Tips for designing circuit interrupters
Electrical engineers should be familiar with how to specify various circuit interruption and emergency electrical disconnects in commercial facilities
- Understand the code changes to NFPA 70: National Electrical Code Article 210.8(B) that impacts commercial kitchens and other commercial locations.
- Learn about hotel and motel guestrooms and dormitories impacted by NEC Article 210.12 (C) and (D) and 406.12.
- Learn about gas stations and other fuel dispensing locations impacted by NEC Article 514.11.
NFPA 70: National Electrical Code Article 210.8(B) has been revised to state, “All single-phase receptacles rated 150 volts to ground or less, 50 amperes or less and three-phase receptacles rated 150 volts to ground or less, 100 amp or less installed in bathrooms, kitchens, rooftops, outdoors, within 6 feet of sinks, indoor wet locations, locker rooms with showers, garages and service bays shall have ground-fault circuit-interrupter protection for personnel.”
The requirements in this section have been expanded to recognize the fact that shock hazards are not limited to 15 and 20 amperes on 125-volt circuits in commercial and industrial installations (nondwelling unit locations). A couple examples are a 100 ampere operator panel with a pin and sleeve receptacle used for special events (see Figure 1) or a 30 ampere twist-lock receptacle for a commercial kitchen mixer (see Figure 2).
There are many electrical hazards in nondwelling kitchens, including damaged cords and wet locations. The recent change applies to only single- and three-phase receptacles, regardless if the receptacles serve countertop areas or are within 6 feet of a sink. Kitchens in restaurants, hotels, churches, dining halls and similar facilities are covered by this requirement. If the appliance is hardwired, this section of the code does not apply.
However, disconnecting means for hardwired equipment needs to be addressed and designers need to be aware of the manufacturer’s listing and installation instructions. Simply cutting off the plug of a cord set to complete a hardwired installation could very well void the listing of the equipment and shall be avoided.
GFCI protection for personnel is also revised in the 2017 edition of NEC Article 422.5. This GFCI requirement applies to the specific appliances identified in NEC Article 422.5(A)(1) through (5): automotive vacuum machines provided for public use, electric drinking water coolers, high–pressure spray washing machines, tire inflation machines for public use and vending machines, whether the equipment is hardwired or cord and plug connected.
NEC Article 422.5(B) states that the GFCI shall be installed in a readily accessible location in which the device can be reached quickly without a person having to climb over or under an obstacle, without using a portable ladder and without tools other than keys per the revised definition in NEC Article 100. This requirement facilitates the required periodic testing as well as resetting of a tripped device. It also states that the GFCI shall be listed and located within the branch circuit overcurrent device, the receptacles (outlet), an integral part of the attachment plug, within the supply cord not more than 12 inches from the attachment plug or factory–installed within the appliance.
GFCI protection requirements are further expanded through new parts of NEC 2017. For outdoor events such as a fair, the NEC Article 525.23 limits where GFCI protection shall be provided. GFCI protection shall not be provided for egress lighting. A new article (D) includes where GFCI protection is provided through the use of GFCI receptacles and the branch circuits supplying receptacles using flexible cords, the GFCI protection shall be listed, labeled and identified for portable use.
GFCI line cords are available with an automatic-set feature for providing safety in applications where equipment is intended for continuous use, but where temporary power failure is undesirable such as pumps, pressure washers or portable lighting. Manual-set GFCIs also are available for applications where operator injury might occur if equipment were to restart after a power failure such as drills, saws, lathes and grinders. Portable GFCIs can be used to provide open-neutral protection for temporary power applications.
GFCI units operate on fault currents between 4 to 6 milliamperes. A fault current level of 5 milliamperes shock can easily be felt by personnel. Equipment connected to receptacles of higher voltage and current ratings present the same shock hazards as those of lower voltage and current ratings. UL indicates the proper rating as Class A GFCI. The other classes of ground fault protection cannot be substituted for Class A GFCI.
Consult with your manufacturer’s representative for the current availability of GFCI protective ratings on the equipment and devices you are specifying. There are limitations for single–phase Class A GFCI above 30 amperes on one-pole circuit breakers and in some cases above 40 amperes on two-pole circuit breakers. The limitations are even more restrictive for three–phase Class A GFCI.
Arc-fault circuit-interrupter protection
NEC Article 210.12(C) has been augmented to include AFCI protection for hotel and motel guestrooms and guest suites. It applies to all 120-volt, single-phase, 15– and 20–ampere branch circuits serving outlets, receptacles, devices and lighting in the guest rooms and suites.
AFCI protection is also required in dormitory units. If a potential hazard exists and protection against series and parallel arcing faults is needed in certain areas of a normal dwelling unit, then the same hazard exists in dormitory units. AFCI protection for dormitory units will help to reduce the number of fires caused by faulty or improper use of premises wiring systems. AFCIs protect the entire circuit. This includes the electrical panel; the downstream wires that run through the walls; the outlets; the switches; all of the connections to those wires, outlets and switches; and anything that is plugged into any of those outlets and connected to switches on that circuit (see Figure 3).
Many options are available on the market for AFCI protective devices, as these have been required for many years in dwelling units. Between all of the AFCI manufacturers’ products, there are now millions of operating hours with AFCIs that shows the successful performance of them.
These tests include the new combination AFCI. Combination AFCIs protect downstream branch circuit wiring, cord sets and power supply cords. The device is intended to mitigate the effects of arcing faults by functioning to de-energize the circuit when an arc-fault is detected. Dual-function circuit breakers combine Class A 5 milliamp GFCI and combination-type AFCI technology, protecting against both arc faults and ground faults.
The 2017 edition of NEC requires both arc fault and ground fault protection on kitchen and laundry circuits. Before the release of dual-function circuit breakers, the only option to comply with this code was to pair an AFCI circuit breaker with a GFCI receptacle. The dual-function circuit breaker combines these two devices into one.
NEC Article 406.12 has been revised to include tamper-resistant receptacles in guest rooms and guest suites of hotels and motels. Tamper-resistance is also required in dormitories. All 125‐ and 250‐volt, 15‐ and 20‐ampere receptacles installed or replaced in dwelling units shall be listed as tamper‐resistant. Three exceptions include receptacles located 5½ feet or more above the floor, a receptacle in space dedicated for an appliance that is not readily moved and receptacles that are part of a luminaire.
Tamper‐resistant outlets have spring-loaded shutters that must be simultaneously engaged by the blades of a plug to release, allowing the metal prongs to make contact to create an electrical circuit. Therefore, when a foreign object, like a paper clip or a pin, is inserted, the safety shutter will not allow access to the live contact. When a plug is removed and the receptacle is not in use, the shutters close and both contact openings are covered.
Emergency electrical disconnects
NEC Article 514.11 has been completely reworded to align with NFPA 30A: Code for Motor Fuel Dispensing Facilities and Repair Garages Chapter 6.7. One item to note is the removal of “to disconnect simultaneously from the source of supply, all conductors of the circuits, including the grounded conductor, if any.” The understanding is that this requirement is already covered within NEC Article 514.13 of the code, but it is not stated in the same fashion and can be misleading.
The emergency shut-off requirements are basically the same in the 2017 NEC and the wording was revised to clearly indicate that the minimum and maximum distances are the same at both attended and unattended fuel dispensing locations. Now, fuel dispensing systems must be provided with one or more clearly identified emergency shut-off devices or electrical disconnects. The disconnects must be installed in approved locations. but no closer than 20 feet and no greater than 100 feet from the fuel dispenser that they serve (see Figure 4). Emergency shut-off devices or electrical disconnects must disconnect power to the dispensing devices, remote pumps serving the dispensing devices, remote pumps serving the dispensing devices and all other electrical equipment in the hazardous (classified) locations surrounding the fuel dispensing devices.
All of the arrangement and use provisions in NEC Article 90.3 apply to motor fuel-dispensing equipment, meaning the requirements in NEC Chapters 1 through 4 apply and can be amended or modified by the special requirements in NEC Chapter 5. In this case, the disconnecting means for this equipment is more restrictive. The specific circuit-disconnecting means rules are in NEC Article 514.11(A), (B) and (C). Subdivision (A) provides general disconnects for servicing and maintenance operations, (B) addresses emergency controls for attended fueling facilities and (C) covers emergency controls for unattended fueling facilities.
NEC Article 514.11(A) includes the general requirements for circuit disconnects that are other than emergency controls. The rule indicates that all power circuits leading to or through dispensing equipment must be provided with a means to simultaneously disconnect all circuit conductors, including the grounded conductor(s) if used in the circuit. The disconnect action also must simultaneously remove all associated power, communications, data and video circuits and equipment for remote-pumping systems. This means a disconnect is required to be provided with an emergency fuel shut-off identification and readily accessible switch or other approved means, located remote from the dispensers. Single-pole breakers using handle ties shall not be permitted to accomplish the simultaneous disconnecting required in this section.
The subdivision (A) requirements call for disconnecting all power-circuit conductors, including any neutral that is part of the circuit. NFPA 70 requirements for emergency controls for motor fuel-dispensing equipment installed in attended fueling facilities are located in NEC Article 514.11(B). These requirements are derived from NFPA 30A Chapter 6.7.1 and are included in the NEC as extracted material. For attended fuel stations, the emergency controls are required to meet the provisions in NEC Article 514.11(A) and must be at a location acceptable to the inspecting jurisdiction and readily accessible.
This disconnect is for emergency purposes and this emergency control is to stop all fuel from being pumped and dispensed when necessary. If there is a fire, the emergency controls will stop fueling the fire. NFPA 70 requirements for emergency controls for motor-fuel-dispensing equipment installed in unattended fueling facilities are located in NEC Article 514.11(C). Note that these emergency control requirements for unattended fueling facilities are derived from NFPA 30A Chapter 6.7.2 and are included in the NEC as extracted material.
If there is a fire, the emergency controls stop fueling the fire and are located at least 20 feet from the dispensing equipment. Anyone having to quickly disconnect the fuel pumping operation in an emergency is most likely the customer pumping the fuel. The disconnect locations of this section require the customer to leave the area of the dispensing operation to activate the emergency disconnect. These controls must disconnect all power to the dispensing equipment and shall be reset by manual means in a manner acceptable to the authority having jurisdiction.
In summary, NEC Article 514.11(B) and (C) cover the emergency shut-off location requirements for motor-fuel-dispensing equipment based on usage and expected occupancy. If one branch circuit supplies a single motor fuel dispenser, a single disconnect switch can often satisfy the requirements of NEC Article 517.11. For multiple dispenser installations, meeting the shutdown requirements means more control and equipment.
To accomplish the simultaneous disconnecting of all dispensing equipment in emergencies, installers often use a single emergency power off button interconnected to panelboards equipped with either shunt-trip main breakers or a power-actuated relay for simultaneously disconnecting all power circuits for the dispenser equipment and associated systems such as communications, video and data circuits. As NEC Article 514.11(A) indicates, all circuit conductors, including any grounded (neutral) conductors, must be opened by the disconnecting means and emergency controls addressed in this section.