metal switchbox

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Old 07-14-02, 10:34 AM
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metal switchbox

I am looking for a steel 4 gang switchbox with a minimum volume of 68 cu.in. has anyone seen such a thing ? I am installing dimmers, so I need the xtra room over conventioanl switches. My box fill calculates to about 56 cu.in. Can you point me in the right direction ?. I have found a plastic one by Raco, but I have one BX cable coming into the box, so I need metal for grounding.

Would I be better off using the plastic box and a grounding wedge ? would that be code ?

Any help appreciated
 
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Old 07-14-02, 12:36 PM
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68 cubic inches isn't all that much for a 4-gang box. Home Depot carries a Raco 4-gang steel box that is 1-5/8" deep that is 72.8 cubic inches (SKU #295828). It costs $9.94.
 
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Old 07-14-02, 02:30 PM
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The 4 by 4 metal box that I think John is talking about often requries what is called a plaster ring. You are probably finding the box but no way to mount the devices to the box with only mounting screws in the two corners of that metal box. If this is what you are finding then you need to buy the metal box and also a plaster ring that provides the mounting means for your devices. Don't forget to bond that metal box to the equipment grounding conductors of your cables.

Wg
 
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Old 07-14-02, 02:42 PM
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Jim,

Metal switch boxes are available that have removable sides. You can then add another box until you have as many gangs as you need. They are available with different clamps inside for the different type of cables. These will come in different depths up to 3 1/2" deep. My Code book is in the truck so I can't tell if 4 of these will give you the required volume.
 
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Old 07-16-02, 10:09 PM
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Thanks JN, WG and PCB for your replies and help.

To be sure I have this figured right to have enough room, and comply with code, please tell me if I have his correct.

I purchased four 3x2x3.5" gangable boxes, removed the sides and ganged them. The table in the 199 NEC lists those boxes at 18cu.in each, so 4x18= 72 cu.in. Is there a reductionor credit for ganging?

I have the following wires to go into the box:

(4) 14/3 w/gnd Romex
(2) 14/2 w/gnd Romex
(1) 12/3 w/gnd BX

Using the table in the NEC, I calculated the wire fill as follows:

(16) 14g wires:16x2.0=32
(3) 12g wires: 3x2.25=6.75

Conducor Fill= 38.75 cu. in.

Grounding conductor allowance = 2.0 (I would NOT figure it as 2.25, because the 12/3 ground is carried in the metal sheath, correct ??)

TOTAL CONDUCTOR FILL = 40.75 cu in.

Device fill figured as such:

3 dimmers with 14 awg: 3x2x2.0=12
1 switch with 12 awg: 1x2x2.25=5
TOTAL DEVICE ALLOWANCE: 17 cu. in.

Clamp Allowance= 2.25 (Figured on the largest conductor in the box)

So, the totals should be:

TOTAL CONDUCTOR FILL = 40.75 cu in.
TOTAL DEVICE ALLOWANCE: 17 cu. in.
Clamp Allowance= 2.25

TOTAL BOX FILL = 60 cu.in
TOTAL BOX VOLUME= 72 cu. in.

This should be plenty of room and be compliant with the code.
Could you please let me know if I have figured this out correctly ?

thanks for all your assistance, it is greatly appreciated
 
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