Nick asked in Home & GardenDo It Yourself (DIY) · 7 years ago

# I need some help with calculating box fill as it pertains to the CEC?

I need some help with calculating box fill as it pertains to the Canadian Electrical Code. I have a four gang box with a capacity of 50 cu. in. There will be a total of #14 - 21 conductors and 9 grounds coming into the box. It will have 6 insulated caps and 4 light switches. This is what I have calculated thus far:

#14 - 21 conductors x 1.5 = 31.5 cu. in

4 switches x 2 = 8 cu. in

6 wire clamps = 1 cu. in

9 grounds = no fill

pig tails = no fill

Total 40.5 cu. in

My problems pertain to the caps. What does 1 cap equal as cu. in. One chart I looked at mentioned 0.75 cu. in per cap...another 1.5 cu. in. Any help would be useful. And if there are problems with the calculations please don't hesitate to fill in. Thanks!

Relevance
• Jim W
Lv 7
7 years ago

I suggest you check your codes again. 21 conductors of 14 ga plus a ground counted as one plus the 4 switches would not fit in a 50 cu in box according to the US N E C. The problem is that a 14 wire needs 2 cu in per conductor plus each device is counted as 2 conductors. The caps are ignored in the US and the 2 codes are in general considered to be the same for fill in box or conduit. I may be wrong but it is best to go for a larger box.

Source(s): 50+ years in the electrical industry
• Anonymous
4 years ago

Box Fill Calculations

• rhode
Lv 4
4 years ago

Electrical Box Fill