Featured Proposed Code Changes affect L2 Charging

In Massachusetts, you don’t have to upgrade unless you pull a permit for that particular work

 

From the code editors' point of view, ground fault protection for equipment (tens of milliamps) and ground fault protection for personnel (few milliamps) are different objectives. If they've decided they want people to be protected, then you could argue the GFPE built into the charger isn't doing that.

 

The ride we're in line for - L2 charges up to almost 20kWs. This speed will likely become more common down the road as longer range vehicles become more & more a part of the market. Even in 5 milliseconds you can still get a serious zap that will take out a pacemaker, but equally important to GFI's that can prevent it from killing you are AFCI's ... (arc fault circuit interrupt) as you will be just as dead from getting a pacemaker Zapped as you can from your house burning down. One would gues the latter would be more painful. The national code doesn't seem to want to act on this, though. Some local codes do for new construction.
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I believe that is the case in most jurisdictions.

Is there any evidence that this code change will make the EVSE, thus plug in, less reliable? The milliamp limit of the internal circuit is based on averting damage to it. It can't be taken as a sign of lower spikes being common during operation.

 

Why would it be ‘possibly in a locked room somewhere’?

 

I hope this might mean that two-pole GFCI breakers are becoming less exotic/expensive/elusive.

I wouldn't mind upgrading my old ConVerdant inverter to have one.

 

Having replaced a melted, NEMA 14-50, I'm fairly sanguine about the change. Hopefully it will mandate better NEMA 14-50 sockets. Ones designed for continuous, 40 A, operation.

Bob Wilson

 

I don't see how this would change EV charging. The existing code requires GFCI for all outlets in garages, including for 240 V, the latter of which is located on the circuit breakers. So, there is no change really. The change is only for outlets not in garages, which didn’t have GFCI requirement before.

 

No, it won’t. Perhaps you had a bad, loose outlet?

 

It looks like the issue here is the hardwired Level 2 charges, not NEMA 14-50 etc. outlets, which are already required to have a GFCI breaker if they are in garages according to the 2020 code. Previously, hardwired EVSEs were exempt from having GFCI in the breaker, but now, it will be required.

It looks like any potential issue would be because of the design of the Level 2 EVSE, not GFCI itself. They had some problems with GFCI in breakers for A/Cs, and they have given an extension to the A/C manufacturers to fix the problems in their units causing GFCI to trip. Level 2 EVSEs should be much easier on the circuits than A/Cs, and I don’t expect as many issues with GFCI for them.

2020 National Electrical Code resets GFCI rule | Pro Builder

 

Installed by a licensed electrician. But this is a common problem:

I went to Granger and found a higher capacity, commercial NEMA 14-50 socket. Only to discover it would require a larger, weather proof box to replace what the electrician installed. So I changed the configuration of the charger:

• Maximum of 8 kWh per charge - this limits the duty cycle giving the unit time to cool off.
• Charging only 6 AM to 11 PM - business hours

The NEMA 14-50 socket was replaced with what the electrician used and the wires were properly prepared and securely clamped. No problems since then.

The Tesla Universal Wall charger uses a 60 A, direct wired unit. Properly dressed wires and mounted on brick facing, it also eliminates the problem of worn connectors or a partially inserted plug and corrosion.

Bob Wilson

 

Why not limit the kW instead of the kWh?

 

The heat comes from the kWh loss. There are secondary effects:

1. Charge limit 8 kWh - minimizes charger monopolization so there are more opportunities for others to charge.
2. Business hours - over night charging leaches go elsewhere.
3. Faster 40 A EVs - still get their charge with the charge limit. My EVs have a 30 and 31 A limit but others can go to 40 A.

Bob Wilson

 

No, the heat in equilibrium comes from the power (kW), not the energy (kWh). The temperature rise in equilibrium is equal to the power times the thermal resistance. You are basically choosing a power that is too high, which is causing a very high equilibrium temperature. Charge it at a smaller current (smaller power), and you can charge it from 0% to 100% SOC with no excess temperatures. In fact, the power across a resistor (your wires and terminals) is proportional to the square of the current; so, you would drastically reduce the heat generated and temperature rise if you reduce the current from 30 A to 20 A or 15 A. A factor-of-two reduction in the current will result in a factor-of-four reduction in the equilibrium temperature rise; so, if your equilibrium temperature was 100 ℃ at an ambient temperature of 20 ℃ (an 80-℃ difference), it would go down to 40 ℃ (a 20-℃ difference).

 

This is how I calculated it:

• 16 A (i.e., 2017 Prius Prime)
  • 3,840 W = 16 A * 240 VAC
  • 2 hrs 5 min to reach 8 kWh
• 30 A (i.e., 2017 BMW i3-REx)
  • 7,200 W = 30 A * 240 VAC
  • 1 hr 7 min to reach 8 kWh
• 40 A (limit of JuiceBox 40 Pro)
  • 9,600 W = 40 A * 240 VAC
  • 0 hr 50 min to reach 8 kWh

The NEMA 14-50 is mounted in a weather proof, external, metal box with air flow from every side but the wall, The cinderblock wall has significant heat absorbing capacity. Regardless, assuming a crappy 0.01 ohm contact resistance:

• (16 * 16) * 0.01 = 2.56 W over 2 hr 5 min
• (30 * 30) * 0.01 = 9 W over 1 hr 7 min
• (40 * 40) * 0.01 = 16 W over 0 hr 50 min

I did my sums based on the kWh to make sure it was EV usable for someone taking an hour at the area stores and restaurants. It would typically take a 10 minute walk to reach and restart a charge session. So worst case 40 A scenario, ~83% duty cycle.

A key element is to minimize charger hogs so other EV owners get a chance to use it too. After all, it is a free charge:

• $0.96 = $0.12/kWh residential (there is a sliding scale)
• $0.64 = $0.08/kWh commercial (there is a sliding scale)

So for a worst case, 8 kWh charge session, it costs the business owner $0.64. A cheap promotional to get us wealthy EV owners to shop there. It saves the frugal EV owner $0.96 to drive there, full charge, and back home. Amazing, everyone is happy.

Bob Wilson

 

Wouldn't it be great if business owners could have free or cheap charging use, via credit cards for their own system? That way they could set maximum limits to, say, 2 hours & then even charge an outrageous camping fee to force free-Loafers to move on.
As for home wiring? I do love me some overkill. Even back in 2012, it made sense we wouldn't be stuck on 3kW charging forever. We wired up a 100 amp breaker (ACFI) so that we could even charge at 80 amps. And now there are a few EVs that can accept those big loads. Charging our measily 7.2kW car is a non-issue. As for wire size & terminals? Go big or go broke




As the Sandy Monroe video shows, it's better to do too much than too little.
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