Re: Low voltage wiring - NEC question

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Sun, 04 Sep 2005 19:22:31 -0400, Robert L Bass
<sales@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<e5vmh11it82p1i3s1dnmd24pg1musvh3af@xxxxxxx>:

>> When I was designing and building a homebrew hard-wired
>> lighting system (still in constant flux ;-), the inspector came
>> over and examined my dimmer panel while it was still on the
>> work bench. He explained what he did and didn't want to
>> see. Seems to me that some decisions/details were a matter
>> of professional preference/judgement and not predictable
>> based exclusively on the NEC no matter how many times I
>> might have read it. I did as he suggested and things went
>> swimmingly.
>>
>> Picture and description here:
>>
>> http://www.econtrol.org/ssr_panel.htm
>
>Good job, Marc.  I do have one suggestion regarding the work in
>case you ever decide to do a similar project.  Consider making
>each cable long enough to go from the entry point of the cabinet
>to the opposite end (top/bottom) then back up/down to the
>connection point making right turns at each point.  The result
>will be neater looking (inspectors like that) and easier to
>service.

Actually all the AC wires do reach all of the SSR's on a given side. What
isn't clear from the photo graph is the heat sink up the middle (with fins
inside and fans top and bottom) divides the cabinet in two with respect to AC
wiring.. Because of the need to route the low voltage wiring in an acceptable
way up the middle, and to provide separation of low voltage from the AC, no AC
lines can cross from one side of the box to the other. If need arose, one
could route AC around outside of course. Also, remember this is a switch box
--not a panel-- for which the NEC specifically changed in IIRC 2000 to clarify
that low-voltage and household AC can be in the same enclosure when need. Some
incoming AC supplies go to  more than relay -- hence the pigtails and wire
nuts. In a commercial building  20amps x 120vac = 2400 watts of lighting on a
single dimmer may be needed, but that would be more than a bit unusual in a
residence. As is, there are 60 amps = 7200 watts per side  ~ 3X times what is
needed.

>For the benefit of some less experienced than Marc, I also like
>to leave enough of the outer jacket on NM cables in place so that
>I can write on the jacket an identification such as "Din Rm
>Recessed Cans" or whatever.  It makes things much easier to
>service.

For some reason I thought that the NEC specified 1/2". Maybe that's a minimum.
I dunno. Good idea if its OK. I use a simple IEC color coding scheme and a
map/table/diagram.

As I understand it, the 2005 NEC addresses wire label ling and makes certain
nomenclature and style a requirement. No more labels like "Joey's old  room"

>We sold the house about a year after I finished fixing just about
>everything in it.

Done that three times now. They'll take me out feet-first from this one ;-)

>> But he also made me tear down and replace an entire partition
>> wall because I only had 28" instead of the required 30"
>> clearance in front of the proposed location for new load
>> center :-(
>
>Heh.  I could have warned you about that one.  :^)

I knew too and crossed my fingers. As luck would have it, it was the one
pre-existing wall in the remodeled space.  The width could have been about 29"
if I pulled off some wooden moulding, but the inspector wasn't going to give
an inch ;-)  (Maybe 1/2"  he said.)

Marc
Marc_F_Hult
www.ECOntrol.org