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Posted by Jamie on November 23, 2007, 11:46 am
Chris Lewis wrote:
>
>>Jamie wrote:
>>
>>
>>> All runs of H/N to each outlet needs to be of equal length. This is
>>>very important especially when it comes to CFCI and arc breakers.
>
>
>
>>Why do they need to be of equal length? In some cases the hot runs to a
>>switch and then back to the outlet making it quite a bit longer. In a
>>completed circuit I can't see how it could matter... ?
>
>
> Er, I don't think they "have to be", other than as a logical
> consequence of all of the conductors for a given circuit
> have to be within the same sheathing (or raceway). Part of
> this is ensuring you don't get confused as to which neutral
> goes with which hot.
>
> Most of the time that is...
>
> A light fixture with a switch leg has a hot path considerably longer
> than the neutral path - twice as long as the switch leg.
>
> This is in contrast to knob and tube where the individual conductors
> were run independently of each other. They often got confused
> as to which neutral went with which hot.
>
> I don't believe that different H/N lengths make much difference to
> GFCI or AFCI, except in extreme and unusual situations. Eg: if you
> wrapped the neutral many times around an operating fluorescent
> ballast I could see it tripping a GFCI. _Maybe_.
Yes, they have to be.
That is why many people have problems with GFCI outlets false tripping.
CFCI's work on load and phase balancing with respect to the race ways.
A while ago we had our electricians replace all the commonly used
outlets on industrial machines with GFCI's only to fine that many
stations were wedging the reset buttons, having the off shift
electricians put noncompliance outlets back in for some area's
They had me go out and examine a few cases to see what was up. over
the years, outlets were added, separate runs of L1 was feed from the
panel for each to have it's own fuse, sharing the L2 line in various
places which throws the balance way off of course...
Of course, most of the time a little indifference isn't going to matter
I had them install a new 120 outlet service system on the outside of
these machines totally isolated from the inner panels of the machines
with each outlet having it's own L1/L2 and (G) all the way to the
distribution panel.
It was a lot of work for them how ever, in the end, they love it now
because they can now use the outlets for their tools while working on
the machines when the machine is locked out at the buss and panels wide
open.
And of course, lighting has not been allowed to use the same outlet
circuit for some time now so that's not an issue any more.
And on a side note, something I saw one day at our facility...
Make sure the emergency lightly intended for a room is connected to the
lighting circuit of that room and not some main circuit breaker for
emergency lighting for lets say a building etc.
Inspectors love catching that one along with insufficient length of
wire hanging out of switch and outlet boxes when opened for inspection! :)
Also, when requested to open the boxes, the inspector may follow you
to watch your procedures of how you disconnected the service before
doing so. They love to spot unsafe work practices.. :)
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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