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

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:

  1. Within sight of (or in the same enclosure with) the controller.

  2. Capable of disconnecting the sign (or outline lighting) and the controller from all ungrounded supply conductors.

  3. 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]:

  1. Listed pressure connectors.

  2. Terminal bars.

  3. Pressure connectors listed for direct burial or concrete encasement [250.70].

  4. Exothermic welding.

  5. Machine screws that engage at least two threads or are secured with a nut.

  6. Self-tapping machine screws that engage at least two threads.

  7. Connections that are part of a listed assembly.

  8. 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.


Locate a sign (or outline lighting system) at least 14 feet above areas accessible to vehicles, unless you mechanically protect it from physical damage [600.9(A)] (Fig. 2 on page 62). Section 225.18(4) requires a minimum of 18 feet of overhead conductor clearance above public streets, alleys, roads, parking areas subject to truck traffic, and driveways on other than residential property. This may be an important consideration if you feed a sign with overhead conductors.

Protect neon tubing from physical damage, if you use it for signs, decorative elements, skeleton tubing, or art forms in locations that are readily accessible to pedestrians [600.9(B)]. Install signs and outline lighting systems in such a way that adjacent combustible materials aren't subjected to temperatures greater than 194°F. An incandescent or HID lamp/lampholder must have at least 2 inches of spacing from wood or other combustible materials [600.9(C)]. If you install signs or outline lighting systems in wet locations, ensure they are weatherproof and have drain holes [600.9(D)].

Portable or mobile signs

Portable or mobile signs must be adequately supported and readily movable without the use of tools [600.10]. Each portable or mobile sign must have an attachment plug. Remember that 400.8(2) and (5) prohibit flexible cords from being run through (or above) a suspended ceiling.

The cords for portable or mobile signs in wet or damp locations must be junior hard service or hard-service types with an EGC. In addition, the signs themselves must have factory-installed GFCI protection. If that's not the case with a particular sign, don't install it in a wet or damp location. The cords for portable or mobile signs in dry locations (as defined in Art. 100) must be SP-2, SPE-2, SPT-2, or heavier (see Table 400.4). These cords can't be longer than 15 feet [600.10(D)] (Fig. 3).

Ballasts, transformers, and electronic power supplies

Ballasts, transformers, and electronic power supplies must be accessible, securely fastened in place, and their secondary conductors must be as short as possible [600.21].

If ballasts, transformers, and electronic power supplies are installed outside of the sign (e.g., in a separate enclosure rather than in the sign), maintain a working space of at least 3 feet high by 3 feet wide by 3 feet deep [600.21(E)].

You can install ballasts, transformers, and/or electronic power supplies in attics and soffits, if the point of entry for each component has:

  • An access door,

  • A passageway not less than 3 feet high by 22½ inches wide, and

  • A suitable permanent walkway at least 1 foot wide.

At least one lighting outlet that contains a switch (or is controlled by a wall switch) must be installed at the usual point of entry to these spaces. The lighting outlet must be at or near the equipment requiring servicing.

Ballasts, transformers, and electronic power supplies can be above a suspended ceiling, if the enclosures are securely fastened in place and don't use the suspended-ceiling grid for support [600.21(F)]. You cannot connect these to the branch-circuit wiring by a flexible cord (Fig. 4 on page 64). Once again, remember that 400.8(2) and (5) prohibit flexible cords from being run through, or above, a suspended ceiling.

Sidebar: Define the Sign

Article 100 defines an electric sign as any “fixed, stationary, or portable self-contained, electrically illuminated utilization equipment with words or symbols designed to convey information or attract attention.”

Outline lighting is an arrangement of incandescent lamps or electric-discharge lighting to outline (call attention to) certain features, such as the shape of a building or the decoration of a window.

Article 600 adds definitions in 600.2. Two important ones are:

  1. Section sign

    A sign or outline lighting system, shipped as subassemblies that require field-installed wiring between the subassemblies to complete the overall sign. The subassemblies are either physically joined to form a single sign unit, or are installed as separate remote parts of an overall sign.

  2. Skeleton tubing

    Neon tubing sign or outline lighting not attached to an enclosure.