Adding 240V Outlets to 3 Wire Service to Subpanel

[winnievan]

New to the forum here -- but it looks like this is the place to get electrical advice.

I am looking to add 2x 240V 30A receptacles in a detached garage -- I am in Washington and my city uses the NEC 2020. I've read a TON online and the codebook -- and I think I am getting close -- or at least I am starting to understand the difference between the EGC, grounded conductor and grounding electrode!



I was planning to add 2x 30A 240V outlets using 10-3 (w/ ground) 4-wire NEMA L14-30 receptacles. Based on my read, this is the current code for new-build 240V outlets.

Unfortunately, it appears the service in my panel is only 3-wire -- and the neutral and grounding bars are bonded -- or rather -- whoever wired it just threw the grounds and neutrals on the same buses -- you can see in the picture here:



I was hoping I had a 4-wire service out here, as then I'd know for sure waht to do to add these outlets -- but seeing the neutrals and grounds bonded like this in a subpanel has me confused about how to make this installation to code.

At first I freaked out -- thinking this whole panel was wired wrong and was a ticking time bomb -- but then realized it was probably grand-fathered in and was to-code when it was installed. The house was built in 1993 -- so I imagine this detached garage is from a vintage where 3-wire service w/ bonded ground/neutral in a detached building was acceptable.

I was hoping the run from the main panel to the sub-panel was in EMT and could serve as the EGC -- but it doesn't appear that is the case!

To complicate matters further -- it also appears *something* is bonded directly to the sheet metal of the panel on a the small ground bus near the lower right hand corner of that picture. The wire is coming in from the lower left of the panel, traced in green:





There is a chance it is a bonded to the water pipes and there's also a chance it IS the EGC -- or maybe it is the connection to a grounding electrode (?). This is not connected in parallel with the neutral bus -- which if it is a grounding electrode, seems like it should be if the neutral and ground bus are in parallel.

This is on the to-do list to determine all of these facts by either trying to find the termination of that wire in the main panel or testing for continuity between that wire and the water pipes or ground stake (if there is one).


If that wire is NOT a separate EGC or bonded to the water pipes -- it seems the exceptions to 250.32(B) have me covered -- and it is OK to use run the EGC and grounded conductor in parallel in this sub-panel - but, still, how in this case should I wire in a couple 240V plugs to pass the NEC 2020 inspection?

Should I use 4-wire receptacles running the neutral and EGC back to the same bonded neutral/EGC bus? Should I use 3-wire receptacles with just a "EGC" wire? These circuits will be for a welder/grinder/dust collector/etc. nothing that is cross-listed as 120V/240V.

I know the *right* thing to do is pull an EGC in from the main panel, add grounding electrodes (if there aren't any) and re-wire the subpanel completely. However, this is a 100 FT+ long wire run underground and I have no idea if it is buried cable or in conduit -- so let's just assume that is out of the question. I'll do it if I have to -- but I really just need a couple 240V plugs for a welder/duster collector/etc.

Isn't electricity fun? I sure think so.

 

[Terry D]

Before 2008 this was ok to run a 3 wire feed to a sub panel in a detached garage. As long as there where no other metal pathways from the garage to the house. Just keep your neutral bonded to ground as you already have. You would wire new circuits to this sub panel the same way you would wire them to your main panel. Neutrals and grounds can be both on the neutral buss or grounds can be on seperate ground bar. Main thing is that the neutral buss is bonded to ground.

You still should have ground rod(s) out there.

Are you sure you have room in that sub for the circuits. On some of those panels, the spaces across from that main back fed breaker are not usable. The buss dosent come over far enough for the breaker to properly make connection

Now that i look at the picture again
Make sure your neutal is bonded to the can and that any neutrals are not on ground bars. They have to be on the neutral buss. Grounds can be on either the ground bar or neutral buss

Sent from my SM-G960U using The Garage Journal mobile app

 

[exranger06]

I was planning to add 2x 30A 240V outlets using 10-3 (w/ ground) 4-wire NEMA L14-30 receptacles. Based on my read, this is the current code for new-build 240V outlets.

There isn't ONE receptacle that's the "current code" standard. There are MANY different 240V receptacles that are "current code." You need to select the correct receptacle for your specific application. This is going to depend on the number of amps the tool/appliance uses, and whether or not it needs a neutral wire. Typically, if the tool/appliance came from the manufacturer with a cord and plug already attached, you simply buy the receptacle that matches the plug. You may need to run a few separate circuits with different receptacles if your tools have different electrical requirements.

Should I use 4-wire receptacles running the neutral and EGC back to the same bonded neutral/EGC bus? Should I use 3-wire receptacles with just a "EGC" wire? These circuits will be for a welder/grinder/dust collector/etc. nothing that is cross-listed as 120V/240V.

If the tools/appliances are 240V only (NOT 240V/120V), then you do not need to run a neutral wire. Even if you ran a neutral, you wouldn't have any place to connect it to. If all of these tools are 240V only, they'll have a 3-prong plug. In which case, you'd use a matching (3-prong) receptacle like I said above. The 3 prongs are for the 2 hot legs and the EGC. There is no place to connect the neutral on a 3-prong receptacle. So you'd run 3 wires to it and connect your hot legs and EGC. There's no point in running a neutral if you're just gonna cap it off in the outlet box.

 

[winnievan]

There isn't ONE receptacle that's the "current code" standard. There are MANY different 240V receptacles that are "current code." You need to select the correct receptacle for your specific application. This is going to depend on the number of amps the tool/appliance uses, and whether or not it needs a neutral wire. Typically, if the tool/appliance came from the manufacturer with a cord and plug already attached, you simply buy the receptacle that matches the plug. You may need to run a few separate circuits with different receptacles if your tools have different electrical requirements.

Thanks for the input - I just reviewed the code-book and you're right -- but only for branch circuits with a SINGLE receptacle (NEC 210.20) and you can only go larger not smaller -- i.e. a 50A plug on a 30A circuit but not a 30A plug on a 50A circuit.

It's probably why most welders use 5-60 plugs, even though many don't pull anywhere near 50A.

I also just learned that if you have multiple receptacles on a single branch -- then per NEC 210.21, you must use receptacles matched to the size of the circuit -- the more you know.. the less your inspector hates you.

If the tools/appliances are 240V only (NOT 240V/120V), then you do not need to run a neutral wire. Even if you ran a neutral, you wouldn't have any place to connect it to. If all of these tools are 240V only, they'll have a 3-prong plug. In which case, you'd use a matching (3-prong) receptacle like I said above. The 3 prongs are for the 2 hot legs and the EGC. There is no place to connect the neutral on a 3-prong receptacle. So you'd run 3 wires to it and connect your hot legs and EGC. There's no point in running a neutral if you're just gonna cap it off in the outlet box.

My read of the NEC 250.32(b) is for detached buildings that you MUST still run both a neutral conductor and equipment ground conductor to any new branch circuits! It's the exceptions that make this weird -- like in my case -- where I have a sub-panel that doesn't have an EGC and was grand-fathered in-- so I can (and must) bond neutral and ground -- but you still need to run two wires to any circuits.



Thus my read of the NEC is that it is totally out of code in my jurisdiction to install an older-style 3-Prong NEMA 10-30 on a 240V 30A circuit. In fact, this is what stemmed my confusion since I am in a position to have a bonded EGC and neutral.

Functionally, nothing I am going to use is going to utilize a 4-prong plug -- so you're right there is "no point" in running that 4th wire -- except for the fact it isn't up to code if I do NOT run it!! All the more strange in a situation like mine -- where my grounds and neutrals are legally bonded.

I suppose running the 4-Prong plug future proofs the installation in-case at some point you do run a separate EGC -- but I agree -- there is functionally "no point" to the 4th wire!!

Electricity codes are weird -- but the more time I spend with them -- the more this is all starting to make sense.

 

[TRWham]

You are correct that a 3 prong 10-30 is no longer accepted, but a 3 prong 6-30 certainly still is. The former has a neutral but no ground while the latter has a ground but no neutral. You might need a 4 prong for an EV charger.

As long as the neutral (grounded conductor) from your sub-panel to the main is insulated there is no hazard except the lack of a redundant ground path in the event the neutral goes TU. That is also why you still run an EGC in a branch circuit even if the neutral and ground bars are bonded- to provide a redundant return path. Consider that the service will have only 3 wires from the PoCo- there is no redundant ground path except via earth in the event you lose the neutral to the utility. Earth return works in a pinch, but it's more effective to use something with better conductivity.

 

[Terry D]

250.32(B)(1) is not referring to branch circuits coming from the sub panel with in the building. It is talking about the feeders or branch circuit feeding the building. Since 2008 you are required to have a separate EGC and neutral feeding detached buildings. And these are not to be bonded in the sub panel.

As already said, if a neutral (the grounded conductor ) is not needed in a branch circuit, you don't need to run one. Examples of 240 volt loads that use a neutral would be a clothes dryer, electric range and a lot of spas. These loads not only need 240 volts they also need 120 volts also. Examples of loads not needing a neutral would be air compressors, welders, a/c condensers, mini splits.

What you do need to run to all branch circuits is a EGC ( the grounding conductor )

 

[alfredeneuman]

Be forewarned that the 2020 Code for GFI protection has changed since the last cycle.
Instead of only 120V (15 and 20) amp receptacles needing it, it's changed to all receptacles (120V to ground) requiring GFI protection.
240 receptacles are 120V to ground.

 

[winnievan]

You are correct that a 3 prong 10-30 is no longer accepted, but a 3 prong 6-30 certainly still is. The former has a neutral but no ground while the latter has a ground but no neutral. You might need a 4 prong for an EV charger.

Awesome! Thank you so much - this makes sense and I had just assumed that since 10-30 wasn't allowed that 6-30 definitely wasn't allowed -- but now I see the distinction and why 10-30 was superseded by 14-30.

As long as the neutral (grounded conductor) from your sub-panel to the main is insulated there is no hazard except the lack of a redundant ground path in the event the neutral goes TU. That is also why you still run an EGC in a branch circuit even if the neutral and ground bars are bonded- to provide a redundant return path. Consider that the service will have only 3 wires from the PoCo- there is no redundant ground path except via earth in the event you lose the neutral to the utility. Earth return works in a pinch, but it's more effective to use something with better conductivity.

All makes sense to me! Thank you so much for this.

 

[winnievan]

250.32(B)(1) is not referring to branch circuits coming from the sub panel with in the building. It is talking about the feeders or branch circuit feeding the building. Since 2008 you are required to have a separate EGC and neutral feeding detached buildings. And these are not to be bonded in the sub panel.

As already said, if a neutral (the grounded conductor ) is not needed in a branch circuit, you don't need to run one. Examples of 240 volt loads that use a neutral would be a clothes dryer, electric range and a lot of spas. These loads not only need 240 volts they also need 120 volts also. Examples of loads not needing a neutral would be air compressors, welders, a/c condensers, mini splits.

What you do need to run to all branch circuits is a EGC ( the grounding conductor )

Ah I see how 250.32(B) applies now -- I assumed it meant that since you 'ought to have mains, EGC and neutral in a sub-panel that you NEED to use them in all cases. But now I see the 6-30 receptacle will work since I really don't need a neutral on my 240V circuits.

I get that running a proper EGC is the *right* way -- but it's super prohibitive in this case and since my panel is "grandfathered" the way to do it according to the exceptions of 250.32(B) is to bond ground and neutral in the subpanel in a separate building, if I'm reading it right. Is that what you are saying?

EDIT: or are you saying that each circuit needs an EGC -- and that it is OK that it's is bonded to neutral for me since I have the 3-wire service a la exceptions to 250.32(B).


Your feedback has been incredibly helpful -- so thank you for the comments thus far!

 

[Terry D]

Ah I see how 250.32(B) applies now -- I assumed it meant that since you 'ought to have mains, EGC and neutral in a sub-panel that you NEED to use them in all cases. But now I see the 6-30 receptacle will work since I really don't need a neutral on my 240V circuits.

I get that running a proper EGC is the *right* way -- but it's super prohibitive in this case and since my panel is "grandfathered" the way to do it according to the exceptions of 250.32(B) is to bond ground and neutral in the subpanel in a separate building, if I'm reading it right. Is that what you are saying?

EDIT: or are you saying that each circuit needs an EGC -- and that it is OK that it's is bonded to neutral for me since I have the 3-wire service a la exceptions to 250.32(B).


Your feedback has been incredibly helpful -- so thank you for the comments thus far!

Yes each branch and branch feeder circuit installed with todays codes requires a EGC. In your situation with just having a 3-wire feed to your sub panel, which is grandfathered in, You would terminate the EGC and neutral the same way you would in your main house panel or where ever your first main OCP device is. All services start with a 3-wire feed. Either both on the neutral buss or the EGC on the ground bar and the neutral on the neutral buss. The main thing is that your neutral in your garage sub panel is bonded to the can (enclosure) by either a screw, strap or bonding jumper

 

[winnievan]

I get it now. Thank you for the feedback!!

Glad I got this in before the font changed, too. I feel like I'm reading an academic journal now