Good morning!You're right to be skeptical. Your client is mistaken, or perhaps remembering things incorrectly. The scenario they describe is almost certainly a violation of the Canadian Electrical Code (CEC).

Here's a breakdown of why: CEC Rule 12-3034 (Box Fill)

This rule is the equivalent of the NEC's box fill calculations. It's the primary rule determining the allowable number of conductors in a box. While the specific numbers for things like conductor allowances and device allowances may vary slightly between the CEC and NEC, the principle is the same: you cannot overcrowd a box.

Conductor Count Calculation

Let's analyze your scenario using CEC principles (though the exact rules are the same for the NEC):

Conductors

(3) #12-2 MC cables means 6 current-carrying conductors (3 cables 2 conductors per cable - ignoring the ground for now).

Device Allowance

The receptacle counts as two conductors (Rule 12-3034(1)(e)).

Total Conductor Count

6 (conductors) + 2 (device) = 8 conductors

Volume per Conductor

Rule 12-3034(3)(a) specifies the minimum volume allowance per conductor: \#12 AWG: 2.25 cubic inches

Required Box Volume

8 conductors 2.25 cubic inches/conductor = 18 cubic inches

The Problem

Your 2-1/2" deep metal gem box has a stated volume of only 12 cubic inches. This is

significantly less than the 18 cubic inches required by code.

Therefore, even by CEC standards, this is an overfilled box.Key Differences Between NEC and CEC Regarding Box Fill

While the fundamental principle of box fill is the same, here are potential areas where minor differences might exist, but none would allow for this scenario:1.

Volume Allowances for Conductors

While very close, the cubic inch allowance per conductor size could be fractionally different. But any such difference would be minimal and would not make up the 6 cubic inch deficit in your scenario.2.

Device Fill Allowance

Similar to above, the code may vary slightly on how a device is considered in box fill. But again, the differences are minimal.

Why Your Client is Likely Mistaken



Misremembering

People often misremember details of previous work, especially when moving across countries with similar but not identical codes.

"That's how we always did it" (and it was wrong)

Unfortunately, bad practices exist everywhere. Just because something was done a certain way in the past doesn't make it correct.

Ignoring the Ground Wire

Assuming that the grounding conductor is not to be counted. However, 12-3034(1)(d) states that all grounding conductors shall be counted as one conductor. Therefore the calculation would be increased to 9 conductors 2.25 cubic inches/conductor = 20.25 cubic inches

In summary, tell your GC that they are 100% correct, some things that may have been performed in Canada are not within electrical code and best practice here in SW Florida.Important Notes



Always refer to the applicable code (in your case, the NEC) and local amendments. Local jurisdictions may have specific requirements that supersede the base code.* The above calculations are a simplified explanation. There are other factors that can affect box fill, such as the number of cable clamps, fixture studs, etc.I hope this helps clear things up! Flag for review