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Old 02-02-2011, 06:58 AM   #31
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Armored Cable replace?


Cowboy,

I think you may be overlooking the bond strip that type AC cable has that the older BX did not. Older BX sheath was not listed for use as a EGC.

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Old 02-02-2011, 07:14 AM   #32
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Let me hijack this thread. Tho I will agree that the solution arrived at is by far a better solution. I would like to explore why the first two diagrams where not correct, because I say that they were. I know that BX has a bad rap for not handling fault current, but that it was designed to be used as such and that AC is still designed without a separate EGC today. Tho I have been wrong in the past so if you could supply a code reference or a thread that discuss the matter inn more depth.
What people call BX (actually a first generation AC cable) was designed before an egc was required. I cannot find anything stating original AC (BX) was designed to actually carry the fault current via the sheathing. Since an egc was not required until 1962, I suspect, since it was designed in 1899, it was not designed to carry fault current. AC of today is designed to carry fault current through the sheath. It has a bonding wire; a bare solid wire that lays on the inside of the metal sheath. This eliminates the impedance problem found in BX that caused the sheath to become a resistance heater when exposed to current.

there is a ton of information available via simple searches in the internet.

code required bonding strip in AC: 1959.

egc required in all branch circuits: 1962

BX, actually called “Greenfield Flexible Steel-Armored Conductors,” patented in 1899 (yes, that Mr. Greenfield was one of the inventors). Sprague Electric Co. of New York is apparently the company he worked for at the time.

BX was apparently an internal designation. There was an AX and BX with the X designating "experimental" (much like the government used). Apparently nobody knows what happened to AX cable. BX went on to become what was later classified in the NEC as AC cable.
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Old 02-02-2011, 07:54 AM   #33
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Armored Cable replace?


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I cannot find anything stating original AC (BX) was designed to actually carry the fault current via the sheathing.
Heres my problem with your argument. I can't find anything saying you can't. Because it was old install. OP only wanted to update visible home run, I ask why he then couldn't have left the old parts if he transitioned from wiring method to method properly? Are we required to bring the whole circuit up to new code if we only touch part of it?


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I think you may be overlooking the bond strip that type AC cable has that the older BX did not. Older BX sheath was not listed for use as a EGC.
let me say thank goodness AC does have a bond strip.
However I don't see a need for our BX it to have one or to be listed. It was already installed therefore legal under rules in effect when it was installed. Does not the BX sheath weather rated for it or not still form a EGC? I am under the impression that it was considered a EGC when installed and only later found out how poor it was.
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Old 02-02-2011, 08:03 AM   #34
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I don't know the whole history on this subject, but since most circuits were still 2 wire and 3 prong receptacles did not exist, I would suspect that it had not been considered that the sheath was needed as a ECG. Might have changed after people had seen the non-bonded sheath glowing and fuses not tripping that the change to require a bond strip was added.

The issue about using the old non-bonded as a grounding means probably goes back to the listing and labeling. NEC 110.3 requires products to be used in accordance with its L&L. Using the old BX as an EGC would violate this.
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Old 02-02-2011, 08:08 AM   #35
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Quote:
=Saturday Cowboy;583062]Heres my problem with your argument. I can't find anything saying you can't. Because it was old install. OP only wanted to update visible home run, I ask why he then couldn't have left the old parts if he transitioned from wiring method to method properly? Are we required to bring the whole circuit up to new code if we only touch part of it?
he is leaving the old parts. I never suggested he couldn't.


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Quote:
et me say thank goodness AC does have a bond strip.
However I don't see a need for our BX it to have one or to be listed. It was already installed therefore legal under rules in effect when it was installed. Does not the BX sheath weather rated for it or not still form a EGC? I am under the impression that it was considered a EGC when installed and only later found out how poor it was
legal at the time. Unless you had an egc system at installation, legal means : circuit without an egc. Adding an egc is altering the system so unless you can prove early style AC cable was listed as an egc, you have now altered your system to be an illegal installation.

If that was prior to 1962, there was no requirement for an egc. If you had 2 terminal receps, there was no intent to include an egc in your system.

sounds like you will have to do some research (like patents, historical UL listings, historical NEC recognition) of how old style AC cable was thought of and treated.

Personally, regardless of whether it was legal or not, due to the problems associated with it, I surely would never suggest using it as an egc system.
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Old 02-02-2011, 10:54 AM   #36
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he is leaving the old parts. I never suggested he couldn't.


llegal at the time. Unless you had an egc system at installation, legal means : circuit without an egc. Adding an egc is altering the system so unless you can prove early style AC cable was listed as an egc, you have now altered your system to be an illegal installation.

If that was prior to 1962, there was no requirement for an egc. If you had 2 terminal receps, there was no intent to include an egc in your system.

sounds like you will have to do some research (like patents, historical UL listings, historical NEC recognition) of how old style AC cable was thought of and treated.

Personally, regardless of whether it was legal or not, due to the problems associated with it, I surely would never suggest using it as an egc system.
Just reiterating what I has been said so I understand. To be code compliant, I can run new romex to the first outlet in the chain. that outlet will be the GFCI outlet that is grounded to the metal box. The existing outlets downstream can be three pronged receptacles but should be labled "No equipment ground". This is the diagram of the proper wiring at the GFCI outlet...
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Old 02-02-2011, 08:55 PM   #37
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looks good other than your hots and neutrals are swapped (which I know you already know)
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Old 02-03-2011, 12:56 PM   #38
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looks good other than your hots and neutrals are swapped (which I know you already know)

thanks nap! I had asked this question in another forum but wanted to get your opinion since the answers kind of stopped. -
I wanted to know if I could run two a/c wall units on 1 20amp circuit? The wall units state they run at 7.5 amps. (The circuit is a dedicated circuit for one of the units now, but I wanted to add one to the bedroom next to it).


thanks again!
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Old 02-03-2011, 03:51 PM   #39
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That's a tough one. They will likely run at the same time BUT when they start or the compressor cycles, you might have some problems. A motor (either fan or compressor) draws a lot more current on start. Obviously, the two together add up to 15 amps which should be fine but that if one is running and the other one starts, it might be a problem.

I presume these are simple little plug in units, right? If you have them now, give it a try.
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Old 02-03-2011, 04:00 PM   #40
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That's a tough one. They will likely run at the same time BUT when they start or the compressor cycles, you might have some problems. A motor (either fan or compressor) draws a lot more current on start. Obviously, the two together add up to 15 amps which should be fine but that if one is running and the other one starts, it might be a problem.

I presume these are simple little plug in units, right? If you have them now, give it a try.
only have one now so I can't really give it a try. Just figured since I was going to be in the attic I could drop another line in the wall of the other bedroom for a future A/c this summer. So even if I have the 20Amp circuit it could cause a problem when they are both going?

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Old 02-03-2011, 04:58 PM   #41
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only have one now so I can't really give it a try. Just figured since I was going to be in the attic I could drop another line in the wall of the other bedroom for a future A/c this summer. So even if I have the 20Amp circuit it could cause a problem when they are both going?
it might but then again, it might not. It all depends on the start up current of the units and how long that current remains high. A 20 amp breaker can often take about 10 times rated load but it will only hold for about a half of a second. It will hold 5 times rated current for about 3 seconds.

a motor starting can often draw 5 times normal run current so, if you have 2 units @7.5 amps each, 5 times that would be 37.5 amps. Double that (2 units) would be 75 amps or 3 3/4 times name rating. A trip curve for a square d qo 20 amp shows that the breaker should hold from 1 3/4 to 6 seconds at that load. (all figures are approximate and guesstimates)

High ambient temp (around the breaker) will generally reduce that time. A bad motor will often increase load which would mean a reduced time. A weak breaker will not hold as well.

It might hold but I wouldn't bet on it.
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Old 02-03-2011, 05:18 PM   #42
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NOTE: regarding the 7.5 amp number. It's to close to call follow the advice of the other sparks in this forum, why.

Because for one thing regardless of the amp rating as soon as wall/window air conditioners start getting a little dirt on the condenser coils and the fan blades the amp readings start rising until they go out on overload. Point do not cut it that close. Run 2 - 12-2s with 15 amp breaker then if you ever wanted to up the BTU rating and get a larger A/C you have the capability to install a 20 amp breaker with the 12 already there.
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Old 02-03-2011, 05:33 PM   #43
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NOTE: regarding the 7.5 amp number. It's to close to call follow the advice of the other sparks in this forum, why.

Because for one thing regardless of the amp rating as soon as wall/window air conditioners start getting a little dirt on the condenser coils and the fan blades the amp readings start rising until they go out on overload. Point do not cut it that close. Run 2 - 12-2s with 15 amp breaker then if you ever wanted to up the BTU rating and get a larger A/C you have the capability to install a 20 amp breaker with the 12 already there.
Thanks for the help. I may have just lucked out. I found that there is a dedicated 20Amp outlet in another room upstairs. No idea why, but I am going to take that line and use it for the A/C. Now my question is, why do you suggest putting a 15Amp breaker on 12/2? Is there a savings of doing that?
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Old 02-03-2011, 05:47 PM   #44
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There would be no savings putting the 15 amp breaker on #12 wire. The breakers cost the same. In fact you would incur additional cost down the road if you changed it to a 20 amp.
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Old 02-04-2011, 07:15 AM   #45
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Thanks for the help. I may have just lucked out. I found that there is a dedicated 20Amp outlet in another room upstairs. No idea why, but I am going to take that line and use it for the A/C. Now my question is, why do you suggest putting a 15Amp breaker on 12/2? Is there a savings of doing that?
" I was thinking it be closer to the amp rating you were looking for, of course you would like to use the amp rating closer to the equipment on that circuit. If you already have a 20 there go for it. I wasn't thinking about cost I was thinking of what fit your circumstance. 2runs 12-2 with 15 amp breakers for each A/C then if you want to up-size the A/Cs you already have the 12 installed just up the breakers to 20, no need to have 20 amp breakers on what you described. Of course if you want put 20s in."

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