System Planning: Power Requirements

When you’re doing the groundwork for your project, a good place to begin is determining the line voltage requirements. Does your equipment have line cords, wall-mounted transformers, or does it require hard-wiring to an electrical junction box?

Hardwiring of line voltage should be clearly stated to be performed “BY OTHERS” on your proposal or invoice to reduce the chance of a misunderstanding, or liability for your company.

You should clearly state the extent of the work you will perform and not assume the client will be thinking like you. Any ambiguity in your wording might become a ‘smoking gun” for some attorney in the event of an accident or fire. If you clearly state where your work stops and another trade will take over, it might diminish your culpability if it is determined a fire or accident was caused by an electrical problem. Make it clear that you and your technicians stay on the low voltage side; you are not charging for working on the line voltage, and consequently you take no responsibility for it.

Line cord and wall-mounted transformers require receptacles. You’ll need to find the circuit breakers which feed the receptacles you plan to use. If other equipment is currently plugged into the receptacle you want to use, then make sure that this device can be powered elsewhere, and your gear will not be unplugged when the person who originally made claim to that receptacle realizes he's been bumped. Or perhaps the cleaning crew uses that one for their vacuum cleaners. When you find the electrical panel(s) and circuit breaker(s), note their location and how many amps they are. Also determine how many other receptacles or other equipment are on the circuit breakers branch circuit, and of course, if your receptacle is on a wall switch.

Another point to consider is how many line cords and wall mount transformers you’ll have to find a home for. Many wall mount transformers are bulky and require planning to accommodate them properly.

We just were involved in a video project for a restaurant. One of the details we discussed with the client was where we would get power for the system. He indicated that the receptacle on the wall of his office, adjacent to the file cabinet upon which he wanted the monitor and DVR, was it. Of course, the receptacle turned out to be dead.

We advised the client to call an electrician and to obtain a UPS for the system to protect from power surges and to enable it to continue to operate in the event of a power outage.

Additionally the system had grown beyond its original single camera, DVR and monitor to a total of three cameras, three wall-mount transformers and two line cords. We had to lay in temporary extension cords and power strips, and finish after the client got the line voltage he had originally promised.

INTERCONNECTIONS (WIRING)

For our camera project, we needed to connect three Day/Night IR cameras back to the manager’s office. They were analog output cameras, meaning that we had to run RG-6 coaxial cable, as well as 12 Volts DC to each camera. Each camera was equipped with a dozen LEDs for viewing in the dark, and each required a surprising 500 ma. We decided to use Siamese cable. This cable was a coax bonded to a pair of #18 stranded for power. We also needed to be sure we had the BNC connectors we’d require to terminate the coax, as well as wire nuts for the splices the camera power would require. Special crimping tools are needed if you’re using certain types of BNC connectors.

Our project was in an old building which had seen its share of renovation over the years. There were concrete walls and dropped ceilings, along with a myriad of PVC pipes, electrical wires, vents and insulating material