and even some materials made right here, I have had issues in the past with sub-standard quality. With so much material being manufactured outside of the U.S. I will NEVER over-current a wire, as I have seen way too many breakers fail to do their job, resulting in major repairs. As far as oversizing the breaker, good luck getting me to go for that! My six grandchildren were sleeping upstairs when the split hvac unit outside compressor locked-up and completely melted the bus bars in the main breaker panel with the breakers never tripping. Unless you can show the inspector in the NEC codebook a valid exception, and gently convince said inspector to give you a variance, you will likely be in for a serious uphill battle. It is the wire insulation that breaks-down, not the current-carrying capacity. Different insulation material ratings just add more confusion, as this will vary your wires maximum ampacity under code. Arguing will very likely cause no end of future grief for the homeowner. One can argue semantics all you want, but the inspector is going to want #14 wire matched up to a 15 amp breaker, #12 wire to a 20 amp, #10 to a 30 amp, etc. Most local inspectors only care about what they see at first impression. In addition, this subject is discussed in further detail by Mike Holt in the following video: See Figure 440-5 and 440-6 in for a clear explanation. It's kind of complicated, but it's all in the NEC, Art.440, Section III.īelow is an excellent overview on Art440 by one of the most respected names in the electrical business, Mike Holt. ![]() This is not a hard and fast rule, but it is typical and works for most installations. Things are NOT always as simple as a chart at the home center or a simple electrical book.įor an air con unit you would typically size the conductors to the minimum circuit ampacity (MCA), and size the breaker to the maximum overcurrent protection (MOP). ![]() I would not expect the average home inspector to know this.Ī/C units, welders and electric motors have different rules than the "standard" breaker sizing rules. The wiring and breakers for these circuits are required to be designed at 125% of the continuous load and 100% of a non-continuous load.It is perfectly within reason to have #12 wire protected by a 30A breaker when the circuit feeds an A/C unit. Many homes have 30-A or 50-A breakers dedicated to larger appliances such as water heaters, baseboard heaters, ovens, stoves, and heavy-duty power tools.Household outlets in North America and some other countries are on a 120V standard.X Research source X Trustworthy Source Official UK government website Official website for the public sector of the UK government Go to source Do not run a device on a voltage supply outside this range. Most electrical codes allow a ± 5% tolerance for the voltage (or slightly more). ![]() In this example, if you were running the device on a 110 volt supply, you would only refer to the first number listed on each line. ![]() If the device can run at two different voltages, it will usually list two values like this: 110V/240V. The intended voltage (V) of the device should be listed so you can confirm that it matches your electrical system. The amperage drawn depends on the voltage of your electrical circuit.
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