Home L2 Charging: 40A versus 48A

[generaltso]

From there 60 amp breaker, #4 thhn to the front of the garage in 3/4" EMT to a hardwired chargepoint.

How did you hardwire the ChargePoint with #4 wire? Did you put a junction box in front of it to reduce it to #6?

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[ponEpwr]

How did you hardwire the ChargePoint with #4 wire? Did you put a junction box in front of it to reduce it to #6?

Whoops, sorry misspoke. #6 thhn for both chargepoint and 14-50 outlet. As previously stated #6 is the largest conductor the chargepoint can take.

 

[dtbaker61]

Yes I have solar with the red warning plates

yes, you MUST isolate from the grid, AND turn off Solar before attempting any type of generator backfeed for emergency power.

The safest way is a full-on automatic 'transfer switch' and computer controlled system that brings your generator online for house power; but this is also the most expensive way to go, often costing $1k-$2k for the electrical work to add the transfer switch or possibly add a small (50amp) sub-panel for loads you want to be sure to back up like refrigerator, kitchen outlets, and mechanical room.

A not very expensive way to prevent accidental generator connection to the grid is with a mechanical 'interlock' which makes it impossible to backfeed thru the designated generator circuit while on-grid since it has a plate forcing one circuit 'on' while the other 'off'. But this doesn't work if you want to use your existing 240v outlet for both normal use charging your car while grid -tied, and dual purpose for emergency back-feed. In that case, you MUST adhere to protocol, and manually :
- isolate the home from the grid by turning main disconnect 'off'
- also disconnect PV if you have grid-tied inverter without hybrid capability and batteries
- manually turn off non-critical circuits to reduce loads
- and THEN plug in Generator (or MME -> inverter ) to backfeed power to house.

You do not want to 'wake up' a grid-tied solar system with a Generator and no batteries available to absorb surplus energy from PV. Grid-tied PV inverters are not designed to throttle output, and the most likely outcome would be system voltage would rise out of spec and fry the backup inverter/generator.

 

[SirLamerok]

I went with a hardwired set up. The biggest advantage to using a Nema is if your chargepoint ever goes out you could still use your mobile charger. Other than that all advantages point to hardwired. It should be cheaper to hardwire IMO.

 

[dtbaker61]

I went with a hardwired set up. The biggest advantage to using a Nema is if your chargepoint ever goes out you could still use your mobile charger. Other than that all advantages point to hardwired. It should be cheaper to hardwire IMO.

materials cost difference for a 240v outlet is about $30. Avoided cost is buying a new charger for $500+ versus just using the 'included' mobile charger.

And.... with n outlet on the wall, you potentially have the option to backfeed power from generator of choice in emergency situations.

 

[JmanMachE]

I installed both. Breaker to junction box split to 14-50 and hardwired so I can use one or the other but not both concurrently. I keep the Ford mobile plugged in for when I park in the garage which is rare, my garage is kind of small and a pain to use. The Flex is hardwired and mounted outsdie, I use it often. If installing outside I’d strongly recommend hardwired. A plug is nice but these are heavy duty and stiff so you will not want to be plugging/unplugging often.

Lots of prior threads on charge capacity, such as this one:
https://www.macheforum.com/site/thr...talling-a-32-or-40-amp-level-2-charger.14206/

Here in Massachusetts there is a rebate program for Flex and Juicebox smart chargers so look into state and federal offers before buying.

 

[agdad]

I had to go with the 60 amp breaker w/ 4g so Id be prepared for any future charger upgrades.
Suggest you do the same as fast as things are changing
I also carry the Ford supplied charger with me at all time

 

[dbsb3233]

Probably. Even welders can have different plugs. Here's the whole NEMA list. But yes, if your outlet matches the EVSE plug, and it's on a 50A breaker, you should just be able to plug right into that.

 

[Fordmaybe]

yes, you MUST isolate from the grid, AND turn off Solar before attempting any type of generator backfeed for emergency power.

The safest way is a full-on automatic 'transfer switch' and computer controlled system that brings your generator online for house power; but this is also the most expensive way to go, often costing $1k-$2k for the electrical work to add the transfer switch or possibly add a small (50amp) sub-panel for loads you want to be sure to back up like refrigerator, kitchen outlets, and mechanical room.

A not very expensive way to prevent accidental generator connection to the grid is with a mechanical 'interlock' which makes it impossible to backfeed thru the designated generator circuit while on-grid since it has a plate forcing one circuit 'on' while the other 'off'. But this doesn't work if you want to use your existing 240v outlet for both normal use charging your car while grid -tied, and dual purpose for emergency back-feed. In that case, you MUST adhere to protocol, and manually :
- isolate the home from the grid by turning main disconnect 'off'
- also disconnect PV if you have grid-tied inverter without hybrid capability and batteries
- manually turn off non-critical circuits to reduce loads
- and THEN plug in Generator (or MME -> inverter ) to backfeed power to house.

You do not want to 'wake up' a grid-tied solar system with a Generator and no batteries available to absorb surplus energy from PV. Grid-tied PV inverters are not designed to throttle output, and the most likely outcome would be system voltage would rise out of spec and fry the backup inverter/generator.

my PV will shut down when the grid shows no power automatically. As often we loss power once every couple years the 2k for automatic switch did not make sense unless your generator auto comes on. I use a gas/propane one that powers a lot And plugs in outside to a outlet. I kill the hot tub breaker although Would draw to much.

 

[dtbaker61]

yes, your existing NEMA 14-50 outlet, with 50amp breaker, will be perfect for use with the (included) Ford Mobile charger. You don't need to buy or change anything.

 

[P. T. Magoo]

No car yet, but I went with a 50 amp breaker, 6 gauge NM cable except the last several feet down from the attic is conduit with the cable sheathing stripped away and the insulated wires running in the conduit to the 14-50 outlet. Plugged into the outlet is a Grizzle-E configured at 40 amp max. I'd have done exactly the same but with 4 gauge wire to be future proofed, but couldn't find any 4 gauge NM cable, and conduit would have been very awkward to run through the attic.

On testing, this setup charges my wife's Gen-1 Volt just fine (but of course the Volt sips power at just 16 amps). It also made for a handy place to plug in a ceiling mounted garage heater I've been lusting after for years! I've really enjoyed having that heater since I installed the wiring back in December.

Had to chuckle to myself as I was finishing the taxes last night when I read the fine print saying the charger had to be put into service during 2021 to qualify for the tax credit. I figure the test charge of Alicia's car means I stumbled into following the rules just by being inpatient to watch the thing do its thing...

Her car has its own 32-amp-max EVSE on her side of the garage, on its own circuit with 8 gauge wire and a 40 amp breaker. We figured the 32 amp setup was way crazy future-proof when it was installed for that car, and I guess we were right since that's what Ford ships as a portable with the MME.

When my car arrives, she can continue using her EVSE, and my car'll have its own.

 

[BadgerGreg]

I've got the hardwired version (60A circuit), so I can get the max 48A charge. Having the extra charging speed is needed ONLY occasionally, usually when I get home with a low SOC and need to leave early the next morning at 90%-100%. However, that's a rare situation for me.

In the summer, charging at 48A can cause the coolant system to ramp up, sometimes resulting in fairly loud fan noise (this was a complaint of some early MME adopters). Although Ford apparently addressed that with an OTA, the louder cooling sounds can still pop up if you have a warm garage. I address this using my ChargePoint app and reducing the circuit amperage from 60A to 50A. This reduces the charging to 40A and is still fine for almost all scenarios.

In short, I'd say you'll probably be fine with a 50A circuit and 40A charging unless you drive a lot of miles and need full overnight charges.

 

[BadgerGreg]

I would hardwire it on the appropriate 60A circuit and then tell the unit it is on a 40A breaker so it charges at 32A. Less thermal issues at 32A..

Yep - during the hottest summer days, I prefer ramping down to 40A or 32A to avoid the coolant fan noise.

 

[SnBGC]

Yep - during the hottest summer days, I prefer ramping down to 40A or 32A to avoid the coolant fan noise.

Yep. Charging the MME at 48A is like filling an ICE vehicle with a NASCAR fuel can. Most times it is unnecessary and can make a mess of things.

Utility demand charges can increase your monthly bill (if your utility company uses that factor), it can overload your panel depending on what other loads are connected and it can pump a bunch of heat into your garage that the car and home A/C will have to manage.

If you don't need to charge that fast then it is better not to. Special situations excluded of course but generally speaking 30A-32A is fine. I drive quite a bit and 32A works fine. I can turn it up to 48A if needed but I've never had that need yet.

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