NEC Questions and Answers based on 2017 NEC - November 2018

Figure 01

Here's the follow-up to yesterday's newsletter.
This includes the answers to the questions sent, so you can see how you did.

Note: The answers to these questions are based on the 2017 NEC. Underlined text indicates a change in the rule for the 2017 NEC.

Q1. What is the NEC rule for the use of supplementary overcurrent protection?
A1. Supplementary overcurrent protection devices aren't permitted to be used as the required branch-circuit overcurrent protection device [240.10].

A supplementary overcurrent protection device isn't required to be readily accessible.

Author's Comment:
• Article 100 defines a Supplementary Overcurrent Protection Device as a device intended to provide limited overcurrent protection for specific applications and utilization equipment. This limited overcurrent protection is in addition to the overcurrent protection provided in the required branch circuit by the branch-circuit overcurrent protection device.
• See 240.24(A)(2) for requirements regarding overcurrent protection devices that are not intended for supplemental use.

Q2. When does the Code require Ground-Fault protection of equipment on electrical services?
A2. Service disconnects and feeder circuits rated 1,000A or more, supplied from a 4-wire, three-phase, 277/480V wye-connected system must be protected against ground faults in accordance with 230.95 [240.13].

The requirement for ground-fault protection of equipment doesn't apply to:
(1) Continuous industrial processes where a nonorderly shutdown will introduce additional or increased hazards.
(2) Installations where ground-fault protection of equipment is already provided.
(3) Fire pumps [695.6(H)].

Author's Comment:
• Article 100 defines Ground-Fault Protection of Equipment as a system intended to provide overcurrent protection of equipment from ground faults by opening the overcurrent protection device at current levels less than those required to protect conductors from damage. This type of protective system isn't intended to protect people, only connected equipment. See 215.10 and 230.95 for similar requirements for feeders and services..
• Ground-fault protection of equipment isn't required for emergency power systems [700.26] or legally required standby power systems [701.17].

Q3. According to the NEC, overcurrent protection devices must be placed at what location in branch circuit or feeder conductors?
A3. Except as permitted by 240.21(A) through (H), overcurrent protection devices must be placed at the point where the branch-circuit or feeder conductors receive their power. Taps and transformer secondary conductors aren't permitted to supply another conductor (tapping a tap isn't permitted) [240.21].

Branch-circuit tap conductors are permitted in accordance with 210.19 and can have overcurrent protection as required by 210.20 [240.21(A)].

Conductors can be tapped from a feeder (feeder taps) as specified in 240.21(B)(1) through (B)(5). The next size up overcurrent protection rule of 240.4(B) isn't permitted for tap conductors [240.21(B)].
10-Foot Feeder Tap Rule. Feeder tap conductors up to 10 ft long are permitted without overcurrent protection at the tap location if the tap conductors comply with the following [240.21(B)]:
(1) The tap conductors must have an ampacity of not less than:
a. The calculated load in accordance with Article 220, and
b. The rating of the overcurrent protection device termination or equipment containing overcurrent protection devices supplied by the tap conductors.

Ex to b.: Listed equipment, such as a surge protection device, can have their conductors sized in accordance with the manufacturer's instructions.

(2) The tap conductors must not extend beyond the equipment they supply.
(3) The tap conductors are installed within a raceway when they leave the enclosure.
(4) The tap conductors must have an ampacity not less than 10 percent of the rating of the overcurrent protection device that protects the feeder.

Informational Note: See 408.36 for the overcurrent protection requirements for panelboards.

Example: A 400A breaker protects a set of 500 kcmil feeder conductors. There are three taps fed from the 500 kcmil feeder that supply disconnects with 200A, 150A, and 30A overcurrent protection devices. What are the minimum size conductors for these taps? Figure 01
Answer:
200A Disconnect Tap: 3/0 AWG is rated 200A at 75°C, and is greater than 10 percent of the rating of the overcurrent protection device (400A).
150A Disconnect Tap: 1/0 AWG is rated 150A at 75°C, and is greater than 10 percent of the rating of the overcurrent protection device (400A).
30A Disconnect Tap: 8 AWG rated 40A at 60°C. The tap conductors from the 400A feeder to the 30A overcurrent protection device can't be less than 40A (10 percent of the rating of the 400A feeder overcurrent protection device).

25-Foot Feeder Tap Rule. Feeder tap conductors up to 25 ft long are permitted without overcurrent protection at the tap location if the tap conductors comply with the following [240.21(B)(2)]:
(1) The ampacity of the tap conductors aren't permitted to be less than one-third the rating of the overcurrent protection device that protects the feeder.
(2) The tap conductors terminate in an overcurrent protection device rated no more than the tap conductor ampacity in accordance with 310.15 [Table 310.15(B)(16)].

Outside Feeder Taps of Unlimited Length Rule. Outside feeder tap conductors can be of unlimited length, without overcurrent protection at the point they receive their supply, if they comply with all of the following [240.21(5)]:
(1) The outside feeder tap conductors are protected from physical damage within a raceway or manner approved by the authority having jurisdiction.
(2) The outside feeder tap conductors terminate at a single overcurrent protection device that limits the load to the ampacity of the outside feeder tap conductors.
(3) The terminating overcurrent protection device for the outside feeder tap conductors is part of the building feeder disconnect.
(4) The building feeder disconnecting means is readily accessible, either outside the building, or nearest the point of entrance of the outside feeder tap conductors.

Q4. What is the Code requirement for the physical location of overcurrent protection devices?
A4. Circuit breakers and switches containing fuses must be readily accessible and installed so the center of the grip of the operating handle of the circuit breaker or switch, when in its highest position, isn't more than 6 ft 7 in. above the floor or working platform, except for [240.24(A)]:
(1) Busways, as provided in 368.17(C).
(2) Supplementary overcurrent protection devices per 240.10.
(3) For overcurrent protection devices, as described in 225.40 and 230.92.
(4) Circuit breakers and switches containing fuses are permitted above 6 ft 7 in. where located next to equipment if accessible by portable means [404.8(A) Ex 2].

Ex. The use of a tool is permitted to access overcurrent protection devices located within listed industrial control panels or similar enclosures.

Overcurrent protection devices aren't permitted to be exposed to physical damage [240.24(C)].

Informational Note: Electrical equipment must be suitable for the environment, and consideration must be given to the presence of corrosive gases, fumes, vapors, liquids, or chemicals that have a deteriorating effect on conductors or equipment [110.11].

Overcurrent protection devices aren't permitted to be located near easily ignitible material, such as in clothes closets [240.24(D)].

Overcurrent protection devices aren't permitted to be located in the bathrooms of dwelling units, dormitories, or guest rooms or guest suites of hotels or motels [240.24(D)].

Author's Comment:
• The service disconnect switch isn't permitted to be located in a bathroom, even in commercial or industrial facilities [230.70(A)(2)].

Overcurrent protection devices aren't permitted to be located over the steps of a stairway 240.24(F)].

Author's Comment:
• Clearly, it's difficult for electricians to safely work on electrical equipment that's located on uneven surfaces such as over stairways.

Q5. What does the Code require if enclosures containing overcurrent protection devices are to be installed in damp or wet locations?
A5. In damp or wet locations, enclosures containing overcurrent protection devices must prevent moisture or water from entering or accumulating within the enclosure. When the enclosure is surface mounted in a wet location, it must be mounted with not less than ¼ in. of air space between it and the mounting surface. See 312.2 [240.32].