3 vs 4 prong 240

[andrew61]

Hi:

We're renting for the summer and were planning to use the unit's 240 dryer plug. However, the plug is 3 prong 240 not 4. I'm sure this is explained elsewhere, so can someone either explain the difference (and whether I can get an adapter for the three prongs) or point me to the discussion?

 

[borski]

I guarantee you @DeaneG knows the answer

 

[scal_air]

Lol...

Learn the Difference Between 3- and 4-Slot Dryer Outlets

Electric dryers use either three-prong or four-prong plugs, designed to match either three-slot or four-slot outlets. Learn about three-prong or four-prong dryer outlets.

www.thespruce.com

Converter plug

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But I'll leave it to the expert DeanneG to tell you if you are going to electrocute yourself or burn your rental down...

 

[thong1999]

I use this set up to charge at home. I had to buy a 14-30 adapter from Lucid since my dryer was connected to a 30 amp circuit. The lower current reduced the risk of a fire. Charging rate is 20 miles per hour.

 

[DeaneG]

Hi:

We're renting for the summer and were planning to use the unit's 240 dryer plug. However, the plug is 3 prong 240 not 4. I'm sure this is explained elsewhere, so can someone either explain the difference (and whether I can get an adapter for the three prongs) or point me to the discussion?

Sounds like the rental has an old style 10-30 outlet for the dryer. It's no longer legal for new installations.

You'd need to buy Lucid's 14-30 adapter for their mobile charging cable to force the car to charge at 24 amps: https://store.lucidmotors.com/nema-14-30-charging-adapter/
and buy a 10-30 to 14-30 adapter as in the previous post to have a compatible outlet to plug it in to.

Most importantly, you'd need to connect the dangling ground wire that the 10-130 to 14-30 adapter comes with to a good ground from a nearby grounded 120V outlet, or a clean cold water pipe. If no 120V outlet is available (washing machine?) but a cold water pipe is nearby, you could clean it with a scrap of sandpaper and clamp the end of the ground wire to the pipe with a screw-type hose clamp.

 

[DeaneG]

Hi:

We're renting for the summer and were planning to use the unit's 240 dryer plug. However, the plug is 3 prong 240 not 4. I'm sure this is explained elsewhere, so can someone either explain the difference (and whether I can get an adapter for the three prongs) or point me to the discussion?

If you try this, you'd also want to check that after charging for an hour or so, the mobile charger's plug pins are not excessively hot. An older dryer receptacle's wire connections may have loosened with time, or its receptacle metal parts lost their temper and become weak. A dryer isn't a continuous load and can get away with a worse connection to 240V than an EV.

 

[Ughwhy]

Sounds like the rental has an old style 10-30 outlet for the dryer. It's no longer legal for new installations.

You'd need to buy Lucid's 14-30 adapter for their mobile charging cable to force the car to charge at 24 amps: https://store.lucidmotors.com/nema-14-30-charging-adapter/
and buy a 10-30 to 14-30 adapter as in the previous post to have a compatible outlet to plug it in to.

Most importantly, you'd need to connect the dangling ground wire that the 10-130 to 14-30 adapter comes with to a good ground from a nearby grounded 120V outlet, or a clean cold water pipe. If no 120V outlet is available (washing machine?) but a cold water pipe is nearby, you could clean it with a scrap of sandpaper and clamp the end of the ground wire to the pipe with a screw-type hose clamp.
View attachment 21748

Also confirm the pipes are not plastic or the grounding will not work.

 

[borski]

If you try this, you'd also want to check that after charging for an hour or so, the mobile charger's plug pins are not excessively hot. An older dryer receptacle's wire connections may have loosened with time, or its receptacle metal parts lost their temper and become weak. A dryer isn't a continuous load and can get away with a worse connection to 240V than an EV.

Purely hypothetically - if you couldn’t properly find a ground to run to, would a GFCI breaker work?

 

[HariK]

You can pick up ground from a water pipe near the washer. That is better than ground from a GFCI outlet.

 

[DeaneG]

Purely hypothetically - if you couldn’t properly find a ground to run to, would a GFCI breaker work?

No. All EVSEs need a ground to operate. They'll error out if ground isn't connected.

 

[andrew61]

Thank you all! This is helpful!! The wiring is old, flaky, and not to code at the rental, so I'll tread carefully. In addition, my wife just found out she can fully charge the car at her office parking garage for a $20 flat fee, so we have a good alternate option as well.

 

[Steveinarizona]

Purely hypothetically - if you couldn’t properly find a ground to run to, would a GFCI breaker work?

I have read that there are problems with a GFCI outlet and an EVSE as some (or all) of the EVSEs have it built in and they can conflict.

 

[borski]

I have read that there are problems with a GFCI outlet and an EVSE as some (or all) of the EVSEs have it built in and they can conflict.

For hardwired EVSEs. A 14-50 receptacle still requires a GFCI breaker according to NEC code, iirc, but according to @DeaneG also needs real ground and the cable will not operate if GFCI is the sole ground protection.

The cables (aka EVSEs) also do have some “smart GFCI” protection (which will reset instead of nuisance tripping a few times so you still get a charge, since ground faults can be transient) but I’m not sure how it works with the conflict between the EVSE not wanting a GFCI breaker and the code *really* wanting one.

@DeaneG likely knows and has explained it before and maybe he can correct all of my errors above lol

 

[DeaneG]

@DeaneG likely knows and has explained it before and maybe he can correct all of my errors above lol

Basically you can't operate an EVSE for charging EVs on a circuit that is protected by a circuit breaker that has a GFCI function (a GFCI breaker or GFCI/AFCI combo breaker). The EVSE will cause the GFCI breaker to trip off, once in a while or frequently.

Some localities require a GFCI breaker on every outlet in a garage, including a 14-50. This essentially forces the user of hardwiring the EVSE instead of installing it as a plug-in, which is much better anyway.

 

[borski]

Basically you can't operate an EVSE for charging EVs on a circuit that is protected by a circuit breaker that has a GFCI function (a GFCI breaker or GFCI/AFCI combo breaker). The EVSE will cause the GFCI breaker to trip off, once in a while or frequently.

Some localities require a GFCI breaker on every outlet in a garage, including a 14-50. This essentially forces the user of hardwiring the EVSE instead of installing it as a plug-in, which is much better anyway.

I see. So the risk of nuisance tripping is too high even if not hardwired then. Got it.

 

[Steveinarizona]

Basically you can't operate an EVSE for charging EVs on a circuit that is protected by a circuit breaker that has a GFCI function (a GFCI breaker or GFCI/AFCI combo breaker). The EVSE will cause the GFCI breaker to trip off, once in a while or frequently.

Some localities require a GFCI breaker on every outlet in a garage, including a 14-50. This essentially forces the user of hardwiring the EVSE instead of installing it as a plug-in, which is much better anyway.

Thanks. As always, I learn something from you. Here in Phoenix my electrician did not have to put in a GFCI circuit when he wired it for me and I do have a plug-in unit (Chargepoint
Flex) which I have never in 18 months unplugged. 50 amp line running at 40 amps continuous.