Thanks! You've been super helpful. The installation cost I'm looking at is around $5K. Yikes! I'm not trying to nickel and dime my job but I thought I could save $$ on the materials by using a smaller diameter wire. But in the long run, it doesn't make sense to spend all that money just to charge at 24A. I think 32A is the minimum I should go with so I may be forced to use 6 gauge wire. I really appreciate you educating me!
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Tesla Wall Charging
- Thread starter Taikos
- Start date
Yup. So much of it is labor... as long as you don't cross the threshold that you need a major panel or service upgrade.
Be sure to get multiple quotes too... can be highly variable.
Trying to enforce only 3% voltage drop is really tight, and shouldn't be necessary for this. You can play around with those voltage drop calculators in both directions. In one direction, you can set the allowed % drop and then let it show you what gauge meets it. I would want to look at it the other way, where you can set the wire gauge, and then let it show you what the % drop would be. See what that is for 8 or 6 gauge and see how much voltage drop it shows for either case.
For lower amp draw, it won't pull the voltage down as hard.
For lower amp draw, it won't pull the voltage down as hard.
If I entered my calculations correctly, the voltage drop using 8-AWG charging at 32 amp = 4.02%. If using 6-AWG at 32 amps = 2.57% drop. I'm not very technical but I'm assuming that you want less drop as possible, right?
I got 2 installation quotes and they came in very close. I didn't even mention that we also have to hire an engineer to design the system and apply for the permitting. We are dealing with a 56-unit condo building with basement parking. It's crazy expensive compared to a residential home.
OK, so here's the deal. If you used 8 gauge, you'd be wasting 4.02 - 2.57 = 1.45% of energy due to extra losses along the 200' compared to 6 gauge.
If you drive 10,000 miles a year, at a normal Model 3 usage of .255 kWh per mile = 2,550 kWh of energy used per year for your car. OK, hike that up by 1.1 since there are normal energy conversion losses, so 2,805 kWh per year. Now you'll be charging at night in Hawaii - do you have off peak rates? The rate chart I was able to find for Oahu shows around $.50/kWh for electricity, no peak rates. So 2,805 x .5 x .0145 losses over 200' for 8 gauge = $20/yr in extra costs for using 8 gauge rather than 6 gauge.
In California, bulk 8 gauge at Home Depot costs .54/ft, 6 gauge at .85/ft, so the price delta for 6 gauge over 8 gauge is .31x200 = $62. I don't know what the electrician would charge though.
So in three years, you'd break even going with 6 gauge, and it would be cheaper after that.
BTW, seems that you could use 1/2" EMT conduit for both 6 and 8 gauge (with a 10 gauge ground).
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Well, not necessarily. It's kind of a question of does it matter or not. As far as the car, it's mostly not going to care. The actual voltage level can be really broad. The onboard charger will just detect and use what is there, from around 100-ish to 250-ish volts. The thing it does look for, though, is that it measures the voltage at the beginning, without load, and then compares when it has ramped up the current. If there is a very large drop, then it will back off the current, because it thinks there might be a loose, resistive connection somewhere in the circuit. But that can be around 4 or 5 or 6% before that triggers, so it doesn't have to be too tight.
Huh. I had never seen numbers run for this that showed a reasonable payoff time. Usually if it's just a one or two percent energy loss, most people blow it off as not being worth it.
Thanks for your very technical assessment. I thought I would be saving a lot more money if I went with 8 gauge but it doesn't look like it. Also as you pointed out the conduit would be the same size too so no savings there. But I will bring all of this up with my electrical engineer and I'm confident we will make the best purchase decision. Thanks! You've been so helpful and I appreciate it!
Eric33432
Member
If you are in a condo with 50 units, you might have 120/208 volts. This is more likely if it is a high rise building, less likely if it is a low rise building. If you have 208 volts, 32 amp charging will give you ~6.6 kW charging instead of 7.7 kW charging. Still enough unless you are perhaps an Uber driver..
You would not want a 5% voltage drop on a circuit that feeds, say, a sub panel in a residence with lights, appliances, etc. But for a branch circuit just being used by the car, it really does not care.
According to the Southwire calculator, here are the voltage drops 200 feet of wire for #8, #6, and #4 wire with 32 amps of current at the different voltages:
#8 240 volts 3.68%
#8 208 volts 4.25%
#6 240 volts 2.36%
#6 208 volts 2.72%
#4 240 volts 1.53%
#4 208 volts 1.77%
Still, 48 amps on #6 is only 3.53% at 240 volts and 4.08% at 208 volts
You could go with #8 but for the difference in cost, if it was me, I would go with #6. I would have no problem running that at 48 amps charging.
Or you could always use upsized AL wire, transitioning to CU for a few feet to connect to the Wall Connector. This would be easy if you need to install a safety switch next to the Wall Connector. The cost difference would be significantly less but will require larger conduit. #4 AL is 3.66% loss at 240 volts and 4.22% loss at 208 volts (48 amp charging / 200 feet run). AL wire is OK if properly installed and most utility wiring is AL.
Another thing you can do is set the Wall Connector up with a 60 amp breaker for 48 amp charging, but dial the car down to whatever it needs to charge that night. Then you would always have 48 amps available in case you had some reason to need to charge the car more quickly like a trip that comes up suddenly.
Wow, electricity is expensive in HI.
What did you decide?
You would not want a 5% voltage drop on a circuit that feeds, say, a sub panel in a residence with lights, appliances, etc. But for a branch circuit just being used by the car, it really does not care.
According to the Southwire calculator, here are the voltage drops 200 feet of wire for #8, #6, and #4 wire with 32 amps of current at the different voltages:
#8 240 volts 3.68%
#8 208 volts 4.25%
#6 240 volts 2.36%
#6 208 volts 2.72%
#4 240 volts 1.53%
#4 208 volts 1.77%
Still, 48 amps on #6 is only 3.53% at 240 volts and 4.08% at 208 volts
You could go with #8 but for the difference in cost, if it was me, I would go with #6. I would have no problem running that at 48 amps charging.
Or you could always use upsized AL wire, transitioning to CU for a few feet to connect to the Wall Connector. This would be easy if you need to install a safety switch next to the Wall Connector. The cost difference would be significantly less but will require larger conduit. #4 AL is 3.66% loss at 240 volts and 4.22% loss at 208 volts (48 amp charging / 200 feet run). AL wire is OK if properly installed and most utility wiring is AL.
Another thing you can do is set the Wall Connector up with a 60 amp breaker for 48 amp charging, but dial the car down to whatever it needs to charge that night. Then you would always have 48 amps available in case you had some reason to need to charge the car more quickly like a trip that comes up suddenly.
Wow, electricity is expensive in HI.
What did you decide?
MikeRTX
Member
OP, FWIW I run a $240 Mobile Connector on a 30A breaker and get a solid 25 miles per hour of charging for my Model 3 SR at 24A. Sounds like you're going to spend a ton of money to get maybe 5 more miles/hour. 
Eric33432
Member
OP, I agree with MikeRTX that most people really don't need the full 48 amp charging.
However, I think when running 200 feet of conduit you might find the cost is not too much different for a 30 amp circuit compared with a 60 amp circuit as the labor and profit is probably 3/4th or more of the cost.
But I just ran this circuit on Mike Holt's Electrical Toolbox app for continuous loads of 48 amps and 40 amps and it says you can run a 48 amp load on #6 CU or a #4 AL circuit about 350 feet and a load of 40 amps on #8 CU or #6 AL about 250 feet without suffering unacceptable voltage drop.
Going down to a 32 amp load requires #8 CU or AL and 24 amps requires #10 CU both of which can run more than 200 feet according to the app.
Note that it also says even # 8 CU should be installed in 3/4" conduit as well that #6 CU or AL should be installed in 3/4" conduit and #4 AL should be installed in 1" conduit. Only when getting down to #10 does the app recommend 1/2" conduit.
As an electrical engineer and with my past dealings with electricians, I think it will serve you best if you are as educated about this as possible since this will be an expensive undertaking, so you know what should be done to do the job. But I would not tell them how to do their job, most will not take kindly to that and won't really listen to a layman anyway. Just be informed when you speak with them.
Here is the 48 amp engineering details from that app:
Circuit Type: Branch Circuit
Circuit Protection Size: 60 Amperes
Continuous Load: 48 Amperes
2. Conductor Size: 6 AWG, rated 65A at 75°C
3. Equipment Grounding Conductor: 10 AWG
4.Maximum Circuit Length: 355 Feet
5. Raceway Size:¾ Inch
6. Maximum Circuit Continuous Load:48 Amperes
7. Maximum Circuit VA:11,520VA
2. Conductor Size: 4 AWG, rated 65A at 75°C
3. Equipment Grounding Conductor:8 AWG
4. Maximum Circuit Length: 344 Feet
5. Raceway Size: 1 Inch
6. Maximum Circuit Continuous Load: 48 Amperes
7. Maximum Circuit VA: 11,520 VA
2. Conductor Size (up to six conductor bundle) [110.14(C)(1)(a)(3)/(b)(1), 210.19(A)(1)(a), 240.4, 310.15, and Table 310.15(B)(16)]
3. Equipment Grounding Conductor Size [250.122]
Sized to the 60A rating of the protection device.
4. Maximum Circuit Length [110.3(B)]
Length limited to ensures the voltage is within 90% of the rated voltage.
5. Raceway Size [Chapter 9, Table 1]
Based on a raceway at 40% fill, with an equipment grounding conductor.
6. Maximum Continuous Load [210.19(A)(1)(a) and 210.20(A)]
Maximum continuous load not to exceed 80% of the circuit protection and conductor ampacity.
60A x 80% = 48A
7.Maximum Circuit Continuous VA: Circuit Voltage x Circuit Amperes 240V x 48.00A x 1 = 11,520 VA
a. The circuit length in the app uses the following formula:
i. Single‑Phase: D = (Cmil × VD)/(2 × K × I)
ii. Three‑Phase: D = (Cmil × VD)/(1.732 × K × I)
b. Distance (D): The distance of the circuit or the length of the circuit conductors.
c. Circular Mils (Cmil): The circular mil area of the circuit conductor as listed in the NEC Chapter 9, Table 8.
d. Voltage Drop (VD): The voltage drop of the branch circuit is based on the 110.3(B) of the NEC, which requires that the operating voltage at utilization equipment to be in accordance with manufacturer instructions. Manufactures typically adopt ANSI C84.1, which specifies that the voltage at utilization equipment must be within 90 percent of the nominal system voltage. The app assumes a 3 percent feeder voltage drop, resulting in a 7 percent branch circuit voltage drop.
e. Constant (K): A value of 12.90 ohms is used for copper and 21.20 ohms for aluminum. These values represents the resistance for a 1,000 circular mils conductor that’s 1,000 ft long, at an operating temperature of 75ºC.
f. Current (I): The current of the circuit is the actual load at 100 percent. According to the NEC, conductors are sized to 125 percent of the load continuous loads, electric space heating, motors, electric vehicles, etc. However, this 125 percent factor has nothing to do with determining the distance (length) of the circuit.
2. Conductor Sizing (Commercial):
a. Conductors are sized based on the following factors:
i. Insulation - THHN, THWN, and THWN-2 (90°C).
ii. Terminals – Conductors are sized to 75°C terminals [110.14(C)(1)(a)(3) and 110.14(C)(1)(b)(2).
iii. Load – The load is considered continuous and a 125% continuous load factor is applied [210.19(A)(1)].
iv. Neutral – Where a neutral is used (slash rated circuits), the neutral is considered current carrying (50 percent or more of the load is considered nonlinear) [310.15].
v. Ampacity Adjustment – For three-phase four-wire circuits, the ampacity of the conductors are adjusted by a multiplier of 80 percent [310.15].
3. Conductor Sizing (Residential):
a. Conductors are sized based on the following factors:
i. Insulation - THHN, THWN, and THWN-2 (90°C)
ii. Terminals – Conductors are sized to 75°C terminals [110.14(C)(1)(a)(3) and 110.14(C)(1)(b)(2), except Type NM Cable, which is sized to 60°C [334.80].
iii. Load – The load is considered noncontinuous.
iv. Neutral – The neutral conductor is not considered a current carrying conductor [310.15].
v. Ampacity Adjustment – There is no ampacity adjustment, since there are not four or more current carrying conductors.
4. Raceway Sizing:
a. Raceways are sized to provide a little more space than the NEC minimum requirement. This is accomplished by sizing all circuit conductors, including the neutral and equipment grounding to the same size as the circuit conductors. The conductor insulation is based on THHN, THWN, and THWN-2 and the raceway is considered Schedule 40 PVC.
i. Single-phase two-wire circuits are sized to three full size circuit conductors.
ii. Single-phase three-wire circuits are sized to four full size circuit conductors.
iii. Three-phase three-wire circuits are sized to four full size circuit conductors.
iv. Three-phase four-wire circuits are sized to five full size circuit conductors.
And here is the 40 amp engineering from the app:
Circuit Type: Branch Circuit
Circuit Protection Size: 50 Amperes
Continuous Load: 40 Amperes
2. Conductor Size: 8 AWG, rated 50A at 75°C
3. Equipment Grounding Conductor: 10 AWG
4.Maximum Circuit Length: 268 Feet
5. Raceway Size:¾ Inch
6. Maximum Circuit Continuous Load:40 Amperes
7. Maximum Circuit VA:9,600VA
2. Conductor Size: 6 AWG, rated 50A at 75°C
3. Equipment Grounding Conductor:8 AWG
4. Maximum Circuit Length: 259 Feet
5. Raceway Size: ¾ Inch
6. Maximum Circuit Continuous Load: 40 Amperes
7. Maximum Circuit VA: 9,600 VA
2. Conductor Size (up to six conductor bundle) [110.14(C)(1)(a)(3)/(b)(1), 210.19(A)(1)(a), 240.4, 310.15, and Table 310.15(B)(16)]
3. Equipment Grounding Conductor Size [250.122]
Sized to the 50A rating of the protection device.
4. Maximum Circuit Length [110.3(B)]
Length limited to ensures the voltage is within 90% of the rated voltage.
5. Raceway Size [Chapter 9, Table 1]
Based on a raceway at 40% fill, with an equipment grounding conductor.
6. Maximum Continuous Load [210.19(A)(1)(a) and 210.20(A)]
Maximum continuous load not to exceed 80% of the circuit protection and conductor ampacity.
50A x 80% = 40A
7.Maximum Circuit Continuous VA: Circuit Voltage x Circuit Amperes 240V x 40.00A x 1 = 9,600 VA
a. The circuit length in the app uses the following formula:
i. Single‑Phase: D = (Cmil × VD)/(2 × K × I)
ii. Three‑Phase: D = (Cmil × VD)/(1.732 × K × I)
b. Distance (D): The distance of the circuit or the length of the circuit conductors.
c. Circular Mils (Cmil): The circular mil area of the circuit conductor as listed in the NEC Chapter 9, Table 8.
d. Voltage Drop (VD): The voltage drop of the branch circuit is based on the 110.3(B) of the NEC, which requires that the operating voltage at utilization equipment to be in accordance with manufacturer instructions. Manufactures typically adopt ANSI C84.1, which specifies that the voltage at utilization equipment must be within 90 percent of the nominal system voltage. The app assumes a 3 percent feeder voltage drop, resulting in a 7 percent branch circuit voltage drop.
e. Constant (K): A value of 12.90 ohms is used for copper and 21.20 ohms for aluminum. These values represents the resistance for a 1,000 circular mils conductor that’s 1,000 ft long, at an operating temperature of 75ºC.
f. Current (I): The current of the circuit is the actual load at 100 percent. According to the NEC, conductors are sized to 125 percent of the load continuous loads, electric space heating, motors, electric vehicles, etc. However, this 125 percent factor has nothing to do with determining the distance (length) of the circuit.
2. Conductor Sizing (Commercial):
a. Conductors are sized based on the following factors:
i. Insulation - THHN, THWN, and THWN-2 (90°C).
ii. Terminals – Conductors are sized to 75°C terminals [110.14(C)(1)(a)(3) and 110.14(C)(1)(b)(2).
iii. Load – The load is considered continuous and a 125% continuous load factor is applied [210.19(A)(1)].
iv. Neutral – Where a neutral is used (slash rated circuits), the neutral is considered current carrying (50 percent or more of the load is considered nonlinear) [310.15].
v. Ampacity Adjustment – For three-phase four-wire circuits, the ampacity of the conductors are adjusted by a multiplier of 80 percent [310.15].
3. Conductor Sizing (Residential):
a. Conductors are sized based on the following factors:
i. Insulation - THHN, THWN, and THWN-2 (90°C)
ii. Terminals – Conductors are sized to 75°C terminals [110.14(C)(1)(a)(3) and 110.14(C)(1)(b)(2), except Type NM Cable, which is sized to 60°C [334.80].
iii. Load – The load is considered noncontinuous.
iv. Neutral – The neutral conductor is not considered a current carrying conductor [310.15].
v. Ampacity Adjustment – There is no ampacity adjustment, since there are not four or more current carrying conductors.
4. Raceway Sizing:
a. Raceways are sized to provide a little more space than the NEC minimum requirement. This is accomplished by sizing all circuit conductors, including the neutral and equipment grounding to the same size as the circuit conductors. The conductor insulation is based on THHN, THWN, and THWN-2 and the raceway is considered Schedule 40 PVC.
i. Single-phase two-wire circuits are sized to three full size circuit conductors.
ii. Single-phase three-wire circuits are sized to four full size circuit conductors.
iii. Three-phase three-wire circuits are sized to four full size circuit conductors.
iv. Three-phase four-wire circuits are sized to five full size circuit conductors.
However, I think when running 200 feet of conduit you might find the cost is not too much different for a 30 amp circuit compared with a 60 amp circuit as the labor and profit is probably 3/4th or more of the cost.
But I just ran this circuit on Mike Holt's Electrical Toolbox app for continuous loads of 48 amps and 40 amps and it says you can run a 48 amp load on #6 CU or a #4 AL circuit about 350 feet and a load of 40 amps on #8 CU or #6 AL about 250 feet without suffering unacceptable voltage drop.
Going down to a 32 amp load requires #8 CU or AL and 24 amps requires #10 CU both of which can run more than 200 feet according to the app.
Note that it also says even # 8 CU should be installed in 3/4" conduit as well that #6 CU or AL should be installed in 3/4" conduit and #4 AL should be installed in 1" conduit. Only when getting down to #10 does the app recommend 1/2" conduit.
As an electrical engineer and with my past dealings with electricians, I think it will serve you best if you are as educated about this as possible since this will be an expensive undertaking, so you know what should be done to do the job. But I would not tell them how to do their job, most will not take kindly to that and won't really listen to a layman anyway. Just be informed when you speak with them.
Here is the 48 amp engineering details from that app:
USER INPUTS
System/Volts: Single Phase, 240 VoltsCircuit Type: Branch Circuit
Circuit Protection Size: 60 Amperes
Continuous Load: 48 Amperes
RESULTS COPPER
1. Circuit Protection Size: 60 Amperes2. Conductor Size: 6 AWG, rated 65A at 75°C
3. Equipment Grounding Conductor: 10 AWG
4.Maximum Circuit Length: 355 Feet
5. Raceway Size:¾ Inch
6. Maximum Circuit Continuous Load:48 Amperes
7. Maximum Circuit VA:11,520VA
RESULTS ALUMINUM
1. Circuit Protection Size: 60 Amperes2. Conductor Size: 4 AWG, rated 65A at 75°C
3. Equipment Grounding Conductor:8 AWG
4. Maximum Circuit Length: 344 Feet
5. Raceway Size: 1 Inch
6. Maximum Circuit Continuous Load: 48 Amperes
7. Maximum Circuit VA: 11,520 VA
CALCULATIONS and NOTES
1. Protection Size [210.20(A), 240.4, and 240.6(A)]2. Conductor Size (up to six conductor bundle) [110.14(C)(1)(a)(3)/(b)(1), 210.19(A)(1)(a), 240.4, 310.15, and Table 310.15(B)(16)]
3. Equipment Grounding Conductor Size [250.122]
Sized to the 60A rating of the protection device.
4. Maximum Circuit Length [110.3(B)]
Length limited to ensures the voltage is within 90% of the rated voltage.
5. Raceway Size [Chapter 9, Table 1]
Based on a raceway at 40% fill, with an equipment grounding conductor.
6. Maximum Continuous Load [210.19(A)(1)(a) and 210.20(A)]
Maximum continuous load not to exceed 80% of the circuit protection and conductor ampacity.
60A x 80% = 48A
7.Maximum Circuit Continuous VA: Circuit Voltage x Circuit Amperes 240V x 48.00A x 1 = 11,520 VA
Application Notes
1. Circuit Distance:a. The circuit length in the app uses the following formula:
i. Single‑Phase: D = (Cmil × VD)/(2 × K × I)
ii. Three‑Phase: D = (Cmil × VD)/(1.732 × K × I)
b. Distance (D): The distance of the circuit or the length of the circuit conductors.
c. Circular Mils (Cmil): The circular mil area of the circuit conductor as listed in the NEC Chapter 9, Table 8.
d. Voltage Drop (VD): The voltage drop of the branch circuit is based on the 110.3(B) of the NEC, which requires that the operating voltage at utilization equipment to be in accordance with manufacturer instructions. Manufactures typically adopt ANSI C84.1, which specifies that the voltage at utilization equipment must be within 90 percent of the nominal system voltage. The app assumes a 3 percent feeder voltage drop, resulting in a 7 percent branch circuit voltage drop.
e. Constant (K): A value of 12.90 ohms is used for copper and 21.20 ohms for aluminum. These values represents the resistance for a 1,000 circular mils conductor that’s 1,000 ft long, at an operating temperature of 75ºC.
f. Current (I): The current of the circuit is the actual load at 100 percent. According to the NEC, conductors are sized to 125 percent of the load continuous loads, electric space heating, motors, electric vehicles, etc. However, this 125 percent factor has nothing to do with determining the distance (length) of the circuit.
2. Conductor Sizing (Commercial):
a. Conductors are sized based on the following factors:
i. Insulation - THHN, THWN, and THWN-2 (90°C).
ii. Terminals – Conductors are sized to 75°C terminals [110.14(C)(1)(a)(3) and 110.14(C)(1)(b)(2).
iii. Load – The load is considered continuous and a 125% continuous load factor is applied [210.19(A)(1)].
iv. Neutral – Where a neutral is used (slash rated circuits), the neutral is considered current carrying (50 percent or more of the load is considered nonlinear) [310.15].
v. Ampacity Adjustment – For three-phase four-wire circuits, the ampacity of the conductors are adjusted by a multiplier of 80 percent [310.15].
3. Conductor Sizing (Residential):
a. Conductors are sized based on the following factors:
i. Insulation - THHN, THWN, and THWN-2 (90°C)
ii. Terminals – Conductors are sized to 75°C terminals [110.14(C)(1)(a)(3) and 110.14(C)(1)(b)(2), except Type NM Cable, which is sized to 60°C [334.80].
iii. Load – The load is considered noncontinuous.
iv. Neutral – The neutral conductor is not considered a current carrying conductor [310.15].
v. Ampacity Adjustment – There is no ampacity adjustment, since there are not four or more current carrying conductors.
4. Raceway Sizing:
a. Raceways are sized to provide a little more space than the NEC minimum requirement. This is accomplished by sizing all circuit conductors, including the neutral and equipment grounding to the same size as the circuit conductors. The conductor insulation is based on THHN, THWN, and THWN-2 and the raceway is considered Schedule 40 PVC.
i. Single-phase two-wire circuits are sized to three full size circuit conductors.
ii. Single-phase three-wire circuits are sized to four full size circuit conductors.
iii. Three-phase three-wire circuits are sized to four full size circuit conductors.
iv. Three-phase four-wire circuits are sized to five full size circuit conductors.
And here is the 40 amp engineering from the app:
USER INPUTS
System/Volts: Single Phase, 240 VoltsCircuit Type: Branch Circuit
Circuit Protection Size: 50 Amperes
Continuous Load: 40 Amperes
RESULTS COPPER
1. Circuit Protection Size: 50 Amperes2. Conductor Size: 8 AWG, rated 50A at 75°C
3. Equipment Grounding Conductor: 10 AWG
4.Maximum Circuit Length: 268 Feet
5. Raceway Size:¾ Inch
6. Maximum Circuit Continuous Load:40 Amperes
7. Maximum Circuit VA:9,600VA
RESULTS ALUMINUM
1. Circuit Protection Size: 50 Amperes2. Conductor Size: 6 AWG, rated 50A at 75°C
3. Equipment Grounding Conductor:8 AWG
4. Maximum Circuit Length: 259 Feet
5. Raceway Size: ¾ Inch
6. Maximum Circuit Continuous Load: 40 Amperes
7. Maximum Circuit VA: 9,600 VA
CALCULATIONS and NOTES
1. Protection Size [210.20(A), 240.4, and 240.6(A)]2. Conductor Size (up to six conductor bundle) [110.14(C)(1)(a)(3)/(b)(1), 210.19(A)(1)(a), 240.4, 310.15, and Table 310.15(B)(16)]
3. Equipment Grounding Conductor Size [250.122]
Sized to the 50A rating of the protection device.
4. Maximum Circuit Length [110.3(B)]
Length limited to ensures the voltage is within 90% of the rated voltage.
5. Raceway Size [Chapter 9, Table 1]
Based on a raceway at 40% fill, with an equipment grounding conductor.
6. Maximum Continuous Load [210.19(A)(1)(a) and 210.20(A)]
Maximum continuous load not to exceed 80% of the circuit protection and conductor ampacity.
50A x 80% = 40A
7.Maximum Circuit Continuous VA: Circuit Voltage x Circuit Amperes 240V x 40.00A x 1 = 9,600 VA
Application Notes
1. Circuit Distance:a. The circuit length in the app uses the following formula:
i. Single‑Phase: D = (Cmil × VD)/(2 × K × I)
ii. Three‑Phase: D = (Cmil × VD)/(1.732 × K × I)
b. Distance (D): The distance of the circuit or the length of the circuit conductors.
c. Circular Mils (Cmil): The circular mil area of the circuit conductor as listed in the NEC Chapter 9, Table 8.
d. Voltage Drop (VD): The voltage drop of the branch circuit is based on the 110.3(B) of the NEC, which requires that the operating voltage at utilization equipment to be in accordance with manufacturer instructions. Manufactures typically adopt ANSI C84.1, which specifies that the voltage at utilization equipment must be within 90 percent of the nominal system voltage. The app assumes a 3 percent feeder voltage drop, resulting in a 7 percent branch circuit voltage drop.
e. Constant (K): A value of 12.90 ohms is used for copper and 21.20 ohms for aluminum. These values represents the resistance for a 1,000 circular mils conductor that’s 1,000 ft long, at an operating temperature of 75ºC.
f. Current (I): The current of the circuit is the actual load at 100 percent. According to the NEC, conductors are sized to 125 percent of the load continuous loads, electric space heating, motors, electric vehicles, etc. However, this 125 percent factor has nothing to do with determining the distance (length) of the circuit.
2. Conductor Sizing (Commercial):
a. Conductors are sized based on the following factors:
i. Insulation - THHN, THWN, and THWN-2 (90°C).
ii. Terminals – Conductors are sized to 75°C terminals [110.14(C)(1)(a)(3) and 110.14(C)(1)(b)(2).
iii. Load – The load is considered continuous and a 125% continuous load factor is applied [210.19(A)(1)].
iv. Neutral – Where a neutral is used (slash rated circuits), the neutral is considered current carrying (50 percent or more of the load is considered nonlinear) [310.15].
v. Ampacity Adjustment – For three-phase four-wire circuits, the ampacity of the conductors are adjusted by a multiplier of 80 percent [310.15].
3. Conductor Sizing (Residential):
a. Conductors are sized based on the following factors:
i. Insulation - THHN, THWN, and THWN-2 (90°C)
ii. Terminals – Conductors are sized to 75°C terminals [110.14(C)(1)(a)(3) and 110.14(C)(1)(b)(2), except Type NM Cable, which is sized to 60°C [334.80].
iii. Load – The load is considered noncontinuous.
iv. Neutral – The neutral conductor is not considered a current carrying conductor [310.15].
v. Ampacity Adjustment – There is no ampacity adjustment, since there are not four or more current carrying conductors.
4. Raceway Sizing:
a. Raceways are sized to provide a little more space than the NEC minimum requirement. This is accomplished by sizing all circuit conductors, including the neutral and equipment grounding to the same size as the circuit conductors. The conductor insulation is based on THHN, THWN, and THWN-2 and the raceway is considered Schedule 40 PVC.
i. Single-phase two-wire circuits are sized to three full size circuit conductors.
ii. Single-phase three-wire circuits are sized to four full size circuit conductors.
iii. Three-phase three-wire circuits are sized to four full size circuit conductors.
iv. Three-phase four-wire circuits are sized to five full size circuit conductors.
My electrician recommended a 40-amp breaker based on my capacity. Thanks for the detailed info. I appreciate it!
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