![]() In a 240 volt circuit, there is no neutral wire. Only the hot wire is connected to the breaker. The amperage in the hot and neutral wires are the same (in the perfect world). In a 120 volt circuit, it flows "out" toward the device via the hot (generally the black wire) and "back" via the neutral (generally the white wire). ![]() In AC current, electricity flows in both directions. So why are they tied together? That is done when the two-pole breaker is to be used to power a 240 volt circuit. If you then powered two, separate 120 volt devices from the two breakers, each breaker would allow 100 amperes to pass to each of the devices before tripping. In actuality, you always had two 100A breakers. To understand this, imagine that you remove the mechanical tie from the two-pole breaker. It does not matter if that breaker is physically tied to another 100A breaker. The wattage rating is irrelevant for sizing in most cases.The breaker will trip at the amperage notated on the breaker. In conclusion, add the loads up by nameplate amps or if available by the VA rating. If I used the wattage rating where I should have used A or VA, I would put twice as many bulbs as safe on a circuit. If you multiply voltage by current, you get 28 VA, showing that it draws more current than is consumed, and we would say it has a power factor of 14.5/28=0.51. However, the power company (in a residential setting) bills you by the power actually consumed, W, which is why devices have it labeled.įor example, this LED bulb I have says "120 V 14.5 W 234 mA". This means current will circulate without being consumed by the device, but using ampacity by still heating up the wires. The circuit can provide 5760 VA.ĭue to a property known as the power factor, a load can draw more energy than it consumes in part of the AC cycle, and gives it back to the line in the other half. A fundamental mistake is to multiply 24 A by 240 V and get 5760 W. Unless you are running only incandescent light bulbs or heaters both without any variable control, you will not get 5760 W.Īs another answer gives, you are allowed to draw 80% of the amp rating continuously, which in your case is 80% of 30A = 24 A. The answer is your circuit can provide anywhere from 0 to 5760 W without tripping. Non-continuous loads (say a large well pump motor), though, can pull the full 7200W from the circuit as the duty cycle of the load provides adequate time for things to cool off between runs. So, you're limited to 5760W for an on-all-the-time (or at least longer than a few hours at a time) load. Than the sum of the continuous load plus the noncontinuous Load to be served after the application of any adjustment orĮxception: If the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operationĪt 100 percent of its rating, the allowable ampacity of theīranch-circuit conductors shall be permitted to be not less ![]() Have an allowable ampacity not less than the maximum (b) The minimum branch-circuit conductor size shall The minimum branch-circuit conductor size shall have anĪllowable ampacity not less than the noncontinuous load Or any combination of continuous and noncontinuous loads, (a) Where a branch circuit supplies continuous loads Conductors shall be sized to carry not less than the larger of Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. While there is such a thing as a 100%-rated breaker, they are typically only found in industrial work.įurthermore, the branch circuit wiring needs an 80% derate for continuous loads as well, as per 210.19(A)(1): The reason why is because garden-variety breakers made to UL 489 (and their counterparts in fuse-land) will eventually trip (or blow) if you run 100% of their rated current through them for hours on end. The sum of the continuous load plus the noncontinuous load. Overcurrent device shall be permitted to be not less than The overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.Įxception: Where the assembly, including the overcurrentĭevices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the ampere rating of the Where aīranch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of You have to consider that the breaker may have other ideas, as stated in 210.20(A): While 210.22 would seem to indicate that you have the full 30A available to you:Ģ10.22 Permissible Loads, Individual Branch Circuits.Īn individual branch circuit shall be permitted to supplyĪny load for which it is rated, but in no case shall the load Use the 80% rule for continuous loads (because the breaker will, even if you don't)
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |