Exterior CCTV Pole Power, Grounding, and Surge Protection
A Connecticut low-voltage contractor is installing eight fixed 4K cameras on a 14-foot galvanized steel pole in a parking lot. The pole is 180 ft from the building. Each camera is rated 24 VAC, 25 W, and the contractor plans to power all eight from a single 24 VAC, 300 VA transformer in the building's IDF. The proposed circuit is one 18 AWG two-conductor cable run underground in Schedule 40 PVC to a junction box on the pole, then daisy-chained to the cameras. The site has frequent lightning. The camera housings are metal and bolted to the pole. The electrical contractor tells the low-voltage contractor, 'It's only 24 volts-no grounding or surge protection is needed.' The general contractor wants the cameras working before the parking lot striping is completed. The low-voltage contractor has a permit for the low-voltage work only.
1. Evaluate the 24 VAC power design. Show why the proposed 18 AWG single-cable daisy chain is likely noncompliant or nonfunctional.
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Start with the load. Eight cameras at 25 W are 200 W total; at 24 VAC that is about 8.3 A. A single 18 AWG conductor has roughly 6.4 ohms per 1,000 ft. For a 180 ft one-way run, the loop is 360 ft, so resistance is about 2.3 ohms. At 8.3 A, the drop would be about 19 V, leaving only about 5 V at the far end-far below any 24 VAC camera's operating range. The daisy chain makes it worse because upstream cable carries the total current and downstream cameras see progressively lower voltage. This is not just a code issue; it will not work. Acceptable solutions include a local power supply at the pole, separate home-run circuits with much larger conductors, or PoE if the cameras support it. Also check that the 300 VA transformer's overcurrent protection and Class 1/Class 2 classification match the wiring method; a 300 VA transformer may not be a Class 2 power source, which changes the allowed wiring.
2. What grounding, bonding, and surge protection should be provided for the pole-mounted cameras?
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The metal pole and metal camera housings are exposed metal parts and should be bonded to the equipment grounding conductor that runs with the power circuit. The earth alone is not an acceptable return path. For the 24 VAC circuit, run an equipment grounding conductor with the circuit and bond the pole and housings to it using listed connectors; do not rely on the mounting bolts. For data/coax, install a listed grounding block or surge protector at the building entry and bond it to the intersystem bonding termination or grounding electrode system per Article 800/820. Because the site has frequent lightning, add listed surge protective devices on both the power and signal sides, coordinated with the camera manufacturer's requirements. Avoid creating a separate remote earth ground at the pole that is not bonded to the building ground; that can create dangerous potential differences. The exact surge-protector rating should be selected for the site's exposure.
3. What licensing and scope issue arises from the 120 V primary connection and the permit?
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The 24 VAC secondary wiring and camera installation can be within the low-voltage scope, but the 120 V primary connection to the transformer is electrical work. It requires the appropriate Connecticut electrical contractor/journeyman license and an electrical permit/inspection; the low-voltage permit does not cover it. The contractor should either exclude the primary connection and have the GC's electrical contractor make it, or bring a licensed electrical contractor onto the team. The same applies to any 120 V receptacle or circuit. The contractor should confirm in writing that the transformer primary, overcurrent protection, and disconnect are by others, and that the low-voltage work will be inspected under its own permit.