Calcs for future EV chargers

jfrog

Member
Occupation
Engineer
I'm looking for some opinions, since this really isn't addressed anywhere in code...

In California, as well as some other places, new building are required to install the infrastructure for X number parking spaces with EV charging stations. In my building, it's 20 parking spaces.

I'm in the process of determining what the load and panel space requirements will be. The load I'm using in my calcs is 32A (40A circuit), 208V 1 phase. However, it's possible that what will be installed will be (10) 2-car chargers. Some of those only require a single 32A/40A circuit - i.e., 32A serving 2 parking spots. Obviously that cuts the load in half, as well as the panel space requirement.

If we were actually installing chargers, I could determine what equipment was going in, but since the requirement is merely to provide for possible future chargers, I have 2 different tacks I can take:

1. Install for projected worst case, i.e., (20) 2-pole circuit spaces and a 150 kVA transformer, or

2. Install for a nominal load, (10) 2-pole circuit spaces and a 75 kVA

I am interested to see what other designers have done (or would do).
 

rc/retired

Member
Location
Bellevue, Colorado
Occupation
Master Electrician/Inspector retired
The jurisdiction I inspected for requires a minimum 50 amp EV charger. At that point, it's up to the EE to have the calculations on their plans.
 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
Are there any demand factors for EV parking areas? Much like there are for ranges/cooktops/ovens. Seems like that could be a valuable addition. On second thought, its not unreasonable to have a full parking lot in a retail location? So I would error on the side of more capacity. Of course this assumes the additional cost is a non issue which is rarely the case. I am not a designer.
 

retirede

Senior Member
Location
Illinois
First, a point of nomenclature. EV chargers are part of the car. What you are being asked to install are called “Electric Vehicle Service Equipment” (EVSE), not chargers.

I don’t know if such a thing exists, but for an application such as this, smart EVSEs that are networked and have the ability to monitor the total load and throttle as the total load approached system capacity would be ideal. This would allow each station to supply maximum power when utilization is lower without overloading the system when the parking lot is full.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
In my opinion there's no requirement at all to provide for potential future equipment in a load calculation even if you run wires conduit and boxes. As long as the circuits aren't hooked up to anything there's no load. Down the road if somebody wants to add them the conduit and wires and whatnot are in place and if they have to they can increase the feeder and service sizes as needed at that point in time.
 

jfrog

Member
Occupation
Engineer
Per the CA Building Code (CBC), I am required to provide provisions for "charging spaces", and the code requires that the EVSE is based upon a minimum 40 A circuits, and the service & panels have to have sufficient capacity. Also, as of now there is no demand factor allowed. Perhaps a couple of code cycles down the road there will be.

I can justify serving the spaces either of the 2 ways described in my original post, but was asking what people have seen installed.

The heart of my question is does a typical EV CHARGER. (The off-board charging equipment used to charge an EV) serving 2 vehicles use 1 or 2 40A circuits? I know they can be provided either way, but was wondering if there was a "usual" way.
 

Charged

Member
Location
Ohio
Occupation
Electrical Designer
You are correct , some manufacturers provide them both ways. What I have been doing to deal with your situation is provide a “Power management load summary” which describes the limited kw to each post based on adjustments in the power management settings , even beyond the standard load share you get with a shared 40A circuit. You need to ensure that your specifying/installing a power management system. One example, Charge point had some good reference tables and I used those standard options, long term, short term, overnight for fleet applications. This way I justified how the same service size would accommodate additional chargers later. Trick is making sure the lowest possible kw meets the needs of the client in terms of how long they will be charging. This isn’t a NEC thing by any means but it’s been accepted where I’ve used it.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
I would not assume installation of anything "smart". You can be sure that if someone goes with the 2 per post scheme, users will not be happy if their cars don't fully charge overnight. If someone tries to retrofit additional stations, they won't have the capacity.
 
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