Article 110 Requirements for Electrical Installations
Article 215 Feeders
Article 220 Branch Circuit, Feeder and Service Calculations
Article 250 Grounding
Article 400 Flexible Cords and Cables
Article 404 Switches
Article 430 Motors, Motor Circuits and Controllers
Aluminum wire terminations
Q:Is there a requirement in the National Electrical Code (NEC) for the use of an oxide inhibitor on aluminum conductor terminations? Some lugs are provided with an antioxidant paste supplied by the manufacturer and some are not. Some cable and wire terminal manufacturers that do not provide a compound in the lug suggest that an antioxidant paste be used but do not require it.
A:There is no rule in the NEC that requires an oxide inhibitor at all aluminum wire terminations. In fact, this sentence appears in Section 110.14 of the Code: “Materials such as solder, fluxes, inhibitors and compounds where employed, shall be suitable for the use and shall be of a type that will not adversely affect the conductors, insulation or equipment.”
This information appears in the General Information for Electrical Equipment Directory (White Book) published by Underwriters Laboratories Inc. under the title Wire Connectors and Soldering Lugs (ZMVV): “Some connectors are shipped prefilled with conductor termination compound (antioxidant compound). For non-prefilled connectors, conductor termination compound may be used if recommended by the connector manufacturer as preliminary preparation of the conductor. Wire brushing of the conductor may also be performed if recommended.”
Underwriters Laboratories listed conductor termination compounds are available. These compounds retard oxidation at the connector-conductor interface, and they do not have an adverse effect on the conductor metal, insulation or equipment.
Connecting ground rods to a service
Q:Am I permitted to connect two ground rods spaced about 10 feet apart directly to the service equipment or must I run the grounding-electrode conductor from one rod to the other then to the service disconnect switch?
A:The 6 AWG-copper grounding-electrode conductor may be run from one rod to the other in an unbroken length, then to the neutral bus in the service disconnect. The grounding-electrode conductor is required to be unbroken in one continuous length or may be spliced by irreversible compression-type connectors or exothermic welding. This requirement appears in 250.62(C). Individual 6 AWG-copper conductors may also be run from each ground rod to the service disconnect; however, individual terminals in the service disconnect must be provided to terminate the two 6 AWG grounding-electrode conductors. This arrangement is permitted by 250.64(F).
Continuous and noncontinuous loads
Q:TI recently installed a 200-ampere, three-wire, single-phase panel for an actual load of 85 amperes. The feeder for this panel is 1 AWG copper with Type THWN insulation protected by a 100-ampere fused switch. The combination inspector said this installation is in violation of the NEC. Is it?
A:Although 75-degree Celsius insulation is on the feeder conductors, the ampacity is limited to 110 amperes because of the termination provisions in 110.14(C). Since these conductors are protected by the 100-ampere fuses as required by 240.4, there is no violation here.
It is stated in the question that the “actual” load is 85 amperes. If this load is continuous (energized for three or more hours), the feeder overcurrent protection is too small. If the “actual” load consists of 60 amperes continuous and 25 amperes noncontinuous, or any combination of continuous and noncontinuous loads that add up to 100 amperes or less, the installation complies with the NEC. The requirements for feeder overcurrent protection that supplies a combination of continuous and noncontinuous loads are found in 215.3.
Electric range load calculations
Q:All the electric ranges being installed in an apartment building have a nameplate rating of 17 kW at 240 volts. My boss says to use a 50-ampere branch circuit for each range. I say they are over 70-amperes and must be direct-wired. Does the Code permit a 50-ampere branch circuit and range cord for these ranges?
A:Demand factors for household electric ranges are found in 220.19 and Table 220.19. Let’s calculate the load for a single range using Column C of Table 220.19 and the notes to the table. Note Four allows the use of the table for a single range, and Note One provides demand factors for ranges rated over 12 kW through 27 kW. This Note One requires an increase in demand shown in Column C of 5 percent for each kW above 12; therefore, (17 – 12) = 5 kW. Each kW above 12 requires 5 percent increase in the demand load shown in Column C. Multiplying this percentage figure (5 x 5 percent) by the demand load shown in Column C of the table results in a demand load of (8 x .25) + 8 = 10kW. Now divide 10,000 watts by 240 volts and the result is 41.6 or 42 amperes. A four-conductor flexible cord or cable with an ampacity that is not less than 45 is adequate. Ampacities of flexible cords and cables are shown in Table 400.5(A).
Disconnect for a separately derived system
Q:Is an enclosed fused switch marked “Suitable Only for Use as Service Equipment” permitted as the main disconnect and overcurrent protection for the secondary conductors of a separately derived system? The secondary voltage is 208Y/120.
A:Yes. But the grounding-electrode conductor must be connected to the neutral bus in the switch, and the neutral conductor must not be grounded anywhere else.
Switches marked “Suitable Only for Use as Service Equipment” have the neutral bus factory bonded to the enclosure; therefore, the grounding electrode conductor must terminate on this bus. This is necessary to eliminate parallel paths for neutral currents and is required by 250.30(A)(1) and (2).
Disconnect for blower motor
Q:There is an air-handling unit and gas furnace in the attic of a one-family dwelling. Is a disconnect switch required for the equipment at the attic entrance? May a toggle switch serve as the required disconnect for the blower motor?
A:There is no requirement for a switch at the entry to an attic for the fan motor; however, there is a requirement for a lighting outlet at or near the heating equipment and this lighting outlet must be controlled by a switch near the entrance to the attic.
Toggle switches are called “snap switch NEC, and they may be used to control motor loads under certain conditions. Permitted uses of snap switches are listed in 404.14. Alternating current general-use snap switches are permitted to control motor loads that do not exceed 80 percent of their rating. Motors with full-load currents of 12 amperes or less may be controlled by a 15-ampere alternating current general-use snap switch, and a 20-ampere switch can serve as the disconnecting means for a motor with a full-load current of 16 amperes or less. Alternating current or direct-current, general-use snap switches are permitted to control motors where the motor full-load current does not exceed 50 percent of the ampere rating of the AC-DC snap switch.
There are additional restrictions on toggle (snap) switches in 430.109(C). This part limits the use of snap switches to stationary motors rated 2 horsepower or less and not over 300 volts.
For the application mentioned in the question, an AC general-use snap switch with a 20-ampere rating is a suitable disconnecting means for a 1-horsepower, 120-volt, single-phase motor with a full-load current of 16 amperes or less, or a 30-ampere switch could serve as the disconnect for a 2-horsepower motor with a full-load current not exceeding 24 amperes.
Oversize distribution panel
Q:I installed a 200-ampere, main-lugs-only, distribution panel in a commercial-building addition and supplied it from a three-wire, single-phase, 1 AWG-copper Type THWN feeder with a 125-ampere overcurrent-protection device. The calculated load for the panelboard is 90 amperes. The main lugs in the panelboard are acceptable for No. 1 copper conductors and are rated for 75 degrees Celsius. The combination inspector has rejected this installation and is requiring an increase in feeder conductor size and overcurrent protection to 200 amperes. Is there anything in the NEC that requires a panelboard to be supplied with conductors and overcurrent protection that equal the ampere rating of the panelboard?
A:Where the total load for the addition is calculated in accordance with 220.3(C) and the feeder and overcurrent protection are sized for this load, there is no requirement for increasing the size of the feeder conductors and overcurrent devices to match the ampere rating of the distribution panel. The feeder conductors must have an ampacity that is not less than required to supply the loads computed in accordance with Parts II, III, and IV of Article 220.
I assume the inspector is concerned about overloading the feeder conductors in the future but should not anticipate a code violation. In fact, 90.8 has a title, “Wiring Planning” and discusses plans and specifications that provide for future expansion and convenience. This may be what the electrical contractor had in mind when the 200-ampere panel was provided.
If the feeder and overcurrent protection are properly sized for the calculated load, the inspector should accept the installation. EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.