Proper Grounding?

[strnjss]

I had a broken 3 prong power outlet in one of my rooms, so I went to replace it.

I have the old asbestos coated wires.

Inside, I found the hot and neutral wires attached properly, but there is no ground wire.

My little tester says the outlet is wired correctly though, so I assume the outlet box itself is acting as a ground to the body of the outlet as there are only 2 wires.

My multimeter shows that the ground prong does have continuity with the 'frame' of the outlet.

Is this ok?

Also, out of curiosity, if a ground is meant to divert bad/excessive or shorted current into the ground, isn't there a risk of someone touching a device that's grounded like that and being a better source of ground than whatever grounds the device? I know it'll take the path of least resistance, I just don't know what ensures the human isn't that path.

 

[THEFIX]

Is this ok?

In short NO! You should either run a new circuit back to the main panel that includes a ground (providing your panel has a proper ground)which is the better option, or at minimum you need a GFCI protected plug. Best option is both.

It would be normal for your ground to have continuity with the wall box, the problem is the wall box does not have a ground, its just connected to the ground on the outlet. If there is a short in a tool or something plugged in, YOU will likely become the path of least resistance to ground. The GFCI plug will look at the current on both the hot and neutral and if there is more than a 5 mA difference, the GFCI shuts the circuit down. The current imbalance that it protects against is when you become a better path to ground than the neutral.

 

[strnjss]

In short NO! You should either run a new circuit back to the main panel that includes a ground (providing your panel has a proper ground)which is the better option, or at minimum you need a GFCI protected plug. Best option is both.

It would be normal for your ground to have continuity with the wall box, the problem is the wall box does not have a ground, its just connected to the ground on the outlet. If there is a short in a tool or something plugged in, YOU will likely become the path of least resistance to ground. The GFCI plug will look at the current on both the hot and neutral and if there is more than a 5 mA difference, the GFCI shuts the circuit down. The current imbalance that it protects against is when you become a better path to ground than the neutral.

haha figures. I've found outlets that are wired backwards in this place and everything. Whatever electrician did this obviously didn't know what they were doing.

Now my outlet tester:

shows the two amber lights that signifies everything's wired right, do you happen to know how it's determining ground?

I've used it on three prong metal box outlets before and it has said there is no ground, but on this one, it's saying there is.

Does that mean the box is just connected to metal shielding going all the way to the panel which is grounded?

 

[spongerich]

Are the old wires in armored cable? If so, the metal casing might be grounded back at your breaker panel.

I'm not an electrical engineer, but my understanding is that a proper ground will almost always be a better path than you will unless you're soaking wet and standing in a puddle.

That's why GFCIs are specified in damp environments.

 

[THEFIX]

Now my outlet tester:

shows the two amber lights that signifies everything's wired right, do you happen to know how it's determining ground?

I've used it on three prong metal box outlets before and it has said there is no ground, but on this one, it's saying there is.

Does that mean the box is just connected to metal shielding going all the way to the panel which is grounded?

Could be a couple of things, yes if metal shielded cable goes back to the box than maybe you are alright. Here in MI shielded cable is not required so every wire would have a ground. Could be the tester, it might have the red light burned out. Tester rule is: use it on a known good circuit, use it on the circuit in question then again on a good circuit. Cumbersome, yes foolproof, pretty much.

I don't work with the shielded stuff and I'm not an electrician, so maybe someone more familiar with will chime in. I'll keep watching cause now I'm curious.

 

[strnjss]

Are the old wires in armored cable? If so, the metal casing might be grounded back at your breaker panel.

I'm not an electrical engineer, but my understanding is that a proper ground will almost always be a better path than you will unless you're soaking wet and standing in a puddle.

That's why GFCIs are specified in damp environments.

Could be a couple of things, yes if metal shielded cable goes back to the box than maybe you are alright. Here in MI shielded cable is not required so every wire would have a ground. Could be the tester, it might have the red light burned out. Tester rule is: use it on a known good circuit, use it on the circuit in question then again on a good circuit. Cumbersome, yes foolproof, pretty much.

I don't work with the shielded stuff and I'm not an electrician, so maybe someone more familiar with will chime in. I'll keep watching cause now I'm curious.

Thanks everyone,

I just took a look in the basement, and yes, I do have metal shielded cable coming out around where the outlet is. It must be acting as the ground.

My tester is working good. Even if the light burned out, "good" wiring is the only state signified by both amber lights lighting up (in other words, there's no condition where all three would light up, and I have the two that mean good).

I'm still curious though how the tester determines ground though.

 

[Gooch]

Thanks everyone,

I just took a look in the basement, and yes, I do have metal shielded cable coming out around where the outlet is. It must be acting as the ground.

My tester is working good. Even if the light burned out, "good" wiring is the only state signified by both amber lights lighting up (in other words, there's no condition where all three would light up, and I have the two that mean good).

I'm still curious though how the tester determines ground though.

hot to ground and hot to neutral are, electrically, the same(serving two different purposes), so inside the tester, there is three lights, one amber one is tied hot to neutral, the other amber is tied hot to ground, the red light is tied neutral to ground.

 

[MrMark]

current takes all paths according to the resistance of the paths, not just the path of least resistance. Two equal resistance paths and the current will split equally. Your body is a big resistor and so is the path down through your feet to get back to the neutral on the transformer. So, if there is come decent wire path and you touch a metal ground or grounded surface hardly anything is going to go through you - virtually nothing.

The problem is two-fold: 1) the increasing resistance of a compromised ground path makes more current flow through you if you touch it and 2) it only takes a really small amount of current (50 ma or so through the heart - someone correct this if way off) to kill you. We have two competing things going on here, on the one hand you are a really bad return path or "ground" pretty much always, but you don't have to be a very good path to get killed. Of course if you complete a circuit where you are the only path you are pretty well burned up.

current doesn't flow to ground. It returns to its source either a battery or the generator.

 

[MrMark]

I hate it when the car diagnosticians refer to ground paths on the cars. The car uses the frame for a return path to the battery neg for most circuits. In a car, return path wires (B-) are usually not run all the way from the device to the battery. Some path of that current path is on the frame. This saves wires and cost. I just like to say B- or return path rather than ground.

 

[strnjss]

thanks!

 

[pprince]

Whatever electrician did this obviously didn't know what they were doing.

Not necessarily.

At one time polarity did not matter but with the profusion of sensitive electronics in the last 40 years polarity does matter.

 

[strnjss]

Not necessarily.

At one time polarity did not matter but with the profusion of sensitive electronics in the last 40 years polarity does matter.

Thanks, that's good to know. What I've always heard though is that the polarity matters even for things like light bulb sockets. Not for it to function, but if it's wired backwards, the socket threads themselves become hot instead of the little contact at the bottom. This is bad since it increases the chances of getting zapped.

On the old two prong plugs that weren't even keyed to polarity I can understand it, but these outlets are relatively modern in that they are 3 prong. I think the electrician who did this was probably just old school.

I wonder if it's still ok by code to use metal sheathing as a ground?

I have some old two prong outlets here that I would love to upgrade to 3 prong. And if they all have metal sheathing going to them, and I find out it's ok, I might give it a shot.

 

[pprince]

Lots of old wiring and techniques do not pass current code.

I am not an electrician so I can't be absolute but my guess is that using the sheathing as a ground is not to current code. In your case though it is the better of evils to use it as a ground as opposed to not having a ground.

Oh, and don't go sticking your finger or screwdriver in that light socket no matter how the polarity is. Either way you are likely to get zapped

 

[strnjss]

Lots of old wiring and techniques do not pass current code.

I am not an electrician so I can't be absolute but my guess is that using the sheathing as a ground is not to current code. In your case though it is the better of evils to use it as a ground as opposed to not having a ground.

Oh, and don't go sticking your finger or screwdriver in that light socket no matter how the polarity is. Either way you are likely to get zapped

haha I'll try not to...

but even like unscrewing a bulb, if you were to by accident touch the metal bulb threads that were touching the improperly hot socket threads, you'd be way more likely to get zapped than where it almost immediately disconnects before threads are visible unscrewing at the bottom of the bulb contact.

I think I may try and see if I have sheathing and get a grounded plug in some of these outlets.

However, I don't want to end up with insurance issues if I were to do something new not to code. But from what I've been reading so far, it seems like it's acceptable to code to do. I have no official word on that though

 

[MrMark]

Thanks, that's good to know. What I've always heard though is that the polarity matters even for things like light bulb sockets. Not for it to function, but if it's wired backwards, the socket threads themselves become hot instead of the little contact at the bottom. This is bad since it increases the chances of getting zapped.

On the old two prong plugs that weren't even keyed to polarity I can understand it, but these outlets are relatively modern in that they are 3 prong. I think the electrician who did this was probably just old school.

I wonder if it's still ok by code to use metal sheathing as a ground?

I have some old two prong outlets here that I would love to upgrade to 3 prong. And if they all have metal sheathing going to them, and I find out it's ok, I might give it a shot.

It's OK if it is thin walled EMT or Rigid conduit. You probably have EMT. You can do one of two things. First you can simply install self-grounding outlets (they have a little clip on the screw that ensures continuity with the grounded metal box) or second, you can install a green self-tapping machine screw in the box and run a jumper from the screw to the outlet.

As for the light bulb, once the circuit is completed, both sides are equally "hot". Under open circuit conditions I see the point.