Overcurrent Protection – Part Four


In Article Overcurrent Protection – Part One ",  which was an Introduction to Overcurrent Protection, I provide the basic information needed for best understanding of the Overcurrent protection. 

Also, In Article Overcurrent Protection – Part Two ", I answered the following questions: 

  • How to size the overcurrent protection devices (OCPDs)? 
  • How to select the proper overcurrent protection for certain applications? 

Also, In Article " Overcurrent Protection – Part Three ", I answered the following questions:

  • How to select the proper overcurrent protection devices (OCPDs) for certain application? 


Today, I will answer the following questions:

Where to locate the overcurrent protection devices (OCPDs)?



Locating of overcurrent protection devices (OCPDs)






Rule#1: Location of overcurrent protection devices (OCPDs)

Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except for the following:

  1. Branch-Circuit Conductors.
  2. Feeder Taps.
  3. Transformer Secondary Conductors.
  4. Service Conductors.
  5. Busway Taps.
  6. Motor Circuit Taps.
  7. Conductors from Generator Terminals.
  8. Battery Conductors.


Noting that Conductors supplied under the above exceptions shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4. (i.e. You can't make a tap from a tap)






1- Branch-Circuit Tap Conductors

Branch-circuit tap conductors include multiwire and range circuits that are meeting the requirements specified in 210.19 shall be permitted to have overcurrent protection as specified in 210.20.

This means that where a branch circuit supplies continuous (runs all the time) loads, or a combination of continuous and non-continuous (intermittent) loads, the rating of the overcurrent device shall not be less than the non-continuous load plus 125% of the continuous load. Branch circuit conductors shall be protected in accordance with Article 240.4. Flexible cords and fixture wires shall be protected in accordance with Article 240.5.






2- Feeder Taps

Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder in the following (5) cases:

  1. Taps Not over 3 m (10 ft) Long.
  2. Taps Not over 7.5 m (25 ft) Long.
  3. Taps Supplying a Transformer [Primary Plus Secondary Not over 7.5 m (25 ft) Long].
  4. Taps over 7.5 m (25 ft) Long.
  5. Outside Taps of Unlimited Length.


Note that the use of the next higher standard size provision of 240.4(B) is not permitted for feeder tap conductor applications.







Feeder Taps Cases permitted to be tapped without overcurrent protection at the tap
Conditions of case application
1- Taps Not over 3 m (10 ft) Long.
If the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:

1- The ampacity of the tap conductors is:

a- Not less than the combined calculated loads on the circuits supplied by the tap conductors, and

b- Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.

2- The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.

3- Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.

4- For field installations, if the tap conductors leave the enclosure or vault in which the tap is made, the ampacity of the tap conductors is not less than one-tenth of the rating of the overcurrent device protecting the feeder conductors.

2- Taps Not over 7.5 m (25 ft) Long
(The most common tap rule for connecting equipment).
Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following:

1- The ampacity of the tap conductors is not less than one third of the rating of the overcurrent device protecting the feeder conductors.

2- The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side.

3- The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

3- Taps Supplying a Transformer [Primary Plus Secondary
Not over 7.5 m (25 ft) Long].
Where the tap conductors supply a transformer and comply with all the following conditions:

1- The conductors supplying the primary of a transformer have an ampacity at least one-third the rating of the overcurrent device protecting the feeder conductors.

2- The conductors supplied by the secondary of the transformer shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-third of the rating of the overcurrent device protecting the feeder conductors.

3- The total length of one primary plus one secondary conductor, excluding any portion of the primary conductor that is protected at its ampacity, is not over 7.5 m (25 ft).
The primary and secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

4- The secondary conductors terminate in a single circuit breaker or set of fuses that limit the load current to not more than the conductor ampacity that is permitted by 310.15.

4- Taps over 7.5 m (25 ft) Long.
Where the feeder is in a high bay manufacturing building over 11 m (35 ft) high at walls and the installation complies with all the following conditions:

1- Conditions of maintenance and supervision ensure that only qualified persons service the systems.

2- The tap conductors are not over 7.5 m (25 ft) long horizontally and not over 30 m (100 ft) total length.

3- The ampacity of the tap conductors is not less than one-third the rating of the overcurrent device protecting the feeder conductors.

4- The tap conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.

5- The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

6- The tap conductors are continuous from end-to-end and contain no splices.

7- The tap conductors are sized 6 AWG copper or 4 AWG aluminum or larger.

8- The tap conductors do not penetrate walls, floors, or ceilings.

9- The tap is made no less than 9 m (30 ft) from the floor.

5- Outside Taps of Unlimited Length.
Where the conductors are located outdoors of a building or structure, except at the point of load termination, and comply with all of the following conditions:

1- The conductors are protected from physical damage in an approved manner.

2- The conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.

3- The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.

4- The disconnecting means for the conductors is installed at a readily accessible location complying with one of the following:

a. Outside of a building or structure
b. Inside, nearest the point of entrance of the conductors
c. Where installed in accordance with 230.6, nearest the point of entrance of the conductors









Definition:
Tap Conductors: is a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.

Tap conductors are those branch circuit and feeder conductors subject to the special overcurrent protection requirements specified in 240.21.






Example#1: Feeder Taps




Fig (1)



  • Fig (1) illustrates a 1/0 AWG, Type THW copper conductor [150 amperes, from Table 310.15(B)(16)] connected to a 3/0 AWG, Type THW copper feeder conductor with an ampacity of 200 amperes (increased in size to compensate for voltage drop) that is protected by a 150-ampere overcurrent protective device. 
  • Because the ampacity of the 1/0 AWG conductor is not exceeded by the rating of the overcurrent device, the 1/0 AWG conductor is not considered to be a tap conductor based on the definition of tap conductors in 240.2. 
  • The overcurrent device protects both sets of conductors in accordance with the basic rule of 240.4, and additional overcurrent protection is not required at the point where the 1/0 AWG conductor is supplied, nor at the point where it terminates. Both the 1/0 AWG and the 3/0 AWG conductors are protected by the 150-ampere circuit breaker. 
  • In this application, the 1/0 AWG conductors are not tap conductors as defined in 240.2. 





Example#2: Taps Not over 7.5 m (25 ft) Long



Fig (2)


  • In fig (2), three 3/0 AWG, Type THW copper tap conductors are protected from physical damage by being installed in a raceway. The tap conductors are not more than 25 ft in length between terminations, and the conductors are tapped from 500-kcmil, Type THW copper feeders and terminate in a single circuit breaker with a rating not greater than the ampacity of the tap conductors. 
  • The ampacity of the 3/0 AWG, Type THW copper conductor (200 amperes) is more than one-third the rating of the overcurrent device (400 amperes) protecting the feeder circuit. See Table 310.15(B)(16) for the ampacity of copper conductors in conduit. Note that the lengths specified in 240.21(B) and (C) apply to the conductors, not to a raceway enclosing the conductors or to the distance between the enclosures in which the tap conductors originate and terminate. 




Example#3
Taps Supplying a Transformer [Primary Plus Secondary Not over 7.5 m (25 ft) Long].



Fig (3)



  • In fig (3), The provisions of 240.21(B)(3) cover applications where the conductor length of 25 ft is applied to the primary and secondary conductors (using the length of one primary conductor plus the length of one secondary conductor for the measurement). 
  • The primary conductors are tapped to a feeder, and the secondary conductors are required to terminate in a single overcurrent protective device. Where the primary conductors are protected in accordance with their ampacity, the provisions of 240.21(C)(6) permit the entire 25 ft measurement to be applied to the transformer secondary conductors. Exhibit 240.9 illustrates the conditions of 240.21(B)(3)(1) through (5). The overcurrent protection requirements of 408.36 for panelboards and 450.3(B) for transformers also apply. 





Example#4: 
Taps over 7.5 m (25 ft) Long.



Fig (4)



  • Fig (4) illustrates the requirements of 240.21(B)(4). It permits a tap of 100 ft for manufacturing buildings with walls that are over 35 ft high where the tap connection is made not less than 30 ft from the floor and conditions of maintenance and supervision ensure that only qualified persons service these systems. 



In the next Article, I will continue explaining the proper locations for the overcurrent protection devices (OCPDs) in the following special cases:

  • Transformer Secondary Conductors. 
  • Service Conductors. 
  • Busway Taps. 
  • Motor Circuit Taps. 
  • Conductors from Generator Terminals. 
  • Battery Conductors. 


Please, keep following.





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