From: neilson@osf.org (Peter Neilson)
Subject: Re: ADVICE WANTED:  Changing house outlets from 2 to 3 prongs
Organization: Open Software Foundation
Distribution: usa
Date: Wed, 29 Jul 1992 08:34:46 GMT

In article <DRAND.92Jul28134807@spinner.osf.org> drand@spinner.osf.org (Douglas Rand) writes:
>In article <1992Jul28.011319.14616@porthos.cc.bellcore.com> patter@dasher.uucp (24224-guthrie) writes:
>
>   In article <1992Jul27.185459.3955@vlsi.ll.mit.edu> ac@vlsi.ll.mit.edu (Andrew V. Curtis) writes:
>
>   >        I just bought a 45 year old house that is in outstanding condition
>   >with one exception: it is equipped with only two-prong outlets throughout
>   > [& wants to replace with grounding outlets.]
>
>   A house that old probably has the old armored cable in it. The stuff I'm
>   thinking of has two insulated wires inside a spiral metal sheath. If that's
>   the case, most or all of your outlet boxes will be grounded back to the
>   box by this sheath. You can check this for each outlet by putting a circuit
>   tester between the hot line and the box. If you get a good, bright, signal,
>   you don't need a third wire; just buy a three prong outlet and put it in.

There are circuit testers, and there are circuit testers.  Only some
can test the efficacy of a ground.  The one you have handy is not
necessarily the right kind.

>   You can then test the result with a circuit tester to the grounding plug.
>
>It's called BX.  Armored cable is generally fine.  It should carry a
>bare third wire, although I believe you're correct on using it 
>as a safety ground

Old BX cable (without the added ground wire) is notorious for
producing poor grounds because it easily pulls loose from the
connector (the clamp that holds it to the box).

>
>   A few points to make here -
>   1. If you ever do major work on this, it'll probably have to be brought
>      up to code. In that case, you'll probably have to replace the line
>      with Romex.
>
>No.  BX should meet modern code.  Modern code still requires BX in
>areas where mechanical problems require greater protection of the
>conductors.  Romex (NMC) is not very protective.
>
>   2. The insulation in cable that old is *very, very* delicate. They
>      typically used rubber and/or cotton, and this will be dry and brittle.
>      If you have to move the wire very much to replace any particular
>      outlet, leave it alone.
>
>It shouldn't be all that delicate.  It isn't as if it were directly
>exposed wiring dating back 100 years.  I've found the wiring in my
>house (35 years) to be in good condition generally,  including 
>the BX.

I had a major problem with old BX when trying to replace a two-prong
outlet with a grounding outlet in an apartment I rented.  The BX had a
sharp end that had cut into the insulation of the hot wire.  Without
bothering to cut the power, I had removed the outlet cover, just to
look at what the job entailed.  I wiggled things slightly, and the
outlet exploded.  Turns out that the original installation (from maybe
1940) was incorrect, because the person who had pretended to be an
electrician did not know how to cut BX.  There is a trick to doing it
right, and if it's done wrong, you get sharp points.  Modern BX
installation requires "redheads" which are little red or orange
plastic grommets that fit into the end of cut BX to protect the wire
from and sharp edges.  They are brightly colored so the inspector can
see them.

 Oh well, I guess I was fortunate.  The outlet could have exploded
-any- time, and it was better to have it happen while I was there
watching it.



-- 
            >>>  Peter Neilson  --- neilson@osf.org  <<<
                  "             ?" said Tom, blankly.
(Quotation changed daily.  If you've seen this one before, it's still yesterday.)
Newsgroups: misc.consumers.house