Electric Signs — Article 600

Give the best answer:

1. Disconnects for electric signs need to be capable of being locked in the open position under some conditions. Which of the following sign disconnects would require this feature? Assume there isn’t any contactor or similar control device ahead of the sign.

  1. Part of the sign wraps around the corner of a building so a portion can’t be seen from a disconnect positioned at 7 ft from the nearest edge.

  2. Part of a large, flat sign is over 50 ft from a disconnect positioned 15 ft from the nearest edge.

  3. Both of the above

  4. None of the above

2. Suppose the signs in the first question operate using magnetic contactors so they can be controlled automatically with a photocell. Which need to have a disconnecting means nearby?

3. If you run liquidtight flexible nonmetallic tubing to a neon sign receptacle 45 ft away from its transformer, what do you have to do to ground metal parts on the sign?

  1. Use a No. 12 (minimum) grounding conductor.

  2. Run the conductor in the same raceway as the ungrounded GTO lead to the receptacle.

  3. Both of the above

  4. None of the above

4. Suppose an overhead canopy at a self-serve gasoline station is 15 ft above grade. How high must an overhanging sign be at the same location?

  1. 14 ft

  2. 15 ft

  3. 16 ft

  4. Unspecified, design issue

5. Which of these signs must be listed (unless exempted by special permission)?

  1. Skeleton neon tubing made up in the field

  2. A self-contained sign using internal fluorescent lamps

  3. A sign lit by floodlights

  4. More than one of the above

6. Suppose NFPA wanted to get into the rental housing business, specializing in facilities for retired code experts. How could it display the “NEC Apartments” sign?

  1. With a fluorescent backlit sign on the building

  2. With skeleton neon tubing on the building

  3. Either of the above

  4. None of the above


Answers and Discussion

1. a, Sec. 600-6(a). Many signs are larger than 50 ft, and the disconnect need only be in the “line of sight” of all sections of the sign. It must, however be within sight of the sign, which brings in the 50 ft limit in Art. 100. In the example, the disconnect is “within sight” of its load, but out of the “line of sight” of one of the sections of that load.

2. d, Sec. 600-6(a), 2nd paragraph. If you provide a disconnect with lock-open capability within sight of an “electronic or electromechanical controller,” the local disconnect rule needn’t be applied. Note that this paragraph used to be an exception, which clearly stated an alternate method of fulfilling the requirement. Now it is an improperly worded second paragraph, which conflicts with the first paragraph. There wasn’t any intent to change the meaning of this rule. Obviously the Code doesn’t have to give permission to install an additional disconnect; the only realistic way to apply this language is as it was applied in the 1993 NEC.

3. a, Sec. 600-7. In order to reduce the voltage gradient around the sign conductor, the Code requires running the grounding conductor outside the raceway. This rule is unique to this article, and it reflects the fact that potential fault currents on the secondary side of sign transformers are very low. On the other hand, running an equipment grounding conductor next to the sign lead for long distances can generate enough ozone from corona discharges to prematurely damage the sign lead. The 1999 NEC will require actual spacing away from the nonmetallic raceway for this conductor. Note that this rule should logically apply to any nonmetallic raceway, including rigid ones. However, based on the literal text, it doesn’t. This is because the wording came into the Code as a result of an appeal and not through panel action. This will be corrected in the 1999 NEC.

4. a, Sec. 600-9(a). The former requirement of 16 ft was reduced because other standards only require 14 ft to the canopy; there wasn’t any sense requiring the sign at 16 ft when the canopy was at 14 ft. The fact that this particular canopy is somewhat higher doesn’t change the rule.

5. b, Sec. 600-3. Field-installed neon tubing isn’t practical to have listed. The article has been restructured so relevant requirements for field judgment by an inspector are in Part B of the article. The definition of an electric sign in Art. 100 declares it to be “utilization equipment.” This precludes classifying a sign illuminated only by external floodlights as within the scope of Art. 600.

6. a, Sec. 600-32(i). Skeleton neon can’t be used either in or on dwelling occupancies, which would include the outside wall of a multifamily building. The fluorescent sign would work, as would skeleton neon mounted to a separate structure remote from the building wall.