Eric33432
Member
Somehow this thread popped up again, and I note that no one has commented on the need to consider de-rating the ampacity of the wire since there are more than three current carrying conductors in the 1-1/4" conduit the OP said he has installed.
If he plans on someday using both wall connectors at the same time with 48 amp charging loads, without load sharing between them, and since he installed two runs of #6 wire connected to 60 amp breakers he can do that, it should determined if #6 is large enough before installing the wire.
How to do this calculation:
Step 1, determine the continuous and non-continuous current that will flow through the conductors, which for the Tesla Wall Connector is 48 amps continuous because an EVSE load is a continuous load.
Step 2, determine the ampacity of the wire needed for the load. To do that, take 100% of the non-continuous load and 125% of the continuous load. 125% X 48 = 60 amps.
Step 3, determine if de-rating is required by referring to Table 310.15(B)(3)(a) which says when 4 to 6 current carrying conductors are contained in a conduit they should be derated to 80% of their normal ampacity. (Note to not count the ground wires, and don't count the neutral conductors (if any) if the circuits are 120/240 volt split phase. You do count the neutrals in certain 3 phase circuits.)
Step 4, determine the ampacity required after the derating factor determined in step 3 by dividing the result of step 2 by the derating factor that was determined in step 3. In this case, 60 ÷ 80% = 75 amps. Therefore wire good for 75 amps is needed after derating.
Step 5, select wire that is good for at least 75 amps, and you need to know how to read the ampacity table.
As an example, this could be #4 THW or THWN, which use the 75˚C column, if you happen to have any such wire laying around; I do not think these kinds are made any more.
In this case, refer to the ampacity table which shows that #6 THHN/THWN-2 wire is good for 75 amps using the 90˚C column.
Note that THHN/THWN-2 wire is rated for 90˚C, but for the complete circuit you have to consider the terminals to which the wire is connected, which for most residential circuit breakers currently made and the Tesla Wall Connector are both 75˚C. So for derating THHN/THWN-2 use the 90˚C column, but for the entire circuit use the 75˚C column.
Therefore #6 THHN/THWN-2 just happens to be OK for this installation.
While it worked out OK for this installation, it does not always, so for anyone considering running more than 3 current carrying conductors in a conduit, it is always best to do this calculation.
I post the above for entertainment and education purposes so you can have an intelligent conversation with your electrician.
Thanks for reading.
If he plans on someday using both wall connectors at the same time with 48 amp charging loads, without load sharing between them, and since he installed two runs of #6 wire connected to 60 amp breakers he can do that, it should determined if #6 is large enough before installing the wire.
How to do this calculation:
Step 1, determine the continuous and non-continuous current that will flow through the conductors, which for the Tesla Wall Connector is 48 amps continuous because an EVSE load is a continuous load.
Step 2, determine the ampacity of the wire needed for the load. To do that, take 100% of the non-continuous load and 125% of the continuous load. 125% X 48 = 60 amps.
Step 3, determine if de-rating is required by referring to Table 310.15(B)(3)(a) which says when 4 to 6 current carrying conductors are contained in a conduit they should be derated to 80% of their normal ampacity. (Note to not count the ground wires, and don't count the neutral conductors (if any) if the circuits are 120/240 volt split phase. You do count the neutrals in certain 3 phase circuits.)
Step 4, determine the ampacity required after the derating factor determined in step 3 by dividing the result of step 2 by the derating factor that was determined in step 3. In this case, 60 ÷ 80% = 75 amps. Therefore wire good for 75 amps is needed after derating.
Step 5, select wire that is good for at least 75 amps, and you need to know how to read the ampacity table.
As an example, this could be #4 THW or THWN, which use the 75˚C column, if you happen to have any such wire laying around; I do not think these kinds are made any more.
In this case, refer to the ampacity table which shows that #6 THHN/THWN-2 wire is good for 75 amps using the 90˚C column.
Note that THHN/THWN-2 wire is rated for 90˚C, but for the complete circuit you have to consider the terminals to which the wire is connected, which for most residential circuit breakers currently made and the Tesla Wall Connector are both 75˚C. So for derating THHN/THWN-2 use the 90˚C column, but for the entire circuit use the 75˚C column.
Therefore #6 THHN/THWN-2 just happens to be OK for this installation.
While it worked out OK for this installation, it does not always, so for anyone considering running more than 3 current carrying conductors in a conduit, it is always best to do this calculation.
I post the above for entertainment and education purposes so you can have an intelligent conversation with your electrician.
Thanks for reading.
