Posted: 9/15/2011 2:33:13 PM EDT
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Quick electrical question. And sorry for asking another generator question, but this is really the best place to get info.
Most generators have a 30 amp, 240 twistlock outlet on their panel as the largest output source. This seems to be what most people run to their transfer switch. Most of the larger portable generators can put out over 30 amps...maybe 35 or 40 peak. With that said, how do you take advantage of the maximum output of the generator? It seems wasteful to take a big genset and be limited by the 30a breaker. is there a secret to this, or are there any portable generators that give the ability to directly hardwire to a panel or transfer switch directly (like the military generators do)? Thanks in advance. |
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IF you use a transfer box (mounted beside/near your regular breaker box) you then have a outlet that is outside the house you would hook the generator too..
I just found the generlink and it seems expensive ($700) but doesnt require your breaker box to be modified at all.. Brian |
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A 30A, 240VAC twistlock inlet box will handle up to 7200W (manufacturers will claim 7500W). Most common generators are capable of less than 7000W output. If you have a larger portable genset you could always look at 50A inlet boxes. At 240VAC one of those will handle 12kW. I wouldn't consider 7kW+ portable gensets to be common, though I know they are out there. |
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We run generators at work all the time. I would not one running close to max. It is really hard on them. If you have a 30amp generator it doesnt mean you should run it to that. Most people figure out what their household needs are and then get a generator rated 1.5x to 2x more than that.
I use a Dewalt 2900 max current is 24.4 amps. Ive ran it up to 18amp draw and it didnt like that at all, it handled it and kept up but you you could tell it was pushing it. I ran it this way for 6 hours. |
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Quoted:
Most generators have a 30 amp, 240 twistlock outlet on their panel as the largest output source. This seems to be what most people run to their transfer switch. Most of the larger portable generators can put out over 30 amps...maybe 35 or 40 peak. With that said, how do you take advantage of the maximum output of the generator? It seems wasteful to take a big genset and be limited by the 30a breaker. is there a secret to this ... a 4 wire, 30 amp, 240Vac twistlock receptacle provides split phase 120Vac power with 30A each leg. in other words, you get up to 30A at 240Vac //or// up to 60A at 120Vac. From L1->L2 = 240Vac; L1->N = 120Vac; L2->N = 120Vac. there is one catch, you can't actually pull 60A at 120Vac for one load; what you instead have are two 30A 120Vac circuits. nevertheless, you can get up to 30A x 240Vac = 7200W //or// 2 x 30A x 120Vac = 7200W from the generator though the 4 wire 30A 240Vac split phase receptacle. the above is exactly how a USA residential power company service drop works as well. when folks say "i have 200A service to the house", they mean 200A at 240Vac, which gives 400A at 120Vac (more specifically, 2 x 200A at 120Vac). the reason for using split phase power is straightforward –– it saves a lot of copper/aluminum in the distribution plant. with split phase power, the hots (L1 and L2) are 180 degrees out of phase with each other; the result is that the neutral (N) conductor only has to carry the difference of L1 and L2 currents, and not the sum. because of the split phase approach, the neutral conductor is the same wire gauge as the L1 and L2 conductors. otherwise, the neutral conductor would have to be sized larger for the total L1+L2 current. ar-jedi |
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Quoted:
a 4 wire, 30 amp, 240Vac twistlock receptacle provides split phase 120Vac power with 30A each leg. in other words, you get up to 30A at 240Vac //or// up to 60A at 120Vac. From L1->L2 = 240Vac; L1->N = 120Vac; L2->N = 120Vac. there is one catch, you can't actually pull 60A at 120Vac for one load; what you instead have are two 30A 120Vac circuits. nevertheless, you can get up to 30A x 240Vac = 7200W //or// 2 x 30A x 120Vac = 7200W from the generator though the 4 wire 30A 240Vac split phase receptacle. ar-jedi OK. I think I understand this, but that still leaves my question: If the generator is capable of >30 amps, is there any way I can take advantage of that. For practical terms, say I'm looking to get the Generac XG8000. It's 8000w running, with a peak of 10,000w. Per the spec sheet, it's rated at 41.7 max amps at 120/240 VAC. The largest single output on the generator's panel is 1xL14-30R. In my non-electrician brain, this looks like I would be losing about 25% of the peak power in the generator. If I tried to pull any more than 30amps (say I'm running close to 30 amps and my fridge or oil fired water heater kicks on), the genset's 30A breaker would trip. ***Edited to add*** Looking at another generator, the Briggs and Stratton 8000 watt "elite series" generator: It produces 8000w running and 10000w surge It's rated at 33.3 running amps and 66.6 surge amps (per the spec sheet) It's top output source is a single 120/240-30 amp locking outlet on the genset. So if I were to hook this generator up to my panel via the 240 plug, I would only be able to use half the surge capacity the generator can produce...correct? |
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Quoted:
Quoted:
a 4 wire, 30 amp, 240Vac twistlock receptacle provides split phase 120Vac power with 30A each leg. in other words, you get up to 30A at 240Vac //or// up to 60A at 120Vac. From L1->L2 = 240Vac; L1->N = 120Vac; L2->N = 120Vac. there is one catch, you can't actually pull 60A at 120Vac for one load; what you instead have are two 30A 120Vac circuits. nevertheless, you can get up to 30A x 240Vac = 7200W //or// 2 x 30A x 120Vac = 7200W from the generator though the 4 wire 30A 240Vac split phase receptacle. ar-jedi OK. I think I understand this, but that still leaves my question: If the generator is capable of >30 amps, is there any way I can take advantage of that. For practical terms, say I'm looking to get the Generac XG8000. It's 8000w running, with a peak of 10,000w. Per the spec sheet, it's rated at 41.7 max amps at 120/240 VAC. The largest single output on the generator's panel is 1xL14-30R. In my non-electrician brain, this looks like I would be losing about 25% of the peak power in the generator. If I tried to pull any more than 30amps (say I'm running close to 30 amps and my fridge or oil fired water heater kicks on), the genset's 30A breaker would trip. Looks like you are correct. |
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Quoted:
If the generator is capable of >30 amps, is there any way I can take advantage of that. For practical terms, say I'm looking to get the Generac XG8000. It's 8000w running, with a peak of 10,000w. Per the spec sheet, it's rated at 41.7 max amps at 120/240 VAC. The largest single output on the generator's panel is 1xL14-30R. In my non-electrician brain, this looks like I would be losing about 25% of the peak power in the generator. If I tried to pull any more than 30amps (say I'm running close to 30 amps and my fridge or oil fired water heater kicks on), the genset's 30A breaker would trip. ***Edited to add*** Looking at another generator, the Briggs and Stratton 8000 watt "elite series" generator: It produces 8000w running and 10000w surge It's rated at 33.3 running amps and 66.6 surge amps (per the spec sheet) It's top output source is a single 120/240-30 amp locking outlet on the genset. the generators you are looking at above are intended primarily as portable "job site" generators; as such they have multiple receptacles to plug a variety of loads into –– temporary lighting, power tools, construction equipment, pumps, heaters/fans, etc. –– rather than one large capacity output suitable for interconnection with a transfer switch in a house. that said, you may not be able to draw the maximum output capacity from a single receptacle. note that a common transfer switch inlet is rated at 30A (split phase), with the next size up a much less common 50A (again, split phase). note also that the next bigger Generac unit, 10KW, has a 50A receptacle on it, so in that case you can pull the entire generator capacity from one receptacle (50A x 240Vac = 12KW). Quoted:
So if I were to hook this generator up to my panel via the 240 plug, I would only be able to use half the surge capacity the generator can produce...correct? the "surge capacity" rating is like jello, difficult to actually pin down. for loads such as motors, starting current may exceed running current by a factor of 2 or 3 or 4 or 5 or 6 –– depending on what type of motor it is and what the load on the motor is. the surge capacity of a generator is a combination of the engine torque, flywheel weight, alternator rotational inertia, and the ability of the circuit breaker to hold the motor start load. the latter is the part i think you are missing here. a typical 30A breaker will hold 100A for a few tenths of a second, 50A for a few seconds, and 40A for tens of seconds. there are also "motor start" rated breakers which will hold higher inrush currents even longer. for this reason, the surge capacity of the generator is realizable despite the breaker rating. just remember that the surge capacity is finite and fleeting –– that capacity lasts only a few seconds and again is highly dependent on the rotational inertia of the moving parts. (this is also why inverter-type generators are generally much worse at starting motor loads, compared to direct-coupled generators such as the type you have noted above). summary: 1) if you want full generator output, find one with a receptacle that supports the full output. 2) surge capacity, for most well behaved motor loads, will in most cases exceed the breaker rating but this is typically not an issue. my PTO generator is rated at 50A 240Vac split phase, but my well pump is 220 feet down and hangs off a 30A breaker in the circuit panel. startup current for the first quarter second or so is a measured 60A. neither the 30A breaker in the circuit panel nor the 50A breaker on the generator is the least bit troubled by the startup current, and the combination of the tractor engine and PTO-driven alternator hardly notice the high, but very brief, startup load. see http://www.ar15.com/forums/t_10_17/644329_.html&page=2 ar-jedi |
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Quoted:
In my non-electrician brain, this looks like I would be losing about 25% of the peak power in the generator. If I tried to pull any more than 30amps (say I'm running close to 30 amps and my fridge or oil fired water heater kicks on), the genset's 30A breaker would trip. Unless the generator also has other outlets that are on their own breakers, then yes, you are limited to a maximum of around 7000 watts. Looking at another generator, the Briggs and Stratton 8000 watt "elite series" generator:
It produces 8000w running and 10000w surge It's rated at 33.3 running amps and 66.6 surge amps (per the spec sheet) It's top output source is a single 120/240-30 amp locking outlet on the genset. So if I were to hook this generator up to my panel via the 240 plug, I would only be able to use half the surge capacity the generator can produce...correct? No. Even a 10,000 watt surge wouldn't last long enough to trip the breakers - and the plug and wiring could also handle that much power for a few seconds or less. So, you should still have the generator's full 10,000 watt surge capacity available at the 30 amp locking plug, even though the continuous power at that outlet will be limited to around 30 amps X 240 volts = 7,200 watts. |
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Quoted:
Quoted:
If the generator is capable of >30 amps, is there any way I can take advantage of that. For practical terms, say I'm looking to get the Generac XG8000. It's 8000w running, with a peak of 10,000w. Per the spec sheet, it's rated at 41.7 max amps at 120/240 VAC. The largest single output on the generator's panel is 1xL14-30R. In my non-electrician brain, this looks like I would be losing about 25% of the peak power in the generator. If I tried to pull any more than 30amps (say I'm running close to 30 amps and my fridge or oil fired water heater kicks on), the genset's 30A breaker would trip. ***Edited to add*** Looking at another generator, the Briggs and Stratton 8000 watt "elite series" generator: It produces 8000w running and 10000w surge It's rated at 33.3 running amps and 66.6 surge amps (per the spec sheet) It's top output source is a single 120/240-30 amp locking outlet on the genset. the generators you are looking at above are intended primarily as portable "job site" generators; as such they have multiple receptacles to plug a variety of loads into –– temporary lighting, power tools, construction equipment, pumps, heaters/fans, etc. –– rather than one large capacity output suitable for interconnection with a transfer switch in a house. that said, you may not be able to draw the maximum output capacity from a single receptacle. note that a common transfer switch inlet is rated at 30A (split phase), with the next size up a much less common 50A (again, split phase). note also that the next bigger Generac unit, 10KW, has a 50A receptacle on it, so in that case you can pull the entire generator capacity from one receptacle (50A x 240Vac = 12KW). Quoted:
So if I were to hook this generator up to my panel via the 240 plug, I would only be able to use half the surge capacity the generator can produce...correct? the "surge capacity" rating is like jello, difficult to actually pin down. for loads such as motors, starting current may exceed running current by a factor of 2 or 3 or 4 or 5 or 6 –– depending on what type of motor it is and what the load on the motor is. the surge capacity of a generator is a combination of the engine torque, flywheel weight, alternator rotational inertia, and the ability of the circuit breaker to hold the motor start load. the latter is the part i think you are missing here. a typical 30A breaker will hold 100A for a few tenths of seconds, 50A for a few seconds, and 40A for tens of seconds. there are also "motor start" rated breakers which will hold higher inrush currents even longer. for this reason, the surge capacity of the generator is realizable despite the breaker rating. just remember that the surge capacity is finite and fleeting –– that capacity lasts only a few seconds and again is highly dependent on the rotational inertia of the moving parts. (this is also why inverter-type generators are generally much worse at starting motor loads, compared to direct-coupled generators such as the type you have noted above). summary: 1) if you want full generator output, find one with a receptacle that supports the full output. 2) surge capacity, for most well behaved motor loads, will in most cases exceed the breaker rating but this is typically not an issue. my PTO generator is rated at 50A 240Vac split phase, but my well pump is 220 feet down and hangs off a 30A breaker in the circuit panel. startup current for the first quarter second or so is a measured 60A. neither the 30A breaker in the circuit panel nor the 50A breaker on the generator is the least bit troubled by the startup current, and the combination of the tractor engine and PTO-driven alternator hardly notice the high, but very brief, startup load. see http://www.ar15.com/forums/t_10_17/644329_.html&page=2 ar-jedi A lot of spot on info in this post! 
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Quoted:
Quoted:
If the generator is capable of >30 amps, is there any way I can take advantage of that. For practical terms, say I'm looking to get the Generac XG8000. It's 8000w running, with a peak of 10,000w. Per the spec sheet, it's rated at 41.7 max amps at 120/240 VAC. The largest single output on the generator's panel is 1xL14-30R. In my non-electrician brain, this looks like I would be losing about 25% of the peak power in the generator. If I tried to pull any more than 30amps (say I'm running close to 30 amps and my fridge or oil fired water heater kicks on), the genset's 30A breaker would trip. ***Edited to add*** Looking at another generator, the Briggs and Stratton 8000 watt "elite series" generator: It produces 8000w running and 10000w surge It's rated at 33.3 running amps and 66.6 surge amps (per the spec sheet) It's top output source is a single 120/240-30 amp locking outlet on the genset. the generators you are looking at above are intended primarily as portable "job site" generators; as such they have multiple receptacles to plug a variety of loads into –– temporary lighting, power tools, construction equipment, pumps, heaters/fans, etc. –– rather than one large capacity output suitable for interconnection with a transfer switch in a house. that said, you may not be able to draw the maximum output capacity from a single receptacle. note that a common transfer switch inlet is rated at 30A (split phase), with the next size up a much less common 50A (again, split phase). note also that the next bigger Generac unit, 10KW, has a 50A receptacle on it, so in that case you can pull the entire generator capacity from one receptacle (50A x 240Vac = 12KW). Quoted:
So if I were to hook this generator up to my panel via the 240 plug, I would only be able to use half the surge capacity the generator can produce...correct? the "surge capacity" rating is like jello, difficult to actually pin down. for loads such as motors, starting current may exceed running current by a factor of 2 or 3 or 4 or 5 or 6 –– depending on what type of motor it is and what the load on the motor is. the surge capacity of a generator is a combination of the engine torque, flywheel weight, alternator rotational inertia, and the ability of the circuit breaker to hold the motor start load. the latter is the part i think you are missing here. a typical 30A breaker will hold 100A for a few tenths of a second, 50A for a few seconds, and 40A for tens of seconds. there are also "motor start" rated breakers which will hold higher inrush currents even longer. for this reason, the surge capacity of the generator is realizable despite the breaker rating. just remember that the surge capacity is finite and fleeting –– that capacity lasts only a few seconds and again is highly dependent on the rotational inertia of the moving parts. (this is also why inverter-type generators are generally much worse at starting motor loads, compared to direct-coupled generators such as the type you have noted above). summary: 1) if you want full generator output, find one with a receptacle that supports the full output. 2) surge capacity, for most well behaved motor loads, will in most cases exceed the breaker rating but this is typically not an issue. my PTO generator is rated at 50A 240Vac split phase, but my well pump is 220 feet down and hangs off a 30A breaker in the circuit panel. startup current for the first quarter second or so is a measured 60A. neither the 30A breaker in the circuit panel nor the 50A breaker on the generator is the least bit troubled by the startup current, and the combination of the tractor engine and PTO-driven alternator hardly notice the high, but very brief, startup load. see http://www.ar15.com/forums/t_10_17/644329_.html&page=2 ar-jedi Best explanation I've seen! Thanks, AR-J! I think I got it now. |