Grounding of two wire circuits

[al hildenbrand]

Some of the findings should make you think twice about accepting unbonded armored cable as an adequate EGC or even safe in its existing condition, grandfathered code or no grandfathered code.

Thank you for the reference to this recent research. It's too bad that it is shrouded by a fee.

Your synopsis has been instructive. I look forward to learning more.

That said, I turn back to the original post and the situation described. Based on the OP and subsequent clarifications, I understand that residential dwelling to have bond wire AC installed.

A ceiling fan was replaced. Does connecting the new ceiling fan EGC to the AC method EGC make the installation worse?

No.

In your own words, Mivey, you wouldn't loose sleep over the slight weakness of the AC bond wire sheath EGC.

A simple resistance check will determine if the workmanship of the OP dwelling's EGC is still most likely to be intact.

Now, I'm still not sure about how a ceiling fan is "ground hungry", in your term, but having the exposed conductive parts of the fan connected to even the AC EGC is better than not. Especially since the NEC has consistantly told us that both non-bond and bond AC are effective grounding means.

 

[mivey]

Thanks Mivey,. for all the info.

You're welcome.

 

[mivey]

Thank you for the reference to this recent research. It's too bad that it is shrouded by a fee.

Your synopsis has been instructive. I look forward to learning more.

You're welcome. The author appeared to have open access to a lot of hard-to-find information and conducted some impressive research.

That said, I turn back to the original post and the situation described. Based on the OP and subsequent clarifications, I understand that residential dwelling to have bond wire AC installed.

A ceiling fan was replaced. Does connecting the new ceiling fan EGC to the AC method EGC make the installation worse?

No.

In your own words, Mivey, you wouldn't loose sleep over the slight weakness of the AC bond wire sheath EGC.

A simple resistance check will determine if the workmanship of the OP dwelling's EGC is still most likely to be intact.

Now, I'm still not sure about how a ceiling fan is "ground hungry", in your term, but having the exposed conductive parts of the fan connected to even the AC EGC is better than not.

I posted before that I did not realize at first that the OP had bonded cable and I have addressed it. A simple resistance check would certainly be a start.

"Ground hungry" meaning that it is required to be connected to ground. Did not used to be a requirement for fixtures.

Especially since the NEC has consistantly told us that both non-bond and bond AC are effective grounding means.

No they have not. Their actions have shown that they do NOT believe non-bonded armored cable is an effective grounding means. Even with bonded cable they realized what they initially THOUGHT was effective turned out to be not so great. In this case, they found they had to tweak the requirements to make bonded cable acceptable. Several changes in fact.

What they have said about the unbonded cable was that it was such a pitiful means of grounding that tweaking was not going to work. Rather, they chose to eliminate it altogether as an acceptable grounding means.

Nothing consistent about it at all other than they consistently got it wrong for so long.

 

[al hildenbrand]

"Ground hungry" meaning that it is required to be connected to ground.

Being required to be connected to the EGC does not have emotion or physiological need in it.

they chose to eliminate it altogether as an acceptable grounding means.

There is no existing Code Rule that retroactively removes cable armor from the list of effective grounding means in previous editions of the Code for installations assembled under those previous editions of the Code. Show me otherwise.

I am loathe to speak for "They", but "They" apparently "intended" to keep existing installations of non-bonded AC classified as effective grounding means because "They" were silent about retroactively reclassifying existing installations. "They" did not choose "to eliminate it altogether," as you claim.

 

[G._S._Ohm]

You can check grounding effectiveness by passing 10 A or 20 A through the armor. If this gives a voltage drop of 1.6 volts or 3.2 volts for every 100' of armor then it is as good as #12 copper, at least on the day that you make the measurement.

 

[tryinghard]

You can check grounding effectiveness by passing 10 A or 20 A through the armor. If this gives a voltage drop of 1.6 volts or 3.2 volts for every 100' of armor then it is as good as #12 copper, at least on the day that you make the measurement.

Not a bad idea - but could be dangerous.

 

[kwired]

You can check grounding effectiveness by passing 10 A or 20 A through the armor. If this gives a voltage drop of 1.6 volts or 3.2 volts for every 100' of armor then it is as good as #12 copper, at least on the day that you make the measurement.

Problem is the impedance changes with the amount of current because of inductive effects. It is not the same thing as a piece of copper. Steel armor because of its magnetic properties, will be much worse than aluminum armor. The whole circuit is an inductor.

 

[mivey]

Being required to be connected to the EGC does not have emotion or physiological need in it.

But if it needs a ground, it requires action on our part. And that action must be code compliant.

There is no existing Code Rule that retroactively removes cable armor from the list of effective grounding means in previous editions of the Code for installations assembled under those previous editions of the Code. Show me otherwise.

I am loathe to speak for "They", but "They" apparently "intended" to keep existing installations of non-bonded AC classified as effective grounding means because "They" were silent about retroactively reclassifying existing installations. "They" did not choose "to eliminate it altogether," as you claim.

Then please show me in the current code where the old AC cable is listed as an effective grounding means.

We are installing a new fixture on an old system. This new fixture has a ground that must be connected. We have to connect it per the code. So let's follow what the code says:

410.40 General. Luminaires and lighting equipment shall be grounded as required in Article 250 and Part V of this article.

OK so now what does article 250 tell us?

250.4(A)(5) Effective Ground-Fault Current Path.
Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.

So we can't just connect to anything. We must connect to an effective path. The old armor has been shown to not be an effective path by testing and as evidenced by the change in the type construction.

Let's now look at what part V of article 410 has to offer:

410.44 Methods of Grounding. Luminaires and equipment shall be mechanically connected to an equipment grounding conductor as specified in 250.118 and sized in accordance with 250.122.
Exception No. 1: Replacement luminaires shall be permitted to connect an equipment grounding conductor from the outlet in compliance with 250.130(C). The luminaire shall then comply with 410.42(A).

So we are required to use an EGC as specified in 250.118 and of appropriate size so let's look at that:

250.118(8) Armor of Type AC cable as provided in 320.108.

320.108 Equipment Grounding Conductor. Type AC cable shall provide an adequate path for fault current as required by 250.4(A)(5) or (B)(4) to act as an equipment grounding conductor.

320.100 Construction. Type AC cable shall have an armor of flexible metal tape and shall have an internal bonding strip of copper or aluminum in intimate contact with the armor for its entire length.

250.122 Size of Equipment Grounding Conductors.
(A) General
...Where a cable tray, a raceway, or a cable armor or sheath is used as the equipment grounding conductor, as provided in 250.118 and 250.134(A), it shall comply with 250.4(A)(5) or (B)(4).

So if we choose to use AC cable, it must have an adequate path. We can't just use any old path we want. The old AC cable did not have an adequate path. The AC cable with an adequate path has the bonding strip.

We could use a different method:

250.130 Equipment Grounding Conductor Connections.
...For replacement of non?grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

250.130(C) Nongrounding Receptacle Replacement or Branch
Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:
(1) Any accessible point on the grounding electrode system as described in 250.50
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
(4) For grounded systems, the grounded service conductor within the service equipment enclosure
(5) For ungrounded systems, the grounding terminal bar within the service equipment enclosure

Or we could use GFCI protection. From 410.42

Exception No. 2: Where no equipment grounding conductor exists at the outlet, replacement luminaires that are GFCI protected shall not be required to be connected to an equipment grounding conductor.

None of the alternatives show where the old AC cable with the faulty ground path is allowed to be used for new connections to the grounding system. It used to be there as an acceptable path, now it is not. If it used to be there, but it is no longer there, it has been eliminated as an acceptable path.

 

[tryinghard]

...It used to be there as an acceptable path, now it is not. If it used to be there, but it is no longer there, it has been eliminated as an acceptable path.

In this light why stop at the fan outlet if you know the rest of the house is the same?

 

[mivey]

In this light why stop at the fan outlet if you know the rest of the house is the same?

Because you have only been contracted to deal with the light. The fix will only take care of that one circuit. If they want me to take care of the rest, I can. I would certainly make some recommendations.

 

[al hildenbrand]

There is no existing Code Rule that retroactively removes cable armor from the list of effective grounding means in previous editions of the Code for installations assembled under those previous editions of the Code.

Then please show me in the current code where the old AC cable is listed as an effective grounding means.

We are installing a new fixture on an old system.

I have already shown you the old Code defining cable armor as an effective grounding means.

You are not altering the "old system". It is already installed to a previous Code.

Hanging a fan, on an existing box, is not installing a box nor is it installing a branch circuit, nor is it installing armored cable. None of today's Code applies to the grounding means in the existing installation, because, there is no current Code that retroactively takes away "effective grounding means" from armored cable installed to the Code of it's original date of install.

 

[mivey]

I have already shown you the old Code defining cable armor as an effective grounding means.

You are not altering the "old system". It is already installed to a previous Code.

And had the light been installed under that code, it would be fine to leave it as is. We can't make a law retroactive.

Hanging a fan, on an existing box, is not installing a box nor is it installing a branch circuit, nor is it installing armored cable.

Show me that code exception. The current code specifies how we must ground a new luminaire.

None of today's Code applies to the grounding means in the existing installation,

Installing a new luminaire is not an existing installation. The code tells us the ways we have to ground the new luminaire and the old AC cable was not listed as one of those means.

because, there is no current Code that retroactively takes away "effective grounding means" from armored cable installed to the Code of it's original date of install.

That means we are not required to pull out the old and replace it with something new. That does not mean we can hook up new stuff to the old and all of the old specs would be "grandfathered" in some way as to forgive the requirements for the new stuff.

 

[G._S._Ohm]

Problem is the impedance changes with the amount of current because of inductive effects. It is not the same thing as a piece of copper. Steel armor because of its magnetic properties, will be much worse than aluminum armor. The whole circuit is an inductor.

It's a coil with low resistances between each turn which sort of shorts each turn. I'd guess the Z of a length of the armor is slightly more than the R of the same length.

Probably somebody has measured this. Aging, rusty cable may be more of an inductor and cable being flexed during measurement will probably give flaky readings.

 

[mivey]

...I'd guess the Z of a length of the armor is slightly more than the R of the same length.

Probably somebody has measured this.

In the paper I referenced, the DC of non-bonded #14 averaged 3.04Ω/100ft, 3.37Ω/100ft at 10 amps, 3.78Ω/100ft at 15 amps, and 4.4Ω/100ft at 20 amps. The bonded average was 0.75Ω/100ft at DC, 0.60Ω/100ft at 10 amps, 0.66Ω/100ft at 15 amps, and 0.70Ω/100ft at 20 amps.

The DC of non-bonded #12 averaged 3.10Ω/100ft, 3.89Ω/100ft at 15 amps, 4.47Ω/100ft at 20 amps, and 5.21Ω/100ft at 25 amps. The bonded average was 0.94Ω/100ft at DC, 0.44Ω/100ft at 15 amps, 0.47Ω/100ft at 20 amps, and 0.49Ω/100ft at 25 amps.

 

[al hildenbrand]

Installing a new luminaire is not an existing installation. .

Correct.

Installing a new luminaire is not an existing luminaire.

The replacement (new) luminaire is installed on an existing Lighting Outlet. That existing Lighting Outlet was installed under a different Code to that Code, not today's Code.

2008 NEC
Article 100 Definitions
Lighting Outlet. An outlet intended for the direct connection of a lampholder or luminaire.

Note that a luminaire or lampholder need not be present for a Lighting Outlet to be a Lighting Outlet. The definition doesn't say that the luminaire is connected, only that it is intended for connection.

Connecting a replacement (new) luminaire to the existing Lighting Outlet does not make the Lighting Outlet a new installation bound by today's Code.

 

[mivey]

Correct.

Installing a new luminaire is not an existing luminaire.

The replacement (new) luminaire is installed on an existing Lighting Outlet. That existing Lighting Outlet was installed under a different Code to that Code, not today's Code.Note that a luminaire or lampholder need not be present for a Lighting Outlet to be a Lighting Outlet. The definition doesn't say that the luminaire is connected, only that it is intended for connection.

Connecting a replacement (new) luminaire to the existing Lighting Outlet does not make the Lighting Outlet a new installation bound by today's Code.

The requirement is for the luminaire. Nothing in the code says we have to use an old outlet. What the code does specify is how we can connect the luminaire. The old wiring does not meet the requirements for the new fixture.

You are trying to argue that there is some kind of "grandfathering clause" and it just isn't there. If it is, the code would have listed the old grounding types to be acceptable under certain conditions. That exception is not in the code. The old wiring method is simply not listed as a proper method of grounding for the new fixture we are installing.

 

[G._S._Ohm]

In the paper I referenced, the DC of non-bonded #14 averaged 3.04Ω/100ft, 3.37Ω/100ft at 10 amps, 3.78Ω/100ft at 15 amps, and 4.4Ω/100ft at 20 amps. The bonded average was 0.75Ω/100ft at DC, 0.60Ω/100ft at 10 amps, 0.66Ω/100ft at 15 amps, and 0.70Ω/100ft at 20 amps.

The DC of non-bonded #12 averaged 3.10Ω/100ft, 3.89Ω/100ft at 15 amps, 4.47Ω/100ft at 20 amps, and 5.21Ω/100ft at 25 amps. The bonded average was 0.94Ω/100ft at DC, 0.44Ω/100ft at 15 amps, 0.47Ω/100ft at 20 amps, and 0.49Ω/100ft at 25 amps.

"Ask and ye' shall receive." :grin:

But, I don't get how the AC impedance can be less than the DC resistance in the bonded cases. Once this is cleared up I should be able to calc. the microhenries per foot of the armor. This is at 60 Hz, right?

 

[al hildenbrand]

The requirement is for the luminaire. Nothing in the code says we have to use an old outlet. What the code does specify is how we can connect the luminaire. The old wiring does not meet the requirements for the new fixture.

Well, go ahead and install a new lighting outlet . . . no one's stopping you. When the client compares your price to the price of the Contractor that uses the existing lighting outlet, well, good luck selling up.

This is real simple.

Consider an existing 120 V 20 A grounding type receptacle outlet installed for a window air conditioner. The single 120 V 20 A grounding type receptacle device is connected to old bond wire armored cable conductors. The electrician comes to help by removing the 30 year old window AC and then sets and plugs in the brand new (bought yesterday) AC.

The window AC must be grounded.

So, by your logic, a grounding type receptacle outlet installed to the Code of the day of original install is retroactively now not installed to that Code.

The window AC is directly analogous to the luminaire (ceiling fan of the OP). Neither is part of the Premises Wiring (System). Both are utilization equipment.

You are claiming that any one who plugs in a cable / satellite converter box (desk top computer, microwave, whatever), with its grounding cord, is redefining the Code approved installation of the bond wire BX supplied grounding type receptacles into a non Code approved installation. Somehow, the utilization equipment has created a new non code installation all the way through the armored cable branch circuit.

 

[mivey]

Well, go ahead and install a new lighting outlet . . . no one's stopping you. When the client compares your price to the price of the Contractor that uses the existing lighting outlet, well, good luck selling up.

Where did I say you should install a new lighting outlet?

This is real simple.

You would think.

So, by your logic, a grounding type receptacle outlet installed to the Code of the day of original install is retroactively now not installed to that Code.

You can keep saying that the code grandfathers previous code all you want but saying it won't make it so. The places in the code where previous methods are allowed are covered with statements like "in existing locations...". There was no such statement for unbonded AC cable.

The AHJ can grandfather in some installations that met prior code but do not meet the current code. And they often do. But that is a AHJ allowance, not an allowance that is in the code.

The window AC is directly analogous to the luminaire (ceiling fan of the OP). Neither is part of the Premises Wiring (System). Both are utilization equipment.

What does that have to do with anything? Are you saying the code does not cover equipment? Why the whole section on luminaires then?

You are claiming that any one who plugs in a cable / satellite converter box (desk top computer, microwave, whatever), with its grounding cord, is redefining the Code approved installation of the bond wire BX supplied grounding type receptacles into a non Code approved installation. Somehow, the utilization equipment has created a new non code installation all the way through the armored cable branch circuit.

That is not what I said and that is not what the code says. The code says what it says, nothing more.

 

[tryinghard]

Because you have only been contracted to deal with the light. The fix will only take care of that one circuit. If they want me to take care of the rest, I can. I would certainly make some recommendations.

Careful with your pronouns; I don't necessarily contract this way.