camasleaf
Posts: 662
Joined: Sun Sep 26, 2010 5:20 am
Delivery Date: 17 Jun 2011
Location: Camas, WA

Re: EVSE source current

Thu Apr 02, 2020 6:05 am

The ampacity table is for 3 current carrier conductors in the conduit. I do not believe we are allowed to rate up for only 2 current carrier conductors. But it is good point, I will look to see if NEC allows any up rate.

For quick conduit fill I usualy use: https://www.southwire.com/calculator-conduit
2011 SLe 06/17/11 Over 92000 miles 59%SOH
2018 Honda Clarity PHEV
2014 Model S P85 87000 miles 250 miles range
5.7kW DC Solar System

camasleaf
Posts: 662
Joined: Sun Sep 26, 2010 5:20 am
Delivery Date: 17 Jun 2011
Location: Camas, WA

Re: EVSE source current

Thu Apr 02, 2020 7:13 pm

https://ieeexplore.ieee.org/iel7/628763 ... 669748.pdf

An interesting paper. A 50A breaker with 40A load will trip at 75C ambient. So my setup 100A breaker, #4 wire at 80A will work but only because #4 is rated 85A/75C and at 80A should not quite reach 75C and therefore not trip the breaker. All this discussion assumes 30C ambient temperature. In PNW the garage where the panel is will I rarely see 20C. In Arizona ....
2011 SLe 06/17/11 Over 92000 miles 59%SOH
2018 Honda Clarity PHEV
2014 Model S P85 87000 miles 250 miles range
5.7kW DC Solar System

nlspace
Posts: 231
Joined: Mon Jun 05, 2017 10:21 pm
Delivery Date: 06 Jun 2017

Re: EVSE source current

Fri Apr 03, 2020 5:39 am

That's a really good find on the paper that investigated the linear temperature sensitivity of trip current for 4 brands of breakers. i think the extrapolation to higher temperatures is reasonably valid and useful based on my experience.

For example a freestanding metal electrical box can easily reach 75C in direct sun. i have used 1/2" thick foam insulation sheets to line the inside of Hoffman boxes that were outdoors with full sun exposure.

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