Application of Rule 4-006 of the Canadian Electrical Code Discussion and Questions Continue

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Although Rule 4-006 was introduced into the Canadian Electrical Code, Part I (CE Code) a few editions ago, (when ampacity tables in the NEC and the CE Code have been harmonized), application of this Rule does not appear to be consistently clear to many Code users.

In the 2018 edition of the CE Code, this Rule reads as follows:

 

4-006 Temperature limitations (see Appendix B)

1)    Where equipment is marked with a maximum conductor termination temperature, the minimum size of conductor used shall be based on the allowable ampacity in the temperature column in Table 1, 2, 3, or 4, with all relevant correction factors being applied as required by Rule 4-004, corresponding to the maximum termination temperature marked on the equipment.

2)    For the purpose of Subrule 1), and except as provided for by other Rules of this Code, where the maximum conductor termination temperature for equipment is not marked, the maximum conductor termination temperature shall be considered to be

  1. a) 60 °C for equipment
  2. i) rated not more than 100 A; or
  3. ii) marked for use with No. 1 AWG or smaller conductors; and
  4. b) 75 °C for equipment
  5. i) rated more than 100 A; or
  6. ii) marked for use with conductors larger than No. 1 AWG.

 

3)    Notwithstanding Subrule 2), for high-voltage equipment where conductor termination temperatures are not marked, it shall be permitted to consult the manufacturer to establish the permitted termination temperature.

 

4)    Subrules 1) and 2) shall apply only to the first 1.2 m of conductor length measured from the point of termination on the equipment.

 

5)    Where a cable transition is made to meet the requirements of Subrule 1) or 2), the length of a conductor terminating on equipment shall be not less than 1.2 m.

 

6)    Where the conductor ampacity is selected from Tables D8A to D11B, Tables D17A to D17N, or Table 12E, Subrules 1) and 2) shall apply.

 

Appendix B Note on Rule 4-006 offers the following clarification to the Code users:

 

Appendix B Notes on Rule 4-006

In accordance with CSA product Standards (e.g., CSA C22.2 No. 4 or CSA C22.2 No. 5), when equipment of 600 V or less is evaluated relative to the appropriate temperature characteristics of the terminations, conductors sized similar to those in the 75 °C column of Table 2 or 4 are used.

 

It is intended by this Rule that the size of conductors terminating on equipment described in Subrules 1), 2), 3), and 4) be not less than the conductor size selected for the maximum insulated conductor ampacity in the corresponding temperature column of Table 1, 2, 3, or 4.

 

This Rule is not intended to address conductor allowable ampacity (see Rule 4-004). Regardless of conductor allowable ampacities determined by other Rules in this Code (for underground conductors, cables, flexible cords, portable power cables, DLO cables, and conductors with higher temperature ratings, etc.), it is intended that the minimum conductor size be based on the requirements of this Rule.

 

Rule 4-006 3)

High-voltage equipment may be tested and rated for termination temperature at 90 °C. For high-voltage installations rated up to 5 kV, where conductors are selected in accordance with Tables 1 to 4, 12E, or D8A to D11B, or for high-voltage installations rated 5 kV to 46 kV, where insulated conductors or cables are selected in accordance with Tables D17A to D17N, the equipment manufacturer should be consulted when insulated conductors or cables are intended for termination on each specific type of high-voltage equipment.

 

Rules 4-006 4) and 5)

The 1.2 m length is based on test requirements from equipment Standards.

 

So, based on the requirements of this Rule and on the explanatory/clarification notes, the application of this Rule should not have any problems.

However, the reality is quite different, and below are some of the typical questions (with the provided answers) in respect to this Rule.

 

Question 1: Why are conductors of a similar size but with different insulation temperatures assigned different ampacity values?

Answer 1:    Assigned ampacity of a conductor with a given size and material is the maximum operating temperature of the conductor. The majority of conductors and cables in Canada are manufactured with the insulation rated for 90˚C. TECK 90, AC 90, RW90, NMD 90 are just a few examples of such conductors and cables. It means that for a conductor manufactured with insulation rated at 90˚C, assigned conductor ampacity from a 90˚C column in Tables 1 – 4  would mean that if the conductor carries current up to (but not exceeding) the assigned ampacity, then the conductor’s operating temperature will not exceed 90˚C, and the integrity of the conductor’s insulation will not be compromised. If, for example, a No. 3 AWG copper conductor is selected from a 90˚C column of Table 2 with the ampacity of 115 A, then the operating temperature of such conductor will not exceed 90˚C if the conductor does not carry current in excess of 115 A.

 

Question 2: Why maximum conductor temperature limitations at the termination point are required by Rule 4-006?

Answer 2: Before harmonization of ampacity tables between the NEC and the CE Code, values of ampacities in 90˚C column of Tables 1 – 4 of the CE Code were almost similar to the current values in a 75˚C column in Tables 1 – 4.

When ampacity values have been harmonized between the NEC and the CE Code, these ampacity values have been increased in Tables 1 – 4 of the CE Code. For instance, in 90˚C column of Table 2, for such common conductor size as No. 3 AWG copper, ampacity value has been raised from 105 A to 115 A, and for No. 3/0 AWG copper – from 210 A to 225 A respectively, etc. However, in accordance with harmonized standards for such equipment as circuit breakers, switches, etc., when equipment of 600 V or less is tested in respect to the appropriate temperature characteristics of the terminations, conductors sized similar to those in the 75°C column of Table 2 or 4 are used. Thus, it became important that the temperature at the termination point at the equipment, which is marked with a maximum conductor termination, does not exceed the marked termination temperature value. It means that the maximum current carried by a conductor with the insulation rated for 90˚C cannot generate temperature at the termination point in excess of the value marked on the equipment.

If a piece of equipment is not marked with maximum conductor termination temperature, this maximum conductor termination temperature shall be in accordance with Subrule 4-006(2) of the CE Code. As the majority of circuit breakers, switches, panelboards are marked with maximum termination temperature at 75˚C, electrical designers and installers (despite the use of conductors and cables with 90˚C insulation), must select reduced ampacity of these conductors and cables based not on 90˚C column, but in accordance with the ampacity values indicated in 75˚C column of Tables 1 – 4.

Of course, these designers and installers are welcome to select ampacities based on 90˚column provided that within 1.2 m of the intended termination, the ampacity of these conductors comply with the provision of Rule 4-006 at the termination point (e.g., that conductors selected with ampacity based on 90˚C column are spliced so that within the first 1.2 m of conductors length measured from the point of termination on the equipment, increased size of the conductors meets the requirements of Rule 4-006 for conductors ampacity at termination point).

 

Question 3: If the referenced equipment is tested based on 75˚C at termination point when ampacities of Table 2 or Table 4 are used, does it mean that single conductor cables are not allowed for termination on such equipment?

Answer 3: Single conductor cables are permitted for use under provisions of the CE Code, and Tables 1; 3; 12E, D8; D9; D17A – D17D; D17I; D17J and D17M represent the perfect testament of this fact. Subrules 8-104(5)(b) and 8-104(6)(b) of the CE Codeoutline specific criteria for the selection of single conductors.

 

Question 4: Are correction factors listed in Rule 4-004 allowed as the substitution of the requirement mandated by Subrules 4-006(1) and (2)?

Answer 4: No, correction factors listed in Rule 4-004(7), must apply independently (or in addition to the requirements of Rule 4-006), where any condition of installation will warrant their use. Let’s consider, for example, that a continuous load in the CRU (commercial tenant unit in the shopping mall) is 75 A, and a feeder conductors supplying a panelboard to such CRU are intended to be protected by a circuit breaker which is marked for continuous operation at 80% of the ampere rating of its overcurrent devices, and it is intended to run copper conductors of this feeder in a raceway.

 

In this case, in accordance with Subrule 8-104(6)(a) of the CE Code, rating of this feeder must be not less than 75 A x 1.25 = 93.75 A. As such, the 100 A rated circuit breaker will be selected, and No. 3 AWG RW 90 copper conductors would be selected in accordance with Table 2. Although, as per 90˚C column of Table 2, the ampacity of such No. 3 AWG conductor is 115 A, in accordance with provisions of Rule 4-006, the ampacity of this conductor would be assigned based on 75˚C column of Table 2, and such ampacity would be 100 A.

If a raceway carrying these feeder conductors would also be used for feeder conductors to a panelboard in another CRU, and as a result, 6 conductors would have to run in this raceway, then provisions of Table 5C would have to apply to already selected (based on Rule 4-006) ampacity of 100 A for No. 3 AWG conductors. In this case, the ampacity of such No. 3 AWG conductors would be not 100 A, but 100 A x 0.8 = 80 A, and use of No. 3 AWG would not be sufficient as the rating of this feeder conductors cannot be less than 93.75 A. Therefore, No. 1 AWG (130×0.8 = 104 A) would have to be selected in order to meet requirement of correction factor in accordance with Table 5C, in addition to the mandatory provisions of Rule 4-006.

Unfortunately, there are numerous statements have been made, and some articles have been published that appear to allow use correction factors of Rule 4-004 as a substitution of Rule 4-006 provisions. It should be noted that when the requirement of Rule 4-006 is met, the designers and installers must validate that all respective correction factors mandated by Rule 4-004(7) are applied. Similarly, provisions of Rule 8-102 for a maximum allowed voltage drop must also be taken into account when conductor size is being selected.

 

Question 5:  When conductors operate in the ambient temperature exceeding 30˚C, must correction factors of Table 5A be based on 75˚C insulation?

Answer 5: No. The maximum conductor termination temperature limitations mandated by Rule 4-006 are applicable only to the first 1.2 m of conductor length measured from the point of termination on the equipment. Conductors may operate in a higher ambient temperature environment for significant distances, and Table 5A applies to the entire ambient environment where such conductors are installed. In addition, it should be noted that the conductor is selected with an insulation rating at 90˚C. Let’s again use the example of No. 3 AWG conductor above.

If this No. 3 AWG copper conductor is intended for termination at a piece of equipment with a maximum allowable temperature of 75˚C, it means and the ampacity of this No. 3 AWG copper conductor with 90˚C insulation is now reduced to the value indicated in 75˚C column of Table 2 and the ampacity assigned to this conductor is 100 A under the ambient temperature not exceeding 30˚C. However, when such No. 3 AWG copper conductor with 90˚C insulation is operating (for example) in the ambient environment of 40˚C, then a correction factor of 0.91 must be applied to this copper conductor with 90˚Insulation. As such, the originally reduced ampacity of such conductors to 100 A to meet the requirements of Rule 4-006 must now be further reduced by multiplying this 100 A ampacity value by 0.91.

In this case, the assigned ampacity to this #3 AWG copper conductor would be 91 A, as this conductor operating in 40˚C ambient environment is not allowed to carry more than 91 A under provisions of Rule 4-006 and Table 5A. It means that the reduced ampacity will not be able to meet a minim allowable rating of 93.75 A in our example above, and No. 2 AWG conductor would have to be selected with the ampacity of 115 x 0.91 = 104.5 A, in order to sufficiently operate in the 40˚C ambient environment.

 

Question 6: Does Rule 4-006 apply only to Tables 1 through 4 of the CE Code?

Answer 6: No. Newly added Subrule (6) of Rule 4-006 clarifies that conductors installed in accordance with Table 12E or in underground runs as per tables in Appendix D, ampacity values indicated in these respective tables, must be multiplied by a correction factor 0.885 or 0.886.

 

Hopefully, this article with clarification answers is helpful.

And as usual, local electrical inspection authorities should be consulted accordingly.

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About the Author

Ark Tsisserev is president of EFS Engineering Solutions, Ltd., an electrical and fire safety consulting company, and is a registered professional engineer with a master’s degree in Electrical Engineering. Prior to becoming a consultant, Ark was an electrical safety regulator for the city of Vancouver. He is currently the chair of the Technical Committee for the Canadian Electrical Code and represents the CE Code Committee on the CMP-1 of the National Electrical Code. Ark can be reached by e-mail at: ark.tsisserev@efsengineering.ca His company web site is: http://www.efsengineering.ca

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