# older house grounding system



## nternes (Sep 25, 2012)

Hello ppl. I recently bought a house built in the early 70s in great shape. Nothing wrong with the electrical in the house as far as problems go. Now I am curious to know how these older homes are grounded. I am a 3rd year apprentice inside wireman. Work commercial and industrial so I am familiar with grounding systems. Now the electrical was run with fmc and metal boxes. No grounding conductors at all. The boxes are grounded somehow because I read voltage from the ungrounded conductor to the box. My question is how was this accomplished? Are the conduits and boxes serving as the low impedence path back to the service? Is the main panel grounded? I did however notice on the service drop there are two cables coming into the meter and three coming out into the panel. One of which is landed into a neutral bus. Didnt see any bonding jumper in there although it was kinda crowded. Any insight would be helpful. Thanx


----------



## 3DDesign (Oct 25, 2014)

nternes said:


> Hello ppl. I recently bought a house built in the early 70s in great shape. Nothing wrong with the electrical in the house as far as problems go. Now I am curious to know how these older homes are grounded. I am a 3rd year apprentice inside wireman. Work commercial and industrial so I am familiar with grounding systems. Now the electrical was run with fmc and metal boxes. No grounding conductors at all. The boxes are grounded somehow because I read voltage from the ungrounded conductor to the box. My question is how was this accomplished? Are the conduits and boxes serving as the low impedence path back to the service? Is the main panel grounded? I did however notice on the service drop there are two cables coming into the meter and three coming out into the panel. One of which is landed into a neutral bus. Didnt see any bonding jumper in there although it was kinda crowded. Any insight would be helpful. Thanx


I've never seen a house wired using Flexible Metal Conduit. Are you sure this isn't BX Armored Cable? Are the conductors similar to THHN or cloth & rubber?


----------



## chicken steve (Mar 22, 2011)

Well first off, there's got to be an MBJ, some GE's, some GEC's proximal to the service.

@ndly, vintage wiring methods vary. You'll need to identify what you have for any of us to expand on them .

If in fact you've BX , you'll find 1000 yrs experience all over it @ ET

~CS~


----------



## tersus (Jul 3, 2012)

In your receptacles, you're getting voltage between the hot wire and the box because the box is grounded by means of the metallic conduit back to the panel. If you have a main breaker panel serving as the first service disconnect means, then the panel should utilize the bonding jumper.


----------



## Switched (Dec 23, 2012)

3DDesign said:


> I've never seen a house wired using Flexible Metal Conduit. Are you sure this isn't BX Armored Cable? Are the conductors similar to THHN or cloth & rubber?


There are a bunch of homes through Cali that are wired in steel FMC, done from the mid 60's up to the early 90's. They are using the FMC as the ground on these places.


----------



## chicken steve (Mar 22, 2011)

i thought FMC was a ground up to 6'.....? :001_huh:~CS~


----------



## macmikeman (Jan 23, 2007)

3DDesign said:


> I've never seen a house wired using Flexible Metal Conduit. Are you sure this isn't BX Armored Cable? Are the conductors similar to THHN or cloth & rubber?


I had to wire a dorm at BYU Hawaii once using flex conduit every circuit to keep my boss happy. That stuff was murder pushing the fish tape thru , I think this may have been before the fiberglass fish tapes showed up at the supply houses around here also. I think labor pulling wire killed any savings he thought he was going to make using flex instead of us wiring it all with emt.


----------



## Switched (Dec 23, 2012)

chicken steve said:


> i thought FMC was a ground up to 6'.....? :001_huh:~CS~


They have a heck of a lot longer runs going than that. The worst part is that most of the installations I have seen have a good amount of rust and deterioration on them.....


----------



## wildleg (Apr 12, 2009)

*older house grounging system*

older house grounging system

here's some utube instructions on grunging


----------



## nternes (Sep 25, 2012)

Its definetlty flex with THHN. There probably is a bonding jumper in there but like I said its kind of crowded in the panel. I was wondering where the ground was derived. Its just my curiosity.


----------



## nternes (Sep 25, 2012)

It was a typo ****


----------



## chicken steve (Mar 22, 2011)

Switched said:


> They have a heck of a lot longer runs going than that. The worst part is that most of the installations I have seen have a good amount of rust and deterioration on them.....


Well that begs the Q, is it hard to repull Switch?

~CS~


----------



## Switched (Dec 23, 2012)

Yes....A complete pain in the A**....but better than having to remove sheetrock!

A good flexible fish tape goes a long way....


----------



## chicken steve (Mar 22, 2011)

Well, that's more than i can say for all the bit & brace installs i reno

Those boys didn't drill 1/16" of wood more than they had to.....

~CS~


----------



## Awg-Dawg (Jan 23, 2007)

Switched said:


> Yes....A complete pain in the A**....but better than having to remove sheetrock!
> 
> A good flexible fish tape goes a long way....



Try a vacuum.


----------



## Switched (Dec 23, 2012)

Awg-Dawg said:


> Try a vacuum.


Have you ever tried a vacuum on flex? I would just assume that it would not work out so well.


----------



## nternes (Sep 25, 2012)

So..................I guess I get the same quality of explanations here as I do from 80% of JWs I have worked with. Nothin but wise cracks and subject changes. To those who gave me decent answers...thank you. And the rest, well


----------



## Switched (Dec 23, 2012)

nternes said:


> So..................I guess I get the same quality of explanations here as I do from 80% of JWs I have worked with. Nothin but wise cracks and subject changes. To those who gave me decent answers...thank you. And the rest, well


Dude, you have your answer, and you knew it all along.

The grounding is being performed via the conduits, albeit probably a poor ground in some locations. The panel/service is likely grounded to the main water supply and/or a ground rod.


----------



## nternes (Sep 25, 2012)

Thanx switched. I was referring to the grunging link. No patience for smart alecs. Anyway I just never seen it before and thought it was strange. Seems like it would be unreliable.


----------



## 3xdad (Jan 25, 2011)

Damn, apprentices be buy'n up castles on here. Congrats to you guys, i think.


----------



## Black Dog (Oct 16, 2011)

nternes said:


> Hello ppl. I recently bought a house built in the early 70s in great shape. Nothing wrong with the electrical in the house as far as problems go. Now I am curious to know how these older homes are grounded. I am a 3rd year apprentice inside wireman. Work commercial and industrial so I am familiar with grounding systems. Now the electrical was run with fmc and metal boxes. No grounding conductors at all. The boxes are grounded somehow because I read voltage from the ungrounded conductor to the box. My question is how was this accomplished? Are the conduits and boxes serving as the low impedence path back to the service? Is the main panel grounded? I did however notice on the service drop there are two cables coming into the meter and three coming out into the panel. One of which is landed into a neutral bus. Didnt see any bonding jumper in there although it was kinda crowded. Any insight would be helpful. Thanx


As a 3rd year apprentice you should be pretty handy with the NEC and understand it, your school should be teaching you the NEC grounding and bonding .

What you are talking about can be found in 250.118, 2014 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 listed fittings.
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-fault current path does not exceed 1.8 m (6 ft).
d. 
If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement 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 listed fittings.
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 ¾ through 1¼), 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 ½) in the ground-fault current path.
d. 
The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
e. 
If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation, an equipment grounding conductor shall be installed.
(7) 
Flexible metallic tubing where the tubing is terminated in listed fittings 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-fault current 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 Type MI.
(10) 
Type MC cable that provides an effective ground-fault current path in accordance with one or more of the following:
a. 
It contains an insulated or uninsulated equipment grounding conductor in compliance with 250.118(1)
b. 
The combined metallic sheath and uninsulated equipment grounding/bonding conductor of interlocked metal tape–type MC cable that is listed and identified as an equipment grounding conductor
c. 
The metallic sheath or the combined metallic sheath and equipment grounding conductors of the smooth or corrugated tube-type MC cable that is listed and identified as an equipment grounding conductor
(11) 
Cable trays as permitted in 392.10 and 392.60.
(12) 
Cablebus framework as permitted in 370.60(1).
(13) 
Other listed electrically continuous metal raceways and listed auxiliary gutters.
(14) 
Surface metal raceways listed for grounding.
Informational Note:  For a definition of Effective Ground-Fault Current Path, see Article 100.





nternes said:


> So..................I guess I get the same quality of explanations here as I do from 80% of JWs I have worked with. Nothin but wise cracks and subject changes. To those who gave me decent answers...thank you. And the rest, well


You are talking to electricians who are not at work, but are talking electrical work and having a little fun too, without all the fun you would not have gotten an answer at all because no one wold be hanging around here.

So chill out and have a little fun brother


----------



## nternes (Sep 25, 2012)

Houses are cheap where I live.


----------



## nternes (Sep 25, 2012)

Im the chillist bro out there. And yes I do understand NEC.


----------



## Black Dog (Oct 16, 2011)

nternes said:


> Im the chillist bro out there. And yes I do understand NEC.


Do You?because I've been reading it 40 years an still don't get it.

If you read the code article I posted that should make it so You understand how the grounding works using metal raceways.


----------



## wildleg (Apr 12, 2009)

nternes said:


> Thanx switched. I was referring to the grunging link. No patience for smart alecs. Anyway I just never seen it before and thought it was strange. Seems like it would be unreliable.





nternes said:


> Im the chillist bro out there. And yes I do understand NEC.


if that were true, you wouldn't have got your panties twisted up at all.

if you aren't going to proof read your posts, expect to be teased.

teach yourself how to use the ignore feature if you don't like it.

carry on.


----------



## Awg-Dawg (Jan 23, 2007)

Switched said:


> Have you ever tried a vacuum on flex? I would just assume that it would not work out so well.


I've never used it on flex.

The runs on a house would be so short it might work.


----------



## Switched (Dec 23, 2012)

This is the best fish tape I have for using on flex or old underground conduits...
http://www.idealind.com/prodDetail.do?prodId=zoom-fish-tapes&div=5&l1=fishtapes&l2=zoom-fish-tapes


----------



## nternes (Sep 25, 2012)

.....


----------



## Black Dog (Oct 16, 2011)

Switched said:


> This is the best fish tape I have for using on flex or old underground conduits...
> http://www.idealind.com/prodDetail.do?prodId=zoom-fish-tapes&div=5&l1=fishtapes&l2=zoom-fish-tapes


Nice, what did that go for?


----------



## Switched (Dec 23, 2012)

I've had it for about 12 years now....I imagine somewhere around $75?


----------



## guest (Feb 21, 2009)

nternes said:


> Thanx switched. I was referring to the grunging link. *No patience for smart alecs.* Anyway I just never seen it before and thought it was strange. Seems like it would be unreliable.


Welcome to the nuthouse.  Get used to it, we have quite a crew of wiseacres here so don't take it so seriously or you'll go bonkers. :thumbsup:


----------



## Big Pickles (Oct 25, 2014)

Alot of cities by me were wired in fmc. Mudrings had a side clip that got in the way of gfci's👎. 6' rule was not in place back then.


----------



## BuzzKill (Oct 27, 2008)

macmikeman said:


> I had to wire a dorm at BYU Hawaii once using flex conduit every circuit to keep my boss happy. That stuff was murder pushing the fish tape thru , I think this may have been before the fiberglass fish tapes showed up at the supply houses around here also. I think labor pulling wire killed any savings he thought he was going to make using flex instead of us wiring it all with emt.


Worked for an EC years ago that swore by using FMC, MC cable was not allowed...pain in the arse fishing wire through these long ass runs of it.


----------



## nternes (Sep 25, 2012)

Big Pickles said:


> Alot of cities by me were wired in fmc. Mudrings had a side clip that got in the way of gfci's?dc4e. 6' rule was not in place back then.


Yes much more than 6 ft runs in this house.


----------



## chicken steve (Mar 22, 2011)

Seems mighty Chicago-ish, was this a local rule? 

~CS~


----------



## Wirenuting (Sep 12, 2010)

Switched said:


> They have a heck of a lot longer runs going than that. The worst part is that most of the installations I have seen have a good amount of rust and deterioration on them.....


Some folks have a "work around" for that problem.


----------



## Switched (Dec 23, 2012)

I had the head inspector for one city recently tell me that I could ground a fixture on a 2 wire circuit by just attaching a pigtail from the metal box to the fixture ground wire. Problem solved!:blink:


----------



## EJPHI (May 7, 2008)

nternes said:


> Yes much more than 6 ft runs in this house.


I have one of those FMC wired houses too. Mine was built in 1968 and I believe the code then did not limit the length of FMC used as the EGC to < 6 feet.

One of the geniuses on here will probably know when the code changed. 

Your wire is probably TW not THHN. I re-pull with a green wire whenever I change anything. A lot of the switches and receptacles have failed so I get to replace them with good ones.

Fishing is a pain, I am gong to get one of those fiber glass fishtapes.

Lots of ribbing going on here, but even a low life egineer like me learns a lot from this forum.

EJPHI


----------



## nternes (Sep 25, 2012)

EJPHI said:


> I have one of those FMC wired houses too. Mine was built in 1968 and I believe the code then did not limit the length of FMC used as the EGC to < 6 feet.
> 
> One of the geniuses on here will probably know when the code changed.
> 
> ...


I havnt had any real issues with this house so I havent replaced any receps just a switch or two and fixtures. Where I live it gets 110+ so THHN is the way we go here.


----------



## EJPHI (May 7, 2008)

nternes said:


> I havnt had any real issues with this house so I havent replaced any receps just a switch or two and fixtures. Where I live it gets 110+ so THHN is the way we go here.



Didn't know THHN was used in the 70's. 

EJPHI


----------

