Rewiring, conduit, junction box access, & code compliance

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  #1  
Old 10-10-01, 07:41 AM
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Question

I am currently undertaking the project of replacing the ungrounded circuits (mostly knob & tube, and some NM cable without ground) of my 90+ year-old home and would appreciate any comments on a number of questions/concerns. Please forgive the length of the questions, but I noted repeatedly that responses to other questions posted on the forum required additonal information. Further, I would hope that the additional detail makes the question more beneficial to other readers.

Background:
The main service was upgraded to a 24 breaker panel with 100amp service. The original fuse box was relegated to use as a sub-panel which supplies power to most of the remaining knob-&-tube wiring throughout much of the 1st and 2nd floors. Some of the basement was re-run at the time of the panel upgrade with 14/2 NM without ground.

Questions:
I have run a 2" diameter grey schedule 40 PVC conduit from the basement to the attic for my 2nd floor home runs. The conduit runs through closets the entire run.
1] Am I incorrect in assuming that an electrical inspector/governing code would not prohibit the use of sched. 40 PVC rather than EMC in my application.
2] If #1 is ok, must I derate my wires? I intend to make 5 or 6 runs (all 2 wire, i.e. - 5 to 6 live wires) up to the attic to accomodate the 2nd floor wiring. I am using all 12/2 romex and would expect that even if derated they would be sufficient for any 15amp circuit. However, I would expect to make a 20amp circuit run for the upstairs bathroom and would like to know if I need to make this feed 10/2? If #1 is not o.k. and I must replace the PVC conduit with EMC, does the derating answer change?

3] Because I am doing "oldwork", I am dropping 12/2 from the attic to the various electrical device boxes. I have no means of stapling the newly fished romex to framing members inside the walls above the receptacle/switch boxes, so I felt it would be preferrable to minimize the number of "loose" wires run in the walls. Therefore, I have chosen to use large, heavy-duty indoor junction boxes in the attic (wiegmann 10x10x4 boxes- one for each home run) to branch my feeder run out to the various device boxes - each being wired in an end-of-run configuration. This prevents the need for a 2nd unstapled wire dangling in the wall above every receptacle switch box, such as you would get on middle of the run outlets. The end result is more of a "tree branch" approach than a classic run. As I understand it the NEC requires all junction boxes to be "accessable". My question is, if I use a flag or some other means of indicating the location of the large junction boxes would it be allowable to cover the boxes with cellulose insulation, or must the boxes be mounted up off the attic "floor" by means of a 2x4s etc?
4] With regard to the wire stapling requirements when entering or exiting a box, would the mounting of my junction boxes off of the floor necessitate the use of enough surrounding surface area to staple wires to?

5] Is it allowable to bring two 12/2 cables in to a larger (say 1.5inch) cable-clamped knock-out on a junction box / service panel,or or must a reducing washer be used such that only one wire travels through a single wire clamp?
6] Is it allowable to bring two 12/2 cables through a single 5/8inch hole in a framing member, or must each wire have its own hole?

Again, I appreciate any comments regarding the above questions. Further, I would appreciate any suggestions regarding websites or other sources of information providing practical answers to questions of electrical code interpretation & compliance. Thank you very much. This site is one of the more promising resources I have found on the Web. Keep up the good work.
 
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  #2  
Old 10-10-01, 09:48 AM
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I only know the answer to two. So we'll start there.
4] With regard to the wire stapling requirements when entering or exiting a box, would the mounting of my junction boxes off of the floor necessitate the use of enough surrounding surface area to staple wires to?
Stapling requirements are suspended when fishing wires.
6] Is it allowable to bring two 12/2 cables through a single 5/8inch hole in a framing member, or must each wire have its own hole?
There is no requirement that each cable have its own hole.
 
  #3  
Old 10-11-01, 01:57 AM
s1nuber
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1) Both PVC and EMT are acceptable in this situation as far as I can tell.

2) Both PVC and EMT will require derating of your conductors. If you run 6 circuits in this conduit, you will have 12 current carrying conductors (6 hots, 6 nuetrals). This means that you will nedd to derate your circuits at 50%. 14 gauge romex would no longer be usable as a general use receptacle circuit at 12.5 amps maximum (50% of 25 is 12.5). 12 gauge romex would be rated at 15 amps, and 10 gauge romex would be rated at 20 amps. I am assuming your conduit run is longer than 24 inches with these figures (short runs of conduit do not need to be derated).

Suggestion: run two 14/3 romex, one 14/2 and one 12/2. This will give you 5 15 amp circuits, and your one 20 amp bath circuit. This will reduce your current carrying conductors to 8 for derating purposes (6 hots and two neutrals), subsequently reducing the derating factor to 70%. This can be done for derating as the 14/3 neutrals will only carry the unbalanced load, and do not count as current carrying conductors. THIS DOES NOT MEAN A NEUTRAL IS NOT NEEDED, OR THAT THE NEUTRAL DOES NOT CARRY CURRENT, IT IS ONLY FOR DERATING! 14 gauge is now rated at 15 amps (70% of 25 is 17.5 or 15 max), 12 gauge is rated at 20 amps (70% of 30 is 21 or 20 amps max), and you no longer need to worry about 10 gauge. This will also help your conduit fill, as pulling this many romex cables into a PVC conduit is quite nasty. I hope this conduit is 2 inch.

Please note that running 12 gauge romex for your general use receptacles is recommended by most people on this forum. You will save money in the long run on less wasted energy, and have better quality power on longer runs of wire. The trade off is higher installation costs, and more installtion time (bigger wire is more difficult to work with, and will affect connectors, boxes, devices, drill holes, and everthing else you do).

3) Romex is not required to be stapled or supported where fished. Your approach is conservative, but time consuming. I would encourage anyone who wants to exceed the code minimums, but it is not required. You will need to staple the romex in the attic within 12 inches of the box, and every 4.5 feet thereafter untill it penetrates the top plate.

Accessability and visibility are different things. If you can physically get to the box in the attic without damaging the finish of your home, you have met the requirement. You do not need neon signs pointing to attic junction boxes ( a slight embellishment on my part). A word of caution - romex can be installed directly to the top of the ceiling joist in attics, IF the romex is at least 6 feet from the attic access, otherwise it must be protected by furring strips or other protection.

4) no, see above

5) Romex connectors must be securely fastened to the box that they enter. A 1/2 inch connector cannot be left loose in a 1.5 inch hole. Each romex connector is different as far as number of cables in the connector. Most 1/2 inch connectors will allow up to two 12/2 romex in the connector. You will have to look at the box for the ratings of the connector (ps. - save the box to show the inspector - they like to fail multiple cables in a connector even if the connector is rated for the application, not all inspectors do this, but better safe than sorry).

6) If the wires easily fit in the drilled hole, it is adequate, there is no specific rule/code governing this.

Enjoy your day!
 
  #4  
Old 10-11-01, 08:33 AM
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Exclamation Questions for s1nuber

s1nuber & demount,

s1nuber, I question the advice you've given to demount concerning the number of current-carrying conductors in multiwire cables (e.g., 14-3).

You claim that there are only two current-carrying conductors in a multiwire cable. I disagree. You make the point yourself that the neutral carries the difference (imbalance) between the two hots. So let's say you have a load of 10 amps on hot #1, and 2 amps on hot #2. That means that the neutral will be carrying 8 amps, and viola, you have three current-carrying conductors. I think that this would be a pretty common situation.

My advice to demount is to not mess with running several branch circuit runs from basement to attic. Instead, run a feeder through the 2" conduit, and put in a 60 amp subpanel on the second floor. The easiest way to do this is to use 6/3 NM w/g (copper), feeding it to the attic. Pick a good location for the subpanel (near the center of the house and not in a closet or bath), route the 6/3 across the attic, through the top plate and to the subpanel. Then run branch circuits from the subpanel. The branch circuit runs will be shorter. And hey, installing a subpanel is FUN!

demount--good questions, you have clearly done your homework. Good luck to you!

p.s. Don't forget to seal that 2" PVC conduit after you've run the wire. Use fire caulk. You don't want a fire in the basement to spread throughout the house through a 2" plastic flue. cp
 
  #5  
Old 10-11-01, 03:42 PM
Wgoodrich
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Cliff, Wirenuts is right about not counting neutral wires carrying unbalanced loads serving two hot conductors. They are exempt from being counted in the de-ration calculations as per 310-15-b-4. Now a grounded conductor that is only a return path and only serves one hot conductor and does not carry an unbalanced load between two hot conductors must be counted in your calculation. See the copy of that part of the rule below;

(4) Neutral Conductor.
a. A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of Section 310-15(b)(2)(a).



As Wirenuts advised he suggested running a three wire cable with two hots using the white as a neutral conductor carrying the unbalanced load between those two hot conductors [multiwire circuit]. He is correct in allowing more conductors in the raceway by using neutrals that do not need to be counted.

As for installing a subpanel for a second floor, I don't believe it would be warranted to install such a nonservice rated panel to serve a second floor. Most second floors do not carry a concentrated amount of load considering that floor's general wiring. I would lead towards the multiwire circuits as Wirenuts suggested.

Good Luck

Wg
 
  #6  
Old 10-11-01, 06:20 PM
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Got it

Thanks WG, and apologies to s1nuber.

I still think a subpanel offers some advantages...if a breaker does trip, it can be reset without a going to the basement. Also, adding a new circuit in the future is much easier.

Cliff
 
  #7  
Old 10-12-01, 01:32 PM
s1nuber
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Wirenuts is a nice guy and all, and a valuable asset to this forum, but how come he gets the kudos for my post? He's not anywhere on this thread. <- this is a fiendly query

Don't concern yourself over the disagreement, Cliff. I would rather have full clarification of anything I post, as it should only make us all better sparky's. What is right concerns me, who is right does not (even if that means that I am proven wrong).

Enjoy your day!
 
  #8  
Old 10-13-01, 02:52 PM
Wgoodrich
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My mistake and apologies to S1nuber.

Cliff if I would have know it was S1nuber that I was backing up I might have found a way to prove you were right! Just kidding. Sorry S1nuber. Now it is my turn to admit my shorcomings. Boy do I seem to do that a lot around you guys. I do have an excuse as to why I confused S1nuber with Wirenuts. Just can't think what of that excuse at this time. Must have been Wirenuts fault! Yep thats it!

Wirenuts, you should be more careful next time.

Sorry for the confusion S1nuber!

Wg
 
  #9  
Old 10-15-01, 11:58 AM
s1nuber
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I know exactly what your saying WG. I feel that disagreement amongst professionals is healthy, but it can confuse the non-professional at times. If you recall, I had asked you about that particular aspect of this forum when I first started posting here. I have since learned to let the chips fall where they may, without trying to be an outright jerk about it.

Enjoy your day!
 
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