PTC Heaters Meet NEC Standards
Posted by Adelle Webber on
Electrical Standards and Codes for Electrical Installations
Standards and codes for electrical installations, panels, and equipment provide minimum safety standards and usability characteristics for all materials and methods used in the construction and installation of electrical devices.
The National Electrical Code originated around 1900 due to efforts by the National Conference of Standard Electrical Rules. The conference was made up of interested national associations involved in electrical construction, fire prevention, and insurance companies to develop a standard for identifying and installing electrical wiring and equipment.
The primary reason for developing the code was to ensure the safety and protection of people and property of every electrical installation in the United States. So what is in the 2020 NEC?
PTC heating elements help meet electrical safety standards
The unique construction and characteristics enable PTC heating elements to meet and surpass international, national, and local standards for electrical heating and installation. Inherent safety features, including max temperature control, voltage isolation, and self-limiting current, meet stringent requirements.
The following sections of the NEC refer to electric heating elements, their installation, and safety.
Article 424
Fixed Electric Space-Heating Equipment
This article primarily addresses electric space heating in dwellings, Control and Protection of Fixed Space-Heating Equipment. PTC heaters don’t require supplementary overcurrent protection in that the devices automatically limit the current to the resistive elements as the temperature of the element increases.
PTC heating assemblies come with factory-installed wiring that are connected to terminal blocks or other junction boxes. The wiring insulation is rated above 60 C to prevent melting close to the heating source.
PTC heating devices are embedded in aluminum or honeycomb fin structures to prevent damage to the heating elements.
The benefits of PTC applies to the lack of need for a thermostat to control switching devices; when the temperature reaches its maximum, the device's resistance increases, decreasing the current and further increase in the temperature.
A switch or circuit breaker is still required to protect the circuits and should be of the type suitable for high inrush current. PTC heating elements have low resistance and high current when power is initially applied to the circuit.
The switch should be marked with on/off positions. If the heating devices contain a fan motor, the power disconnect can be shared with the heating element or a separate circuit.
ARTICLE 425
Fixed Resistance and Electrode Industrial Process Heating Equipment
PTC heating elements are often used in industrial process heating equipment. These include contact, surface, duct, immersion, and air heaters. The standards relate to safety from human connection and near combustible materials.
Since PTC heating elements have no exposed elements that can cause combustion, they minimize the need for protective barriers and distance from combustible materials. There is no combustion taking place in PTC heating elements. The temperature of the elements never reaches a combustible temperature point.
The small ceramic resistive disks making up the actual heating element are embedded in aluminum or stainless steel fins or cartridges that prevent the element from getting damaged or coming into contact with other materials. This minimizes the need for additional protective insulation.
Wires connecting PTC devices are insulated, rated for high-temperature use and are intended to be connected by terminal blocks or custom prewired harnesses. An on/off switch is required, but no other temperature sensors or controls are needed for proper installation.
ARTICLE 426
Fixed Outdoor Electrical Deicing and Snow Melting Equipment
PTC heating elements are ideal for external locations where continuous monitoring is not feasible. The heaters, once turned on, will heat the surface or space requiring deicing without temperature or other control systems.
Since these devices react to ambient temperature increasing or decreasing current flow, they will maintain the desired temperature to melt snow or keep equipment and materials from freezing. How PTC heaters work.
These resistive heating elements can be strip, surface, air, tubular, or fan heaters. Either must be isolated and protected from snow and ice coming into contact with the electrical elements.
ARTICLE 427
Fixed Electric Heating Equipment for Pipelines and Vessels
The term “vessel” refers to a container such as a barrel, drum, or tank for holding fluids and other materials. Flexible heaters that wrap around the vessel's surface to be heated or immersion cartridge heaters are inserted into the outer wall to heat materials contained in the pipe or vessel are referred to in this article.
Cord and plug-connected equipment with factory-installed wiring are allowed if rated 20 ampers or less and 150 volts to ground or less. This would most often be electric resistive heaters in silicone rubber bands attached to the outside of drums to be heated.
These drum heaters are portable devices that can be moved from one location to another. DBK drum heaters are prewired for plugging into a nearby outlet but also contain thermostatic controls and an off switch on the heater itself. Types of drum heaters.
An important guideline is the resistive elements do not come into direct contact with the pipeline component and are insulated from human touch. The protective silicone insulating layer used in HSSD drum heaters prevents the grounding of the resistive wires to the metal surface of pipelines or drums.
Where installed on pipelines, their assemblies, or valves, the heating elements must have flexural capabilities to conform to the vessel's surface without damaging it. It is also required that these heating elements have a grounded conductive covering on the opposite surface side to be heated to prevent personnel contact and include a weatherproof jacket.
Check for the latest updates to local and national codes.
This overview of PTC heating elements and the National Electrical Code is not intended as a substitute for ensuring your installation meets code requirements. Always check your national and local code requirements before installing any electrical heating devices.