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

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

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

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

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 422.12. © Cengage Learning 2015

FIGURE 23-1 (cont’d.) © Cengage Learning 2015

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

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

Effect of Voltage Variation  

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

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

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

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. © Cengage Learning 2015

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

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

FIGURE 23-9 Position of electric baseboard heaters. © Cengage Learning 2015

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

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

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

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

FIGURE 23-14 Types of receptacles. © Cengage Learning 2015

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

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

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)

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

Noncoincidental Loads Loads that do not operate at the same time are called noncoincidental loads Examples include heating and air conditioning NEC® 220.60 allows feeders that supply both loads to be sized according to only the larger of the two loads

Receptacle Needed for Servicing HVAC Equipment NEC® 210.63 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

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