Add switch to multiwire branch and question on code

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  #1  
Old 04-08-14, 07:30 PM
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Add switch to multiwire branch and question on code

Hello everyone,
I Have a family room that currently doesn't have any lighting, and i wanted your advice on my plan for using an existing circuit. btw, i've studied as much as i can to try to ask clear questions.
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"sorry, i didnt have time to build the model to scale" ahah

I want to add a 600w dim switch to the end of one multiwire branch circuit. it currently only serves 3 duplex outlets, one of which is below where i plan to add a switch to control 8 10w pr30 LED recessed lights. i will account for 65w as max

FIRST OFF! in the diagram, the first duplex outlet BOX is a "home run" that i found by mistake (Red wire was still hot even after outlet breaker was off). the two circuit breakers i found feeding this multiwire are NOT connected with a device to flip both breakers that are on different phases> do i need to add one for code?

THis house already mixes outlets and switches, i assume that is okay for code?

i will be around 520 max at the switch, leaves around 1800 watts for 3 outlets...should be okay for dinning room?

I look forward to your feedback and questions< thanks! -travis
 
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Old 04-08-14, 08:15 PM
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I want to add a 600w dim switch to the end of one multiwire branch circuit. it currently only serves 3 duplex outlets, one of which is below where i plan to add a switch to control 8 10w pr30 LED recessed lights. i will account for 65w as max
Per fixture? To be code compliant you must use the maximum rated wattage of the fixtures to calculate your load. You should should treat the lighting load in a family room as a continuous load in your calculations.

65W/fixture x 8 fixtures x 1.25 = 650W for your 8 new fixtures at 65W each (1.25 is the factor for a continuous load).

THis house already mixes outlets and switches, i assume that is okay for code?
Yes.

i will be around 520 max at the switch,
As a draw, yes. Factoring in the continuous load, however, puts you at 650W for your new lighting.

leaves around 1800 watts for 3 outlets...
If this is a 20A circuit you will have 14.583A, or 1,750W, available for other loads. If it's a 15A circuit you will have 9.583A, or 1,150W, available.

should be okay for dinning room?
A dining room must have two dedicated 20A small appliance circuits to meet current requirements. If you have those in addition to this circuit then you should be fine.
 
  #3  
Old 04-08-14, 08:17 PM
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You need to find another way. Wiring feeding dining room receptacles is considered to be on a Small Appliance Branch Circuit so can not feed anything but receptacles in the kitchen/dining room/pantry.

Current code is that both handles need tied together on a MWBC or use a two pole breaker.
 
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Old 04-08-14, 08:54 PM
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Thanks for the quick replies. I was not aware that the dining room was a receptacle only branch. Looks like my only shot is to run a new circuit or look into my entry way lighting circuit in the morning. As for the switch, i will seperate the lights onto two different dimmers. Thank you!
 
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Old 04-08-14, 09:14 PM
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I meant to say earlier that you need to join the handles of the two breakers supplying the MWBC with a handle tie. Buy one designed to fit the breakers you have.

Looks like my only shot is to run a new circuit or look into my entry way lighting circuit in the morning.
I would run the two 20A SABCs to the dining room if they are not already there. By blanking off the box with the receptacle in the DR that is on this circuit, or by running one of the new circuits to that location to feed the receptacle and splicing this circuit through (use a deep box), you can free up this circuit for your new lights plus giving your DR the power it needs.

As for the switch, i will separate the lights onto two different dimmers>
Fine, if you want to. But why? Are the fixtures actually rated for more than 65W each?
 
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Old 04-09-14, 10:43 AM
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Incidentally, in a general sense, you may tap off of one hot (and the neutral) of a multiwire branch circuit and control that subcircuit using a switch. That subcircuit, with or without a switch, is not treated as a MWBC. You would have to evaluate the expected load for that subcircuit plus everything else on the half of the MWBC it was tapped off of (e.g. when planning built in light fixtures).
 
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Old 04-09-14, 11:35 AM
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The can lights are rated at 65w each and i will look for a breaker coupler.

Now that im aware this is a small appliance circuit, connecting to this branch wont be in code. I will call an electrician to install a new circuit for the lights, as all my other circuits are pretty full
 
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Old 04-09-14, 11:43 AM
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The NEC only required that the dining receptacles be feed from one of the small appliance branch circuits, not both. Given most people's usage of a dining room I would not go to any effort to add a second 20 amp circuit to the dining room.

Prior codes only required a handle tie or two pole breaker if both hots landed on the same device yoke. The neutral did need to be pigtailed.
 
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