Re: Home Wiring Question

["Robert L Bass" <RobertLBass@xxxxxxxxxxx>]

"Jim" wrote:
>
> ...I am trying to decide between doing a floor outlet(s) vice
> ceiling pendants to satisfy SWMBO desire for end table lighting in
> what is becoming the home theater.  I can cost the latter, but was
> not sure what the former would require.
>
> The NEC is not rocket science, but there was nothing I could find
> WRT to this kind of work, thus the post.

Although NEC doesn't help as much as one might hope, it isn't totally
silent on the subject.  The following is quoted from the 2002 NFPA 70
(NEC):

"300.6 Protection Against Corrosion. Metal raceways, cable trays,
cablebus, auxiliary gutters, cable armor, boxes, cable sheathing,
cabinets, elbows, couplings, fittings, supports, and support hardware
shall be of materials suitable for the environment in which they are
to be installed."

"(A) General. Ferrous raceways, cable trays, cablebus, auxiliary
gutters, cable armor, boxes, cable sheathing, cabinets, metal elbows,
couplings, fittings, supports, and support hardware shall be suitably
protected against corrosion inside and outside (except threads at
joints) by a coating of approved corrosion-resistant material such as
zinc, cadmium, or enamel. Where protected from corrosion solely by
enamel, they shall not be used outdoors or in wet locations as
described in 300.6(C). Where boxes or cabinets have an approved
system of organic coatings and are marked ?Raintight,? ?Rainproof,?
or ?Outdoor Type,? they shall be permitted outdoors. Where corrosion
protection is necessary and the conduit is threaded in the field, the
threads shall be coated with an approved electrically conductive,
corrosion-resistant compound."

"(B) In Concrete or in Direct Contact with the Earth. Ferrous or
nonferrous metal raceways, cable armor, boxes, cable sheathing,
cabinets, elbows, couplings, fittings, supports, and support hardware
shall be permitted to be installed in concrete or in direct contact
with the earth, or in areas subject to severe corrosive influences
where made of material judged suitable for the condition, or where
provided with corrosion protection approved for the condition."

See also:

"ARTICLE 342 ?INTERMEDIATE METAL CONDUIT: TYPE IMC"

"342.1 Scope. This article covers the use, installation, and
construction specifications for intermediate metal conduit (IMC) and
associated fittings."

"342.10 Uses Permitted."

"(B) Corrosion Environments. IMC, elbows, couplings, and fittings
shall be permitted to be installed in concrete, in direct contact
with the earth, or in areas subject to severe corrosive influences
where protected by corrosion protection and judged suitable for the
condition."

"342.42 Couplings and Connectors."

"(A) Threadless. Threadless couplings and connectors used with
conduit shall be made tight. Where buried in masonry or concrete,
they shall be the concretetight type.  Where installed in wet
locations, they shall be the raintight type.  Threadless couplings
and connectors shall not be used on threaded conduit ends unless
listed for the purpose."

I've done exactly what you're wanting to do, except we planned it
before the floor was poured so we laid the conduit first.  The job
was in my old church.  The pastor wanted floor outlets at his desk
for 110VAC, LAN and phones.  We laid 2 separate runs of RNC and
attached the boxes ~1/4" below finished floor height, then left pull
cables in each one.  We affixed blank covers so cement wouldn't get
inside the boxes.  When all was done we pulled the cables, attched
brass finish plates and tested everything.  There was no problem with
the inspector or the insurance company (though the latter wasn't
actually tested since we didn't have a fire... yet :)).

I've not yet had to retrofit power cable in a cement floor so I'd
just ask the AHJ how deep he wants the conduit.  You can rent a
diamond-edged saw and a rotary hammer for a day to make the kerf.

--

Regards,
Robert L Bass

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