Eric,
Boy did you say a mouth full ! I am going to try to get through all you said hopefully without getting lost.
YOU SAID;
We are in the process of adding recessed lights in my family room (16x16),
located at the south-west corner of the first floor of a two-story house.
We have settled for 14 low-voltage lights (MR-16 bulbs) in two different
circuits (10 on room lighting, 4 on accent --> 50watts*14=700watts).
We have wired the cans using 14-3 NM cable throughout and back to a set
of existing switches where power will be drawn and to which we will add
two magnetic dimmers.
REPLY;
You are saying low voltage lights but you are saying your installed 14/2wGrnd instead of the wires that come with the low voltage tranformer and lighiting kit. Have you researched how you plan to connect in your low voltage tranformer to your much larger 14/2wGrnd Romex? I am a bit concerned with this wiring design. If you are installing 14/2wGrnd why are you trying to go to low voltage lights 16 volts instead of 120 volt recessed tanks CT rated? You confuse me a bit on this low voltage with Romex wiring design. Seems you are mixing 120 volt wiring design with low voltage desires. Can you do your research and tell me what you plan to do on the secondary side of this transformer or are you a commercial electrician used to more than 600 volt wiring systems and calling 120 volts as low voltage? Curious on this one.
YOU SAID;
Those existing switches are used to power all the plugs in the living
room + pantry lights + kitchen sink light + kitchen lights + guest
bathroom lights. I haven't calculated the load but it seems a bit much,
considering that the home entertainment equipment is using one of the
plug already (TV,amplifier,cd,dvd,vcr,...). This circuit is a 15 amp
branch circuit.
REPLY;
I am seeing several Code violations. The wiring I am taking to be in an existing dwelling. Even being existing you are asking for heart ache if you don't redesign these receptacles circuits. The NEC requires any bathroom receptacle to be 20 amp rated GFI protected and with no other outlets outside that bathroom. The NEC declares any receptacle in the kitchen, pantry, dining, nook all to be small appliance branch circuits. The NEC forbids any lighting, fastened in place appliances, or ANYTHING IN ANY OTHER ROOM to be on the same branch circuit as these receptacles that are also required to be 20 amp rated in the kitchen, dining, nook pantry. Also any small appliance branch circuit receptacle that serves the counter area must be GFI protected. Then The NEC forbids anything else except laundry receptacles to be on the same branch circuit as those laundry receptacles only. Yet you are intermixing all these areas in one branch circuit. I would say you need to sit back do some reading and replan your plan of attack on this project. Sounds like you need to install a few 20 amp branch circuits isolating the kicthen, nook, dining and pantry receptacles from anything else and also installing a dedicated laundry receptacle circuit 20 amp rated with nothing other than laundry receptacles on that dedicated laundry branch circuit. Then again you need to install a 20 amp branch circuit dedicated as bathroom receptacles only again with nothing but bathroom receptacles only. I suspect if you don't you will be making many trips back to your panel for years to come.
YOU SAID;
The circuit breaker panel is at the exact opposite corner of the house
on the north-east side. It would be very difficult and expensive to run
an additional line inside or outside of the house to this location.
REPLY;
Do you have a basement or crawl space in this house. If not you might consider building a bulkhead in the upper corner of you rooms to run your wires in that bulkhead to the panel area. You need to think this project out. You have issues of concern. Boy I always liked using that word issues. Makes me feel like I know something just kidding on this sentence.
YOU SAID;
Now the questions
-------------------
a) To alleviate the load on that circuit I have run a 12-3 NM cable
into a new plug that will power the entertainment center. There are
two choices to tap power for this run (both possible according to an
electrician):
- the dining room plugs which are on a dedicated 20 amp circuit,
- the plug in the pantry that was used for a gaz clothes dryer that
is now located in the garage (that pantry used to be more of a
space to put a washer/dryer combination).
Which is the best choice, considering that the amount of work is the
same regardless of the plug that is chosen ?
REPLY;
None of the above choices that I can see.
YOu have concern for an entertainment center that may at most pull around 5 or 6 amps most commonly 2 or 3 amps. But your big loads are the kitchen, bathroom, and laundry. The entertainment center while it does use many plug in devices are all electronic and light in amp load. However I would run a dedicated branch circuit whether 15 or 20 amp rated to that entertainment center in hopes to limit any interference caused by sharing with a multioutlet branch circuit with other loads that may cause your entertainment to go down hill due to interferece not due to amp load.
YOU SAID;
b) I am also thinking tapping one of those two plugs to power the
recessed lights. (again possible according to an electrician).
Is this true ?
REPLY;
I am questioning the lighting design altogether right now. I am seeing 14.2 then low voltage mentioned then a calculation of watts without mentioning amp load at voltage supplied. We need to dissect this lighting all by itself. However mixing lighting with a transformer on the same circuit as electronics such as an entertainment center is not a good move due to possible interferrence possibilities.
YOU SAID;
If so the problem is that the recessed lights are wired with 14awg
since I originally thought to tap the 15 amp circuit. Now if I tap
the 20 amps circuit then the wire will not match since 20 amps require
12 awg.
REPLY;
You may mix 20 amp wire with 15 amp wire but not advisable. When you mix wire size you must reduce the breaker on that branch circuit not to exceed the ampacity rating of the smallest conductor on that branch circuit. This circuit would now be a 15 amp rate branch circuit requiring a 15 amp breaker because of the 14 awg wire mixed on the circuit. Remember that kitchen, dining, pantry, nook, bathroom rececptacles, laundry receptacles must be dedicated for their use as discribed above and must be 20 amp rated with a 20 amp breaker not a 15 amp breaker because of a 14/2 added to that circuit this would be forbidden by the NEC.
YOU SAID;
On the other hand maybe it is ok since the load the recessed lights
will draw (500 on one branch + 200 watts on the other) is well within
the bounds of what a 14awg cable can handle.
What are you thoughts on doing this ?
REPLY;
Don't do it for reasons explained above.
YOU SAID;
c) Unrelated question: I know that it is allowed to make a hole in
a floor supported joist in order to run cable. That hole cannot be
bigger than one third (1/3) of the height of the joist. So a one and
a half (1 1/2) inch hole in a 2x10 joist should be well in the limits.
Is this correct ?
REPLY;
Everything in this last C part is correct as you said it.
Do some research and separate the light wiring design out as a new post. Then explain to me what you mean by 14/2wGrnd but with low voltage stated. This is one we need to work on separately then we can worry about getting power to these lights once we know for sure what we actually are deailing with on these lights. Confused right now what you want and are doing.
Take the time now as you are working this project to research and see what is on what circiut in your kitchen and bathrooms. You may be fine but you may need some work there too.
I suspect you will be fine picking up power from a bedroom from upstairs or something like that for you new lights. We just need to pick on this project one part at a time.
Let confirm your existing wiring is ok or if in need of correcting some branch circuit designs first. Then we will work on where and how to get clean power for your entertainment center. Then we can tackle power for your lights and sort out your wiring design for those lights.
The tanks you speak of, are these recessed tanks 120 volt rated or are they a part of a low voltage lighting package?
Hope this didn't confuse too much, Just want you to get started on the right track with little heart ache later and keeping your cost down. You can do it but just a little at a time.
Try reading the "installing wiring in a kitchen" found on the left column at the following link. Better yet take the time to read the entire article of Wiring a Dwlling so you can get a whole picture of what you need in your home before we go too far into this. That way you will have a safer and more powerful capable wiring system in your home as we work your project. Might help you to avoid future mistakes unknowing of what you shouldn't or should do.
http://www.homewiringandmore.com/hom...l/newdwel.html
Hope this helps some,
Wg
