The Electrical Code

215.3 Overcurrent Protection. This is describing the need for the proper breaker for the wire size that is needed for the presumed loads. People that write the code book are being carful to leave no stone unturned. So articles like this are all over the code book. It might seem like if they are repeating what seems to have been discussed. What this article is principle about is non continuous vs continuous loads.

I did a job once in a store and had the opportunity to see this in action for myself. A store kept on adding more show cases to fill this empty space above the racks.and with the show case there was always a four head light fixture that came along as visual effect. It looked great. So the owner hired a carpenter and trying to provide great customer service he installed the cabinet and the lights. Guy did incredible work. I mean he used connectors and mounted the light fixture correctly. The only thing he did wrong was he kept adding them to the same circuit. When the circuit tripped from over amperage. He added another pair of wires from the panel to the light switch box and added a switch over switch to accommodate for the new circuit of lights. It worked great until he ran out of space in the conduit, witch by now was full to the brim with wires and he could not put no more wires. Then I was called in because the owner kept smelling a burnt smell and said it was coming from the panel. Well when I got there the pipe that fed the switches was hot to the touch and a neutral was beginning to show copper because the sheathing was melting off. Now you might be asking right about now why. And the answer is simple. If the conduit was handling a load the turned off every once and a will(non continuous) then the wire would get a chance to lower the temperature, but in this case the lights would be on the whole day and did not have a chance to do that. So when you kept adding wires every wire he added kept adding more heat to the inside of that conduit. By the time you add all the wires that had no ventilation and each wire added heat that heat combined to exceed the temp that the wire sheathing can handle. Even if you installed a different type of wire that can hold more heat it to will eventually either fail or the wires would fuse together. Well the fix was to run two more conduits one for now and the other for future. Make the switch box double stacked with more then enough room for expansion and night light that the owner wanted. I had to take all the wires out because it was all beginning to melt, and distribute them through out the other conduit that I added. Now this is before the whole LED lighting craze that we are having today, and the fix would have been to change the bulbs all to LED and done. He would not have had the night light feature I installed, but it would have fixed the problem or better said he might have never had if LED’s were part of the equation.

“Feeders shall be protected against overcurrent in accordance with the provisions of Part I of Article 240. Where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.

Exception No. 1: Where the assembly, including the overcurrent devices protecting the feeder(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

Exception No. 2: Overcurrent protection for feeders between 600 and 1000 volts shall comply with Parts I through VIII of Article 240. Feeders over 1000 volts, nominal, shall comply with Part IX of Article 240.”