Tables (Minnesota Class A Journeyworker)

Learning Objectives

Apply Table 1 of Chapter 9 and the notes to the Chapter 9 tables to conduit and tubing fill.

Use Table 5 and Table 5A to obtain approximate conductor areas and diameters.

Explain how Table 9 defines effective impedance and the power factor at which its values are valid.

Use Informative Annex C and Informative Annex D, including Example D8, in calculations.

Apply Table 11(A) and Table 11(B) and their notes to Class 2 and Class 3 power sources.

10.1 How the Chapter 9 Tables Are Organized

The notes that precede the Chapter 9 tables carry as much examinable content as the tables. Note 1 sends the reader to Informative Annex C for the maximum number of conductors and fixture wires of the same size, total cross-sectional area including insulation, permitted in trade sizes of conduit or tubing. Note 3 requires equipment grounding or bonding conductors to be included in the fill calculation. Note 9 treats a multiconductor cable or flexible cord as a single conductor. Note 10 explains that the approximate values in Table 5 are worst-case and indicate round concentric-lay-stranded conductors, with compact-stranded values in Table 5A.

10.2 Conduit and Tubing Fill — Table 1 and Table 4

Table 1 gives the percent of cross section of conduit and tubing permitted for conductors and cables: 53 percent for one conductor or cable, 31 percent for two conductors or cables, and 40 percent for over two conductors or cables.

Note 4 to the tables states that where conduit or tubing nipples, not including connectors, having a maximum length not to exceed 600 mm (24 in.) are installed between boxes, cabinets, and similar enclosures, the nipples may be filled to 60 percent of their total cross-sectional area, and the adjustment factors of 310.15(C)(1) need not apply to that condition.

Table 4 supplies the areas those percentages apply to. For electrical metallic tubing (EMT) in metric designator 16, trade size 1/2, the tabulated values are 78 mm2 (0.122 in.2) at 40 percent, 104 mm2 (0.161 in.2) at 53 percent, 61 mm2 (0.094 in.2) at 31 percent, 118 mm2 (0.182 in.2) at 60 percent, and 196 mm2 (0.304 in.2) at 100 percent. The percentage columns are identical in every Table 4 table because they come from Table 1.

10.3 Conductor Properties — Table 5 and Table 5A

Table 5 lists approximate areas and diameters of insulated conductors and fixture wires by conductor type group. For the type group containing THHN, THWN, and THWN-2 the tabulated values are:

Conductor Size	Approximate Area	Approximate Diameter
14 AWG	6.258 mm2 (0.0097 in.2)	2.819 mm (0.111 in.)
12 AWG	8.581 mm2 (0.0133 in.2)	3.302 mm (0.130 in.)
10 AWG	13.61 mm2 (0.0211 in.2)	4.166 mm (0.164 in.)
8 AWG	23.61 mm2 (0.0366 in.2)	5.486 mm (0.216 in.)

Two mistakes are common. Reading the diameter as the area is how 3.302 mm gets mistaken for the area of a 12 AWG conductor, when 8.581 mm2 is its area and 3.302 mm is its diameter. Reading the wrong row confuses the 12 AWG conductor with the 14 AWG conductor at 6.258 mm2 or with the 8 AWG conductor at 23.61 mm2. Note 10 qualifies the table: the values are worst-case and round concentric-lay-stranded, so actual published dimensions may be used instead, and compact-stranded values come from Table 5A.

10.4 Alternating-Current Resistance — Table 9

The notes to Table 9 define effective impedance and state the condition under which the tabulated values apply. Effective Z is defined as R cos(theta) plus X sin(theta), where theta is the power factor angle of the circuit, and multiplying current by effective impedance gives a good approximation of line-to-neutral voltage drop.

The limitation to memorize is that the effective impedance values shown in the table are valid only at 0.85 power factor. For a circuit at another power factor the effective impedance is recalculated from the tabulated R and XL values as:

Ze = R x PF + XL x sin[arccos(PF)]

Reading the table as valid at 1.0 power factor is wrong: at unity power factor the reactance term drops out, so the tabulated effective impedance no longer describes the circuit.

10.5 Informative Annex C and Informative Annex D

Informative Annex C tabulates the maximum number of conductors and fixture wires of the same size, total cross-sectional area including insulation, permitted in trade sizes of conduit and tubing. A fill question that asks for a count of conductors rather than a percentage is usually an Annex C question.

Informative Annex D contains worked examples, and Example D8 applies Table 430.250 to motors. In that example a 25 hp, 460 V, three-phase squirrel-cage motor has a nameplate full-load current of 32 A, while the current used for minimum conductor ampacity comes from Table 430.250 in accordance with 430.6(A). For that motor the table current is 34 A, multiplied by 1.25 in accordance with 430.22 and 430.23(A):

34 A x 1.25 = 43 A

A separate overload calculation in the same example applies 125 percent of the nameplate current under 430.32(A)(1), giving 40 A for the 25 hp motor, which is a different requirement from conductor ampacity. The 34 A figure is the table current before the multiplier and the 43 A figure is the minimum conductor ampacity.

10.6 Class 2 and Class 3 Power Sources — Table 11(A) and Table 11(B)

These tables provide the required power source limitations for Class 2 and Class 3 sources. Table 11(A) applies for ac sources, and Table 11(B) applies for dc sources, and both are organized by source voltage columns rather than by circuit class.

The power is either inherently limited, requiring no overcurrent protection, or not inherently limited, requiring a combination of power source and overcurrent protection. Overcurrent devices, where required, shall be located at the point where the conductor to be protected receives its supply and shall not be interchangeable with devices of higher ratings. A listed power source must be durably marked with the class of supply and its electrical rating.

The notes carry the values exam questions hinge on. Note 2 states that for nonsinusoidal ac, Vmax shall not be greater than 42.4 volts peak, and that where wet contact, immersion not included, is likely to occur, Class 3 wiring methods shall be used or Vmax shall not be greater than 15 volts for sinusoidal ac and 21.2 volts peak for nonsinusoidal ac. Note 4 governs dc interrupted at a rate of 10 to 200 Hz, for which Vmax shall not be greater than 24.8 volts peak, with the same wet-contact alternative.

Two 60-volt figures used as wrong answers belong to other articles: 820.15 permits coaxial cable to deliver power to radio frequency equipment at not over 60 volts, and 721.60 sets the limitation for premise-powered broadband sources.

Code Navigation

Topic	Table, Annex, or Section	What It Contains
Conduit and tubing fill percentage	Chapter 9 Table 1	53 percent for 1; 31 percent for 2; 40 percent over 2
Insulated conductor areas	Chapter 9 Table 5, Table 5A	12 AWG THHN: 8.581 mm2 (0.0133 in.2); 3.302 mm (0.130 in.)
Effective impedance	Chapter 9 Table 9 notes	Valid at 0.85 power factor; Ze = R x PF + XL x sin[arccos(PF)]
Maximum conductors in trade sizes	Informative Annex C	Number of conductors of the same size permitted
Motor calculation example	Informative Annex D, Example D8	34 A x 1.25 = 43 A using Table 430.250 and 430.22
Class 2 and Class 3 sources	Chapter 9 Table 11(A), Table 11(B)	ac sources and dc sources; notes for nonsinusoidal ac and dc

Common Exam Traps

Applying 53 percent to a multi-conductor fill. Table 1 gives 53 percent for one conductor, 31 percent for two, and 40 percent for over two; 60 percent belongs to nipples not exceeding 600 mm (24 in.).

Confusing the area and diameter rows of Table 5. A 12 AWG THHN, THWN, or THWN-2 conductor has an area of 8.581 mm2 (0.0133 in.2) and a diameter of 3.302 mm (0.130 in.); 6.258 mm2 is the 14 AWG area.

Applying Table 9 at the wrong power factor. The tabulated effective impedance values are valid only at 0.85 power factor.

Taking motor full-load current from the nameplate. Example D8 uses the Table 430.250 value of 34 A for a 25 hp, 460 V motor whose nameplate reads 32 A, then applies 1.25 for a minimum conductor ampacity of 43 A.

Reversing Table 11(A) and Table 11(B). Table 11(A) applies to ac sources and Table 11(B) to dc sources.

Reading the wet-contact rule from the wrong note. Note 2 governs nonsinusoidal ac at not more than 42.4 volts peak, with wet-contact alternatives of Class 3 wiring methods or 15 volts sinusoidal and 21.2 volts peak nonsinusoidal; 24.8 volts peak belongs to Note 4 for dc interrupted at 10 to 200 Hz.

Practical Field Points

Use Table 1 percentages with Table 4 areas for a fill check, and count equipment grounding conductors toward the fill under Note 3.

Substitute Table 5A values for compact-stranded conductors, or use the manufacturer's actual dimensions, as Note 10 permits.

Apply the 60 percent nipple allowance only to nipples not exceeding 600 mm (24 in.) between boxes, cabinets, and similar enclosures.

Recalculate voltage drop from the tabulated R and XL values whenever the circuit power factor differs from 0.85.

Keep the Table 430.250 current and the nameplate current separate: the table current drives conductor ampacity.

Summary

The Chapter 9 tables are read through their notes. Table 1 permits 53 percent of the conduit cross section for one conductor or cable, 31 percent for two, and 40 percent for over two, with Note 4 allowing 60 percent for nipples not exceeding 600 mm (24 in.) between boxes, cabinets, and similar enclosures. Table 5 gives approximate insulated conductor areas and diameters, with 8.581 mm2 (0.0133 in.2) and 3.302 mm (0.130 in.) for 12 AWG THHN, THWN, or THWN-2, and Note 10 directs compact-stranded conductors to Table 5A. The notes to Table 9 define effective Z as R cos(theta) plus X sin(theta), state that the tabulated values are valid only at 0.85 power factor, and give the recalculated value as R x PF plus XL times the sine of the arccosine of PF. Informative Annex C answers how many conductors of one size fit in a trade size, and Example D8 of Informative Annex D multiplies the Table 430.250 current of 34 A for a 25 hp, 460 V motor by 1.25 to reach 43 A of minimum conductor ampacity. Table 11(A) applies to ac sources and Table 11(B) to dc sources, and any overcurrent device must sit where the conductor receives its supply and must not be interchangeable with devices of higher ratings; Note 2 caps nonsinusoidal ac at 42.4 volts peak, and Note 4 caps dc interrupted at 10 to 200 Hz at 24.8 volts peak.

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