Jump to content

Bundled Conductors:


Mark P
 Share

Recommended Posts

As I understand the relevant portions of the 06' IRC, the cables need to be either spaced or derated. Derating would cause problems with the existing overcurrent protection becoming no longer adequate and perhaps also cause problems with the house's general purpose outlets no longer adequate for the area served. From the photo, I don't know if spacing the cables is feasible, but I'll say this...That's the work of one lousy electrician.

Power cables that are bundled are not ventilated as well as cables that are spaced, so yes, they are more likely to overheat. The magnetism generated by the electric currents in the conductors exerts a force on them that tends to either pull them together or push them apart. Once the insulation is hot enough and fluid enough, that's what happens and arcing/fire results.

I would certainly write it up, one way or the other.

Marc

Link to comment
Share on other sites

Jim,

If we ever cross paths you've got your choice of dinner and drinks on me – you’re a real educator. Not literally on me, I’m not that kinky, but I'll pay for whatever you want.

I love this job, something different every day and I’m always expanding my knowledge. I knew there was an issue with bundling – but during the inspection I could not remember the specifics and said “there may be an issue here, I’ll have to research it and I’ll report it if neededâ€

Link to comment
Share on other sites

From one of the more memorable discussion on this type of thing over at the ASHI board - this post was from Douglas:

The readings that Eric, Jerry, and others are getting of several amps of current on the GEC or the water pipe electrode surprise me, but they aren't indicative of a shock hazard. We know that the service neutral carries the imbalanced load difference back to the utility transformer. We also know that the grounding electrode is a parallel path for that current, and that the currents will divide up in accordance with the resistance of each and will follow Ohm's law. What we don't have on either the neutral or the grounding electrode conductor is significant voltage. The only voltage we have is the amount of voltage drop in those conductors. In most cases, that is going to work out to less than one volt. It isn't going to shock anyone. The voltage will divide up per Kirchoff's law.

I agree with Dr. Katen about the hazard arising from interrupting the path such that a person completes the circuit (rather than the neutral conductor completing the circuit). The degree of hazard depends upon the presence or lack of other parallel paths. In commercial wiring, the reason for the high number of injuries and fatalities on the neutrals of 480 volt systems is for an entirely different reason - the nature of a wye 3-phase is such that the neutral will carry the full current of any two phase conductors when the third hot conductor is turned off.

As to him salting my glass of water - heck - I always have the thing plugged into a portable GFCI for that parlor trick. It would trip it before I even got to take a sip.

Douglas Hansen

Link to comment
Share on other sites

...

What I don’t understand why the ALLOWABLE AMPACITIES table list #12awg at 30 amps, when everywhere else it is rated at 20 amps?

Mark, it's an "exemption" found in 240.4(D) of the NEC. I believe it has been there for a long, long time. This is only a guess, but I would imagine the guys who wrote the code recognized that the wiring making up the majority of a house's circuits needed an extra safety fudge factor, and hence the #14-15-amp, #12-20-amp rule.

The allowable ampacity depends not only on the size and composition of the conductor but also on the temperature rating of the insulation. If the insulation can withstand higher temperatures then a higher amperage can be permitted.

Marc

I have to assume you are answering Mark's question, the same one in the quotes above. NO, the allowable ampacity permitted by the NEC for a #12 (cu) branch circuit is set in stone at 20-amps. It wouldn't matter if it had a combination kevlar/asbestos coating.

Link to comment
Share on other sites

One question for Jim:

So with #14 & #12 cables, you can have up to 9 current-carrying conductors and the derating will be invisible.

Is the grounding equipment conductor considered to be a current carrying conductor?

Marc

No. The NEC actually tells us this in no uncertain terms in 310.15(B)(5). It says, "A grounding or bonding conductor shall not be counted when applying the provisions of 310.15(B)(2)(a)."

- Jim Katen, Oregon

Link to comment
Share on other sites

Jim,

If we ever cross paths you've got your choice of dinner and drinks on me – you’re a real educator. Not literally on me, I’m not that kinky, but I'll pay for whatever you want.

You should know that I never refuse offers of food. I'm partial to Italian white truffles. If those aren't available, then a really good falafel will do.

I love this job, something different every day and I’m always expanding my knowledge. I knew there was an issue with bundling – but during the inspection I could not remember the specifics and said “there may be an issue here, I’ll have to research it and I’ll report it if neededâ€
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...