Article 424: Fixed Electric Space Heating Equipment

Article 424 Fixed Electric Space Heating Equipment

I. General



This article does not apply to heating and room air conditioning. It does apply to heating cables, unit boilers, central systems, and other fixed electric space heating equipment.


Other Articles

If it incorporates a hermetic refrigerant motor-compressor, then it must also comply with Article 440.


Branch Circuits

(A) Branch-Circuit Requirements. It can be any size as long as it is an individual branch circuit supplying only one appliance. If more than one appliance is on the circuit, 30 A is the largest rating permitted (50 A for nondwelling fixed infrared heating equipment).

(B) Branch-Circuit Sizing. This equipment is to be considered a continuous load.

II. Installation




Special Permission


Supply Conductors



This equipment cannot be installed where it may be severely damaged unless protected. When installed in damp or wet locations, the equipment has to be listed for such locations and constructed and installed so that water cannot accumulate on or enter wired sections, electrical components, or ductwork.


Spacing from Combustible Materials

Adequate spacing must be provided unless approved for direct contact.

III. Control and Protection of Fixed Electric Space Heating Equipment


Disconnecting Means

This must be provided. When more than one source is used, all disconnecting means must be grouped and marked.

(A) Heating Equipment with Supplementary Overcurrent Protection. Must be in sight of the supplementary over-current device and on the supply side of the overcurrent device if fuses and in addition item 1 or 2 following.

1. Heater containing no motor rated over 1/8 horsepower. This disconnecting means or a unit switch complying with Section 424.19(C) can be used as the disconnecting means for the motor controller and heater if it is in sight of the motor controller and heater or can be locked in the open position.

2. Heater containing a motor(s) rated over 1/8 horsepower. The same holds true as noted in the preceding subparagraph (1). In addition, if it is not in sight of the heater, a separate disconnect complying with Section 424.19(C) can be installed. If it is not in sight of the motor controller location, a disconnect means must be installed in accordance with Section 430.102, and where the motor is not in sight of the controller must comply with Section 430.102(B).

(B) Heating Equipment without Supplementary Over-current Protection

1. Without motor or with motor not over 1/8 horsepower. The branch-circuit switch or circuit breaker can serve as the disconnecting means if the switch or circuit breaker can be locked in the open position or is within sight of the heater.

2. Over 1/8 horsepower. A disconnecting means must be located within sight of the motor controller except when installed in accordance with Section 424.19(A)(2).

(C) Unit Switches as Disconnecting Means. A unit switch that is part of the heater disconnects all ungrounded conductors and has a marked off position can be used as the disconnecting means if other disconnecting means are installed as follows:

1. In multifamily family dwellings, this disconnecting means must be installed at least on the same floor as the heater. It can control other heaters and lamps.

2. In two-family dwellings this disconnecting means can be installed either inside or outside the dwelling unit. There is also a provision for additional control.

3. In one-family dwellings the service disconnect can serve this purpose.

4. In other occupancies, if readily accessible, the branch-circuit switch or circuit breaker can be used.


Thermostatically Controlled Switching Devices

These devices can also serve as the disconnecting means if all the following conditions are met; have a marked off position, interrupt all ungrounded conductors when manually put in that position, cannot be automatically energized in the off position, and are located in accordance with Section 424.19.


Switch and Circuit Breaker to Be Indicating


Overcurrent Protection

Branch-circuit protection as provided in Article 210 can be used. Motors must comply with Articles 430 and 440. Resistance element cannot be protected at a higher rating than 60 A. Equipment rated at more than 48 A must be subdivided, with each subdivision rated not more than 48 A. The manufacturers must provide the division and overcurrent protection for the division. Conductors that supply supplementary overcurrent devices are branch circuit conductors. There are notations concerning heaters over 50 kW.

Field conductors between the heater and supplementary overcurrent protection must be sized at 125% of the load if the heater is rated less than 50 kW.

If the heater is rated at least 50 kW the conductors can be sized at 100% of the rating if the heater is marked for 100% conductor rating and the conductors are not smaller than the marked rating. Also, a temperature control device must be installed.

IV. Marking of Heating Equipment



Must have proper marking information: volts, amperes, horsepower, etc.


Marking of Heating Elements

Volts and amperes or volts and watts.

V. Electric Space Heating Cables


Heating Cable Construction

Nonheating cables of at least 2.1 m (7 ft.) must be installed at the factory.


Marking of Heating Cables

Proper marking is required. Special color coding is required for different voltages of heating cables: 120 V, yellow; 208 V, blue; 240 V, red; 277 V, brown.


Clearances of Wiring in Ceilings

Fifty millimeters (two inches) of space is required above a heated ceiling. An operating ambient temperature of 50°C is to be used for all sizing and appropriate correction factors used. If located above thermal insulation 50 mm (2 in.) in thickness, the temperature correction is not needed.


Area Restrictions

The cables cannot go beyond the room in which they originate. They cannot be installed in closets or over a partition that extends to be ceiling. There is also a restriction as to how they may be run over cabinets. They may be used in closet ceilings for low-temperature sources for humidity control, if there are no obstructions between floor and ceiling in that part of the ceiling.


Clearance from Other Objects and Openings

The heating cables must be at least 200 mm (8 in.) from boxes used for surface-mounted lighted luminaires (fixtures) and 50 mm (2 in.) from recessed lighting luminaires (fixtures). They cannot be installed where they are covered by any surface-mounted unit.



The cable's length cannot be changed.


Installation of Heating Cables on Dry Board, in Plaster and on Concrete Ceilings

(A) Cables are not permitted in walls unless it is a single run to reach a dropped ceiling.

(B) A minimum spacing of 38 mm (1½ in.) is required for cables rated at 9 watts/m (2¾ W per foot) and under for adjacent runs.

(C) Heating cables cannot be applied directly to metal surfaces. They can be only to fire-resistant surfaces. A coat of plaster must be applied to a metal surface.

(D) The entire heating cable, at least 75 mm (3 in.) of the nonheating cable and the splice between them must be embedded in plaster or dry board.

(E) The surface of the ceiling must have a coating of at least 13 mm (½ in.) of plaster or other approved material.

(F) Cables have to be secured at a maximum of 400 mm (16 in.) on center unless approved for 1.8 m (6 ft.) on center.

(G) When dry board is used for the ceiling, it cannot be thicker than 13 mm (½ in.).

(H) Cables cannot come in contact with metal or other surfaces which can conduct electricity.

(I) The cables must be installed parallel to joists in a dry board installation and at least 65 mm (2½ in.) between center of adjacent runs of cable under the center line of the joist. Care must be taken not to drive nails through the heating cables.

(J) The cables can cross joists at the end of the room or to comply with a manufacturer's requirement.


Finished Ceilings

Coverings cannot have thermal insulating properties. Paint and wallpaper can be used.


Installation of Nonheating Leads of Cables and Panels


Installation of Cables in Concrete or Poured Masonry Floors


Inspection and Tests


VI. Duct Heaters








Elevated Inlet Temperature

Duct heaters must be approved for mounting in ducts and at the expected temperatures, as well as assure proper air-flow.


Installation of Duct Heaters with Heat Pumps and Air Conditioning




Fan Circuit Interlock


Limit Controls


Location of Disconnecting Means

Must be within sight of the controller except as noted in Section 424.19(A).




VII. Resistance-Type Boilers






Overcurrent Protection


Overtemperature Limit Control


Overpressure Limit Control


VIII. Electrode-Type Boilers






Branch-Circuit Requirements


Overtemperature Limit Control


Overpressure Limit Control






IX. Electric Radiant Heating Panels and Heating Panel Sets










Clearances of Wiring in Ceilings


Location of Branch-Circuit and Feeder Wiring in Walls


Connection to Branch-Circuit Conductors


Nonheating Leads


Installation in Concrete or Poured Masonry


Installation under Floor Covering

Article 90 Introduction


Wiring and Protection

Wiring Methods and Materials

Equipment for General Use

Special Occupancies

Special Equipment

Special Conditions


Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size

Annex D. Examples

Annex E. Types of Construction

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Pocket Guide to the National Electrical Code 2005
Pocket Guide to the National Electrical Code(R), 2005 Edition (8th Edition)
ISBN: 0131480014
EAN: 2147483647
Year: 2004
Pages: 120 © 2008-2017.
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