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| Subject - amperage and phases..... | |
| smartlight |
How many total amps of potential energy are available in a 100 AMP Single phase 3-wire service? how about a 4-wire 3-phase service? I'm trying to win a bet.... |
| Ryan_J | Isn't potential energy measured in Joules? ;) |
| smartlight | Yippee! I won! ....no really... |
| Jorren | If you're talking about available short circuit current, the formula is 100(kva)/1.732(KV)(Z)=Isc where Isc=max symmetrical short circuit amps KVA= transformer nameplate KVA KV Transforme line to line voltage Z= transformer impedance Jorren Example:2000 kva trans @5% impedance 480 volt side= 100(2000)/1.732*.48*5= 48114 available fault current |
| lctrc789 | Smartlight, this is a loaded question to me. How many total amps of potential energy is in any breaker. Potential being a system that measures between 2 points and energy like this is generally measured in Volts or Resistance. If you have a 100 amp breaker and it is 120/240 then your Potential is the difference between two voltages and or 100 amps is the difference in the amperage. This is over my head why a question like this would be asked, I would say the difference between two points here is the voltage. However, energy could be expressed in amperage as well so the potential energy in a 100 amp breaker to me is 100 amps. Any one else here have any ideas on this . |
| JimmyDee | quote: Yes Ryan you are correct but he really wants to know (talked to him last night on the chat room  ) how many amps @ 120 volts will he get on a 100 amp service. The answer of course is 100 amps on each leg or 200 amps @ 120 volts. On the 4 wire, three phase system (208,3 phase) if it were a l00 amp service, there would be 100 amps X 3 or 300 amps @ 120 volts. Replace the word potential with the word available and I think you will be closer to his question. We are digging to deep into the question. Jim |
| smartlight | Believe it or not...this is an actual question on a test that I had to take. I was a bit confused at what "the total amps of potential energy available" were but I answered 100 amps per leg in any system. At 120v, of course. 240 changes things a bit. Thanks for the replies. |
| JimmyDee | It really is a bad question because the answer changes depending on the voltage required. Jim |
| Scott Vickrey | Another very important variable missing from this question is time. There is no mention of it in the question. Are we talking about instantaneous? Which I presume is the case. True, this is a poorly worded question. Probably produced by someone who had to come up with a hundred questions off the hip. The correct answer in this case would be inconclusive due to insufficient and incorrect information provided. Most circuit breakers used today are inverse time breakers. An inverse time breaker means that as the amps increse the amount of time to trip the breaker decreases. How many amps are available on a hundred amp service? That depends on the amount of time and load. Are we going to trip the breaker or not? All that aside, let's assume you're just talking about a short circuit calculation. This information will be marked on the breaker and vary from manufacturer to manufacturer and minutely within their individual breakers. |
| Ryan_J | I was thinking what Jorren was thinking. |