3 Prong 240v plug, no neutral

[Rodneycl]

Hi, I just ran into a similar this issue at my new home. When plugging my Tesla portable charger into a 240v 10-30R dryer outlet that was added by the previous owner, it works fine overnight unless someone uses the microwave or is in the fridge too long for the compressor to kick in. I can actually reproduce the issue whenever I want by microwaving a cup of water after plugging in the charger and car.

I took a peek into the outlet box and noticed they used 4wire #10 with the hot going to the blades and the neutral going to the middle. The ground is wired to the outlet box. I followed the wire back to the panel and it's on a 30Amp ge breaker circuit switch with the white neutral is on a bar down the right side and the ground is on a bar down the left.

From reading here I wonder if the box is wired incorrectly and if the ground should have been connected to the middle of the plug and the neutral should have been left in the back of the box. any thoughts on this?

 

[Rodneycl]

Hi, I just ran into a similar this issue at my new home. When plugging my Tesla portable charger into a 240v 10-30R dryer outlet that was added by the previous owner, it works fine overnight unless someone uses the microwave or is in the fridge too long for the compressor to kick in. I can actually reproduce the issue whenever I want by microwaving a cup of water after plugging in the charger and car.

I took a peek into the outlet box and noticed they used 4wire #10 with the hot going to the blades and the neutral going to the middle. The ground is wired to the outlet box. I followed the wire back to the panel and it's on a 30Amp ge breaker circuit switch with the white neutral is on a bar down the right side and the ground is on a bar down the left.

From reading here I wonder if the box is wired incorrectly and if the ground should have been connected to the middle of the plug and the neutral should have been left in the back of the box. any thoughts on this?

 

[Bull]

Hi, I just ran into a similar this issue at my new home. When plugging my Tesla portable charger into a 240v 10-30R dryer outlet that was added by the previous owner, it works fine overnight unless someone uses the microwave or is in the fridge too long for the compressor to kick in. I can actually reproduce the issue whenever I want by microwaving a cup of water after plugging in the charger and car.

I took a peek into the outlet box and noticed they used 4wire #10 with the hot going to the blades and the neutral going to the middle. The ground is wired to the outlet box. I followed the wire back to the panel and it's on a 30Amp ge breaker circuit switch with the white neutral is on a bar down the right side and the ground is on a bar down the left.

From reading here I wonder if the box is wired incorrectly and if the ground should have been connected to the middle of the plug and the neutral should have been left in the back of the box. any thoughts on this?

Edited to correct wrong advice:

For a 10-30 outlet the middle blade should be connected to neutral. In most cases ground and neutral are connected one way or another in the main panel so it usually does not make much difference.
Assuming that your charging amps are set to a max of 24a, I would be more concerned that it looks like the lines supplying the 10-30 outlet are also feeding another circuit such as your microwave or fridge. The 10-30 outlet should be on a dedicated circuit (and ideally so should the fridge circuit).

 

[ucmndd]

Why the down vote @tga ? You have a better interpretation?

A NEMA 10-30 is two hots and a neutral, so your “middle blade should be connected to ground” advice is not correct.

In a nutshell this is why 10-30s have been banned since the 90s.

Two hots and a ground is a 6-30.

 

[ucmndd]

Hi, I just ran into a similar this issue at my new home. When plugging my Tesla portable charger into a 240v 10-30R dryer outlet that was added by the previous owner, it works fine overnight unless someone uses the microwave or is in the fridge too long for the compressor to kick in. I can actually reproduce the issue whenever I want by microwaving a cup of water after plugging in the charger and car.

I took a peek into the outlet box and noticed they used 4wire #10 with the hot going to the blades and the neutral going to the middle. The ground is wired to the outlet box. I followed the wire back to the panel and it's on a 30Amp ge breaker circuit switch with the white neutral is on a bar down the right side and the ground is on a bar down the left.

From reading here I wonder if the box is wired incorrectly and if the ground should have been connected to the middle of the plug and the neutral should have been left in the back of the box. any thoughts on this?

Given you have four wires available, I would recommend replacing the 10-30 outlet with a 14-30, which has four prongs to include a dedicated neutral and ground.

You’ve got something fishy going on, likely not with the 10-30 circuit but rather the kitchen circuit(s) the fridge and microwave are on.

 

[Bull]

A NEMA 10-30 is two hots and a neutral, so your “middle blade should be connected to ground” advice is not correct.

In a nutshell this is why 10-30s have been banned since the 90s.

Two hots and a ground is a 6-30.

Correct. I was wrong and edited my answer to reflect the correct answer. Thanks

 

[Bull]

Given you have four wires available, I would recommend replacing the 10-30 outlet with a 14-30, which has four prongs to include a dedicated neutral and ground.

You’ve got something fishy going on, likely not with the 10-30 circuit but rather the kitchen circuit(s) the fridge and microwave are on.

If the fridge and/or microwave are affecting the 10-30 circuit it indicates that the 10-30 circuit may not be a dedicated circuit.

 

[tga]

For a 10-30 outlet the middle blade should be connected to ground. In most cases ground and neutral are connected one way or another in the main panel so it usually does not make much difference.

This is what cause me to jump on the disagree. Connecting the middle blade to the ground wire is a code violation and potential fire risk. More detailed explanation later.

But I agree with the second part, so a total disagree was probably overkill.

A NEMA 10-30 is two hots and a neutral, so your advice is not correct.

Two hots and a ground is a 6-30.

+1

@Rodneycl, since your outlet box has all four wires (hot-hot-neutral-ground) the right thing to do is replace your 10-30 with a 14-30 and get the 14-30 UMC adapter (there is no 6-30 adapter, so that isn't an option).

I'm also a little concerned about the fact that turning on a high current 120V load causes charging to stop. This sounds like the neutral is being pulled away from 0V, which could be a loose neutral (a bad thing). Do room lights dim or brighten noticeably when the microwave or fridge compressor kick in? Especially in other rooms? You might need to have an electrician check things out.

 

[tga]

If the fridge and/or microwave are affecting the 10-30 circuit it indicates that the 10-30 circuit may not be a dedicated circuit.

Or a high resistance connection on the neutral bus bar, not a good thing indeed. Electricians ears perk up if you say "I think I have a loose neutral." Partially because it could be dangerous, partially because it means lots of labor charges for them!

 

[ucmndd]

If the fridge and/or microwave are affecting the 10-30 circuit it indicates that the 10-30 circuit may not be a dedicated circuit.

No, I don’t think so. The 10-30 is 240v and isn’t sharing anything with the 120v fridge and microwave.

I think the more likely explanation is the EVSE is seeing the spike in return current flow or voltage fluctuation on the neutral when the compressor kicks in or the microwave turns on and is treating it as a ground fault and shutting things down. Moving to a 14-30 with a real ground connection (from the description OP provided the neutrals and grounds might not be bonded in the panel) may well clear this up.

 

[tga]

Hi, I just ran into a similar this issue at my new home. When plugging my Tesla portable charger into a 240v 10-30R dryer outlet that was added by the previous owner, it works fine overnight unless someone uses the microwave or is in the fridge too long for the compressor to kick in. I can actually reproduce the issue whenever I want by microwaving a cup of water after plugging in the charger and car.

I took a peek into the outlet box and noticed they used 4wire #10 with the hot going to the blades and the neutral going to the middle. The ground is wired to the outlet box. I followed the wire back to the panel and it's on a 30Amp ge breaker circuit switch with the white neutral is on a bar down the right side and the ground is on a bar down the left.

From reading here I wonder if the box is wired incorrectly and if the ground should have been connected to the middle of the plug and the neutral should have been left in the back of the box. any thoughts on this?

No, the plug is wired 100% correctly. The change you propose is a code violation and a potential/shock fire risk. Don't do it.

The 10-30 is technically an "ungrounded 120/240V" outlet, meaning you can legitimately pull 30A@120V (OK, it's unlikely you ever would, but you could...). Any 120V load is returning current on the neutral. If you connect the bare ground wire (EGC or "equipment grounding conductor" in NEC terminology), you've now connected power to your home's ground circuit. If the connection to your ground system (wire pipe, ground rods, etc) is bad, loose, broken, corroded, etc (happens more often than people realize) you could get a shock touching a metal appliance elsewhere in the house.

Worse, if it's a 10-50 outlet wired with Romex, you could overload the bare ground, since code allows smaller ground wires on high-current circuits (6ga romex, for a 50A outlet, generally has a 10ga ground), since the EGC is never supposed to carry current. Now drawing 50A@120V, you're drawing power on a 6ga feed, but returning on an undersized 10ga EGC. Not a good thing.

Normally, none of this matters. A properly installed NEMA-10 outlet is on a dedicated home run circuit with a properly sized neutral (not undersized), running right back to the breaker panel, with the neutral connected to a bus bar that is properly bonded to ground. In that case, you can use the neutral as a current return or EGC safely.

I recall seeing 10-30 dryer outlets wired with 10-2 romex in older homes. I think this was allowed under old versions of the code, since 10 gauge circuits require a 10ga ground. So 10/2 romex is 2 10 ga hots and a 10 ga ground. But ideally they should have used 10/3, which makes conversion to a 14-30 easy.

 

[Rodneycl]

Edited to correct wrong advice:

For a 10-30 outlet the middle blade should be connected to neutral. In most cases ground and neutral are connected one way or another in the main panel so it usually does not make much difference.
Assuming that your charging amps are set to a max of 24a, I would be more concerned that it looks like the lines supplying the 10-30 outlet are also feeding another circuit such as your microwave or fridge. The 10-30 outlet should be on a dedicated circuit (and ideally so should the fridge circuit).

Thanks for the reply! I know this is going to sound crazy, but I actually traced the wire (cut the wall and everything!) from the outlet box to the breaker panel and it's going directly to the 30Amp GE circuit. The only thing that could be shared is where the neutral wire and the ground wire are connected (those side bars in the panel.)

My guess now is there is a faulty outlet or circuit, or somehow the ground bar or neutral bar are being electrified (maybe via an incorrectly wired switch?)

Could that be it?

 

[tga]

Thanks for the reply! I know this is going to sound crazy, but I actually traced the wire (cut the wall and everything!) from the outlet box to the breaker panel and it's going directly to the 30Amp GE circuit. The only thing that could be shared is where the neutral wire and the ground wire are connected (those side bars in the panel.)

My guess now is there is a faulty outlet or circuit, or somehow the ground bar or neutral bar are being electrified (maybe via an incorrectly wired switch?)

Could that be it?

It sounds like you have already opened up the breaker panel and poked around. If you know what you are doing and feel like you can do it safely (wear rubber soled shoes, one hand in your pocket at all times, etc), I'd clamp on a voltmeter and measure H1-H2, H1-N, H2-N while someone turns the microwave on and off.

You mentioned separate neutral and ground busbars. Do you recall how many wires are coming into the panel? Is the ground bonding there or possible outside in the meter pan/main shutoff? Is this the main panel or a subpanel?

Take some pictures if you open it up.

 

[Rodneycl]

It sounds like you have already opened up the breaker panel and poked around. If you know what you are doing and feel like you can do it safely (wear rubber soled shoes, one hand in your pocket at all times, etc), I'd clamp on a voltmeter and measure H1-H2, H1-N, H2-N while someone turns the microwave on and off.

You mentioned separate neutral and ground busbars. Do you recall how many wires are coming into the panel? Is the ground bonding there or possible outside in the meter pan/main shutoff? Is this the main panel or a subpanel?

Take some pictures if you open it up.

I know enough to poke but this scared me. LOL

Thanks for all the advice btw! I'm leaning to the suggestion of changing to 14-30. I'll go buy a box today.

 

[Bull]

No, I don’t think so. The 10-30 is 240v and isn’t sharing anything with the 120v fridge and microwave.

I think the more likely explanation is the EVSE is seeing the spike in return current flow or voltage fluctuation on the neutral when the compressor kicks in or the microwave turns on and is treating it as a ground fault and shutting things down. Moving to a 14-30 with a real ground connection (from the description OP provided the neutrals and grounds might not be bonded in the panel) may well clear this up.

You are probably correct but I have seen 110v circuits fed improperly by pulling a single leg from a jbox. Horribly bad work but it does happen.

 

[Bull]

I know enough to poke but this scared me. LOL

Thanks for all the advice btw! I'm leaning to the suggestion of changing to 14-30. I'll go buy a box today.

Changing to a 14-30 is by far the best advice. It will also likely fit in the existing box (ideally 2-gang) so you will probably just need the new recep. Leviton 14-30R

 

[tga]

You are probably correct but I have seen 110v circuits fed improperly by pulling a single leg from a jbox. Horribly bad work but it does happen.

That brings back memories... I've lived in houses where prior owners were clearly big DIY'ers, but didn't know their limitations. I was constantly coming across weird hacks in the electrical, plumbing, and HVAC. The best (or worst!) was a ceiling outlet in the garage for the garage door opener, that was wired with the ground pin live. That was a fun one. Lots of sparks and swearing when I hung a (grounded) trouble light off the (live) strapping supporting the opener.

 

[roblab]

This thread is from 2015. Should we stop and ask ourselves if it actually needs to be continued?

As much as I love that we’re still calling out @roblab for his decidedly bad, ignorant, dangerous advice 6.5 years later, it might be time to let this one go.

Hey, I love the notoriety! And I haven't been electrocuted nor burned down either my house or garage. I've wired several houses in several states, and they haven't burned down either, nor have any persons been shocked. So, it might be that there's a LOT of over protection going on. But you electricians keep on electricianing!

 

[ucmndd]

Hey, I love the notoriety! And I haven't been electrocuted nor burned down either my house or garage. I've wired several houses in several states, and they haven't burned down either, nor have any persons been shocked. So, it might be that there's a LOT of over protection going on. But you electricians keep on electricianing!

“I’m not dead yet” is far and away my favorite excuse for doing stupid things.

If that’s your thing, more power to you (pun intended). I’m more interested in making sure you don’t get someone else hurt with bad advice than changing your ways.

 

[Rodneycl]

Changing to a 14-30 is by far the best advice. It will also likely fit in the existing box (ideally 2-gang) so you will probably just need the new recep. Leviton 14-30R

Sooooo, I went to the Tesla service desk today after work. Just my luck they are out of the 14-30 but I was able to grab their last 240v adapter, which was a 14-50. :-(

Next stop was home Depot where I grabbed a Leviton 14-50R flush mount outlet.

I've read that many people are using 14-50 and the 4 wires in the outlet box should be the right ones for this job.

I'll try to swap it tonight and will update if the microwave issue persists after this change.

Thanks.