NEC 2017

[hhsting]

I have EV charger fed from 60A breaker and cable size provided is #4. Would not the normal size for EV charger breaker of 60A be #6 cu or the size of the cable has to equal the breaker sizing?

 

[Little Bill]

#4 is larger than #6, all you are required to do is use the minimum size conductor that matches the OCPD. Larger is perfectly fine, it may be wasteful but perfectly fine to use.

 

[hhsting]

#4 is larger than #6, all you are required to do is use the minimum size conductor that matches the OCPD. Larger is perfectly fine, it may be wasteful but perfectly fine to use.

Ok but I am trying to determine if 250.122(B) is used or not. If they upsize phase then they have to upsize EGC.

So I was wondering if #6 would be minimum size on 60A breaker for EV charger or minimum size for EV charger 60A bkr is higher than #6?

 

[Little Bill]

Ok but I am trying to determine if 250.122(B) is used or not. If they upsize phase then they have to upsize EGC.

So I was wondering if #6 would be minimum size on 60A breaker for EV charger or minimum size for EV charger 60A bkr is higher than #6?

Why don't you put all the information in your OP instead of dropping little bits in each post?

 

[hhsting]

Why don't you put all the information in your OP instead of dropping little bits in each post?

Its not intentional. Sometimes I forget to write details but I try to be thorough as possible. Its not like I have been thinking about posting since yesterday. Whenever I see the plans I have limited amount of time also to verify so I post quickly but that also comes with sometimes just forget to post details or comes later on.

 

[infinity]

What kind of cable? #6 MC cable would have an ampacity of 65 amps. NM cable 55 amps. #4 would be an increase is size (MC), the other (NM) would not.

 

[hhsting]

What kind of cable? #6 MC cable would have an ampacity of 65 amps. NM cable 55 amps. #4 would be an increase is size (MC), the other (NM) would not.

Cables are underground in PVC conduit. At 60C #6 would have 55A and #4 would have 70A

 

[wwhitney]

Are the EVSE terminals listed for 75C connections? Someone might have assumed they are limited to 60C connections because the equipment is rated not more than 100A.

If something in the circuit requires use of the 60C column, then #4 is the minimum size for a 48A continuous EVSE, so there is no upsizing for 250.122(B). If everything allows the use of the 75C column, they you get into which version (NEC year) of 250.122(B) is operative and why the upsizing was done.

Cheers, Wayne

 

[hhsting]

Are the EVSE terminals listed for 75C connections? Someone might have assumed they are limited to 60C connections because the equipment is rated not more than 100A.

If something in the circuit requires use of the 60C column, then #4 is the minimum size for a 48A continuous EVSE, so there is no upsizing for 250.122(B). If everything allows the use of the 75C column, they you get into which version (NEC year) of 250.122(B) is operative and why the upsizing was done.

Cheers, Wayne

I believe someone assumed to be 60C because the equipment is less than 100A. Two questions though:

1. It is 48A continuous EVSE. How do you figure minimum size cable is #4 based off of 60C? I am looking at 625 NEC 2017 does not say anything about sizing cables only overcurrent protection. So 48x1.25 = 60A so breaker is 60A however cable size can be #6 at 60C which is 55A and would still be protected by 240.4(B) no?

2. If lets says someone does look at terminal of EVRSE at turns out to be 75C and they used #4 would it require upsize of EGC in that case NEC 2017 version?

 

[wwhitney]

1) See 210.19(A)(1). FWIW, this is a case where I feel the NEC is overly restrictive and that 55A ampacity conductors on a 60A breaker for a 48A continuous load should be allowed, but it is not.

2) Yes, the year is in the thread title, I didn't see that. For 2017, 250.122(B) isn't limited to voltage drop, so it would apply whenever the ungrounded conductors are upsized. Of course, this leads to some ridiculous requirements: upsizing the EGC if the insulation on the ungrounded conductors is 75C but not if its 60C; upsizing if the equipment is marked for 75C but not if it's limited to 60C. The conductors might even be run before the EVSE has been selected, so it isn't known if the the EVSE's terminals are rated for 60C or 75C. So some common sense should be used in applying 250.122(B).

Cheers, Wayne

 

[rc/retired]

FWIW, a #10 copper equipment grounding is suitable for branch circuits rated from 25 amps to 90 amps per table 250.122.
Unless I'm mistaken, that can be for conductors sized from #10 to #3. Without any extenuating circumstances.
So, in this case, if you upsize from #8 to #6, your egc should be fine.

 

[hhsting]

1) See 210.19(A)(1). FWIW, this is a case where I feel the NEC is overly restrictive and that 55A ampacity conductors on a 60A breaker for a 48A continuous load should be allowed, but it is not.

2) Yes, the year is in the thread title, I didn't see that. For 2017, 250.122(B) isn't limited to voltage drop, so it would apply whenever the ungrounded conductors are upsized. Of course, this leads to some ridiculous requirements: upsizing the EGC if the insulation on the ungrounded conductors is 75C but not if its 60C; upsizing if the equipment is marked for 75C but not if it's limited to 60C. The conductors might even be run before the EVSE has been selected, so it isn't known if the the EVSE's terminals are rated for 60C or 75C. So some common sense should be used in applying 250.122(B).

Cheers, Wayne

I hate to add twist to this thing but from the above info from what I understand is that you are saying 48A one EV unit draws has continuous load of 60A so I need minimum 60A cable to EV chargers.

I have in one 1.5 inch conduit following cables going to two 208V single phase EV chargers and 120V single phase for screen on each EV:

1. 4#4 (2-208V single phase circuit)
2. 4#10 (2-120V single phase circuit)
3. #6 gnd

Based on above their would be 8 current carrying conductors right? So #4 at 60C is 70A times that by 0.7 ampacity of cable is 49A so this size would not comply?

Even if its 4 current carrying conductors then it would be 56A less than 60A.

Would not the phase conductors need up size and 250.122(B) do they need up size?

 

[infinity]

FWIW, a #10 copper equipment grounding is suitable for branch circuits rated from 25 amps to 90 amps per table 250.122.
Unless I'm mistaken, that can be for conductors sized from #10 to #3. Without any extenuating circumstances.
So, in this case, if you upsize from #8 to #6, your egc should be fine.

Wouldn't going from #8 to #6 with the ungrounded conductors require a proportional increase in the EGC?

 

[rc/retired]

In this case, I'm not sure. According to 250.122, a #10 egc is allowed for breaker sizes from 30 to 90 amps.
It doesn't make sense to me if the OP has a #8, #6 or #4 conductor terminated on a 50 Amp breaker.
The #10 is still approved.
I guess my question now would be, what would you size it to?
In this case, the OP never gave a reason for the wire size. Ergo, (fun word), my comment on the egc size.
I hope I made some sense there.

Ron

 

[augie47]

I hate to add twist to this thing but from the above info from what I understand is that you are saying 48A one EV unit draws has continuous load of 60A so I need minimum 60A cable to EV chargers.

I have in one 1.5 inch conduit following cables going to two 208V single phase EV chargers and 120V single phase for screen on each EV:

1. 4#4 (2-208V single phase circuit)
2. 4#10 (2-120V single phase circuit)
3. #6 gnd

Based on above their would be 8 current carrying conductors right? So #4 at 60C is 70A times that by 0.7 ampacity of cable is 49A so this size would not comply?

Even if its 4 current carrying conductors then it would be 56A less than 60A.

Would not the phase conductors need up size and 250.122(B) do they need up size?

If you use THWN-2 or XHHW-2 you can use the 90 column for your derating. 95 amps X ,7 = 66 amps.

 

[don_resqcapt19]

In this case, I'm not sure. According to 250.122, a #10 egc is allowed for breaker sizes from 30 to 90 amps.
It doesn't make sense to me if the OP has a #8, #6 or #4 conductor terminated on a 50 Amp breaker.
The #10 is still approved.
I guess my question now would be, what would you size it to?
In this case, the OP never gave a reason for the wire size. Ergo, (fun word), my comment on the egc size.
I hope I made some sense there.

Ron

You need to look at 250.122(B). Any time the ungrounded conductor is larger than the minimum permitted by the NEC you have to provide a proportionate increase in the size of the EGC The question here, is what is the minimum permitted size of the EGC.
The 60 amp OCPD requires a 10 AWG EGC, but if 6 is the code minimum size of the ungrounded conductor, and you install 4, that increase is a factor of 1.59. 10 has a circular mil are of 10380 and when you apply the 1.59 factor you get 16511. 8 AWG is has an area of 16510

 

[wwhitney]

Based on above their would be 8 current carrying conductors right? So #4 at 60C is 70A times that by 0.7 ampacity of cable is 49A so this size would not comply?

In addition to what augie said, note the difference in 210.19(A) between (1) and (2). Part (2) is explicitly after derating for conductor count and temperature, so implicitly part (1) is before derating. For part (1) you'd compare 70A (if 60C terminals in the EVSE) (and no 70% factor) against 125% * 48A = 60A, which is fine. And for part (2) you'd compare 70A (if 60C insulation, which would be unusual) * 70% = 49A against 48A (no 125% factor), and that's also fine. For this scenario, with 60C terminals and 60C insulation temperature, #4 would be the smallest size allowed, so 250.122(B) would not require upsizing the EGC; you could use a #10 EGC.

However, if you have 75C terminals (more likely) and 90C temperature insulation (quite likely), then #6 Cu would be sufficient: for part (1) 65A (75C ampacity) > 125% (continuous load) * 48A = 60A. And for part (2) 75A (90C ampacity) * 70% (conductor count derating) = 52.5A > 48A. So in this case, since there are #4 ungrounded conductors instead #6 ungrounded, the minimum EGC size is #8 instead of #10, per 250.122(B).

But you listed a #6 EGC, so that's certainly large enough.

BTW, the information about 8 CCCs in one conduit would have been helpful to include in the first post.

Cheers, Wayne

 

[wwhitney]

The 60 amp OCPD requires a 10 AWG EGC, but if 6 is the code minimum size of the ungrounded conductor, and you install 4, that increase is a factor of 1.59. 10 has a circular mil are of 10380 and when you apply the 1.59 factor you get 16511. 8 AWG is has an area of 16510

The difference is a rounding error. AWG is geometric, so an additive size increase in AWG (2 sizes) is a proportionate increase in area (a factor of about 2^(2/3)).

Cheers, Wayne

 

[rc/retired]

You need to look at 250.122(B). Any time the ungrounded conductor is larger than the minimum permitted by the NEC you have to provide a proportionate increase in the size of the EGC The question here, is what is the minimum permitted size of the EGC.
The 60 amp OCPD requires a 10 AWG EGC, but if 6 is the code minimum size of the ungrounded conductor, and you install 4, that increase is a factor of 1.59. 10 has a circular mil are of 10380 and when you apply the 1.59 factor you get 16511. 8 AWG is has an area of 16510

Got it. Many thanks!

Ron

 

[augie47]

BTW, the information about 8 CCCs in one conduit would have been helpful to include in the first post.

Cheers, Wayne

any resemblance between any of sting's first post and the actual "situation" is purely accidental