flightline
Senior Member
Have you ever had one of those days when you felt sure you knew the answer to a question, but after speaking with someone, didn't know what was true? I had one of those days while speaking with another inspector. We are both planning on obtaining the new NFPA/IAEI CEI-R and CEI-M certifications. In the sample questions, there was one that spoke to 2002 NEC 312.8. It concerned other wiring, [ another circuit] passing through, let's say, the bottom of a disconnect switch to other disconnect switches. It concerned fill in this area within the disconnect switch. The not-to-exceed 40% for wiring, 75% for splices governs this installation.
The controversy revolves around what I believed was correct, in that it is the actual area of the conductors in any cross section that is to be used for calculations. The other inspector contends it should be based upon Table 314.16(B) Volume Allowance Required per Conductor.
His contention is that it is easier and quicker to use that method as it would take into account any slack or loop that the electrician may leave in this area. He asked me how I could physically measure these loops or slack to effectively make a calculation? He went on to further ask, how I would actually calculate the area of a splice, liked a split both that was properly insulated? He said "it's only a stinkin' disconnect; how much time are you supposed to invest in these calculations"?
I guess his argument was persuasive. So I went to the 2002 NEC handbook. It said:
Most enclosures are intended to accommodate only those conductors that will be connected to terminals for switches or overcurrent devices within the enclosures themselves. Where adequate space is provided for additional conductors, such as control circuits, the total conductor fill in the enclosure may not exceed 40 percent of the cross section of the wiring space in the enclosure, and no more than 75 percent if splices or taps are necessary. Example
If an enclosure has a wiring space of 4 in. by 3 in., the cross-sectional area is 12 in.2 Thus, the total conductor fill (see Chapter 9, Table 5 for dimensions of conductors) at any cross section cannot exceed 4.8 in.2 (40 percent of 12 in.2), and the maximum space for conductors and splices or taps at any cross section cannot exceed 9 in.2 (75 percent of 12 in.2).
In general, the best way to avoid overcrowding enclosures is to use properly sized auxiliary gutters (366.5 and 366.8) or junction boxes (314.16 and 314.28).
It would seem that my position is supported, but he did raise some pragmatic issues. If you have had the occasion to make these calculations, how did you do it?
The controversy revolves around what I believed was correct, in that it is the actual area of the conductors in any cross section that is to be used for calculations. The other inspector contends it should be based upon Table 314.16(B) Volume Allowance Required per Conductor.
His contention is that it is easier and quicker to use that method as it would take into account any slack or loop that the electrician may leave in this area. He asked me how I could physically measure these loops or slack to effectively make a calculation? He went on to further ask, how I would actually calculate the area of a splice, liked a split both that was properly insulated? He said "it's only a stinkin' disconnect; how much time are you supposed to invest in these calculations"?
I guess his argument was persuasive. So I went to the 2002 NEC handbook. It said:
Most enclosures are intended to accommodate only those conductors that will be connected to terminals for switches or overcurrent devices within the enclosures themselves. Where adequate space is provided for additional conductors, such as control circuits, the total conductor fill in the enclosure may not exceed 40 percent of the cross section of the wiring space in the enclosure, and no more than 75 percent if splices or taps are necessary. Example
If an enclosure has a wiring space of 4 in. by 3 in., the cross-sectional area is 12 in.2 Thus, the total conductor fill (see Chapter 9, Table 5 for dimensions of conductors) at any cross section cannot exceed 4.8 in.2 (40 percent of 12 in.2), and the maximum space for conductors and splices or taps at any cross section cannot exceed 9 in.2 (75 percent of 12 in.2).
In general, the best way to avoid overcrowding enclosures is to use properly sized auxiliary gutters (366.5 and 366.8) or junction boxes (314.16 and 314.28).
It would seem that my position is supported, but he did raise some pragmatic issues. If you have had the occasion to make these calculations, how did you do it?
