The Code users quite often express concerns on perceived inconsistency between these two Rules, particularly in light of the changes to Rule 4-004 for the 2015 edition of the CE Code.
It should be noted that although Rule 12-2210 appears in the 2015 edition of the Code without any changes, the Technical Committee for the CE Code, Part I has recently approved deletion of Rule 12-2210 and relocation of this Rule to Section 4 – to become an extension of Rule 4-004.
Such decision of the Technical Committee was based on the fact that Section 12 of the CE Code covers wiring methods, and the requirements for determination of conductors’ ampacities should be located in Section 4.
So, as the result of such relocation of Rule 12-2210, already very extensive Rule 4-004 will be even bigger in the 2018 edition of the Code.
Let’s take a look at this Rule, the way it is written in 2015 edition of the CE Code:
“4-004 Ampacity of wires and cables
(see Appendix B)
(1) The maximum current that a copper conductor of a given size and insulation is permitted to carry shall be as follows:
(a) single-conductor and single-conductor metal-sheathed or armoured cable, in a free air run, with a cable spacing not less than 100% of the larger cable diameter, as specified in Table 1;
(b) one, two, or three conductors in a run of raceway, or 2- or 3-conductor cable, except as indicated in Subrule (1)(d), as specified in Table 2;
(c) four or more conductors in a run of raceway or cable, as specified in Table 2 with the correction factors applied as specified in Table 5C;
(d) single-conductor and 2-, 3-, and 4-conductor cables and single-conductor and 2-, 3-, and 4-conductor metal-armoured and metal-sheathed cables, unshielded and rated not more than 5 kV, in conductor sizes No. 1/0 AWG and larger, installed in accordance with configurations described in Diagrams D8 to D11 in an underground run, directly buried or in a raceway, as specified in Tables D8A to D11B or as calculated by the IEEE 835 calculation method;
(e) underground configurations not specified in Item (d), in conductor sizes No. 1/0 AWG and larger, as calculated by the IEEE 835 calculation method;
(f) underground configurations in conductor sizes smaller than No. 1/0 AWG, as specified in Item (b) or as calculated by the IEEE 835 calculation method; and
(g) shielded cables rated 5 kV to 46 kV in sizes No. 2 AWG to 1000 kcmil, as specified in Tables D17A to D17N for the configurations described therein and the conditions described in Table D17, or as calculated by the IEEE 835 calculation method.
(2) The maximum current that an aluminum conductor of a given size and insulation is permitted to carry shall be as follows:
(a) single-conductor and single-conductor metal-sheathed or armoured cable, in a free air run, with a cable spacing not less than 100% of the larger cable diameter, as specified in Table 3;
(b) one, two, or three conductors in a run of raceway, or 2- or 3-conductor cable, except as indicated in Subrule (2)(d), as specified in Table 4;
(c) four or more conductors in a run of raceway or cable, as specified in Table 4 with the correction factors applied as specified in Table 5C;
(d) single-conductor and 2-, 3-, and 4-conductor cables and single-conductor and 2-, 3-, and 4-conductor metal-armoured and metal-sheathed cables, unshielded and rated not more than 5 kV, in conductor sizes No. 1/0 AWG and larger, installed in accordance with configurations described in Diagrams D8 to D11 in an underground run, directly buried or in a raceway, as specified in Tables D8A to D11B or as calculated by the IEEE 835 calculation method;
(e) underground configurations not specified in Item (d), in conductor sizes No. 1/0 AWG and larger, as calculated by the IEEE 835 calculation method;
(f) underground configurations in conductor sizes smaller than No. 1/0 AWG, as specified in Item (b) or as calculated by the IEEE 835 calculation method; and
(g) shielded cables rated 5 kV to 46 kV in sizes No. 2 AWG to 1000 kcmil, as specified in Tables D17A to D17N for the configurations described therein and the conditions described in Table D17, or as calculated by the IEEE 835 calculation method.
(3) A neutral conductor that carries only the unbalanced current from other conductors, as in the case of normally balanced circuits of three or more conductors, shall not be counted in determining ampacities as provided for in Subrules (1) and (2).
(4) When a load is connected between a single-phase conductor and the neutral, or between each of two phase conductors and the neutral, of a three-phase, 4-wire system, the common conductor carries a current comparable to that in the phase conductors and shall be counted in determining the ampacities as provided for in Subrules (1) and (2).
(5) The maximum allowable ampacity of neutral supported cable shall be as specified in Tables 36A and 36B.
(6) A bonding conductor shall not be counted in determining the ampacities as provided for in Subrules (1) and (2).
(7) The correction factors specified in this Rule
(a) shall apply only to, and shall be determined from, the number of power and lighting conductors in a cable or raceway; and (b) shall not apply to conductors installed in auxiliary gutters.
(8) The ampacity correction factors of Table 5A shall apply where conductors are installed in an ambient temperature exceeding or anticipated to exceed 30 °C.
(9) Where the free air spacing between adjacent single-conductor cables is maintained at not less than 25% nor more than 100% of the diameter of the largest cable, the ampacity shall be obtained from Subrules (1)(a) and (2)(a) for copper and aluminum conductors respectively, multiplied by the correction factor obtained from Table 5D.
(10) Where up to and including four single-conductor cables in free air are spaced at less than 25% of the diameter of the largest conductor or cable, the ampacity shall be the same as that obtained from Sub-rules (1)(a) and (2)(a) for copper and aluminum conductors respectively, multiplied by the correction factor obtained from Table 5B.
(11) Notwithstanding Subrule (10), where not more than four non-jacketed single-conductor mineral-insulated cables are grouped together in conformance with Rule 4-010(3) and are installed on a messenger or as open runs with a maintained free air space of not less than 2.15 times the diameter of the largest cable contained within the group and adjacent groups or cables, the ampacity of each conductor in the group shall be permitted to be determined in accordance with Subrule (1)(a) without applying the correction factors of Table 5B.
(12) More than four single-conductor cables in free air, when spaced at less than 25% of the largest cable diameter, shall have an ampacity obtained from Tables 2 and 4 for copper and aluminum conductors respectively, multiplied by the correction factor obtained from Table 5C based on the total number of conductors.
(13) Notwithstanding Subrule (12), when the length of a single-conductor cable run spaced at less than 25% of the largest cable diameter is less than 600 mm, the correction factor from Table 5C shall not apply.
(14) Where multi-conductor cables are run in contact for distances greater than 600 mm, the ampacity of the conductors shall be corrected by applying the correction factors in Table 5C based on the total number of conductors in the cables.
(15) The ampacity of conductors of different temperature ratings installed in the same raceway shall be determined on the basis of the conductor having the lowest temperature rating.
(16) The ampacity of conductors added to a raceway and the ampacity of the conductors already in the raceway shall be determined in accordance with the applicable Subrules.
(17) Where more than one ampacity could apply for a given circuit of single-conductor or multi-conductor cables as a consequence of a transition from an underground portion to a portion above ground, the lower value shall apply except as permitted in Subrule (18).
(18) Where the lower ampacity portion of a cable installation consisting of not more than four conductors in total does not exceed 10% of the circuit length or 3 m, whichever is less, the higher ampacity shall be permitted.
(19) When the load factor of the load is less than 1.00 and is known or can be supported by documentation, the ampacity of conductors derived from Subrules (1)(d) and (2)(d) shall be permitted to be increased by application of that load factor in the calculation of the ampacity.
(20) In consideration of the increased ampacity of any conductor derived in accordance with Subrule (19), no further factors based on load diversity shall be permitted.
(21) The ampacity of nickel or nickel-clad conductors shall be calculated using the method described in IEEE 835.
(22) The maximum allowable ampacity of bare or covered conductors in free air shall be as specified in Table 66.
(23) Notwithstanding Rule 4-006, 3-wire 120/240 V and 120/208 V service conductors for single dwellings and feeder conductors supplying single dwelling units of row housing of apartment and similar buildings and terminating on equipment having a conductor termination temperature of not less than 75 °C shall be permitted to be sized in accordance with Table 39.”
For the purpose of our discussion, let’s so far concentrate only on requirements of this Rule for selection of ampacities for single conductors in free air based on the spacing between conductors.
The following is the set of conditions for selecting ampacities of single conductors in free air:
“1. When single conductors are run in the free air environment and are spaced at least 100% diameter of the largest conductor, ampacity values of Table 1 or Table 3 must apply [see Subrules (1)(a) and (2)(a)].
- When single conductors are run in the free air environment and are spaced at not less than 25% and not more than 100% diameter of the largest conductor, ampacity values of Table 1 or Table 3 must be used with application of de-rating factor of Table 5D, and de-rating factors of Table 5D allow up to 6 of such conductors being spaced in free air [see Subrule (9)]. It should be noted that compliance with Table 5D is also mandated by Rule 12-2210 (see Rule 12-2210 below), and when Table 5D is applied for installation of single conductors in a cable tray, Table 5D covers the additional arrangement with one or two vertical layers.
- When up to 4 single conductors are run in the free air environment and are spaced at less than 25% diameter of the largest conductor, ampacity values of Table 1 or Table 3 still should apply, however de-rating factor of Table 5B must be now used for number of conductors in such run. [see Subrule (10)]. It should be noted that Table 5B was always intended to be applied in conjunction with Tables 1 and 3, but in the 2012 edition of the Code, Subrule 4-004(10) required the use of Table 5B in conjunction with Tables (2) and (4), thus needlessly penalizing the Code users by not only applying ampacity Tables for conductors in raceway (or for 2 and 3 conductor cable), but also penalizing the Code users – by mandating to multiply these reduced ampacity values by de-rating factors in Table 5B. Fortunately, this error was fixed in 2015 edition of the Code. A side note: as we are aware, Tables 2 and 4 are intended to be used only for up to 3 conductors in a raceway or for a multi-conductor cable containing 2 or 3 current carrying conductors [not including a neutral conductor, as neutral conductor is not considered to be a current carrying conductor under provisions of Subrule (3), and this aspect of Rule 4-004 will be discussed later in this article]. If the neutral conductor carries a full load current, then it must be taken into account in determination of ampacities, and this fact is reflected in Subrule 4-004(4).
- If a raceway contains more than 3 current carrying conductors, or a multi-conductor cable contains more than 3 current-carrying conductors, then Table 5C must be used, and this provision of Rule 4-004 is articulated in Subrules (1)(c); (2)(c) and (14). It should be noted that the similar requirement is mandated by Subrule 12-2210(1)(b) and 12-2210(3) for cables installed in a cable tray (see Rule 12-2210 below).
- When more than 4 single conductors are run in the free air environment and are spaced at less than 25% diameter of the largest conductor, the requirement for selection of conductors’ ampacity becomes more restrictive, and ampacity values for such single conductor cables must be now derived not from Table 1 or Table 3, but from Table 2 or Table 4, and de-rating factors of Table 5C must be also applied in conjunction with these ampacity Tables. [See Subrule (12)].
- Subrules (13) and (14) allow one to disregard use of correction factors of table 5C, if single conductor (or multi-conductor) cables are running in contact for not more than 600 mm.”
Now, let’s take a look at Rule 12-2210 (which has not changed in the 2015 edition of the CE Code):
“12-2210 Ampacities of conductors in cable trays
(1) In ventilated and ladder-type cable trays, where the air space between adjacent conductors or cables, or both, is maintained at greater than 100% of the diameter of the larger conductor or cable, the ampacity of the conductors or cables shall be as follows:
(a) for single conductors, single-conductor metal-sheathed or armoured cable, and single-conductor mineral-insulated cable: as specified in Tables 1 and 3; and
(b) for multi-conductor cables: as specified in Tables 2 and 4, multiplied by the correction factor in Table 5C for the number of conductors in each cable.
(2) In ventilated and ladder-type cable trays, where the air space between adjacent conductors or cables, or both, is maintained at not less than 25% nor more than 100% of the diameter of the larger conductor or cable, the ampacity of the conductors or cables shall be the value specified in Subrule (1), multiplied by the correction factor specified in Table 5D for the arrangement and number of conductors or cables involved, unless a deviation has been allowed in accordance with Rule 2-030 for other correction factors.
(3) In ventilated and ladder-type cable trays, where the air space between adjacent conductors or cables, or both, is less than 25% of the diameter of the larger conductor or cable, and for any spacing in a non-ventilated cable tray, the ampacity of the conductors or cables shall be as specified in Table 2 or 4, multi-plied by the correction factor specified in Table 5C for the total number of conductors in the cable tray.
(4) In determining the total number of conductors in the cable tray in Subrule (3), Rule 4-004(7) shall apply.
(5) Where cable trays are located in room temperatures above 30 °C, the temperature correction factor of Table 5A shall be applied to the ampacities determined from Subrules (1), (2), and (3) as applicable”.
It could be seen that requirements of Rule 12-2210 are similar to the above stated provisions of Rule 4-004. However, Subrule 12-2210(3) mandates use of Table 2 or 4 for all types of cables (for multi-conductor cables and for single conductor cables), as its requirement appears to be based on assumption that there will be more than 4 single conductor cables in a cable tray. Hopefully, such inconsistency with similar provisions of Rule 4-004 will be corrected when the requirements of Rule 12-2210 will be moved into Rule 4-004, and necessary clarification will be added in this regard. Most likely Section 4 S/C will also clarify Rule 4-004 by adding a new Subrule or by adding Appendix B Note on Subrules (1)(b) and (2)(b) – to indicate that these Subrules apply not only to conductors in a raceway and to multi-conductor cables, but to single conductor cables bundled/grouped together as well. It should be noted that the request on this subject has been already submitted to Chair of the S/C for Section 4.
Now, let’s chat about selection of ampacity of a neutral conductor of a typical 3 phase, 4 wire service, feeder or circuit, where such neutral conductor carries only unbalanced current, and it does not carry a full load current, as when it is used in a 2 wire circuit.
Ampacity of a neutral conductor of a 3 phase, 4 wire feeder is not based on the requirements of Subrules 4-004(1) or (2), but is selected in accordance with Rule 4-024 of the CE Code.
This means that a neutral conductor which carries only unbalanced current will be already allowed by Rule 4-024 to be sized smaller than a current carrying conductor required to be sized in accordance with Subrule 4-004(1) or 4-004(2).
This is the reason that Subrule 4-004(3) allows the users not to take the neutral conductor into account, when the conductor’s ampacity is selected only in accordance with Subrules 4-004(1) or (2).
However, it should be noted that relaxation allowed by Subrule 4-004(3) is only valid in conjunction with Subrule (1) or (2), but it does not apply to other Subrules which mandate compliance with the appropriate de-rating factors. Thus, regardless whether all 4 conductors of such 3 phase, 4 wire feeder are selected based on Subrules 4-004(1) or (2), or whether only ampacity of current carrying conductors is chosen in accordance with Subrules 4-004(1) or (2), and the neutral conductor is selected as per Rule 4-024, the fact is that when 4 single conductors of such 3 phase, 4 wire feeder are spaced in free air in accordance with Subrule 4-004(9), then de-rating factor of 0.84 would have to be applied to the selected ampacity, as specified by Table 5D. It should be noted that Table 5D is intended to be used in conjunction with up to 6 single conductors spaced in accordance with Subrule (9).
If 4 single conductors of such 3 phase, 4 wire feeder (or any other 4 single conductors) are spaced in free air in conformance with Subrule 4-004(10), then the selected ampacity of single conductors would have to be multiplied by the de-rating factor of 0.8 from Table 5B.
The requirement for taking a neutral conductor into account under Subrules (9) or (10) is based on the reality that although the neutral conductor in such 3 phase, 4 wire feeders may not carry a full load current, it still carries unbalanced current, and as such, it generates heat. In addition, the heat from the presence of a neutral conductor is also based on the existence of inductive and capacitive reactance between adjacent conductors.
Perhaps, it is also worth noting that Subrule 4-004(19) allows one to increase the ampacity of conductors rated at not more than 5 KV and installed in underground runs as shown in configurations of Diagrams D8 to D11 by applying the load factor in the calculation of ampacity, provided that the load factor is known to be less than 1.00, and that such fact is supported by relevant documentation.
All other provisions of Rule 4-004 should be reasonably straight forward, but as usual, in case of concerns, the local AHJ should be always consulted.
