| Author |
Message |
    
jrbell
Citizen
Username: Jrbell
Post Number: 9
Registered: 10-2003
| | Posted on Monday, November 10, 2003 - 10:01 am: |     |
Our house is wired with BX cable (the kind that has the metal sheath protecting the two wires) and most of the outlets are the old 15 amp two-prong jobs.
I want to replace them with three prong outlets to accomodate the ground prong, but there's no ground cable that runs with the black/white supply wires. I've been told that I can use the metal sheath as a ground... any truth in that?
Also, should I just purchase lengths of copper wire, attach to the sheath and to the ground screw on the new outlet? Does the copper need to be insulated?
Thanks! |
peteglider
Citizen
Username: Peteglider
Post Number: 330
Registered: 8-2002
| | Posted on Monday, November 10, 2003 - 10:06 am: | |
yes, the metal sheathing is your ground. the cable should be fastened securely to the metal junction box (the box your outlet or switch is mounted in).
you can wire in a 3 prong outlet by running the ground wire from the outlet to the junction box itself (with a green, self-tapping "ground" screw).
i have not done this in a number of years -- maybe someone can offer more current advice
pete |
us2innj
Citizen
Username: Us2innj
Post Number: 884
Registered: 5-2001
| | Posted on Monday, November 10, 2003 - 10:48 am: | |
Go to Radio Shack or any hardware store, and buy a 3 prong circuit tester. It will show you if a wire is reversed, or if there is an open ground. Most of the time, replacing a two prong outlet with a three prong grounded outlet will automatically create the ground just through the outlet box.
The 3 prong circuit tester costs about $5. |
us2innj
Citizen
Username: Us2innj
Post Number: 885
Registered: 5-2001
| | Posted on Monday, November 10, 2003 - 10:50 am: | |
circuit tester |
jrbell
Citizen
Username: Jrbell
Post Number: 10
Registered: 10-2003
| | Posted on Monday, November 10, 2003 - 11:39 am: | |
Thanks for the tips. I did get a circuit tester and on the couple I've replaced, it does tell me that it is wired correctly... looks like I don't need the copper wire connected to the green ground screw as long as there is solid contact between the outlet and the box.
Thanks again. |
peteglider
Citizen
Username: Peteglider
Post Number: 331
Registered: 8-2002
| | Posted on Monday, November 10, 2003 - 11:43 am: | |
jrbell -- while I believe that would work in theory (the metal of the outlet screwed to the metal of the box) -- I don't think that would pass code. adding the grounding pigtail is a good step to take -- pete |
jrbell
Citizen
Username: Jrbell
Post Number: 11
Registered: 10-2003
| | Posted on Monday, November 10, 2003 - 11:45 am: | |
Good advice. Doesn't seem like too much additional effort, so I'll do it. Do I need to insulate the copper wire? |
jgberkeley
Supporter
Username: Jgberkeley
Post Number: 3290
Registered: 5-2001
| | Posted on Monday, November 10, 2003 - 12:27 pm: | |
When you buy the copper pigtails, buy them pre-made. They come with a self tapping green screw attached to a green coated wire stripped to copper at exactly the length needed to do what you are doing. |
tourne
Citizen
Username: Tourne
Post Number: 223
Registered: 1-2003
| | Posted on Monday, November 10, 2003 - 2:20 pm: | |
Another option is to just purchase a GFCI outlet and install it in an outlet at the beginning of the run and it will provide protection to all outlets further down the line as well. |
jgberkeley
Supporter
Username: Jgberkeley
Post Number: 3296
Registered: 5-2001
| | Posted on Monday, November 10, 2003 - 2:34 pm: | |
Tourne,
A GFIC is not a solution to the discussion in this thread.
The discussion is to add an outlet that has the third prong providing a 'True' ground.
GFIC is an entirely different matter.
If you take a look in the Attic, I posted a 'white paper' on what a GFIC does and how it does it.
If one does not do the 'third' prong conversion, GFIC would do nothing to the down stream outlets.
|
tourne
Citizen
Username: Tourne
Post Number: 224
Registered: 1-2003
| | Posted on Wednesday, November 12, 2003 - 12:12 am: | |
jgberkeley et. al.,
The NEC forbids replacing a two slot receptacle on an old ungrounded system with a new three-slot variety, because, with no ground wire present, the receptacle cannot be grounded. However, the code provides for the replacement of a two slot receptacle with a GFCI. Although the GFCI is not itself grounded in this situation, it protects the users by shutting off the current in the case of a ground fault. The code allows you to replace downstream outlets with regular three-slot non-GFCI receptacles which must be labeled that they are GFCI protected. The labels come in the box with the GFCI. |
tourne
Citizen
Username: Tourne
Post Number: 225
Registered: 1-2003
| | Posted on Wednesday, November 12, 2003 - 1:25 am: | |
In addition, GFCI's provide much better protection against shock than just a ground. Note that the grounding of the BX metal cover should be verified by measuring voltage between hot and ground. Personally, I would add both a GFCI and ground to box in this case. |
NRL
Citizen
Username: Nrl
Post Number: 303
Registered: 8-2003
| | Posted on Wednesday, November 12, 2003 - 9:40 am: | |
I dont understand, I just replaced a 2 prong with a three prong and ran the ground to the box with a self tapping ground screw and cooper wire. Why is this not acceptable? |
jgberkeley
Supporter
Username: Jgberkeley
Post Number: 3307
Registered: 5-2001
| | Posted on Wednesday, November 12, 2003 - 11:03 am: | |
NRL,
It is acceptable. You provided the ground pigtail.
You can call the local building department and get in touch with the Electrical inspector (Mike)if you want it from his mouth.
One thing to consider, is to test to assure that the BX metal connection is intact to the Earth ground. Rarely, someone breaks that connection during a re-model job. A voltage check will not do it for you. You need to measure the resistance from the local box you mounted your pigtail into against a true earth ground such as a cold water pipe. That is the only way to test that.
Oh, and if the true earth ground in not in tact, a GFIC will not function, at all. |
tourne
Citizen
Username: Tourne
Post Number: 227
Registered: 1-2003
| | Posted on Wednesday, November 12, 2003 - 11:46 am: | |
jgberkeley,
I don't get the comments in your last post. First, why would a voltage check not establish that a ground exists? Second, GFCI's provide protection by measuring the difference between the current in the hot and neutral wires. An imbalance in current trips the GFCI. It has nothing to do with the ground or ground wire. Thirdly, if the town electrical inspector doesn't know this, than someone else should be doing the inspections. |
jgberkeley
Supporter
Username: Jgberkeley
Post Number: 3308
Registered: 5-2001
| | Posted on Wednesday, November 12, 2003 - 12:11 pm: | |
The answer to your question is more complex that I care to post.
In short, voltage checks will not determine if you have a ‘true’ ground. Voltage is a measurement that is relative. Meaning, that the voltage is an indication of the difference of potential from one point to another.
If meter polarity is used correctly, if I have 5 volts on one line and 110 on another and a ‘true’ ground, if I measure from the ground to the 5 volt point I will see 5 volts. If I measure from the ground to the 110 point I will see 110 volts. If I measure from the 5 volt point to the 110 volt point I will see 105 volts, 105 being the difference from 5 to 110.
That is simple, now add in a real factor of many home electrical systems, ground loops and floating voltages, (caused by appliances, bad or failed wiring connections). When you add these items you have lost your ‘true’ reference.
The only real way is to use impedance or resistance checks, using an ‘Earth’ ground as the reference.
The internal electronic design of the GFIC needs a ‘true’ ground reference. It gets that from the ground connection. So if the ground connection is ‘floating’ or ‘looped’ then the GFIC will fail to do what you want it to do.
Since you seem to have a meter, put it on the lowest scale then measure the AC voltage from a ‘true’ ground and the Neutral. If you see any bounce on the meter you will be looking at a floating voltage. As I said, not uncommon.
I can assure you the Township inspector knows his business. While this is a place to post opinions, it is not fair to post a statement like that. The man is not even involved and is a third party to this discussion.
|
tourne
Citizen
Username: Tourne
Post Number: 228
Registered: 1-2003
| | Posted on Wednesday, November 12, 2003 - 1:47 pm: | |
jgberkeley,
Do you mean that, say, a rusted BX cable may not ground properly. See http://www.mikeholt.com/misc.php?id=unformatted/recept2wire&type=u&title=GFCI%20 -%20Receptacles%20Without%20A%20Ground%20(12-30-99)for an explanation of GFCI. Why does there seem to be a difference in this reference to your comments? I am trying to understand and the apparent disconnect bothers me. No offense to the present electrical inspector. |
jgberkeley
Supporter
Username: Jgberkeley
Post Number: 3309
Registered: 5-2001
| | Posted on Wednesday, November 12, 2003 - 3:31 pm: | |
A rusty BX cable and far more.
Tourne, I suggest we keep this board simple. I do not need the references. Just ask your question, in common English.
I can read and truly do understand the meaning of, "The impedance of the fault current path equals the sum of the impedances of the power supply; the phase conductors, the ground-fault, and the fault-current return path."
Not many other on this board would. |
Brett
Citizen
Username: Bmalibashksa
Post Number: 421
Registered: 7-2003
| | Posted on Wednesday, November 12, 2003 - 3:50 pm: | |
I understand it completely.
.
.
.
{runs to call an electrician, this sounds serious and I don’t want it}
|
tourne
Citizen
Username: Tourne
Post Number: 229
Registered: 1-2003
| | Posted on Wednesday, November 12, 2003 - 3:58 pm: | |
For all,
Stated simply, all references I have seen state that a GFCI outlet can be used in a two wire system to provide protection against electrical shock without the need for the GFCI outlet to be connected to a ground wire. It will also protect all other two wire outlets down the line. For those who do like references, Leviton(they make the most advanced GFCI's) has a very good tech line at http://www.leviton.com/sections/techsupp/techindx.htm. Keep in mind that surge protectors, such as the ones most of us have on our computers, DO need a ground wire to operate properly. |
jgberkeley
Supporter
Username: Jgberkeley
Post Number: 3310
Registered: 5-2001
| | Posted on Wednesday, November 12, 2003 - 4:32 pm: | |
I give up.
Tourne, you must be selling GFIC and ARC devices.
Now surge protectors to?
The original question was simple. How to convert a 2 prong to a 3 prong and now you have spun this into an endless sprial with each post introducing yet another device and web link, all having nothing to do with the question.
Have fun.
If I read a serious question, I will respond. |
NRL
Citizen
Username: Nrl
Post Number: 306
Registered: 8-2003
| | Posted on Wednesday, November 12, 2003 - 10:02 pm: | |
I agree with George. Tourne, what on earth are you talking about? Just the sight of a GFI in my guest bedroom to replace a 2 prong outlet doesnt look right, let alone answer the original question of converting to 3 prong. |
tourne
Citizen
Username: Tourne
Post Number: 230
Registered: 1-2003
| | Posted on Wednesday, November 12, 2003 - 11:01 pm: | |
Hooey! I was going to let this topic go to sleep. But since you ask, my first post was pertinent in that I was suggesting that another way to deal with a two-wire system is to use a GFCI outlet. If you want to use a three-prong outlet on a two wire line(ie. ungrounded) then this is another approved(NEC code compliant) way to do it without having to add a ground wire or depending on the metal jacket of BX cable for the ground. It also happens to add a great deal of safety to the line for very little cost or time to install. In fact, an ungrounded cable with a GFCI is safer than a grounded cable without a GFCI. If the BX cable jacket is properly grounded too, that's great. Sometimes the metal cable jacket is not in good shape, though(maybe rusted, etc.) and should not be used. It is never a good idea or code compliant to depend on the screws on the outlet case alone, for the ground to the BX cable, regardless of what your plug in analyzer says. These mounting screws often come loose. In any case, as my references illustrate, a GFCI outlet does work and is approved for use on an ungrounded circuit. Enough said, take it--or leave it. |
tjohn
Citizen
Username: Tjohn
Post Number: 1875
Registered: 12-2001
| | Posted on Thursday, November 13, 2003 - 5:45 am: | |
A tangible point at last. George - does Maplewood code permit the use of the metal jacket on BX cable to serve as a ground? I think it does since I have had good electricians do it that way and they are typically up to speed on building codes. |
jgberkeley
Supporter
Username: Jgberkeley
Post Number: 3314
Registered: 5-2001
| | Posted on Thursday, November 13, 2003 - 12:32 pm: | |
Maplewood code does permit that.
I was just on the phone with Bob Mittimier when I read your Email so I asked him.
His answer, "With out question, yes!" |
sullymw
Citizen
Username: Sullymw
Post Number: 199
Registered: 5-2001
| | Posted on Thursday, November 13, 2003 - 2:55 pm: | |
thank goodness! That's how I've been grounding my outlets for years |
tourne
Citizen
Username: Tourne
Post Number: 232
Registered: 1-2003
| | Posted on Thursday, November 13, 2003 - 9:15 pm: | |
Hey, just came across a really cool illustration. See http://www.codecheck.com/250_50_commentary.html |
tjohn
Citizen
Username: Tjohn
Post Number: 1882
Registered: 12-2001
| | Posted on Thursday, November 13, 2003 - 9:54 pm: | |
Isn't it true that even with grounded circuits, GFI outlets are still used in bathrooms and in the vicinity of kitchen sinks? My kitchen certainly seems to be wired in that way. |
jgberkeley
Supporter
Username: Jgberkeley
Post Number: 3321
Registered: 5-2001
| | Posted on Friday, November 14, 2003 - 8:50 am: | |
Yes, that is true. During my Master bedroom remodel I added outlets where none were before.
During the inspection, Mike pointed out that one of the Bedroom outlets would have to be GFI as it was within 6' of the toilet. That 6' is measured as if it were an extension cord that can be wrapped around a door and then dropped into the water source.
|
Michael Janay
Citizen
Username: Childprotect
Post Number: 65
Registered: 1-2003
| | Posted on Friday, November 14, 2003 - 9:56 am: | |
Home Depot sells self grounding receptacles.
They work great if your junction box is metal and wired with BX.
No pigtail needed, and they only cost a few cents more. |
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