Woodnet Forums
240 wire - Printable Version

+- Woodnet Forums (https://www.forums.woodnet.net)
+-- Thread: 240 wire (/showthread.php?tid=7347545)

Pages: 1 2


240 wire - Wipedout - 04-07-2019

So years ago I had a guy put a second breaker box in my garage for me to use in the shop. He put a bunch of 120 outlets each on their own breaker for my request with 20 amp breakers he used 12-2 wiring. He also put in two 240 outlets with 30 amp breakers and he use 10 to wiring

When I was looking to add another outlet for my 240 I was going to go buy some wire but here's a stupid question I assume I should just go with more 10 2 wire like he did a friend told me I had to use 10-3 wire?

Thanks for your help


RE: 240 wire - fredhargis - 04-07-2019

The confusion may be that flexible cable counts the ground as a conductor while house wire identified as 10-2 will have 2 insulated conductors and a ground wire. Flexible cable like SO cord will be identified as 10-3, which would be the 2 conductors along with an insulated ground wire.  So for what you are doing the 10-2 WG (with ground) is what you need. If you bought 10-3 WG, it would have red, white and black conductors along with the ground wire.


RE: 240 wire - Wipedout - 04-07-2019

Thanks Fred? That clears up my confusion


RE: 240 wire - bottd - 04-07-2019

(04-07-2019, 11:19 AM)Wipedout Wrote: So years ago I had a guy put a second breaker box in my garage for me to use in the shop. He put a bunch of 120 outlets each on their own breaker for my request with 20 amp breakers he used 12-2 wiring. He also put in two 240 outlets with 30 amp breakers and he use 10 to wiring

When I was looking to add another outlet for my 240 I was going to go buy some wire but here's a stupid question I assume I should just go with more 10 2 wire like he did a friend told me I had to use 10-3 wire?

Thanks for your help

Not the expert here, I am sure they will be along soon but I believe if you are wiring up outlets for straight 240 loads you do not need the 10-3, 10-2 will do just fine. If you were wiring up for an appliance like an electric dryer or range that had both internal 240 and 115 loads then you would need the third wire for your neutral.


RE: 240 wire - srv52761 - 04-07-2019

(04-07-2019, 11:39 AM)bottd Wrote: Not the expert here, I am sure they will be along soon but I believe if you are wiring up outlets for straight 240 loads you do not need the 10-3, 10-2 will do just fine. If you were wiring up for an appliance like an electric dryer or range that had both internal 240 and 115 loads then you would need the third wire for your neutral.

This is true.  If running a specific appliance you may just need two hots to complete the circuit, don’t even need the neutral.
But I don’t think this, or even a three wire system satisfies code any longer.  The NEC wants any new outlet to be fully functional for any 240v use.  I think they require any new outlet be the 4-wire variety.

Could be wrong, I’m sure someone else will either confirm or refute.


RE: 240 wire - Roly - 04-07-2019

(04-07-2019, 12:33 PM)srv52761 Wrote: This is true.  If running a specific appliance you may just need two hots to complete the circuit, don’t even need the neutral.
But I don’t think this, or even a three wire system satisfies code any longer.  The NEC wants any new outlet to be fully functional for any 240v use.  I think they require any new outlet be the 4-wire variety.

Could be wrong, I’m sure someone else will either confirm or refute.

That is the way I read it also.  If you are running a new circuit, it should be 3 wire plus ground.  Roly


RE: 240 wire - Cecil - 04-07-2019

(04-07-2019, 11:19 AM)Wipedout Wrote: So years ago I had a guy put a second breaker box in my garage for me to use in the shop. He put a bunch of 120 outlets each on their own breaker for my request with 20 amp breakers he used 12-2 wiring. He also put in two 240 outlets with 30 amp breakers and he use 10 to wiring

When I was looking to add another outlet for my 240 I was going to go buy some wire but here's a stupid question I assume I should just go with more 10 2 wire like he did a friend told me I had to use 10-3 wire?

Thanks for your help

You did not state the amperage for the new circuit.  If you are adding a 30 amp circuit, like the others, then yes, 10 gauge wire.  Others have answered the 2 vs 3 dilemma.


RE: 240 wire - Wipedout - 04-07-2019

Same 30a. Thanks.


RE: 240 wire - TDKPE - 04-07-2019

Since the 1996 Code cycle, range and dryer circuits were not allowed to use ungrounded circuits, and they were usually wired with SE cable (2 insulated hots, 1 uninsulated neutral, no ground). Now they’re required to be on a 3-wire plus ground circuit, where all the current carrying conductors (both hots plus neutral) are required to be insulated.

But 240V only circuits only need two hot conductors plus ground. Unless something changed that I’m not aware of.

The confusion probably comes from people being aware of 240V appliances, specifically ranges and dryers (which are actually 120/240V), having 3 conductors plus ground these days. Most folks aren’t really aware of 240V (only) water heater circuits or air conditioning circuits, since those aren’t something you normally replace yourself, and they don’t normally even have plugs. So the three conductor plus ground thing is what most are aware of, but most never see or deal with 240V loads or general purpose 240V (only) circuits, with a receptacle on the wall and a machine or tool that plugs into it.


RE: 240 wire - Roly - 04-07-2019

(04-07-2019, 06:04 PM)TDKPE Wrote: Since the 1996 Code cycle, range and dryer circuits were not allowed to use ungrounded circuits, and they were usually wired with SE cable (2 insulated hots, 1 uninsulated neutral, no ground).  Now they’re required to be on a 3-wire plus ground circuit, where all the current carrying conductors (both hots plus neutral) are required to be insulated.  

But 240V only circuits only need two hot conductors plus ground.  Unless something changed that I’m not aware of.

The confusion probably comes from people being aware of 240V appliances, specifically ranges and dryers (which are actually 120/240V), having 3 conductors plus ground these days.  Most folks aren’t really aware of 240V (only) water heater circuits or air conditioning circuits, since those aren’t something you normally replace yourself, and they don’t normally even have plugs.  So the three conductor plus ground thing is what most are aware of, but most never see or deal with 240V loads or general purpose 240V (only) circuits, with a receptacle on the wall and a machine or tool that plugs into it.

You are right Tom,   I was thinking all 240v receptacles needed to be 4 wire but many AC's and tools use the 240v 20a receptacle without a neutral.  Knew the direct wire did not need it.
 Having said that if I was running a new 240 receptacle circuit I would include a neutral in case a tool required it.   Roly   What happened with the fridge ?