Is old BX "safe" or not?

Page 2 of 2  
snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

I realize that you're Canadian and have a patriotic reason for asserting the superiority of the Canadian Electrical Code however I have an equally patriotic reason for asserting the opposite. In fact, what Canada does wiring-wise has IMO as much relevance as the electrical code of ... oh, say Bulgaria <g>. Canada doesn't allow AC? Well that's nice to know. They probably do have special problems wiring igloos <g>.

So you say. However NYC, hardly a slouch in the imposition of onerous regulations, has always insisted on the use of AC (nowadays with the follower wire) and in using the armor as the EGC. Only in the last few years have there been the minutest changes to allow NM in some very suburban style non-rental houses. Commercial and rental buildings are still conduit or EMT or AC. I believe many of the large older US cities are in the same situation.
If the problem is as severe as you and Horne assert it would seem logical that, needing the rodent-protecting capabilities of armored cable, NYC would have changed to MC long ago. But they haven't.
Further, do you realize that there are hundreds of thousands (perhaps millions) of feet of old style (non-follower-wire) AC installed in thousands of buildings much of it dating to the forties and earlier? And that old-style AC is being used as a ground by its very nature. The metal box with the switch or the device is connected to the armor of the AC by a screw (not a clamp), the armor of the AC is connected to the load center metal (probably your denigrated steel) by another screw, and the load center is connected to the ground (likely the water main). Whether it actually forms an E(quipment) ground depends on the connection between the device and the box but in the case of direct wired lamps (isn't this Horne's dramatic case) it's almost certainly electrically bonded.
So applying your horror scenario, if a fault develops in the lamp or the box or in part of the cable the weak and ineffective armor will not be able to carry enough current to blow the circuit breaker and the home owner (or tenant), presuming a defective bulb, will be electrocuted when he investigates. Alternatively the AC will heat to incandescence (your earlier assertion and presumably Horne's dramatic case) and burn the building down.
Wow! I guess the NYC electricians guild hasn't thought of this. Just think of the work replacing all that old-style AC with more-expensive-than-new-style-AC MC. Just think of the mega bucks rolling in.
OK, I'm being sarcastic but the point stands. If old-style or new-style AC represented any significant danger then there'd be moves afoot to replace it (mandatorily) and there certainly wouldn't be any more installed. Isn't this what's happening with Knob & Tube?

Aw come on! The current carrying conductors have to be wound around screws and bent in tight arcs. I'd be the first to agree that steel is not suitable for this use.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's a stupid comment! About equivalent to saying "Yeah they use lighted palm frond torches in Florida or Hawaii"! A reason for quoting the Canadian code was probably merely to point out "Here is an authority not unknown for good safety practices in many technical fields that regulates to the following standard."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The problem with using the BX cable armor as a ground is probably due to the difficulty of making and maintaining a good electrical connection to the armor at the ends of the cable. The clamps at the boxes are not the most reliable.
And how do you deal with plastic boxes? The dedicated copper ground wire is much easier to connnect to.
Mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
But is BX armor cable ever used with plastic boxes? I don't think metal or even plastic conduit is used with plastic boxes, ... is it? I would assume that metal conduit or cable would mandate the use of metal boxes? --Phil
Mark wrote:

--
Phil Munro Dept of Electrical & Computer Engin
mailto: snipped-for-privacy@cc.ysu.edu Youngstown State University
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'm sorry, I took (and have taken over the years) it to mean, "Hey, you dumb Americans. Wake up and learn what we Canadians, the smartest people in the world when it comes to electrical codes, mandate for our electrical installations. Just follow our lead and you'll be alright; second-best maybe but OK."
I only know of one thing the Canadians have to teach us and that's how to set up a single payer health care system but then again most countries of the developed world, probably even Bulgaria, could teach us something about health care systems.
Igloo construction too, perhaps <g>.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload



That entire interpretation was silly when you consider I had also posted a long discussion on how Canada is slowly adopting American style rules for GFCIs in kitchens.
As Terry suggests, it was merely given as an example of an equally competent electrical authority having reasons for and choosing not to go the "use armor as ground" route.


The US govt. and construction industry is rather fond of our R2000 construction methodology and quote/reference it a lot.
But they're not igloos.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yup. Here too.

But of only minimal use as a ground. Those outlets were two prongs.
Just how good do you think 50 year old BX armor is as a ground, given the oxidation it, the boxes, and clamps have gotten over the years?
And it's proposed to utilize this as a classic three prong outlet grounding system. I've seen too much of that stuff to trust it.
Like the perfectly well panel-grounded chunk of BX in my friend's basement that recently raised an enormous bang when a contractor slung a grounded metal trouble light on it. You see, the end had a hot-armor short, and the armor didn't have enough conductivity to trip the breaker.
Contractor: "we see this all the time...".
The house is about 100 years old.

It happens. My co-author has seen it. And, IIRC, it was the cause of the major casino fire in Vegas.

No. Very few jurisdictions, if _any_, are requiring mandatory replacement of K&T, except in renovation work to new code. It's the insurance companies in the private sector making K&T difficult to insure. Despite the fact that aside from burial in insulation, existing K&T is usually quite safe. Better than some later wiring systems.
Similarly aluminum. Proven track record of hazard. Is there a mandatory recall? No.
Asbestos.
UFFI.
Lead paint.
PT lumber.
Etc. Except for few cases (mostly commercial or local rules), none of these are required to be removed. Mitigated in many cases, but rarely mandatory removal.
You can argue that they're not as hazardous as some claim all you want, but, they have been deemed hazardous, and _none_ of them are subject to mandatory complete removal. Because it costs too much.

Bus bars and terminal tabs aren't steel either, they don't have to be bent at all. Steel isn't suitable for that use either. Steel simply isn't suitable as a conductor (except perhaps conduit, and even that we don't permit).
[Canadian code, and I suspect US too, even doesn't really permit you to use a metal box as part of a ground conduction path - you gotta bond those copper ground wires together in NM, rather than run them under different box screws. Except with US AC...]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 18 Jan 2005 06:51:04 GMT, SpamFree

Intersting...... I never knew where the names BX and Romex came from...
The ideal solution is to use greenfield. Use a black, white and green wire. On a flat surface, such as a basement ceiling, use steel conduit.
I did actually see some of the old BX (without grounding conductor) start a fire. I used to do handyman work and had a guy call me one evening, insisting I come immediately because his lights were going on and off and getting dimmer. When I got there I smelled smoke. When I got to the old fuse box in the basement I felt a very hot BX cable (#14 wire) with a 30A fuse. I shut off the power, called the fire dept, and busted a hole in the wall right above the box. The BX was very hot, and had charred the wood, but not yet caused flame. Another hour, maybe less, that place would have burned. The AC cable, eliminated that problem pretty much. While I understand the resistance issue, I never could totally understand how a spiral would cause the resistance, since it was still a continuous piece of steel. However, I DID see the result.
Needless to say, that place needed complete rewiring.
Yes, it is STILL called BX in the stores.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
sounds like that was simply a case of the wrong fuse and wasn't the fault of the spiral armor, the wires inside the armor were getting hot.
I think the worst electrical saftey issue I have seen (I live in the US) is older 220V dryers. They are plugged in via a big 3 prong plug. Two of the prongs are 220 and the third prong is a COMBINATION return and saftey ground!!!. In my dreyer, the heating coils are across the 220 pongs. But the 110 volt motor and clock are connected from one 220 pin to the combination return / ground pin which also connects to the chassis.
SO...if this retun line should fail OPEN someplace, there will be 110V on the dreyer chassis (through the motor). And of course the dreyer sits right next to the washer which is grounded by it's regular 110v outlet. so by a simple open failure, there can be 110V ac across my washer and dreyer. I see the cat walk across there all the time not to mention the wife and kids. I was so concerned about this, that I added a hard WIRE between the washer and dreyer chassis.
I think all newer dreyers have a 4 prong plug where the return and saftey ground are seperate. But it boggles my mind that any saftey organization would have ever alllowed the older three prong system. Mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.