Yet another wiring question

[cgallery]

To refresh everyone's memory, I'm cutting a piece of 12-gauge Romex that has some extra slack in it, and I'm inserting a box with two receptacles (so I guess electricians call that a double duplex).

Per earlier suggestions, I found the wire was 12-gauge so decided to use pigtails to make fighting the stiff wire a little easier-going.

But I was reading more and found this (http://www.wikihow.com/Install-an-El...t-from-Scratch step #9):

Connect the ground wire. If a metal box, cut (2) eight inch lengths of bare copper wire, and combine them and the bare wire from the romex cable under a properly sized wirenut. The free end of one wire will connect to the green ground screw of the outlet, and the other free end is to be connected to the metal box with a green screw (expressly for that purpose) or other approved means (special clips, etc). If a plastic (or other non-conductive material) box is used, simply connect the bare copper wire directly under the green screw of the outlet

I'm using a metal box and a metal cover, with metal screws connecting the two.

Do I really have to wire a ground to the receptacle, and another ground to the metal box? Or would it be sufficient to wire the two grounds to the box and let the metal screws carry the ground to the receptacles?

My layman thinking is that the screws would be sufficient for the ground. But I may be overlooking a scenario in which they wouldn't, and I want to get it right.

But if conduit can serve as a ground, why can't my all metal box (box and cover that holds the receptacles) do the same thing?

[Mr__Bill]

I am sure an electrician will correct me on this but....
They make receptacles that have a built in/on clip that connects ground to the metal box and this may meet code for grounding the box. Otherwise it's really a good idea to ground the box with a wire and screw.

The box needs to be grounded because when a fault from a hot or even the common is to the box you want the electricity to flow somewhere other than to you if you happen to touch the box while grounded. The screw that holds the receptacle to the box really is not a good ground.

I have seen electricians bring the wire into the box and wrap the ground around the green grounding screw and then bond the grounds; in, out and pigtail, with a crimp on sleeve. So it may not be necessary to have two pigtails, one for the box and one for the receptacle.

Bill
I'm not an electrician or an electrical engineer and while I play at both I don't do it on TV

[cgallery]

The only advantage I can think of so far for grounding both the box and the receptacle is that if someone unscrews the cover from the box and pulls it out a little bit, they break the ground.

[LCHIEN]

i'm pretty sure the ground terminals on the box and the receptable are much better grounded by the force of the screw on the wire and the forces of the wirenuts than depending upon the screws that hold the face plate to the receptacle and the receptacle to the box... those are typcially not torqued real hard to finish and are not intended as a high current electrical path.

[crokett]

You need to ground the box and the receptacles separately for the reasons mentioned. You can also leave the ground wire long, loop it around the box screw and then attach it to the outlet screw.

[cgallery]

You need to ground the box and the receptacles separately for the reasons mentioned. You can also leave the ground wire long, loop it around the box screw and then attach it to the outlet screw.

Okay. Do I need to run the ground to BOTH receptacles, or do I wire just one and use the metal cover to carry the ground to the other?

[Tom Slick]

Everything needs to be bonded with wire: both duplex receptacles and the box.

For future reference, switches and fixtures also must be directly bonded as well as the box according to the NEC.

[cgallery]

After all this screwing around with the notion of "cutting-in" an outlet, I looked up in my ceiling just ten minutes ago and realized that if I turn one 4' fixture around and plug it into a different outlet (previous homeowner put outlets up in ceiling to plug figures into), I can free up an outlet and my problem is solved.

Which is good, because the line I was going to cut into is 12-gauge. And quite frankly, wrestling that much 12-gauge into a box wasn't gonna be the highlight of my Sunday.

Thanks for the help anyway. I learned quite a bit. And identified a shortcoming in another area (electrical) that I need to address.

***
Oh, and this just-in. Apparently, the new code says that if you remove the cardboard washer from the screws, you can skip the grounds to the receptacles. This was posted by Tom Brady at SMC. He learned this from a code class he attended. However, local code may not be (likely isn't) the same.

Point being, if I waited 10-12 years, wiring it w/o the grounds to the receptacles may have been fine.

[tseavoy]

My Seattle house had knob and tube wiring with no ground to the outlets. No one ever got a shock. In my opinion, this grounding thing requirement is the work of a paranoid.
I just wrap the ground around the box cover screw in the case of a metal box after wrapping the other ground wires around the wire used.

Tom on Marrowstone

[cabinetman]

My Seattle house had knob and tube wiring with no ground to the outlets. No one ever got a shock. In my opinion, this grounding thing requirement is the work of a paranoid.
I just wrap the ground around the box cover screw in the case of a metal box after wrapping the other ground wires around the wire used.

Tom on Marrowstone

I gotta agree with you. We have several receptacles without a ground. Never had a problem with them. I guess if we made a special attempt to get shocked, we could be successful. I'm not saying having everything to code is not important, just good sense.
.

[master53yoda]

Bonding and providing a ground path was put in the code in the sixties. When it was added it reduced the number of electrocutions that were starting to get out of hand in the late 40s and 50s. If the tool you are working with has a wire insulation get bad and start shorting it to the case without a ground when you pick it up you could very well be a functional ground path back to the transformer on the power pole. the power pole transformers have the center tap winding grounded, the center tap is also the neutral.

The purpose of an uninterrupted ground path is to provide a low resistance path for any ground currents in the system. I worked on a factory in Kirkland WA. that had the panel ground cut off. Touching the conduit at one end of the factory had a very minor power trickle measuarable at about 5 volts to the earth, but at the other end of the factory at the shipping docks the voltage between the conduit and the earth was in the 40 to 60 volt range. on wet days it hurt. When we found the disconnected ground in the service entrance and reconnected it the problem was removed. The power that was on the conduit was from induction in the system due to the 800 ft from one end of the factory to the service panels.

Knob and tube wiring works but, many houses have burned down and people killed because of it, mostly due to the insulation detererating and puting 110 on the box or resepticle. with no ground it gets back to the transformer however it can, the person touching the box with wet or oily hands or a damp cloth etc. The ground has no effect on a tools operation it only comes into play when something goes wrong. then it either blows the fuse or trips the breaker.

I will not use tools that are not either double insulated or grounded, if the ground terminal gets bad on a cord I replace the cord end or the cord. I know of to many people that have been hit using ungrounded tools over the last 35 years .

[eccentrictinkerer]

***

Point being, if I waited 10-12 years, wiring it w/o the grounds to the receptacles may have been fine.

Just to add fuel to the fire, if you use a GFI-type receptacle, no ground is necessary!

I live in a 98 year old house and have been replacing wiring for the last 35 years.

There are four circuits that I couldn't get to due to old plaster in perfect condition.

You can't imagine how pleased I was to find out that all I had to do was use a GFI.

Hail to the technology angels.

[cgallery]

Just to add fuel to the fire, if you use a GFI-type receptacle, no ground is necessary!

Interesting.

Now, there are some rules to using GFI's, right? Or can you just replace any receptacle w/ a GFI?

[eccentrictinkerer]

Interesting.

Now, there are some rules to using GFI's, right? Or can you just replace any receptacle w/ a GFI?

As long as the new GFI isn't downstream from another GFI, you're good to go.

The GFI outlet has electronics that compare current in the neutral and hot legs. If the difference is more than 4 or 5 milliamps, it trips. The difference might be due to bad tool wiring or current leaking to a puddle of water (through you).

I feel safer with a GFI in a circuit than I do with a grounded outlet. All my extension cords, for my handyman business, are equipped with GFI's.

[woodturner]

You can't imagine how pleased I was to find out that all I had to do was use a GFI.

Hail to the technology angels.

Code does allow a GFCI to be used to create a "virtual" safety ground.

This virtual ground will protect life but not equipment. If you plug your computer or TV into such a receptacle, it will be much more likely to be damaged by transients and high voltage noise than on a grounded circuit.