI's don't need dedicated grounds.

 

[mschumacker]

Sorry, didn't get it in the picture. Inside that metal junction box, I've already knocked out one of the back knockouts and cut a hole open into the wall directly below the panel. The plan was to fish the wire through that knockout in the panel, with a plastic, no-slip grommet, and then through the hole in the wall and into the box, with use of a NM clamp connector.

I wasn't sure about the right-angle piece but of course two of the workers at an orange big box store said it was fine.

 

[surferdude2]

You can't use open wire inside a wall... it must be in conduit.

 

[mschumacker]

The wire inside the wall will be Romex 12 gauge.

 

[mschumacker]

Ok...time to eat it. I found the reason for the spark. Turns out when I screwed in the box, the tip of the screw penetrated the wire supplying the box with its 90 amps. Even though I used a very small screw, it was just enough and with that rigid wire, it just nicked it.

Removed everything for now and did put tape around the wire. I take it the proper way is to splice this wire with two junctions? The hole in the wire was about the 2mm circle. It's taped for now.

Damn.

 

[seharper]

Yeah, screws will getcha every time!

A few details.

That 45 to the left of the metal box there, cannot be that kind of 45. It must be an LL or LR, or just a normal sweep. As is, it creates an impossible pull, which begs the question of how you pulled wire through there in the first place Especially since it's balky, hard to use solid wire It's illegal to assemble the conduit around the wire.

By the way, a real timesaver: stranded THHN wire. Since you're terminating on GFCIs anyway, and can just terminate on their screw-and-clamps. Putting stranded wire on a screw is an ...acquired... skill that I wouldn't advise to a novice.

I own zero #14 wire, zero solid wire and 10 colors of #12 stranded wire. I will consider my collection complete when I get pink, white-blue stripe, and white-orange stripe.

Since you're using Romex inside the wall, that's ohhhh...kay..... but you will need cable clamps on both hole entries. I think you can open up the slot underneath the panel to get in there with a needle-nose and attach the cable clamp nut there... on the box, remove the box (you have to anyway to fix the conduit elbow) and fit your cable clamp with the conduit nut on the back.

This here isn't Code, just an opinion... but whoever runted off all your wires so they barely reach where they're going right now, that's no act to follow. Hot and neutral should be able to reach any breaker in the panel, so you can move things around, add AFCI/GFCI, or what have you.

 

[surferdude2]

Let that be your second lesson on this project.

Some people get their name in the paper for little slips like that. Consider yourself lucky... I do.

Never run a screw into the wall on center with the feeders to a panel. Don't drill any holes there either. The top and bottom wall area of flush mounted panels are danger zones.

I haven't yet figured out how you need all those wires I see in the 4S box. That's why I thought you would have trouble getting the required number of NM cables into the panel. With only 2 available circuits, I don't see any application for anything but 2 colors, 2 whites and 1 green. The 2 whites are necessary since you say you're using a tandem breaker which will be stabbing only one phase. So..... you will need two 12/2 NM cables into the panel. Be sure to use the approved 2-screw connector for doubling cables through it, not all of them are.