3-wire and 4-wire 240V on same circuit?

[jjwillac]

Forgive the long "background" section; my actual question is down a bit, but I want to minimize confusion since this conversation could easily go sideways. Everyone please try to make it clear what part of the question you're contributing to.

In my single-man home shop the general purpose 240v circuits each have two receptacles (the two receptacles are never used at same time). All the circuits are run with 3X 10 ga THHN (red, black, and green ground) in 1" emt conduit and currently have 20a receptacles and breakers.

I want to bring 240v + 120v to my tablesaw workstation that is about 12ft from the nearest wall. The 120v will power the router station and a general use outlet or two. Two separate commercial electricians have both come-up with the same solution using a multi-wire branch circuit:

1. add a neutral (white) to the circuit feeding the receptacle nearest the saw to make it 120/240v with a L14-20 receptacle
2. run a 10ga SJOW "cord" from the L14-20R to a box mounted to the saw workstation
3. In the box at the workstation, the red, black, and ground would connect to a 20a 240v receptacle (L6-20), while the black, white, and green would connect to a 20a 120v duplex receptacle.

QUESTIONS: Up to this point, the two electricians are in agreement and it all makes sense to me. There are two points the electricians disagree on:

1) one says that we only need to run the 4th (white) wire to the receptacle that will bring 120v to the workstation, NOT the second receptacle that is on the same circuit. The other insists the white would also need to be run to the 2nd receptacle even though it would just be capped in the box.

Adding a white to the conduit leading to the 2nd receptacle on the circuit could (depends on question 2 below) force us to use a 70% derating instead of the current 80%, which would mean the 10 ga wires would no longer be able to be used for a 30a circuit. One of the other circuits in the conduit is currently 30a and I'd like to keep it as an option for all the "general purpose" 250v circuits.

This brings us (finally!) to the 2nd QUESTION: the electrician suggesting the white needs to also be run to the 2nd receptacle on the circuit says that derating isn't an issue because the white doesn't count as a current carrying conductor on this circuit. The other electrician says that it would indeed be counted as a CCC. I know this can get confusing, so wanted to get some additional opinions.


Thanks for any help and sorry again for the long post.

 

[PCustoms]

Who cares?

You're talking a dollar or two for a few extra feet of a single wire. Pick the contractor you like better and let them do the job.

 

[wyliesdiesels]

Neutral does count as a CCC but im not understanding why you would need to run it when it wont be used...

Is all of this being breakered at 20a? If so, why are you using 10ga cord?

If not and you plan to use a 30a breaker, then it's a no go. Cant put 20a receptacle on 30a breaker

 

[Norcal]

Neutral does count as a CCC but im not understanding why you would need to run it when it wont be used...

Is all of this being breakered at 20a? If so, why are you using 10ga cord?

If not and you plan to use a 30a breaker, then it's a no go. Cant put 20a receptacle on 30a breaker

Plus the OP is in Oregon, which is on the 2020, GFCI protection is required, also. BTW, CA adopted the 2020 as of this year.

 

[dogdog]

@jjwillac
Both electrician are correct dependents on what you want to do. If you have extra space for beakers I would just keep my 120 and 240 circuit separate. It’s not like wires are that expensive and electrician have to run another wire anyways. Not much extra work. If any.

Not 100% sure about NEC required for your townships.

240v only requires hot L1 and hot L2 and ground wire ( that’s your 3 wire ) 240v

If you need 120v then you would need Hot L1 and Hot L2 , neutral and ground wires and that is your 4 wires

From the 4 wires if you tap for 120v and that is your mwbc . In this case which ever hot wire you tap for the 120v that would be unbalanced on the 240v. It would work because you said one man shop, probably not NEC kosher. As long as you keep it 20amps.

Just saying it’s just easier and cleaner to keep them separate.

 

[cgrutt]

I'm not an electrician but would run another breaker for the 120v and keep it separate.

That said, I had a hot tub with 3 240v motors and believe it ran some 120v things (circulating pump, lights, etc) off the same 240v, 4-wire circuit so it's probably fine.

 

[dogdog]

This brings us (finally!) to the 2nd QUESTION: the electrician suggesting the white needs to also be run to the 2nd receptacle on the circuit says that derating isn't an issue because the white doesn't count as a current carrying conductor on this circuit. The other electrician says that it would indeed be counted as a CCC. I know this can get confusing, so wanted to get some additional opinions.

Neutral is ccc, return path for 120v
Ground doesn’t normally count as ccc and you can share it. As long as you don’t have bonded neutral in the sub panel. This is answered in post 3.

Base on this I would go for the electric ma son that says neutral is ccc. And ask them to keep my 120/240 separate.

 

[klassenl]

The "identified" conductor as part of a 3 wire 240v single phase circuit or a 4 wire 3 phase circuit does not count as a current carrying conductor in Canada.

 

[theoldwizard1]

Neutral does count as a CCC but im not understanding why you would need to run it when it wont be used...

Is all of this being breakered at 20a? If so, why are you using 10ga cord?

Probably not code, but is common to "upsize" cordage.

 

[dogdog]

The "identified" conductor as part of a 3 wire 240v single phase circuit or a 4 wire 3 phase circuit does not count as a current carrying conductor in Canada.

except when you are using the 4 wire (including ground) 240v with a 120V tapped in... the "identified" conductor will be CCC

 

[jjwillac]

Neutral does count as a CCC but im not understanding why you would need to run it when it wont be used...

Is all of this being breakered at 20a? If so, why are you using 10ga cord?

If not and you plan to use a 30a breaker, then it's a no go. Cant put 20a receptacle on 30a breaker

There are two receptacles on the 240v circuit, one of which would need the neutral. The other receptacle doesn't need the neutral and one electrician says there is no reason to run the neutral to it just to cap it off and the other says both receptacles on the circuit need to have the same wires run to them.

The 10 gauge is oversized so that any of the circuits are capable of carrying 30a, that way if I need a 30a circuit all I need to do is swap the CB and receptacle. No issue with 10 ga wire on 20a crcuits; 12 ga is the  minimum.

@jjwillac
Both electrician are correct dependents on what you want to do. If you have extra space for beakers I would just keep my 120 and 240 circuit separate. It’s not like wires are that expensive and electrician have to run another wire anyways. Not much extra work. If any.

Not 100% sure about NEC required for your townships.

240v only requires hot L1 and hot L2 and ground wire ( that’s your 3 wire ) 240v

If you need 120v then you would need Hot L1 and Hot L2 , neutral and ground wires and that is your 4 wires

From the 4 wires if you tap for 120v and that is your mwbc . In this case which ever hot wire you tap for the 120v that would be unbalanced on the 240v. It would work because you said one man shop, probably not NEC kosher. As long as you keep it 20amps.

Just saying it’s just easier and cleaner to keep them separate.

I agree keeping them separate would be great, and if it were just a wire or two I wouldn't be worried at all, but my understanding is that adding a separate 120v circuit to the location would mean adding 2 more conductors (a hot and neutral) to the conduit, which would mean 7 conductors in the conduit, which means 70% derating, which means my 10 ga wire is no longer approved for 30a and I'd need to replace the existing wiring with 8 ga to meet my needs. Obviously, that is an adventure I would be happy to avoid. Also, separate 120v and 240v receptacles at the wall would mean two cords going to the workstation instead of one.

Neutral is ccc, return path for 120v
Ground doesn’t normally count as ccc and you can share it. As long as you don’t have bonded neutral in the sub panel. This is answered in post 3.

Base on this I would go for the electric ma son that says neutral is ccc. And ask them to keep my 120/240 separate.

It makes sense that the neutral is a CCC between the 120v receptacle and the neutral bus, so I guess it would also be a CCC along the run that is ultimately capped at the 2nd 240v receptacle on the circuit (which will be 240v only and thus not use the neutral)? Guess I'm still not sure whether it is really necessary to run a neutral to the 2nd receptacle if it is just going to be capped off.

Thanks for everyone's input thus far.

 

[dogdog]

I agree keeping them separate would be great, and if it were just a wire or two I wouldn't be worried at all, but my understanding is that adding a separate 120v circuit to the location would mean adding 2 more conductors (a hot and neutral) to the conduit, which would mean 7 conductors in the conduit, which means 70% derating, which means my 10 ga wire is no longer approved for 30a and I'd need to replace the existing wiring with 8 ga to meet my needs.

Eh!!! I am no conduit expert but maybe you need to check the conduit fill chart, there are online calculators for you. Dependents on your conduit emt ent pvc what nots sizes. Dunno how you got 7. Even if you wanted a 4 wire L14-20 it’s still only 6 connectors. But you really have to check fill chart.

For 240v you need hot(1) hot(2) ground(3) and for 120v you need hot(4) neutral(5) and shared ground. That is 5. Pretty sure I have done it on 1/2” emt to do 1 240@30amp and 1 120v @20amp to corners in my garage. I did 2 10ga and 3 12ga in each conduit. It’s been a while don’t remember. Or was it 3x 10ga and 2x 12.

Not too sure about derating, maybe some one can comment on that

 

[dogdog]

Guess I'm still not sure whether it is really necessary to run a neutral to the 2nd receptacle if it is just going to be capped off.

2nd receptacle ? You mean splitting off from that mwbc circuit.z if you plan to have 120v at that receptacle. Then it needs a neutral to it. From the shared neutral. It really don’t make any sense. Technically it’s a yes you need it, but if you plan to cap it off why even bother having that receptacle ?

Would make more sense to separate your 240 and 120v and if you need to have more than one 120 receptacle just link it to the 120v 20amp circuit. Would still be better than doing these mwbc and tapping 240v etc. just my 2 cents.

 

[jjwillac]

2nd receptacle ? You mean splitting off from that mwbc circuit.z if you plan to have 120v at that receptacle. Then it needs a neutral to it. From the shared neutral. It really don’t make any sense. Technically it’s a yes you need it, but if you plan to cap it off why even bother having that receptacle ?

Would make more sense to separate your 240 and 120v and if you need to have more than one 120 receptacle just link it to the 120v 20amp circuit. Would still be better than doing these mwbc and tapping 240v etc. just my 2 cents.

All of the 240v circuits in my shop have 2 receptacles on them; none are single receptacle, dedicated circuits. A key bit of info for all issues.

Conduit fill is not an issue unless I need to cange to 8 ga wires due to derating. In the conduit going to the receptacle I would like to make 4-wire, 120v/240v there is currently 2 separate 240v circuits, so 4 CCC (2 red, 2 black). Adding the neutral will make 5, which means I only need to derate to 80% (32a on 10ga wire). However, in the conduit to the other receptacle that is on the same circuit I want to add the neutral to, there are currently 3 separate 240v circuits, so 6 CCC (3 red, 3 black), which still only requires deratingto 80%. If I have to run the neutral through this conduit also (even though it will just be capped), and it IS A CCC, then the conduit would now contain 7 CCC, requiring derating the wires to 70% (28a on 10 ga wire), and precluding any circuits in the run from being 30a circuits.

If I only need to run the neutral to the receptacle I need it at then there is no issue, but if I do need to run a dead-leg to the other 240v receptacle on the same circuit, then there are a bunch of problems.