Article 600: Electric Signs and Outline Lighting

Jun 1, 2008 12:00 PM, By Mike Holt, NEC Consultant

How to light up signs, not people

Every commercial occupancy needs a form of identification, the standard method of which is typically the electric sign. This is one reason why you'll be working with Art. 600 if you do much commercial or industrial work.

Article 600 covers the installation of conductors and equipment for electric signs and outline lighting (see Define the Sign). It also discusses installations and equipment that use neon tubing for signs, decorative elements, skeleton tubing, or art forms [600.1].

Electric signs, section signs, and outline lighting — fixed, mobile, or portable — must be listed and installed per the listing instructions. Field-installed skeleton tubing and outline lighting needn't be listed if you wire them per Chapter 3 [600.3].

Branch circuits

Fig. 1. Each commercial building and commercial occupancy accessible to pedestrians must have at least one sign or outline outlet supplied by a 20A branch circuit.

If a tenant location is accessible to pedestrians, install at least one sign outlet at each entrance (service hallways and corridors don't count as entrances) [600.5]. Dedicate an individual branch circuit (rated at least 20A) for this purpose. The circuit can serve multiple sign outlets but no other load (Fig. 1).

Terminate sign wiring at the enclosure, box, or conduit body of the sign (the same applies to outline lighting). Poles used for sign support can contain the sign circuit conductors, if the installation complies with 410.30(B) [600.5(C)(3)]. Each circuit that supplies a sign (or outline lighting system) must be controlled by an externally operable switch or circuit breaker that opens all ungrounded conductors [600.6].

The “within-sight” (see Art. 100) rule applies to parts of the sign you can energize. This rule requires the disconnecting means to be within sight of a sign, unless the disconnecting means can be locked in the open position [600.6]. The provision for locking (or adding a lock to) the disconnecting means must be on the switch or circuit breaker whether the lock is there or not. A portable locking means doesn't meet this requirement.

If you install signs (or outline lighting systems) operated by electronic or electromechanical controllers external to the sign (or outline lighting system), install the disconnecting means so it is:

Within sight of (or in the same enclosure with) the controller.
Capable of disconnecting the sign (or outline lighting) and the controller from all ungrounded supply conductors.
Capable of being locked in the open position. The locking provision requirements are the same as for the disconnect.

Grounding and bonding

Connect signs (and metal equipment of outline lighting systems) to the equipment-grounding conductor (EGC) of the supply circuit using an EGC specified in 250.118 [600.7(A)(1)]. Size the EGC per 250.122, based on the rating of the overcurrent device protecting the conductors that supply the sign. Terminate each EGC using one of the following methods [250.8]:

Listed pressure connectors.
Terminal bars.
Pressure connectors listed for direct burial or concrete encasement [250.70].
Exothermic welding.
Machine screws that engage at least two threads or are secured with a nut.
Self-tapping machine screws that engage at least two threads.
Connections that are part of a listed assembly.
Other listed means.

Auxiliary grounding electrodes are not required for signs, but they are permitted [600.7(A)(4)]. If you install any, they must comply with 250.54. Some facts about auxiliary electrodes:

You don't have to bond them to the building or structure grounding electrode system,
The grounding conductor to the electrode need not be sized per 250.66, and
The contact resistance of the electrode to the earth does not have to comply with the 25-ohm requirement of 250.56.

Don't try to use the earth as your effective ground-fault current path. It doesn't qualify as such a path for meeting the requirements of 250.4(A)(3). Because the contact resistance of a grounding electrode to the earth is high, very little ground-fault current returns to the electrical supply source via the earth. Consequently, the circuit overcurrent device will not open and clear the ground fault. This means metal parts will become and remain energized with dangerous potential.