Posted: 6/2/2012 2:03:19 PM EDT
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I have a well pump which can be wired for either 115 or 230. Right now it running at 230 with both hots on their own double breaker (with a trip handle). When they say it draws 7.4 amps do they mean on BOTH hots or per each hot?
Can I put both the hot wires on the same breaker if I am running 230? The table below is from the manual. VoltsAmpsRec Breaker Size 115 14.8 20 230 7.4 15 |
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No, each hot will supply approximately half the current, and no you can not put both hots on the same breaker, they have to be on separate phases A double pole breaker is on different phases. It's unsafe to put them on separate breakers. On a double pole, a short or overload in either line will trip both lines. |
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No, each hot will supply approximately half the current, and no you can not put both hots on the same breaker, they have to be on separate phases Yes, which is why the 120v wiring requires 14.8 amps, and the 230 only requires 7.4 amps. And you need two hots for 230v, from different phases. Using one double-pole breaker is required, as having half a breaker trip, for whatever reason, is bad. |
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You're not an electrician, are you?
Kirchoff's amperage law states the current in a circuit is the same in the whole circuit. So, if you measured the current, (you can use a clamp on meter to do this), when the switch is on, the current will be 7.4A measured on either leg. Now, it' not 7.4A on each leg, for a total of 14.8, but just 7.4. Think of it in watts V*A. 240V*7.4A od 1776 watts of power to turn the motor. |
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No, each hot will supply approximately half the current, and no you can not put both hots on the same breaker, they have to be on separate phases Yes, which is why the 120v wiring requires 14.8 amps, and the 230 only requires 7.4 amps. And you need two hots for 230v, from different phases. Using one double-pole breaker is required, as having half a breaker trip, for whatever reason, is bad. Yup. It will run off of 110, but it is twice as efficient at 220. |
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You're not an electrician, are you? Kirchoff's amperage law states the current in a circuit is the same in the whole circuit. So, if you measured the current, (you can use a clamp on meter to do this), when the switch is on, the current will be 7.4A measured on either leg. Now, it' not 7.4A on each leg, for a total of 14.8, but just 7.4. Think of it in watts V*A. 240V*7.4A od 1776 watts of power to turn the motor. Each leg does draw 7.4 amps, but only half the time. 
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You're not an electrician, are you? Kirchoff's amperage law states the current in a circuit is the same in the whole circuit. So, if you measured the current, (you can use a clamp on meter to do this), when the switch is on, the current will be 7.4A measured on either leg. Now, it' not 7.4A on each leg, for a total of 14.8, but just 7.4. Think of it in watts V*A. 240V*7.4A od 1776 watts of power to turn the motor. Each leg does draw 7.4 amps, but only half the time. Yer talking about that AC shit ain't ya? 
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You're not an electrician, are you? Kirchoff's amperage law states the current in a circuit is the same in the whole circuit. So, if you measured the current, (you can use a clamp on meter to do this), when the switch is on, the current will be 7.4A measured on either leg. Now, it' not 7.4A on each leg, for a total of 14.8, but just 7.4. Think of it in watts V*A. 240V*7.4A od 1776 watts of power to turn the motor. Each leg does draw 7.4 amps, but only half the time. Yer talking about that AC shit ain't ya? Naa, I leave that to the HVAC guys. 
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You're not an electrician, are you? Kirchoff's amperage law states the current in a circuit is the same in the whole circuit. So, if you measured the current, (you can use a clamp on meter to do this), when the switch is on, the current will be 7.4A measured on either leg. Now, it' not 7.4A on each leg, for a total of 14.8, but just 7.4. Think of it in watts V*A. 240V*7.4A od 1776 watts of power to turn the motor. Each leg does draw 7.4 amps, but only half the time. winner |
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Here is the problem, I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel.
So if I get two 15amp double pole breakers (one for each pump) I should be good? 15+15+15 = 45 |
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Quoted: Here is the problem, I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel. From what I got reading the replies it seems I am short 15amps on the subpanel. You have a 30 amp sub. It can feed 30 amps 230 or 30 amps 115 (at the consumer). Each leg is 115 volts measured to ground, it is 230 volts when measured leg to leg (the legs are180 degrees out of phase to each other, hence the 230 volts). The 15 amp tied breakers are 15 amps at 230 volts, you can run two 15 amp 115 circuits for a total of 30 amps. You will need to upgrade or remove the 115 outlet circuits to run the other pump off this sub. You listed no specifics on the wire length and gauge leading to the sub panel. |
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Quoted: Here is the problem,I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel. So if I get two 15amp double pole breakers (one for each pump) I should be good? 15+15+15 = 45 Really? and you are running 220V motors from this sub panal? You should just hire an electrican. |
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I mean 60 amps at 115v, 30 amps at 230v
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Here is the problem,I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel. So if I get two 15amp double pole breakers (one for each pump) I should be good? 15+15+15 = 45 Really? and you are running 220V motors from this sub panal? You should just hire an electrican. |
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The wires and subpanel were installed when the house was built, I dont have any plans to mess with them. The subpanel is right where the pumps are so it would simply be a matter of running wires down to a existing box on the side of the house (about a foot), installing a double pole switch and adding a flex conduit and wires to the pump.
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Here is the problem, I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel. From what I got reading the replies it seems I am short 15amps on the subpanel. You have a 30 amp sub. It can feed 30 amps 230 or 30 amps 115 (at the consumer). Each leg is 115 volts measured to ground, it is 230 volts when measured leg to leg (the legs are180 degrees out of phase to each other, hence the 230 volts). The 15 amp tied breakers are 15 amps at 230 volts, you can run two 15 amp 115 circuits for a total of 30 amps. You will need to upgrade or remove the 115 outlet circuits to run the other pump off this sub. You listed no specifics on the wire length and gauge leading to the sub panel. |
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Quoted: are we talking peak voltage, peak to peak voltage or rms voltage? 110/115/120....who cares? The sub panel SHOULD deliver 120, you should be seeing 115 at the end of the circuit, the consumer should see 110 volts. All RMS, this is sine wave so most DVMs will indicate correct, RMS voltage. |
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No, each hot will supply approximately half the current, and no you can not put both hots on the same breaker, they have to be on separate phases Yes, which is why the 120v wiring requires 14.8 amps, and the 230 only requires 7.4 amps. And you need two hots for 230v, from different phases. Using one double-pole breaker is required, as having half a breaker trip, for whatever reason, is bad. Yup. It will run off of 110, but it is twice as efficient at 220. Not true. It is exactly as efficient either way, with a small line loss increase at the lower voltage. That is why the amperage is exactly doubled from 7.4 to 14.8 when switching to the lower voltage. Exact same power usage. |
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"you have a 30 amp sub. It can feed 30 amps 230 or 30 amps 115 (at the consumer)."
Does he mean "60 amps at 115v, 30 amps at 230v", it is fed by two 30 amp breakers? Right now I am getting this: when you up the voltage (230 vs 115) you divide the amps available by two. If I cant figure this out I am going to call someone but I would at least like to be able to have an understanding of what is going on and make sure I am not being ripped off. Quoted:
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Here is the problem,I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel. So if I get two 15amp double pole breakers (one for each pump) I should be good? 15+15+15 = 45 Really? and you are running 220V motors from this sub panal? You should just hire an electrican. |
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"you have a 30 amp sub. It can feed 30 amps 230 or 30 amps 115 (at the consumer)." Does he mean "60 amps at 115v, 30 amps at 230v", it is fed by two 30 amp breakers? Right now I am getting this: when you up the voltage (230 vs 115) you divide the amps available by two. If I cant figure this out I am going to call someone but I would at least like to be able to have an understanding of what is going on and make sure I am not being ripped off. Quoted:
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Here is the problem,I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel. So if I get two 15amp double pole breakers (one for each pump) I should be good? 15+15+15 = 45 Really? and you are running 220V motors from this sub panal? You should just hire an electrican. Power is measured in watts. You can either increase the voltage and lower the amperage, or vise versa. These motors need a certain ammount of power to operate. A lot of motors that run on 240 only may be just a little cheaper to purchase because the of less copper used to mfg (windings) |
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Here is the problem,I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel. So if I get two 15amp double pole breakers (one for each pump) I should be good? 15+15+15 = 45 Really? and you are running 220V motors from this sub panal? You should just hire an electrican. But not one from ARFCOM GD
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Quoted: "you have a 30 amp sub. It can feed 30 amps 230 or 30 amps 115 (at the consumer)." Does he mean "60 amps at 115v, 30 amps at 230v", it is fed by two 30 amp breakers? Right now I am getting this: when you up the voltage (230 vs 115) you divide the amps available by two. If I cant figure this out I am going to call someone but I would at least like to be able to have an understanding of what is going on and make sure I am not being ripped off. Quoted: Quoted: Here is the problem,I have a subpanel with 60 amps capacity (it is fed by two 30 amp breakers on the main panel). Right now it has two 15amp breakers for one pump and another 15amp breaker for a tool shed and outdoor lighting, total here 45 amps. I have another pump that is exactly the same that is running on 115v wired from the main panel. I want to switch the motor to 230v and run it on the subpanel. So if I get two 15amp double pole breakers (one for each pump) I should be good? 15+15+15 = 45 Really? and you are running 220V motors from this sub panal? You should just hire an electrican. The 30 amp 230/240 volt sub panel has two legs of 120 volts nominal that are protected by a pair of 30 amp breakers. Each leg is 180 degrees out of phase to the other, this means the voltage between the two is 240 or double their voltage with respect to neutral (or ground, ideally). This also means you cannot add these legs together to get 60 amperes (double) to drive a single 120 volt load. |
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This is an AC circuit. The current actually moves back and forth. Phase to neutral will be 120V potential difference. Phase to phase is 240V. The motor will pull a certain amount of Watts, which is Volts * Amps. So if you double the Volts, you will half the Amps. So you see, you can't have "half the amps" on each leg. The amps on one leg will be +7.4 when the amps on the other leg will be -7.4. ETA: So you see, you can't put them on the same breaker. They need to be on opposing phases or you'll get no current flow. ETA2: The amp ratings on panels is PER PHASE. So if you have a 30A panel, you can put 30 amps on each side, so 60A on 120V breakers if you split them over both phases, or 30A in 240V breakers. |
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This is an AC circuit. The current actually moves back and forth. Phase to neutral will be 120V potential difference. Phase to phase is 240V. The motor will pull a certain amount of Watts, which is Volts * Amps. So if you double the Volts, you will half the Amps. So you see, you can't have "half the amps" on each leg. The amps on one leg will be +7.4 when the amps on the other leg will be -7.4. ETA: So you see, you can't put them on the same breaker. They need to be on opposing phases or you'll get no current flow. Actually he can put them on the same breaker if it is a double pole. |
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Quoted: Quoted: This is an AC circuit. The current actually moves back and forth. Phase to neutral will be 120V potential difference. Phase to phase is 240V. The motor will pull a certain amount of Watts, which is Volts * Amps. So if you double the Volts, you will half the Amps. So you see, you can't have "half the amps" on each leg. The amps on one leg will be +7.4 when the amps on the other leg will be -7.4. ETA: So you see, you can't put them on the same breaker. They need to be on opposing phases or you'll get no current flow. Actually he can put them on the same breaker if it is a double pole. I took it as him asking if he can put in on a single phase breaker. |
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This is an AC circuit. The current actually moves back and forth. Phase to neutral will be 120V potential difference. Phase to phase is 240V. The motor will pull a certain amount of Watts, which is Volts * Amps. So if you double the Volts, you will half the Amps. So you see, you can't have "half the amps" on each leg. The amps on one leg will be +7.4 when the amps on the other leg will be -7.4. ETA: So you see, you can't put them on the same breaker. They need to be on opposing phases or you'll get no current flow. Actually he can put them on the same breaker if it is a double pole. I took it as him asking if he can put in on a single phase breaker. Oh. Then it would of course be a negatory. 
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Two lines(or legs) not two phases. http://i45.photobucket.com/albums/f52/GlocksareGood/split20phase20small.gif I think the correct term would be split phase when single phase is stepped down with a center tapped transformer. |
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Ok, got it now! 60 amps at 115v = 30 amps at 220v. This is what I was trying to wrap my head around!
"ETA2: The amp ratings on panels is PER PHASE. So if you have a 30A panel, you can put 30 amps on each side, so 60A on 120V breakers if you split them over both phases, or 30A in 240V breakers." |
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Quoted: Two lines(or legs) not two phases. http://i45.photobucket.com/albums/f52/GlocksareGood/split20phase20small.gif Touche. |
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The next question I have is this:
I know all the breakers in my main panel add up to more that the service since they are not always at 100% load. Does this apply in sub panels as well? I mean each pump has a max startup draw 7.4 amps (per the manual) at 220v on a dedicated circuit. This would be about 15 amps at 115 each. 15+15 = 30 would mean I would still have enough for the 15amp 115v run to the shed and a little margin for error. Am I thinking right here? |
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Two lines(or legs) not two phases. http://i45.photobucket.com/albums/f52/GlocksareGood/split20phase20small.gif I think the correct term would be split phase when single phase is stepped down with a center tapped transformer. But the wires are called lines. Line A or 1 and Line 2 or B |
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Two lines(or legs) not two phases. http://i45.photobucket.com/albums/f52/GlocksareGood/split20phase20small.gif I think the correct term would be split phase when single phase is stepped down with a center tapped transformer. But the wires are called lines. Line A or 1 and Line 2 or B No argument there. 
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The next question I have is this: I know all the breakers in my main panel add up to more that the service since they are not always at 100% load. Does this apply in sub panels as well? I mean each pump has a max startup draw 7.4 amps (per the manual) at 220v on a dedicated circuit. This would be about 15 amps at 115 each. 15+15 = 30 would mean I would still have enough for the 15amp 115v run to the shed and a little margin for error. Am I thinking right here? It's rated in terms of Load, not in terms of how much the breakers add up to. This is why your main service panel has breakers that add up to more than what it is rated for. There are ways to calculate what your load is to determine what size service panel you need. Stuff like ovens, motors, water heaters, heating are all calculated differently as prescribed per the NEC. If you run your pump on 120V(not 110 or 115 or whatever), it's going to draw 15 amps on one line. You are only going to use one line so no need to add up 15+15. If the only things on your sub panel are the pump and the 15amp breaker feeding your shed, you'll be alright. |
This is how a panel is laid out(most of them anyways) You have two lines coming in. Rows of breakers alternate between line A and B. Therefore, position 1 and 2 are both joined on Line A, position 3 and 4 are on Line B etc etc. If you are going to plug your pump on 120V, be sure to put both the breaker feeding your shed and the breaker feeding your pump on the same side of the panel to distribute the load on both lines(15A shed breaker on say position 1 and 20A pump breaker on position 2). If you run your pump on 240V, you'll have a double 15A breaker on one side(positions 1 and 3) and the shed breaker on the other(position 2 or 4, doesn't matter) |
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Thanks!
I am going to run my pumps at 230V, I said 15amps at 115 just to calculate. I would have two pumps with a max startup draw 7.4 amps at 230v and one 15amp 115v circuit to the shed. Using your chart above how would I do this? 1 and 3 for one pump, 2 and 4 for the other and the shed on either side? Quoted:
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The next question I have is this: I know all the breakers in my main panel add up to more that the service since they are not always at 100% load. Does this apply in sub panels as well? I mean each pump has a max startup draw 7.4 amps (per the manual) at 230v on a dedicated circuit. This would be about 15 amps at 115 each. 15+15 = 30 would mean I would still have enough for the 15amp 115v run to the shed and a little margin for error. Am I thinking right here? It's rated in terms of Load, not in terms of how much the breakers add up to. This is why your main service panel has breakers that add up to more than what it is rated for. There are ways to calculate what your load is to determine what size service panel you need. Stuff like ovens, motors, water heaters, heating are all calculated differently as prescribed per the NEC. If you run your pump on 120V(not 110 or 115 or whatever), it's going to draw 15 amps on one line. You are only going to use one line so no need to add up 15+15. If the only things on your sub panel are the pump and the 15amp breaker feeding your shed, you'll be alright. |