Wire gauge and circuit breaker requirement

[diyguy15]

I'm finding different answers talking to different electricians and doing my own research reading code books so I'm positing here.

I have 110 feet of 6/2 Metal Clad wire running to my garage (wire is routed completely indoors). The wire is hardwired into a Chargepoint charger CHP50 installed in the garage. I want to know what rating of circuit breaker do I need on the other end. Is it 50Amp or 60Amp?

MC has 3 leads (Hot+Hot+Ground) that are all THHN cables. Some people say it should go by 90C rating (so 75Amp) and some say it should be derated to 60C (so 55Amp).

What is correct and according to NEC code?

 

[nicholi]

Take a look at 110.14. It’s the 75 degree column. Since you are hard wired you can use a 60a breaker.

 

[ZX3ST]

You should only use the 90C column if you're calculating rating adjustment due to ambient temps not at 104 degF. You'll be limited by the least common denominator of your termination points. Will either be 60C or 75C, never 90C.

I don't have anything newer than NEC2017 handy ATM (could be a different table), but it's table 310.15(B). After accounting for any applicable derating for ambient temps, multiple conductors, voltage drop, etc..... you'll still need to use the lower of that number vs whatever the lowest temp capacity of your terminations are. 75C is the most common, but I've seen plenty of terminals that bring you straight down to 60C.

So you'll need to check your termination points, but you can likely get away with the 75C rating of 65A. Then you'll need to derate that further because it's a continuous load. So 65/1.25 = 52A

 

[diyguy15]

This is in the charger which is at the other termination point. It states to use 90C copper conductors. Does this mean termination point is rated at 90C? Obviously the 60Amp circuit breaker in the box is rated at that as well.

 

[Bert_]

The big question is what temperature the terminals are rated for. They aren't rated 90*. Most terminals that size would be 75* C. #6 thhn is good to 65A at 75*C

If you want the full 50A rating of the charger you would need 50A x 125%= 62.5A breaker, but it doesn't exist. Next closest breaker size is 70A

 

[diyguy15]

The CHP50 charger has a configuration for "208/240V AC 60Hz single phase @ 16A, 24A, 32A, 40A, 48A, 50A".

Based on what you guys are saying 48Amp config will work well with 60Amp breaker.

 

[wyliesdiesels]

I'm finding different answers talking to different electricians and doing my own research reading code books so I'm positing here.

I have 110 feet of 6/2 Metal Clad wire running to my garage (wire is routed completely indoors). The wire is hardwired into a Chargepoint charger CHP50 installed in the garage. I want to know what rating of circuit breaker do I need on the other end. Is it 50Amp or 60Amp?

MC has 3 leads (Hot+Hot+Ground) that are all THHN cables. Some people say it should go by 90C rating (so 75Amp) and some say it should be derated to 60C (so 55Amp).

What is correct and according to NEC code?

whoever said that is wrong and you shouldnt follow anything they tell you. the 90°c column is for derating purposes only because there are no breakers with 90°c rated lugs....

 

[Norcal]

whoever said that is wrong and you shouldnt follow anything they tell you. the 90°c column is for derating purposes only because there are no breakers with 90°c rated lugs....

Home Depot was known for spewing that diarrhea of the mouth.