240/120 outlet?

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Old 04-12-20, 10:47 AM
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240/120 outlet?

I have a 10-4 wire that runs directly from a double 30A breaker in the main panel that runs to a room I use a lot of electrical equipment in (ham radio stuff). Currently I have it running in to a double duplex box, one 120 circuit on one duplex (black) and the other 120 circuit on the other duplex (red) and am using the white as a common for both. I know it's possible, but what is the electrical code (I know it sort of varies by county) as far as first making the 10-4 into a 240 outlet with the appropriate socket and then breaking that out into another box as a double 120 outlet like I currently have.

I know a fellow that has a 240 outlet, and what he does is put a 240 extension in the socket and run it into extension boxes that have it broken out into 120 circuits. I'm just looking for the best way to do this, I would like to have a 240 outlet in this room also for one piece of equipment.
 
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Old 04-12-20, 11:29 AM
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Regular duplexes are limited to a 20 amp maximum. You could install a small subpanel and install circuits from it.
 
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Old 04-12-20, 02:46 PM
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Hi, you can’t have 120 volt 20Amp outlets on a 30 Amp breaker, install a sub panel as PCBOSS suggested.
Geo
 

Last edited by Geochurchi; 04-12-20 at 05:45 PM.
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Old 04-12-20, 04:08 PM
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So far so good with one change mandated, change the breaker to 20 amps. The two duplex receptacles would be properly wired using black and white for one and red and white for the other.

After you run the 10-3 with ground cable into the subpanel mentioned earlier you can have 20 amp subpanel circuits the rest of the way (using two 12-2s or with some caveats, one 12-3) to the existing receptacles. Add another pair of breakers to the subpanel for a new 240 volt or 120/240 volt receptacle, and up the breaker back in the supra panel to 30 amps again

Add yet another breaker or pair of breakers to the subpanel for third and fourth in-wall 120 volt duplex receptacles elsewhere in the room..By this time you are likely running up against the 30 amp limit of the incoming 10-3 and will need manual discipline for what you are running in the room at any one time.
 

Last edited by AllanJ; 04-12-20 at 04:30 PM.
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Old 04-13-20, 08:22 AM
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I really don't need a 30A circuit, and actually there is a dual 20A breaker on the 10-3 w/ground to the double duplex outlet. Would it be ok for me to remove one of those duplex outlets and wire in a 20A 240 duplex outlet in it's place (as 240 of course)? And then re-wire the single 120 duplex as alternate phases top/bottom. the only thing I want the 240 for is the KW amp that I can re-wire from 120 to 240. The room is otherwise typically wired for 120 off another 15A circuit I use for lights and a computer. I could run all my other ham gear off the 120 duplexes easily with one of those multiple plug surge protector devices. I'd run the 50A 12V power supply off one 120 phase and the rest off the other 120 phase and the KW amp off one of the 240 outlets. Seems that would accomplish the same thing without going to an exotic sub panel. Seems the hookup/wiring would be essentially the same.
But maybe it's not copacetic to put a 120 and 240 duplex in the same box?

Adding a sub panel would be a real chore, the double duplex is in a real inconvenient place behind a bench.
 
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Old 04-13-20, 02:27 PM
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Hi, just curious what a 240 volt duplex would be, what exactly are you trying to accomplish?
Geo
 
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Old 04-14-20, 06:24 AM
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I have a KW amplifier that I can re-wire from 120V to 240V, making it work a bit more efficient, and less current draw (and voltage drop) on the #10 wire. It draws about 12A at 120V, so 6A at 240 max. The #10 wire is about 90' long. So I only need actually one 20A 240V socket, but it looks like they come like the 20A 120V duplex outlets, that is a double 240V outlet. And they're the same cover size so I could use the same cover.
 
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Old 04-14-20, 06:58 AM
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If you run the 6 ampere 240 volt amplifier using the 12 amp 120 volt setting (and 120 volt plug), and run other stuff on the other leg of the 120/240 volt circuit then you get almost the same efficiency compared with using the 6 amp 240 volt setting and distributing the other stuff across the two legs.
 
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Old 04-15-20, 05:42 AM
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Hi, here are some parts that you maybe able to use to make up your supply, you must refuse the circuit to 20 amps.
The#10 will enter the box with a proper connector and you will need to pigtail # 12 from the #10 to connect to the receptacles, you may also need a box extension to fit this all in.
Geo
 
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Old 04-15-20, 09:12 AM
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Found this:Amazingly enough, this is actually permitted by Code under certain (common, but not universal) circumstances!

What you are creating is a multiwire branch circuit as per 210.4. Normally, only line-to-neutral loads are allowed, but IF the breaker for this circuit is a two pole common trip unit (most two and three pole breakers are, although if the circuit is fed from the outer sections of a quadruplex breaker, you definitely can't do this as there is no way to get two common trips in that form factor), Exception 2 to 210.4(C) allows the circuit to feed both line-to-neutral and line-to-line loads (and even three phase loads for wye connected three phase MWBCs)
210.4 Multiwire Branch Circuits.

(A) General. Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors of a multiwire branch circuit shall originate from the same panelboard or similar distribution equipment.

(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Informational Note: See 240.15(B) for information on the use of single-pole circuit breakers as the disconnecting means.

(C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.
 
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Old 04-15-20, 09:28 AM
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A lot of words to say this:

Only one handle to kill the entire circuit.
No earth ground currents in non-fault operation.
Upstream current protection must accommodate all wires and all receptacle ratings.
 
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Old 04-15-20, 01:45 PM
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With proper loading I can probably even get the neutral wire to carry minimum load, not that it even needs to.
 
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