Car charger

[hhsting]

I have car charger that draws 45A of current 208V single phase with two phase conductor and ground.

If I have two such car chargers and I put all conductors in one conduit then would I need #4 awg or #3 awg copper?

I get #3 awg copper because #4 awg has 70A ampcity and 4 phase conduxtors one conduit i would derate to 70x0.8=56A however my EV charger is continuous then 45x1.25=56.25A thus #3 awg copper.

Am I wrong?

 

[wwhitney]

I have car charger that draws 45A of current 208V single phase with two phase conductor and ground.

If I have two such car chargers and I put all conductors in one conduit then would I need #4 awg or #3 awg copper?

I get #3 awg copper because #4 awg has 70A ampcity and 4 phase conduxtors one conduit i would derate to 70x0.8=56A however my EV charger is continuous then 45x1.25=56.25A thus #3 awg copper.

Am I wrong?

45A is a bit unusual for the setting of an EVSE. But taking that at face value, two things need to be true:

1) For the termination, using either the 60C or 75C column according to the termination rating, you need the unadjusted table value to be at least 45A * 1.25 (continuous use) = 56A.

2) For the conduit, using the 90C column (assuming 90C rated insulation), you need the adjusted ampacity to be at least 45A (no 125% continuous use factor). For 4 CCCs the adjustment is 0.8.

Assuming no temperature correction is required, that means you need a conductor whose 60C (or 75C) column value is at least 56A, and whose 90C (most likely) column value is at least 45/0.8 = 56A again.

So the answer is #6 if the EVSE terminals are 75C rated, or #4 if the EVSE terminals are only 60C rated. I am assuming the breaker has 75C rated terminals.

Cheers, Wayne

P.S. There is a 3rd thing that needs to be true, which is that the ampacity calculated in (2) is large enough for the OCPD, which needs to be at least the value calculated in (1). So assuming a 60A OCPD, you need a conductor with ampacity at least 51A (per 240.4(B)). In other words the 90C column has to be at least 51A / 0.8 = 64A. But this doesn't change the conclusion on required wire size; while this requirement is stricter than (2) above, (1) above is the strictest and controls.

 

[hhsting]

45A is a bit unusual for the setting of an EVSE. But taking that at face value, two things need to be true:

1) For the termination, using either the 60C or 75C column according to the termination rating, you need the unadjusted table value to be at least 45A * 1.25 (continuous use) = 56A.

2) For the conduit, using the 90C column (assuming 90C rated insulation), you need the adjusted ampacity to be at least 45A (no 125% continuous use factor). For 4 CCCs the adjustment is 0.8.

Assuming no temperature correction is required, that means you need a conductor whose 60C (or 75C) column value is at least 56A, and whose 90C (most likely) column value is at least 45/0.8 = 56A again.

So the answer is #6 if the EVSE terminals are 75C rated, or #4 if the EVSE terminals are only 60C rated. I am assuming the breaker has 75C rated terminals.

Cheers, Wayne

P.S. There is a 3rd thing that needs to be true, which is that the ampacity calculated in (2) is large enough for the OCPD, which needs to be at least the value calculated in (1). So assuming a 60A OCPD, you need a conductor with ampacity at least 51A (per 240.4(B)). In other words the 90C column has to be at least 51A / 0.8 = 64A. But this doesn't change the conclusion on required wire size; while this requirement is stricter than (2) above, (1) above is the strictest and controls.

I am putting 4 conductors one for each EV charger in one conduit so would not Table 310.15(b)(3)(a) 80% adjustment factor apply? Assume everything is 60C.

 

[wwhitney]

I am putting 4 conductors one for each EV charger in one conduit so would not Table 310.15(b)(3)(a) 80% adjustment factor apply?

It does apply, but only to check (2) in my earlier post, not to check (1). I.e. the 80% adjustment factor never applies concurrently with the 125% continuous use factor.

Assume everything is 60C.

Seems unlikely. The termination rating may be 60C, but the conductor insulation rating is surely 90C.

Cheers, Wayne

 

[hhsting]

It does apply, but only to check (2) in my earlier post, not to check (1). I.e. the 80% adjustment factor never applies concurrently with the 125% continuous use factor.

Where is this is NEC 2017?

 

[wwhitney]

Where is this is NEC 2017?

For branch circuits, 210.19(A)(1)(a) and (b). It not as clear as it could be, but notice that (b) refers to ampacity "after the application of any adjustment or correction factors," while (a) just refers to "allowable ampacity" without that modifier. "Allowable ampacity" is the term in the title of Tables 310.15(B)(16) et al, and so (a) is referring to the straight table value without adjustment or correction.

Cheers, Wayne

 

[hhsting]

For branch circuits, 210.19(A)(1)(a) and (b). It not as clear as it could be, but notice that (b) refers to ampacity "after the application of any adjustment or correction factors," while (a) just refers to "allowable ampacity" without that modifier. "Allowable ampacity" is the term in the title of Tables 310.15(B)(16) et al, and so (a) is referring to the straight table value without adjustment or correction.

Cheers, Wayne

So if we dont take 125% in your (1), then I can do amapcity correction factor of 80% that is 45/.8 =56.25A which would be #4 awg at 60C?

 

[wwhitney]

So if we dont take 125% in your (1), then I can do amapcity correction factor of 80% that is 45/.8 =56.25A which would be #4 awg at 60C?

I don't understand your comment. In my (1) (which is 210.19(A)(1)(a)), we have a 125% continuous use factor and no ampacity adjustment or correction. In my (2) (which is 210.19(A)(1)(b)), we do not have any continuous use factor, and we do have ampacity adjustment and correction.

Anyway, the upshot was that (1) controls, and so if the EVSE's terminations are only 60C rated, we need a 60C column entry of 45 * 125% = 56A, which means #6 Cu is 1A too small, and we need #4 Cu.

Cheers, Wayne

 

[hhsting]

I don't understand your comment. In my (1) (which is 210.19(A)(1)(a)), we have a 125% continuous use factor and no ampacity adjustment or correction. In my (2) (which is 210.19(A)(1)(b)), we do not have any continuous use factor, and we do have ampacity adjustment and correction.

Anyway, the upshot was that (1) controls, and so if the EVSE's terminations are only 60C rated, we need a 60C column entry of 45 * 125% = 56A, which means #6 Cu is 1A too small, and we need #4 Cu.

Cheers, Wayne

What about (2) with 60C?


Sent from my iPhone using Tapatalk

 

[wwhitney]

What about (2) with 60C?

Well, you're not likely to find conductors with 60C insulation in new installation these days.

But instead of 125% for continuous use, in your example, (2) has 1/0.8 for number of CCCs. Which equals 125%. So it's the same answer.

(3) (from my postscript) is stricter than (2), as it's 51/0.8 instead of 45/0.8. But even that works for a #4 Cu with 60C insulation.

Cheers, Wayne

 

[tortuga]

which means #6 Cu is 1A too small, and we need #4 Cu.

Why is that so often the case with 6AWG? I say we bring 5AWG back (it used to be in in the table) . 5 AWG ( 33.1 kcmil ) is closer to 16mm which I think is a common size internationally.

 

[qcroanoke]

Why is that so often the case with 6AWG? I say we bring 5AWG back (it used to be in in the table) .

We don't like your kind in here........

 

[hhsting]

Well, you're not likely to find conductors with 60C insulation in new installation these days.

But instead of 125% for continuous use, in your example, (2) has 1/0.8 for number of CCCs. Which equals 125%. So it's the same answer.

(3) (from my postscript) is stricter than (2), as it's 51/0.8 instead of 45/0.8. But even that works for a #4 Cu with 60C insulation.

Cheers, Wayne

For (3) at 90C it requires 60A breaker?

 

[wwhitney]

For (3) at 90C it requires 60A breaker?

A 45A continuous load requires a minimum 125% * 45 = 56A circuit breaker per 210.20(A) (barring a rare 50A 100% rated breaker), which means 60A in practice. Then 240.4(B) requires a minimum 51A ampacity for any 60A breaker.

Ampacity (not allowable ampacity) can always be computed starting with the allowable ampacity (table value) at the insulation temperature rating.

Cheers, Wayne

 

[tortuga]

A 45A continuous load requires a minimum 125% * 45 = 56A circuit breaker per 210.20(A) (barring a rare 50A 100% rated breaker), which means 60A in practice. Then 240.4(B) requires a minimum 51A ampacity for any 60A breaker.

Ampacity (not allowable ampacity) can always be computed starting with the allowable ampacity (table value) at the insulation temperature rating.

Cheers, Wayne

Looking at the 1947 NEC Chapter 10 Table 1, the column for type 'RU ' (it eventuality becomes the 60C table) 5AWG had an ampacity of 63 amps, that would allow a EVSE to easily charge at ~48 A.
6awg had 54 and has 65A today so it has not changed much.
I suppose there is nothing stopping a manufacturer from making 5-AWG NM cable it just would not have an entry in the ampacity table, DLO cable is like that.

 

[brycenesbitt]

45A is a bit unusual for the setting of an EVSE. But taking that at face value, two things need to be true:

Not taking that at face value.

45A is an oddball, and would require custom programming on the EVSE side, with any consumer level unit.
48A is the only nearby value. But the other approach is run a single wire of whatever to the charger area,
then use a load balancing charger like the Grizzl-E Duo 40A or WattZilla® DUO Dual 80-AMP.

It's all single phase, and 208V a fine voltage, just going to give you less kW per hour than 240V (or 277V .