if my generator can output 30 amps 240, i can take the 240 and split it to
120 and output a total of 60 amps, 30 each leg, now how much current is flowing on the neutral? i have a 10/3 stranded cable about 90 feet long, i dont know if it will be 60 or 30. my service entrance cable all three look the same size wire so i guessing it will be 30. thanks tony
The current on the neutral would be the difference between current on one leg and current on another leg, if they share a neutral. Never more than current on one of the legs.
I am attaching a AWG table. I would suggest brushing up on electricity a little bit before starting any ambitious projects. You may save a life.
AWG Wire Table for BARE COPPER Wire Compiled by a program written by Fr. Tom McGahee
Compiled by Fr. Tom McGahee tom snipped-for-privacy@sigmais.com Permission granted to copy freely so long as credit line above is included
AWG = American Wire Gauge size Dia-mils = Diameter in mils (1 mil = .001 inch) TPI = Turns Per Inch (Ignoring thickness of unknown insulation) Dia-mm = Diameter in millimeters (For comparison with non-USA coilers) Circ-mils = Circular Mils. (circular mils = diameter in mils squared) Ohms/Kft = Ohms Per 1,000 Feet Ft/Ohm = Feet Per Ohm Ft/Lb = Feet Per Pound Ohms/Lb = Ohms Per Pound Lb/Kft = Pounds Per 1,000 Feet NormAmps = Normal Average Amp Capacity based on 500 circular mils per Amp MaxAmps = Maximum recommended Average Amp Capacity in Open Air based on 438.489 circular mils per Amp
Actual Amp capacity of a wire depends on form factor and method of cooling! MaxAmps assumes free flow of air around wire. Do NOT exceed this maximum without cooling! Wire wrapped in a coil or without any form of cooling may over-heat at MaxAmps! Many factors govern the ACTUAL Max Amps you can pass through a wire continuously. Be careful!
thanks for the info, we just went from a 3500 generator, that ran constant for 1 week then 1.5 weeks,because of 2 hurricanes, i knew that 10 gauge stranded could handle the amps of the 3500 but the new 7550 puts out 62 amps so i wanted verification that the neutral would not be overloaded. thanks tony
You don't necessarily rate the wire size by what current the generator can source, but how much power the loads draw. Usually we treat them one and the same, but it's an important distinction. If you don't change your loads, but upgrade your generator, then upgrading the wiring isn't a necessity.
| > The current on the neutral would be the difference between current on | > one leg and current on another leg, if they share a neutral. Never | > more than current on one of the legs. | >
| >> i have a 10/3 stranded cable about 90 feet long, i | >> dont know if it will be 60 or 30. my service entrance cable all three | >> look | >> the same size wire so i guessing it will be 30. thanks tony | >
| > I am attaching a AWG table. I would suggest brushing up on electricity | > a little bit before starting any ambitious projects. You may save a | > life. | >
| > AWG Wire Table for BARE COPPER Wire Compiled by a program written by Fr. | > Tom McGahee | >
| > Compiled by Fr. Tom McGahee tom snipped-for-privacy@sigmais.com | > Permission granted to copy freely so long as credit line above is included | >
| > AWG = American Wire Gauge size | > Dia-mils = Diameter in mils (1 mil = .001 inch) | > TPI = Turns Per Inch (Ignoring thickness of unknown insulation) | > Dia-mm = Diameter in millimeters (For comparison with non-USA coilers) | > Circ-mils = Circular Mils. (circular mils = diameter in mils squared) | > Ohms/Kft = Ohms Per 1,000 Feet | > Ft/Ohm = Feet Per Ohm | > Ft/Lb = Feet Per Pound | > Ohms/Lb = Ohms Per Pound | > Lb/Kft = Pounds Per 1,000 Feet | > NormAmps = Normal Average Amp Capacity based on 500 circular mils per Amp | > MaxAmps = Maximum recommended Average Amp Capacity in Open Air based on | > 438.489 circular mils per Amp | >
| > Actual Amp capacity of a wire depends on form factor and method of | > cooling! | > MaxAmps assumes free flow of air around wire. Do NOT exceed this maximum | > without cooling! | > Wire wrapped in a coil or without any form of cooling may over-heat at | > MaxAmps! | > Many factors govern the ACTUAL Max Amps you can pass through a wire | > continuously. Be careful! | >
I know this isnt a TRICK question. But, with both 110 lines loaded the same, and resistive, there will be no current in the neutral, even though power is being delivered to the two loads.
If it's setup as a center-tapped neutral like normal, and you are drawing an even 30 amps on each 120V leg at the end of the cable run, the current on the neutral is zero. They balance each other out. Worst case is 30 amps on the neutral if one hot leg is unloaded.
But you do not want that neutral to go open under any circumstances, because very bad things happen when the loads get unbalanced - the voltages start swinging.
Some old generators can be jumpered to provide true 60A 120V with the windings in parallel. But then you can't use that 10/3 cable, more like 4-3 - and voltage drop is a more serious problem...
| Tony | | I know this isnt a TRICK question. But, with both 110 lines loaded the | same, and resistive, there will be no current in the neutral, even though | power is being delivered to the two loads. | | Jerry
Alright, I had to think about this one, and for the sake of the unknowing, it should be explained. If a 220V load is being used, then current flows from leg to leg, not leg to neutral, so the neutral carries no current, as noted by older 220V circuits not using the neutral or ground, just the two legs. If both legs are running 110V loads, however, then when one leg is at maximum positive voltage, current will also be at a maximum through that leg. However, the other leg will also be at maximum negative voltage, so current will also be at a maximum on that leg too. If the loads are equally balanced, then the neutral line that is shared between the two (not the neutral for each leg) will have no current, as the current will be going from leg to leg and not through the common neutral. However, since current is rarely balanced between legs, only the difference between the currents will pass through the neutral, and no more than the maximum current of one leg (say, if one leg is maxxed out and the other one with no load) then the common neutral will carry no more than the load from the loaded leg. It can get fancy with inductive loads, where currents and voltage do not always line up evenly, but I'm too rusty on this one to make any more statements.
I'm not sure what sort of application this table deals with ampacity wise, but it certainly aint normal wiring methods, or else I'm reading it wrong. 12awg at 14.something amps? Better to consult your NEC tables. The other data is interesting but in light of the 'max amps' data might be questionable also.
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