Electric Vehicle Charging Station's tough Q.

[olly]

I am trying to size a service/main for 9 Ev chargers. Each EV FLC is 30a, each one is on a 40a breaker. This is an outside install. I'm having a hard time interpreting 626.11 (A) & (B).

"The calculated load of a feeder or service shall be not less then the sum of the loads on the branch circuits."

Does that mean I have to: 30a X 9 = 270a? and then divide that by the demand factor on table 626.11 (B)? (table is on page 574 NEC 2014)

I have a feeling I'm way off.

Thank you very much for any input!

 

[petersonra]

I am by no means an expert on EV but it appears to me that article 625 would be where I would start.

 

[MWh_Pro]

Olly--

These are the just theories of a madman up past his bedtime, so use at your own risk. That said, I can recommend a couple of ideas for places to look:

1. See Table 220.3. It tells you to ref 625.41.
2. 625.41 says "... EV charging loads are continuous ..." => (implies) load = charger FLA
3. Go back to general requirements for feeders: 215.2(A)(1). It says see 220 sections III, IV, V. There's nothing about EV in there, but maybe something that affects your case. Otherwise, 215(A)(1)(a) just says feeder ampacity = 125% sum(charger FLA)
4. Supposing load really is the sum of the charger FLA... 625.40 says feeder OCPD > 125% x # chargers x FLA
5. Absent any demand factors, then, your feeder might look like: 75C copper conductors in a raceway (310.15(B)(16)) => 500 kcmil (before conditions of use) and OCPD > 125% x 9 x 30A = 338A => 350A, since 240.4(B) allows you to use the next available OCPD rating up to 800A.
6. I really don't know about the demand factors. They are used for everything else with feeders, so it is logical there should be some. Article 625 is pretty young, so Table 626.11(B) might be the next best option. I mean, although 625 might not require it, the customers will be quite livid if the charging system trips the main breaker, etc. I would highly recommend that you consult a professional, as well as the charger manufacturer to determine what will work for you best.

Cheers,
Dave