The National Electric Code (NEC) provides recommendations for electrical installations in explosive environments. When it comes to fixed lighting systems in hazardous locations (Class I, Division 2), the manual suggests that fixed units should include components that offer protection from physical damage, using effective guards or by location.
“Each luminaire shall be protected against physical damage by a suitable guard or by location (NEC Article 501.13).”
The guideline contains vague terms, including “physical damage”, “suitable guards” and “by location.” These phrases are open for interpretation and requires a breakdown of the ruling in order to determine the best method of compliance with the provision.
Interpreting Physical Damage
The NEC does not provide a clear definition for the term “physical damage.” In addition to NEC Articles 501 and 502, the term appears in other parts of the safety manual to describe protection required for outlet assemblies (NEC Article 380.12), non-metallic raceways (NEC Article 388.12), etc. The term “severe physical damage” also appears in the book to describe installations pertaining to electrical metallic tubing (NEC Article 348).
Without an official definition from the NEC, the phrase must be interpreted, based on the type of installation and hazards to be encountered in the area. Due to the wide range of working environments within the industrial sector, as well as the myriad of different ways to utilize a work site, it would be difficult to provide an all-encompassing definition for “physical damage.” In most cases, a localized definition of the term is needed from a relevant Authority Having Jurisdiction (AHJ) or local inspector.
It is also important to highlight that formal requests to the NEC have been made to define “physical damage” in relation to specific NEC provisions, as seen in 1-69 Log #1455 NEC-P01 (2010 Annual Revision Cycle). The NEC Panel rejected the proposal although there was a recommendation to accept it.
The reason for the rejection:
“The submitter has not provided any evidence that a problem exists with the term as it is currently used in the code.”
Conditions and Suitable Methods of Protection
The next part of the NEC guideline focuses on protection by a “suitable guard.” Based on general interpretation, a suitable guard to deter physical damage could include the use of shields that incorporate non-sparking materials. A mesh-type guard may also be used to protect fixed-mount lights in Class I, Division 2 sites, if the unit is installed in a location that calls for it.
Hazardous conditions wherein a “suitable enclosure” can serve as adequate protection against physical damage is defined in NEC Article 501.13(b)(2):
“Where there is danger that falling sparks or hot metal from lamps or luminaires might ignite localized concentrations of flammable vapors or gases, suitable enclosures or other effective protective means shall be provided.”
A suitable enclosure could be a non-sparking, NEMA-rated enclosure (NEMA rated for sake of compliance, as NEMA ratings are clearly defined based on specific types of environments and hazards, e.g. water spray, corrosion, dust, external ice formation). The guideline is lax on types of protective methods to be used, as long as it is “effective” and does not contradict other related NEC guidelines applicable to the installation.
Protection by Location
In the context of “physical damage” interpretation of “by location” could refer to the physical location of the lighting system. The phrase was likely included in the guideline to discourage exposure to dangerous (physical) elements at the site. Recommendations surrounding protecting lights in Class I, Division 2 areas “by location” are not fully elaborated in the NEC manual.
Interestingly, NEC Article 501.13 suggests that a “suitable guard” or “by location” may serve as sufficient protective methods against physical damage for hazardous location lights. It seems that any of the two methods, either by applying a suitable guard or by physically installing the light at an area that is not prone to physical damage, is adequate for compliance based on the language used.