424.100 part X Low-Voltage Fixed Electric Space-Heating Equipment.
Code Change Summary: A new Part was added to Article 424.
New to Article 424 in the 2017 NEC® is Part X which covers low-voltage fixed electric space heating equipment.
Fixed electric space heating products currently exist on the market that operate on a low voltage source (e.g. products operating at 30 V ac or less). Generally, the power source originates from a 120 volt branch circuit, then uses an isolating transformer to drop the voltage and isolate the secondary from the main supply. Low voltage equipment does not pose the same level of shock hazard or risk of fire as a line voltage product, which is why it is appropriate to apply different requirements specific to low voltage products.
The 2014 NEC® did not not contain specific requirements for low voltage heating cables or heating panels. Without specific language on low voltage, fixed electric space heating, essentially a “low voltage” product would need to meet all the same requirements as “line voltage” (e.g. 120V, 240V) products.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.
2017 Code Language:
N Part X. Low-Voltage Fixed Electric Space-Heating Equipment
424.100 Scope. Low-voltage fixed electric space-heating equipment shall consist of an isolating power supply, low-voltage heaters, and associated equipment that are all identified for use in dry locations.
424.101 Energy Source.
(A) Power Unit. The power unit shall be an isolating type with a rated output not exceeding 25 amperes, 30 volts (42.4 volts peak) ac, or 60 volts dc under all load conditions.
(B) Alternate Energy Sources. Listed low-voltage fixed electric space-heating equipment shall be permitted to be supplied directly from an alternate energy source such as solar photovoltaic (PV) or wind power. See the actual NEC® for remainder of subsection…
424.102 Listed Equipment. Low-voltage fixed electric space-heating equipment shall be listed as a complete system.
424.104 Branch Circuit.
(A) Equipment shall be permitted to be supplied from branch circuits rated not over 30 amperes.
(B) The equipment shall be considered a continuous duty load.