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Old May 28th, 2005, 05:20 PM   #1
ea44rl
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code question

does the nec permit coax and current conductors in the same conduit?
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Old May 28th, 2005, 06:01 PM   #2
rsdoran
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Its not a question of can you as much as should you. If the current conductors are AC, especially motor leads, they have a high probability of inducing voltage onto any cables parallel to them. Therefore any cable may give a false signal or have noise that interferes with its signal.

If the current carrying conductors are DC, with no inductance/motors, the probability is low.
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Old May 28th, 2005, 06:19 PM   #3
Terry Woods
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"Rock... Paper... Scissors..."

My local inspector said... "NO!"

That caused me some grief.

Considering that my coax is typically shielded, what's the big deal?

With respect to the NEC... the NEC sorta-kinda says no. Local jurisdiction has the final say... sorta...

When I say that the NEC "sorta-kinda says no", there are a couple of clauses which surrender the decision. One is a clause that says that rulings by local jurisdictions can over-ride the NEC. This happens quite often in my state (OR). Then there is a clause which then says that a local Professional Engineer can over-ride the NEC.

There is no clear statement (that I have found) regarding the authority of the local jurisdiction vs. the local Professional Engineer... or vice-versa.

It's almost like a case of... "Rock... Paper... Scissors..."

Aside from the FACT that the NEC is gobbledy-gook ((Humpty-Dumpty speak in Alice in Wonderland (do a search on this site for Humpty-Dumpty or Humpty.), or maybe Double-Speak from "1984")), it also appears that they (the NEC) want to maintain an impeccablly high degree of separation (deniability).

Gee, why does that attitude seem so popular lately... so current... so much in the news (as poor as it is) lately?

Gee... imagine a government running under the auspices of the NEC...

Lot's of rules, and yet, minimum accountability on the part of the rule-givers.

If it looks like a duck and quacks like a duck... damn, it must be....
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Old May 28th, 2005, 07:29 PM   #4
Rick Densing
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We recently had a discussion along these lines.

If you are looking for for a code violation,- if the voltage in the current carrying conductors is higher than the insulation rating of the coax, you are in violation.
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Old May 28th, 2005, 10:46 PM   #5
TConnolly
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All of the conductors in the same conduit must have an insulation voltage rating equal to the voltage rating of the highest voltage conductor. So if you have 480VAC motor leads in the conduit then all wires in that conduit must have a 600VAC insulation rating. That means that the 300V rated insulation on your coaxial cable isn't going to cut it. As far as I know, the NEC doesn't concern itself with the quality of signals you send, thats your problem.
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Old May 28th, 2005, 10:57 PM   #6
rsdoran
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Its not a question of can you as much as should you.

Its sad when the Engineers dont/wont take the time to read what is said.

The best thing to do if having to deal with NEC code is obtain the book. The next thing to do is talk with any inspecting authority on their requirements.

The OTHER thing is that there is DEFINITELY NOT a code AGAINST using multiple conduits/raceways etc for different cables/wires
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Can you or should you?
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Old May 29th, 2005, 12:00 AM   #7
TConnolly
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Article 300.3

(C) Conductors of Different Systems.
(1) 600 Volts, Nominal, or Less. Conductors of circuits rated 600 volts, nominal, or less, ac circuits, and dc circuits shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.

(2)Over 600 Volts, Nominal. Conductors of circuits rated over 600 volts, nominal, shall not occupy the same equipment wiring enclosure, cable, or raceway with conductors of circuits rated 600 volts, nominal, or less unless otherwise permitted in (C)(2)(a) through (C)(2)(e).

Last edited by TConnolly; May 29th, 2005 at 12:04 AM.
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