Article 210—Branch Circuits
Article 424—Fixed Electric Space Heating Equipment
Article 700—Emergency Systems
Bonding gas piping
Q: The November 2000 issue of Electrical Contractor magazine included a question about the required size of the bonding conductor to be used to bond the gas piping to the grounding electrode. You suggested using Table 250-122 if it could be determined which circuit could energize the gas pipe. Where there are plenty of gas-fired appliances, such as boilers, water heaters with circulating pumps, gas clothes dryers, etc., it may be difficult to determine what wiring or equipment could energize the piping. Also, cable wiring methods are probably in random contact with the piping somewhere in the structure. For these reasons, it makes sense to size the bonding conductor according to Table 250-66. What do you think? After the size of the bonding jumper has been determined, is it permissible to connect the bonding conductor to the metal water pipe?
A: To the question that appeared in the November issue, I responded that Table 250-122 should be used where it was not possible to find out what equipment or wiring could energize the gas pipe. In the “Report on Proposals” to revise the 1999 National Electrical Code (NEC), there were 15 proposals to revise Section 250-104(b). This is the part of Section 250-104 that requires bonding of the above-ground portions of metal gas pipes. Four proposals were to require the size of the bonding jumper to be according to Section and Table 250-66. Six were to require the bonding jumper to be sized according to Section and Table 250-122. The remaining five either suggested deletion or revision to the language in Section 250-104(b). The Code Making Panel (CMP) accepted the proposal that suggested deleting all of Section 250-104(b), because part (c) of this Section covers all interior metal piping that may become energized. This part (c) requires all interior metal piping that may become energized to be bonded to the service equipment enclosure, the grounded conductor at the service entrance, etc., with a bonding jumper that is sized according to Table 250-122. The ampere rating of the overcurrent device protecting the circuit that could energize the piping determines the size of the bonding conductor.
The bonding conductor that is fastened to the metal gas pipe is permitted to be connected to the buried metal water pipe within 5 feet of where the pipe enters the building. Part (b) of Section 250-104 requires that the bonding conductor be connected to the grounding electrode system. And where metal water pipe is the grounding electrode, it stops, or is no longer a grounding electrode, beyond 5 feet of where it enters the building.
Branch circuits for electric heating loads
Q: From time to time, I have noticed that other electricians install more baseboard heat than is required in residential properties. They also install too many 20-ampere, 240-volt, single-phase circuits for these heaters. Also, many times I see a thermostat in each of the adjoining rooms that are separated by an arch. Does the NEC require a thermostat in each room under these conditions?
Am I allowed to run No. 10 copper conductors protected by 30-ampere circuit breakers instead of No. 12 conductors protected by two-pole, 20-ampere circuit breakers for baseboard heating loads?
A: I can’t answer the statement that indicates more baseboard heaters than necessary are often installed in residences. A building’s requirements for electric heat are generally based on its size, geographical location, and R-factor of the thermal insulation in its walls and ceiling.
The load on branch circuits that supply fixed electric space heating equipment cannot exceed 80 percent of the branch circuit rating. For a 20-ampere, 240-volt circuit, the maximum heating load is limited to (20 x 240 x 0.8) 3,840 watts, and for a 30-ampere, 240-volt single-phase circuit, the maximum wattage is (30 x 240 x 0.8) 5,760.
If the total heating load is 28 kW, you need five 30-ampere, 240-volt circuits, or eight 20-ampere, 240-volt branch circuits. Section 424-3(a) recognizes 30-ampere branch circuits for supplying multioutlet fixed electric space heating equipment, and part (b) requires branch circuit overcurrent protective devices and conductors sized at 125 percent of the heating load.
The NEC does not require a thermostat to control the baseboard heaters in each room. However, disconnecting means are required to disconnect the heaters from their power source.
Where line voltage thermostats are being used as the disconnect means, it may be necessary to install one in each room, even though these rooms are only separated by an arch. To qualify as a disconnect, the line voltage thermostat must have a marked “off” position and meet the other requirements in Section 424-20(a). It also must be within sight of the heater or be capable of being locked in the open position. These additional requirements are found in Section 424-19(a)(1).
An “on/off” switch on a baseboard heater qualifies as a disconnecting means where another disconnecting means meeting the requirements for the types of occupancies mentioned in (c)(1), (2), (3), or (4) of Section 424-19 is also present.
High-wattage hair dryers
Q: How can some independent testing laboratories list 1,600-watt, 120-volt, hand-held hair dryers with a 15-ampere attachment cap? This is a 13.3-ampere load. Section 210-21(b)(2) appears to limit the load to 12 amperes for cord-and plug-connected appliances. Am I missing something?
A: Many sections of the NEC must be considered while dealing with this subject. First, Section 210-6(b) permits 120-volt circuits in dwelling units to supply cord-and plug-connected electrical equipment. Sec-tion 210-19(a) also requires the branch circuit conductors to have an ampacity that is not less than the load served. Overcurrent protection for branch circuit conductors and receptacles is mentioned in Sections 210-20(b), (c), and (d), and 240-2 and -3.
Although Section 210-21(b)(2) and the table limit the cord-and-plug-connected load on a 15-ampere branch circuit to 12 amperes, this table only applies to branch circuits that supply two or more receptacle outlets. Also, notice that Section 210-21(b)(3) and the Table permit 15-ampere receptacles on a 20-ampere branch circuit and the total cord-and-plug-connected load on a 20-ampere branch circuit is permitted to be 16 amperes.
This sentence in Section 210-23 allows the hair dryer to be connected to a 15-ampere branch circuit: “An individual branch circuit shall be permitted to supply any load for which it is rated.” For multiple-outlet branch circuits, a single cord-and-plug-connected appliance on a 15-ampere branch circuit cannot exceed 80 percent (12 amperes) of the branch circuit rating. This rule is in Section 210-23(a). A summary of branch circuit requirements appears in Table 210-24. Notice that this table applies to multioutlet branch circuits only.
Rules in Article 422 deal with branch circuit ratings and overcurrent protection for appliances. Generally, Section 422-11(e) allows the branch circuit overcurrent protection to be 20 amperes for this hair dryer.
Since this appliance is generally used in the bathroom of a residence, and Section 210-11(c)(3) requires a 20-ampere receptacle circuit within 3 feet of the wash basin (Section 210-52(d)), there should not be any problem with overloading this circuit.
To summarize: A 1,600-watt, 120-volt cord-and-plug-connected hair dryer can be used in compliance with the NEC. It can either be used on an individual 15- or 20-ampere branch circuit or on a multioutlet 20-ampere branch circuit.
Grounding small transformers
Q: We installed a 5 kVA 480-volt single-phase transformer with a 120/240-volt secondary. We used No. 12 copper conductors for the primary, and No. 10s for the secondary. No. 14 copper wire was used as the grounding electrode conductor for the secondary neutral. The electrical inspector said the grounding electrode conductor cannot be smaller than No. 8 copper. Is he right?
A: According to the NEC, this is a separately derived system and the requirements for grounding in Sections 250-26 and 250-30 apply. The secondary neutral must be grounded, and the grounding electrode conductor has to be sized according to Section 250-30(a)(2). This part requires the grounding electrode conductors to be sized according to Section 250-66. Table 250-66 specifies a No. 8 copper grounding electrode conductor for this installation and Section 250-64 supplies the rules for installing this conductor.
Q: Is it permissible to connect an emergency lighting power pack “EXIT” fixture to a receptacle outlet circuit in a room with only one lighting branch circuit?
A: No, it is not permissible to connect the unit equipment (battery-operated emergency lighting) to a receptacle circuit. The battery powered “EXIT” fixture must be connected to the lighting circuit ahead of any local or wall switches. This requirement appears in Section 700-12(e) of the NEC. EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.