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Old 07-30-2008, 04:08 PM   #1
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1930s armored cable wiring


Hello all,

I hope you can help me. My house was built sometime between 1927-1930. There was knob and tube in the attic and detached garage. My electrician replaced the K&T and upgraded my service to 150 amp service, as well as re-wired all of the outlets in the kitchen and the outlets for the tv, stereo, computer. I wanted to get blown-in insulation but found out I can't if there is K&T. So I called my electrician back and he said that I don't have K&T, but have something called armored cable wiring. It is very old looking and sheathed in a black fabric. He said I can get the insulation, but that he thinks it would be a good idea to replace the wiring since it is very old and looks it. He wants to charge me $100 per outlets (meaning outlets, light switches and light fixture outlets). He will also charge $100 per circuit (there are plenty of circuit left on my panel).

All the research I've done points to replacing it. But I'm curious what all of you think. Should I replace it? And if I get blown-in insulation now, how hard will it be to replace it after that?

Thanks in advance for the advice. As you can glean from this - I have no idea about anything electrical.

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Old 07-30-2008, 04:20 PM   #2
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1930s armored cable wiring


I have some of that stuff in my old house. Sounds like old "snakeskin" wire to me. Certainly bettern than knob and tube. The jacket of the old wire becomes old and brittle, and can fall apart pretty easily if the conditions are right. With it being as old as it is, replacement would probably be worth considering. That doesn't mean that you couldn't go on using it with no issue for many more years. Only way to know for sure is to see it.

It would be easier for sparky to pull the wires before you have insulation blown in, but it certainly could be done later. The insulation just makes it a challenge to fish through concealed spaces, where without the insulation he can work much easier.

As for the price, there are so many variables. I'd suggest getting a few bids and meeting with a few electricians. Make sure they are going to get the required permits and inspections, and don't necessarily go for the cheapest bid. If they don't want to pull a permit, I'd suggest thanking them and end the meeting right there...Many contractors are resistant to being held to the minimum standards of the code, and for no good reason. Also make sure they'll be the ones doing the work and not subcontracting the job out. Nothing wrong with checking prices to make sure you're getting a fair deal.

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Old 07-31-2008, 08:13 AM   #3
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1930s armored cable wiring


Thanks for the reply! And your dog is so cute! My electrician is a master electrician and therefore able to pull a permit and he wouldn't do anything that isn't up to code. I've spoken with a few electricians and his price is competitive. What I like about his price this that it is a flat rate - so there are no surprises. I can count the outlets and I'll pretty much know the cost. Also, he does all the work himself.
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Old 07-31-2008, 08:24 AM   #4
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1930s armored cable wiring


Armored cable has a spiral wound metal jacket. What you described is not armored cable.
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Old 07-31-2008, 08:37 AM   #5
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1930s armored cable wiring


Hi Jim Port

I could be wrong, but everything I've researched calls it armored cable - it is just the very first version of it. It is also called BX or armor clad cable.
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Old 07-31-2008, 09:03 AM   #6
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1930s armored cable wiring


This is BX, or armored cable. MC and "greenfield" are similar.

You mentioned a black fabric coating, which is not armored cable. If your electrician calls that armored cable, find yourself a new electrician!
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Old 07-31-2008, 09:47 AM   #7
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1930s armored cable wiring


Hi again


Don't mean to be difficult, but this is where I'm getting my information from. Perhaps these sites are incorrect?

AC(BX) Armor clad cable BX is the common trade name for AC. BX was the trademark of cable made by G.E.'s Sprague Electric division.
189?- Gus Johnson and Harry Greenfield patent AC
1910- AC receiving acceptance.
1920s or the early 1930s widespread adoption.
1932 NEC- Armored cable was officially called Type AC
1952- Aluminum clad AC introduced.
1959 NEC- Aluminum bonding wire required under metal sheathing.



And this part too:



After K&T, they invented multi-conductor cable. The first type
you will see is roughly a cloth and varnish insulation. It
looks much like the romex cable of the last decade or two.
This stuff was used in the 40's and 50's. Again, no grounding
conductor. It was installed much like modern wiring. Its
major drawback is that this type of insulation embrittles.
We've seen whole systems where the insulation would fracture
and fall off at a touch. BX cable of the same vintage has
similar problems. It is possible for the hot conductor to
short out to the cable jacket. Since the jacket is rusted, it
no longer presents a low resistance return path for the current
flow, but rather more acts like a resistance heater. In
extreme cases the cable jacket will become red hot without
blowing the fuse or circuit breaker. The best thing to do with
old style BX is to replace it with modern cable whenever it's
encountered and there's any hint of the sheath rusting.

This stuff is very fragile, and becomes rather hazardous if the
wires become bare. This wiring should be left untouched as
much as possible - whenever an opportunity arises, replace it.
A simple receptacle or switch replacement can turn into a
several hour long frustrating fight with electrical tape or
heat-shrink tubing.

After this wiring technique, the more modern romex was
invented. It's almost a asphalt impregnated cloth. Often a
bit sticky. This stuff stands up reasonably well and doesn't
present a hazard and is reasonably easy to work with. It does
not need to be replaced - it should be considered as safe as
the "modern" stuff - thermoplastic insulation wire. Just don't
abuse it too much.
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Old 07-31-2008, 10:48 AM   #8
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1930s armored cable wiring


Lisa, you're not being difficult...You're educating yourself.

The paragraph you posted definately differentiates between armored (BX, etc) cable and impregnated cloth covered multi-conductor cable here...

"After K&T, they invented multi-conductor cable. The first type
you will see is roughly a cloth and varnish insulation. It
looks much like the romex cable of the last decade or two.
This stuff was used in the 40's and 50's. Again, no grounding
conductor. It was installed much like modern wiring. Its
major drawback is that this type of insulation embrittles.
We've seen whole systems where the insulation would fracture
and fall off at a touch. BX cable of the same vintage has
similar problems."

It goes on to discuss the potential shorting and rusting of the armored metal jacket of the old BX.

If you can post a picture we can tell you what you've got for sure. I'm taking odds that it is not armored.
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Old 07-31-2008, 02:11 PM   #9
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1930s armored cable wiring


Cool! I'll take a picture of it, and then you can take a picture of yourself recoiling in horror at the state of it.

Thanks!
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Old 08-01-2008, 09:24 AM   #10
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1930s armored cable wiring


Quote:
Originally Posted by Lisa_90 View Post
Cool! I'll take a picture of it, and then you can take a picture of yourself recoiling in horror at the state of it.

Thanks!
LOL. I run into both of these. And it's very common, especially in light fixtures due to heat, to have all the insulation fall off the conductors when disturbed. Both types are non grounding. The cloth covered only contained two conductors, and the old AC (BX) sheath is not listed for grounding, until the strip was added under the armor.

I'm replacing all the knob and tube in an old house now. All the lath and plaster has been removed to open the walls and ceilings for new plumbing and electric. New insulation and drywall will be installed.

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Last edited by jrclen; 08-01-2008 at 09:27 AM.
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