Power to Switch vs Power to Fixture?

mfleming

Is there any difference are benefit in doing one over the other? I'm installing new electrical and want to to be installed properly/most efficient not necessarily the cheapest?

Also, the switch I purchased from HD don't have the green grounding screw. Do I ground it somewhere else or do I need a different kind of switch? What is this one used for if I do need the one with the green grounding screw?

joed

Either way is fine. I would go to which ever uses the least cable.

mfleming

Can I go from PANEL to Room A Light switch (then to 8 recessed lights) as well as go from Room A Light Switch to Room B Light Switch.

Room B Light Switch to Single Recessed light.


a) Do I need a junction box to connect the circuit from Room A Light Switch to get Power to Room B Light Switch?

b) Can I use a double gang box but only install a single light switch and not cut out that side of the drywall? (possible future expansion)

SD515

Yes. As long as the entire load doesn't exceed the circuit's rating.

Just run an appropriate size cable from sw box to sw box. (14/2=15 Amps, 12/2=20A) The switch boxes will be your junction boxes (use appropriate size for fill capacity). At sw bx A, one cable brings power in, one leaves to the lights, another leaves to sw bx B.


The drywall can't be the box cover. I'd just cut the d-wall for the 2 gang box, and use a switch & blank, 2 gang cover. Or you could use a single device, 2 gang mud ring for now...and change it out later to a 2 device, 2 gang mud ring.

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Kyle

Just because you can, doesn't always mean you should

mfleming

I was thinking i would be using a single metal basic gangable device 2-1/2" deep (1104) 12.5 cu.in. and using 12/2 - 12/2 - 12/2 for one of my "junctions box's and the other 14/2 - 14/2 - 14/3 for the other "junction" box.

From what I understand about fill capacity 14/2 = 1.50*2= 3cu.in and 12/2 = 1.75*2= 3.5cu.in. so both junction box's will be at 10.5 which is fine correct?

SD515

Use of 14 ga anywhere in the circuit will limit the entire circuit to 15A, so use 14 ga for the entire circuit, if possible (lessens the fill capacity numbers). The entire circuit would have to be 12 ga if you want it on a 20A brkr.

Your box fill numbers are incorrect. 14 ga=2.00 cubic inches (each), 12 ga=2.25 cu in.

Also, these need to be included:

Internal clamps: A single volume allowance based on the largest conductor present in the box. No allowance required for a cable connector with its clamping mechanism outside the box. All internal clamps count as one.

Device or equipment fill: Each yoke/strap, based on the largest conductor connected to that yoke/strap=a double volume allowance per yoke/strap.

Equip Grounding Fill: A single allowance based on the largest EGC present in the box.

A conductor, no part of which leaves the box, shall not be counted.

I know this is 'wordy', but it's a nutshell of what the code says. Read it carefully.

Example: A switch box with 2 # 14/2 NM cables, one switch, no internal clamps.... wires=5 (2 blk, 2 wht, 1 gnd), switch=2. 5+2=7, 7*2.00=14.00 cu in.

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Kyle

Just because you can, doesn't always mean you should

mfleming

So in a nutshell I will never be able to use a single gang box if I have 3 or more 12/2 or 14/2 wires in it with a switch/receptacle? My 1.50cu.in and 1.75cu.in number was from a Canadian Thomas&Betts IBERVILLE Fill chart. Are you saying this chart is wrong?

I have another location where I have 20A 12/2 wire for receptacles that's why I brought that up. I know I can't use smaller wire than the circuit requires or what is already there.