Article 200 Use and Identification of Grounded Conductors; Article 210 Branch Circuits; Article 430 Motors, Motor Circuits, and Controllers
I am wiring a single-family home with stackable washer and dryer in the laundry room. These appliances are supplied from a 125-volt, 30-ampere receptacle. Is a 20-ampere, 125-volt receptacle also required?
Yes, a 20-ampere, 125-volt receptacle must be provided in the laundry room to comply with 210.11(C)(2). The rule also prohibits other outlets on this branch circuit. Since an iron and ironing board are generally located in this area, the receptacle and separate branch circuit are put to good use and are needed.
Sizing motor circuits
Will you give the National Electrical Code (NEC) references and examples showing sizes of overcurrent protection, branch circuit conductor size, overload relay size and calculations for a complete motor circuit?
In our example, let’s use a 50-horsepower, 480-volt, three-phase motor with an across-the-line starter. According to Table 430.250, the full-load current for this motor is 65 amperes. The full load current for a 460-volt motor is used as permitted by the notes to the table, which allows use of the 460-volt column for 480-volt motors. We are allowed to use the table values for motor full-load current by 430.5(A)(1).
Motor branch-circuit conductor size for a continuous-duty motor cannot be less than 125 percent of motor full-load current to comply with 430.22(A). Therefore, the minimum size branch circuit conductor size is 81.25 amperes (65 × 1.25). This results in a branch circuit conductor size of 3 AWG copper where terminations are marked 60°C or 4 AWG copper with 75°C insulation where terminations are marked 75°C. This is permitted by 110.14(C)(1)(a).
Overload relays in the motor starter are sized to comply with 430.32(A)(1). Motors with a service factor of 1.15 or greater and motors with a marked temperatures rise of 40°C or less require overload devices that are rated 81.25 amperes (1.25 × 65). Where this value of overload relay does not allow the motor to start and accelerate the load, the relays may be increased to 140 percent of full-load current by 430.32(C). A fine print note following 430.32(C) indicates that a Class 20 or 30 overload relay may provide additional time delay without an increase in ampere rating to allow more time for the motor to accelerate.
If the disconnecting means and short circuit and ground-fault protection is provided by dual-element time-delay fuses, they are allowed to be sized at 175 percent of motor full-load current. This results in a fuse of 113.75 amperes (65 × 1.75). A 200-ampere fused disconnect with 125 amperes dual-element time-delay fuses satisfies this requirement. Where nontime-delay fuses are used, they may be sized at 300 percent of full-load current of the motor. This calculation (65 × 3.00) = 195 allows a 200 switch with 200-ampere fuses. For inverse time circuit breakers, the size is 162.5 amperes (65 × 2.5). The exception to 430.52(C)(1) allows these values to be increased to the next larger standard size fuse or circuit breaker as given in 240.6. Therefore, 125-ampere dual-element time-delay fuses, 200-ampere nontime-delay fuses or a 175-ampere inverse time circuit breaker may be used. There also are provisions for use of an instantaneous circuit breaker. This device may be set at 800 percent of motor full-load current. An instantaneous circuit breaker could be calibrated to trip at 530 amperes (8.00 × 65). To use an instantaneous circuit breaker, the motor starter must be acceptable for this application (see 430.53(C)(3)).
This covers the basic rules for motor branch circuits and devices that are used in most installations. Additional information on motor circuit calculations may be found in example D8 in the back of the NEC.
A properly sized circuit breaker or disconnecting means must be located in sight from or visible and not more than 50 feet away from the controller and motor. Where the disconnecting means for the controller is not within sight of the motor, another disconnecting means within sight of the motor must be provided. These requirements are in Section 430.102(A) and (B).
If a reduced voltage start/stop pushbutton is part of the motor branch circuit, and the control transformer is part of the motor controller, rules for motor control circuits are in 430.71 through 430.75 and cover installations that are connected to a control transformer that is mounted in the controller and separately installed transformers.
Outdoor AC service receptacle
I have a job to install an outdoor 20-ampere, 125-volt receptacle within 25 feet of a remote condensing unit in an area with a fence for an office building. Does this receptacle have to be protected by a GFCI?
Yes, it does. The receptacle is required by 210.63, and 210.8(B)(4) requires GFCI protection. The exception to 210.8(B)(4) does not apply to this installation.
Twenty-ampere, 125-volt receptacles are installed outdoors at a commercial restaurant. The area is not normally accessible to the general public but is not enclosed by gates or fences. Is ground-fault protection required for these receptacles?
Yes, outdoor receptacles at this and similar locations must be protected by ground-fault circuit interrupters (GFCIs). A change in 210.8(B)(5) was accepted by Code-Making Panel 2. The references to “public spaces” in the 2005 edition of the NEC have been removed in the 2008 edition. Now the requirement for GFCI protection for all 15- and 20-ampere, 125-volt receptacles applies to all public areas. The exception that applies to receptacles for snow melting and de-icing equipment remains, and a new exception has been added to not require GFCI protection of outdoor receptacles in “Industrial establishments only, where the conditions of maintenance and supervision ensure that only qualified personnel are involved, an assured equipment-grounding conductor program as specified in 590.6(B)(2) shall be permitted for only those receptacle outlets used to supply equipment that would create a greater hazard if power is interrupted or having a design that is not compatible with GFCI protection.” Three members of CMP 2 did not vote for this change.
Do fixture (luminaire) whips used in buildings that have two different voltage systems (120/208 and 277/480) need to be individually identified by system and phase, or is only system identification required?
A change in 210.5(C) requires that all conductors of one system be identified where there is more than one nominal voltage system. Part of the change reads, “Where the premises wiring system has branch circuits supplied from more than one nominal voltage system each ungrounded conductor of a branch circuit shall be identified by phase or line and system at all termination, connection, and splice points. The means of identification shall be permitted to be by separate color coding, marking tape, tagging, or other approved means. The method utilized for conductors originating in each branch-circuit panelboard or similar branch-circuit distribution equipment shall be documented in a manner that is readily available or shall be permanently posted at each branch-circuit panelboard or similar branch-circuit distribution equipment.”
In the 2005 NEC, different voltage systems required conductor identification to be different for systems only. There was no requirement for different identification for each phase conductor of each system.
Where the grounded (neutral) conductors of the two different systems are installed in the same raceway, cable assembly or other enclosure, the neutral conductors must be identified so that the 480-volt neutral conductor can be distinguished from the 208-volt neutral conductor. This requirement is in 200.6(D).
Motel room receptacle spacing
There are five receptacles installed around the guest room of a motel sleeping room. Two receptacles are readily accessible, two are within 10 feet of each other on both sides of the bed and one is 18 feet away for the television set. Do any receptacles have to be added because one is 18 feet from the other receptacle?
The requirement for receptacle spacing in a guest room in hotels, motels and sleeping rooms in dormitories is in 210.60. The minimum number of receptacles is determined from 210.52(A). Receptacle outlets must be spaced so that no wall space is more than 6 feet from an outlet. Where the wall space measured around the room would require four or five receptacles, the maximum spacing requirements between receptacles in 210.52(A) and (B) may be ignored, and receptacle spacing may comply with 210.60(B). In other words, the number of receptacles required by 210.52(A)(1) is the minimum number of receptacles permitted, but their spacing is not required to comply with the 6-feet spacing.
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.