I’m putting up a new light fixture in our house. I’m pretty sure much of the house is original wiring (the woven insulation). If one doesn’t have a ground wire, can we assume the conduit is acting as the ground?
Also, when the two wires aren’t marked, how can one tell which is neutral and which is hot? If using an outlet tester, can I just test each wire grounding do the box each time?
Discover a concrete-free foundation option that doesn't require any digging.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
OK, the hot wire was easy enough to figure out with the circuit tester.
The ground I'm a bit confused by, though...the metal conduit is clearly acting as the ground, but in newer homes, you typically won't see conduit to begin with, so what, exactly is acting as the ground at outlets and light fixtures?
I too am a little confused by this. One thing though is that the neutral ends up going to ground in the system. I have heard the neutral being described as a current carrying ground. I take that to mean that in a fault situation the current goes to ground. Man, go figure.
Also I say this as more of a question. In modern wiring, the boxes and other fixtures are "bonded" to the building ground. That ground is intact by its interconnection with a ground wire. Hence, no ground conductor, no ground, except in the case where the bonding is effected by metal conduit.
I would appreciate a comment on that.
Regards:
me
I'm an idiot. Just looked at some romex...duh...it's a 3 wire system so there's obviously a ground in it.OK, that makes sense. Is it common in older houses like mine to use all-metal conduit for the ground? Was that the intended purpose or just a happy accident when we figured grounding was a good thing later on?
ok i'm thinking you just signed on tonight and everyone gets one free dumb question,then i look and you been 5 years ,1300 post.
man that question about how does romex ground is going to cost ya,i'm just waiting for all the sparky guys to get here ,this is going to be a fun sat. nite after all.lol
old house's with knob and tube don't have conduit,so no ground no way.
oh,if you can't figure out which is hot,lick your fingers wet and grab a water pipe with one and start touching wires with the other,works everytime.[you do know i'm just bs'ing]larrywhy pay someone to screw it up,i can do it for free....
"Is it common in older houses like mine to use all-metal conduit for the ground?"No. In some areas code only allowed conduit to be used. In some areas that is still true (mainly the Chicago area). This is for single family homes and typically for duplex. When you get in to multi-family buildings the codes are much different.But it was also common for old homes to have colth sheathed non-metallic cables (pre romex) and even K&T wiring.Now I don't know the history or how and when EGC's (equipment grounding conductors), AKA, the GROUND, but metallic conduit is allowed to be used for an EGC.".it's a 3 wire system so there's obviously a ground in it."I am confused. What does Romex have to do with this.If you are talking about romex that is just sleaved by conduit for a short distance, such as running basement wall then that conduit is not a "wiring system" and can not be used as the EGC. The romex needs to have it's own EGC. But the ground wire needs to be connected to the metal box and thus to the conduit so that the conduit is grounded and can't become "hot" if there is abreak in the romex insulation.Where cable or separate wiring is used the EGC will be either bare or green colored.By convention the ground is not counted when designating Romex.Thus modern 14-2 romex had 2 #14 insulated wire, plus a bare ground.older romex (Mid 60's???) would only have 2 wires and no ground.So I don't know if your 3 wire romex is an old cable with 3 insulated wires and not ground or a newer one with 2 insulated wires and a ground..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
"I am confused. What does Romex have to do with this."Heh. It's late. I'm recovering from the flu. And the cold medicine isn't helping. ;o)I know modern fixtures and outlets are all grounded...I spaced and forgot that the ground is PART of the Romex...so that all makes sense on new wiring.I was interested in how 'old' wiring was grounded but it seems that that wasn't really ever considered to be an issue, and that grounded systems are a (relatively) new concept.Where we have the old wiring in our house we have conduit with the cloth covered two-wire system. Neither is colored (From what I can tell) so had to get the tester out to figure out the hot one. Most of the fixtures are hooked up to the old wiring.
and that grounded systems are a (relatively) new concept.
As far as I know, services and service equipment (in this country anyway) have always been grounded.
It's the branch-circuits that weren't required to have a grounding means until late 50's or early 60's.
Actually, originally electric service was not always grounded. But grounding became the norm by the 20s or so.
If your view never changes you're following the wrong leader
"Actually, originally electric service was not always grounded. But grounding became the norm by the 20s or so."
I have a copy of the "Minnesota Farmstead Wiring Regulations" manual from March 1938, and grounding the electrical service was in effect by that time. There weren't a whole lot of other rules, though - the book is only 4" x 6" and 20 pages long. Quite a difference from today.
By the 30s electricity was pretty well standardized. But earlier were the wild and wooly days -- DC, 25 and 50 cycle AC, 50ish volt systems, etc. Even where supply systems were "standard", residental K&T installs didn't bother keeping hot and neutral consistent. It was common to fuse both hot and neutral.
If your view never changes you're following the wrong leader
There is a lot of the old "romex" rag wire out there that has a bare conductor for a "ground". It is usually a size or two smaller that the main conductors. I see it in many bathroom remodels and also kitchens. Does not meet current standards but better than the water pipe in most cases.
That could be confusing some.
Bob
Went back for sanity check:
http://www.codecheck.com/wiring_history.htm#nmnoground
Edited 9/23/2007 8:09 pm ET by rasconc
I have only see one short section of it.And based on that house I was under the impression that it was only used for a few years. And that was used to tape off an old 3 wire drier circuit that ran to a fused disconnection where this was tapped off to run to dishwasher. And the drier had been move and cable ran from the disconnect to an addition on the oposite side of the house.I read on one of the electrican sites that since it was code at the time then it is grandfathered in.But was not speced in the NEC as part of being NM then it might not have been code. But on the other hand the UL listing (or similar) is really what is the defining point.Also to see how the code changes got in a couple of discussions about switch legs. And a lot of people don't release that the white in a switch leg is suppose to be remark (reidentified).Some one found it in a 62 copy. But then it got dropped until recent additions..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Evidently it was pretty common here in mid-late 50's, I see a pretty good bit of it.
Is one of the wires uninsulated? If not, you have no guarantee that one of them is ground.Chicago used to (and may still) require conduit in homes. At various times St Paul and Minneapolis copied codes from other cities, and there may have been a time when the Chicago code was used. It was never commonly required outside of a few cities, though.Where conduit is used, it's still common to use it as ground -- not always wise, but common. Code only requires an explicit ground wire in specific cases (such as corrosive environments) where the conduit ground may be compromised.
If your view never changes you're following the wrong leader
Ground wires were not commonly used in residential wiring until maybe 1960, and 3-prong outlets were 5-10 years later. So there's no assurance that any of your wiring is grounded. If it is indeed in conduit the conduit is SUPPOSED to be grounded, but there are no guarantees.
Not sure what the technical code requirements are, but from a practical point of view the old light fixture wasn't grounded (unless to the conduit), so there's no increased safety hazard in failing to ground the new one.
If the wire isn't color-coded, the simplest way to tell which wire is hot is to use a neon tester. If you hold one wire and touch the other wire to the "hot", the tester will glow. (Note that the wire must be switched on.) Alternatively, you can use a voltmeter between the wire and a known good ground (such as the ground pin in a properly grounded 3-prong extension cord). (Once you sort it out it would be good to wrap a bit of white tape around the neutral wire, and/or a bit of black tape around the "hot".)
(It should be noted that color coding may be unreliable, depending on the electrician's mood at the time -- it may be wise to test as describe above even if the wires are color-coded.)
No, you can't assume that the conduit is acting as ground. The conduit will not be as conductive as copper, there is likely to be additional resistance at the various points where conduit connects to outlet boxes, and there may actually be a break in connectivity. It was common in the '70s to retrofit grounded (three-prong) outlets into systems wired with two conductors and conduit, or even two conductors and old armored cable, but it is not common (or usually legal) to do so today.
2005 NEC"250.118 Types of Equipment Grounding Conductors The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:(1) A copper, aluminum, or copper-clad aluminum conductor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.(2) Rigid metal conduit.(3) Intermediate metal conduit.(4) Electrical metallic tubing.(5) Listed flexible metal conduit meeting all the following conditions:
a. The conduit is terminated in fittings listed for grounding.
b. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
c. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).
d. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.(6) Listed liquidtight flexible metal conduit meeting all the following conditions:
a. The conduit is terminated in fittings listed for grounding.
b. For metric designators 12 through 16 (trade sizes 3/ 8 through 1/2), the circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
c. For metric designators 21 through 35 (trade sizes 3/ 4 through 1 1/ 4), the circuit conductors contained in the conduit are protected by overcurrent devices rated not more than 60 amperes and there is no flexible metal conduit, flexible metallic tubing, or liquidtight flexible metal conduit in trade sizes metric designators 12 through 16 (trade sizes 3/ 8 through 1/ 2) in the grounding path.
d. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).
e. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.(7) Flexible metallic tubing where the tubing is terminated in fittings listed for grounding and meeting the following conditions:
a. The circuit conductors contained in the tubing are protected by overcurrent devices rated at 20 amperes or less.
b. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).(8) Armor of Type AC cable as provided in 320.108.(9) The copper sheath of mineral-insulated, metal-sheathed cable.(10) Type MC cable where listed and identified for grounding in accordance with the following:
a. The combined metallic sheath and grounding conductor of interlocked metal tapeûtype MC cable
b. The metallic sheath or the combined metallic sheath and grounding
conductors of the smooth or corrugated tube type MC cable (11) Cable trays as permitted in 392.3(C) and 392.7.(12) Cablebus framework as permitted in 370.3.(13) Other listed electrically continuous metal raceways and listed auxiliary gutters.(14) Surface metal raceways listed for grounding.Look at items 2, 3, 4, and 8.Metal conduit and AC cable can be used as an EGC.Now there is some controversy about where older AC can be used or not. 320.108 calls out a bonding strip that is not connected at either end, but it is not in older AC cable. If you look at the discussion at places place like Mike Holt and similar you will see about 1/2 of them say yes and the other 1/2 say no..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I just read through this whole thread again.
No one has mentioned that your old wiring may not be rated for your new fixtures. FHB has an article in the current issue that addresses that very common mistake. Your old wiring is likely rated for 60 degrees C or less. Your new fixtures are rated for the newer 90 degree C rated wiring.
Check out CAPs' explanation of the problem and fix in the latest isue.
Dave
That was not CAP's article.But I did post some complaints about it and CAP responded in the thread with some suggestions.http://forums.taunton.com/tp-breaktime/messages?msg=94784.13.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.