NEC requirements regarding pull boxes for fixed electric heating systems
When is it permitted to install a pull box that is not visible under normal operating conditions, but can be accessed by moving material covering the pull box?
A. When installing pull boxes for pulling the electrically insulated conductor in the ferromagnetic envelope of a skin-effect heating system, provided their locations are indicated by permanent markings on the insulation jacket surface and on drawings.
B. When the voltage of a skin-effect heating system exceeds 600V.
C. When the insulated conductor of a skin-effect heating system passes through a pull box uncut and unspliced.
Article 427 of the 2011 NEC focuses on fixed electric heating equipment for pipelines and vessels. As noted in Sec. 427.46, "Pull boxes for pulling the electrically insulated conductor in the ferromagnetic envelope shall be permitted to be buried under the thermal insulation, provided their locations are indicated by permanent marking in the insulation jacket surface and on drawings. For outdoor installations, pull boxes shall be of watertight construction."
Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at firstname.lastname@example.org.