1. Special-Purpose Outlets— Electric Heating, Air Conditioning
Chapter Twenty Three
Special-Purpose Outlets— Electric Heating, Air Conditioning

2. Objectives After studying this chapter, you should be able to:
Understand the NEC® requirements for embedded resistance heating cable, electric furnaces, electric baseboards, and heat pumps
Understand how the heating output of resistive heating elements is affected by voltage variation

3. Objectives (cont’d.)
Understand the data found on the nameplate of HVAC equipment, and determine electrical installation requirements in conformance to the NEC®
Realize that a 120-volt receptacle must be installed near HVAC equipment
Understand energy rating terminology

4. Introduction Advantages of electric heating
Quiet, clean, safe operation
Does not depend on non-electric fuels and fuel tanks
Does not require a chimney
Does not remove oxygen from the air

5. FIGURE 23-1 (partial) An electric furnace is considered to be a continuous load, subject to sizing the conductors, disconnecting means, and overcurrent devices as 125% of the load, NEC 424.3(B). Central electric heating equipment must be supplied by an individual branch-circuit, NEC
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6. FIGURE 23-1 (cont’d.) © Cengage Learning 2015

7. Resistance Heating Cables
Can be embedded in the plaster or between two layers of drywall
When premises wiring is located above ceilings and subjected to heat from heating cables keep the wiring
Not less than 2 in. above the heated ceiling
Above the thermal insulation that is at least 2 in. thick

8. Electric Furnaces
The source of heat is the resistance heating elements
Many of the NEC® requirements have already been met because of being listed by a recognized testing laboratory
Voltage must be maintained at not less than 98 percent to ensure full output

9. Effect of Voltage Variation

10. Control Of Electric Baseboard Heating Units
Line-voltage and low-voltage thermostats can be used to control electric baseboard heating units
Most line-voltage thermostats are ampere rated for noninductive resistive loads
May need to convert watts to amperes to select the right size thermostat

11. FIGURE 23-3 Wiring for an electric baseboard heating unit having a low-voltage thermostat and relay. © Cengage Learning 2015

12. Marking the Conductors of Cables
Two-wire cable contains one white and one black conductor
According to 200.7(C), 2-wire cable is permitted for the 240-volt heaters provided the white conductor is permanently reidentified by paint, colored tape, or other effective means

13. FIGURE 23-4 Wiring for a single electric baseboard heating unit
FIGURE 23-4 Wiring for a single electric baseboard heating unit. The thermostat is a line-voltage thermostat. See Figure 23-3 caption for color-coding requirements.
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14. Circuit Requirements for Electric Baseboard Heating Units
Supply conductors must be rated 90°C
Some heaters have 120-volt, 15- or 20-ampere receptacle outlets
When receptacle sections are included in a baseboard heating systems, they must be supplied separately using conventional wiring methods

15. Location of Electric Baseboard Heaters in Relation to Receptacle Outlets
Do not install below wall receptacle outlets unless the instructions furnished with the baseboard heaters indicate that they may
Fire and shock hazards can result from a cord hanging over or touching the electric heater

16. FIGURE 23-9 Position of electric baseboard heaters.
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17. Wall-Mounted Heaters Can be used in bathrooms
Typically have a can or enclosure that is installed at the rough-in stage
Should be located to avoid conflict with furniture layout
Available with or without a built-in thermostat and in a variety of heating capacities

18. Heat Pumps Dual-purpose equipment that functions
As a heating unit
An air conditioner operating in reverse
Reversing valve: changes the direction of the flow of the system’s refrigerant
Split heat pump system: consists of an outdoor unit with a hermetic motor-compressor, a fan, and a coil

19. Grounding Covered in Article 250 of the NEC®
Never ground electrical equipment to the grounded (white) circuit conductor of the circuit

20. Circuit Requirements for Room Air Conditioners
Window or through-the-wall units are available in both 120-volt and 240-volt ratings
Article 440 specifies Code rules for air conditioning
LCDIs: Leakage Current Detection and Interruption Protection devices

21. FIGURE 23-14 Types of receptacles.
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22. Central Heating and Air Conditioning
Lower energy rates for air-conditioner and/or heat pump loads can be found through special programs, e.g., “time-of-use” usage and sliding scale energy rates

23. Understanding the Data Found on an HVAC Nameplate
HVAC: heating, ventilating, and air-conditioning
Article 440
Applies when HVAC equipment employs a hermetic refrigerant motor-compressor(s)
Supplemental to the other articles of the NEC®
Needed due to their unique characteristics

24. HVAC Nameplates (cont’d.)
Special terms
Rated-load current (RLC)
Branch-circuit selection current (BCSC)
Minimum circuit ampacity (MCA)
Maximum overcurrent protection (MOP)
Locked-rotor current (LRC)

25. Energy Ratings Energy efficiency rating (EER)
Seasonal energy efficiency rating (SEER)
Annual fuel utilization efficiency (AFUE)
Heating seasonal performance factor (HSPF)

26. Noncoincidental Loads
Loads that do not operate at the same time are called noncoincidental loads
Examples include heating and air conditioning
NEC® allows feeders that supply both loads to be sized according to only the larger of the two loads

27. Receptacle Needed for Servicing HVAC Equipment
NEC® requires a 125-volt, single-phase, 15- or 20-ampererated receptacle installed:
At an accessible location,
On the same level as the HVAC equipment,
Within 25 ft (7.5 m) of the equipment, and
Don’t connect receptacle to the load
Side of the equipment disconnecting means

28. Gas Explosion Hazard
Gas meters must be located at least 3 ft (900 mm) from sources of ignition
Possible sources of ignition
Electric meter
Disconnect switch
Some utility regulations require a minimum of 3 ft (900 mm) clearance between electric metering and gas equipment