[jpm]

A (probably crazy) thought has been nagging at me the past few days.  Since a lot of our US domestic 220v lines are created by doubling 110v lines, is it possible to tap into one of the individual 110v lines for a separate 110v outlet?

My curiosity stems from it not being financially viable to run a dedicated 110v spur to my equipment, however one wall of my room is adjacent to the laundry room wall with the 220v run for the dryer. Most of the time, this run is unused and has no other equipment on it. Seems like a waste of a relatively clean run ...

[Wayner]

First, lets use the correct voltage. Its 120, not 110 and the mains are 240, not 220.

The answer to your question is yes. Our homes in the US have two 120 volt lines and a neutral coming in. When we use one of the 120 volt lines and the neutral, we get, well...120 volt. When we put the 2 120 volt lines in series, we get 240 volt.

Its as simple as that.

Wayner

[srb]

The dryer when on high could possibly be using 70 - 80% of your 30A circuit capacity.  The motor in a dryer is fairly small so relatively not too much additional current draw starting and running it .... but it is a motor.

If you have high wattage mono amplifiers I would consider running both legs of the dryer circuit to separate 120V receptacles to distribute the load when the dryer is on.  Otherwise, if running just one extended 120V receptacle I would choose the leg that the motor isn't on (most dryer motors are 120V) as motors, even small ones, can create noise on the line.

Steve

[Scott F.]

You likely won't be able to scab off a 240 circuit with one leg and do a 120 outlet. Reason being, the 240 volt line goes back to a two pole breaker that is (likely) physically tied together. When you introduce additional ampacity on one leg of that circuit, you create an imbalanced load and would not provide proper circuit protection, hence a code violation. You'll need to run a dedicated circuit or tie into an existing 120 circuit that has spare ampacity to run your system.

[electricbear]

Scott, isn't a residential 240v 2 pole breaker simply 2 x 120v breakers running side by side with a physical jumper bar between the trips on them? When one side sees a fault condition or too much current being drawn it trips and the jumper bar activates the trip on the second one.
I would have thought the big issue would be where to find the neutral.

[Wayner]

You likely won't be able to scab off a 240 circuit with one leg and do a 120 outlet. Reason being, the 240 volt line goes back to a two pole breaker that is (likely) physically tied together. When you introduce additional ampacity on one leg of that circuit, you create an imbalanced load and would not provide proper circuit protection, hence a code violation. You'll need to run a dedicated circuit or tie into an existing 120 circuit that has spare ampacity to run your system.

Lots of older model stoves had 120 volt outlets on them. Much of the electronics in a stove runs on 120 volt, like the clock, timers, lights. Dryers also have 120 volt circuits in them to run timers and lights.

[srb]

Many older 240V appliance circuits were 3-wire, but that was still 2 x hot + neutral conductor.  Modern appliance circuits are 4-wire to include a separate ground wire.  But either has a neutral conductor to facilitate the 120V sub-components.

It's certainly electrically doable, but like one point that Scott F. made, it's unlikely that any such extension of a 240V appliance circuit would pass code (or any fire insurance investigation if it was determined that the fire source was related to that circuit).

Steve

[jea48]

A (probably crazy) thought has been nagging at me the past few days.  Since a lot of our US domestic 220v lines are created by doubling 110v lines, is it possible to tap into one of the individual 110v lines for a separate 110v outlet?

My curiosity stems from it not being financially viable to run a dedicated 110v spur to my equipment, however one wall of my room is adjacent to the laundry room wall with the 220v run for the dryer. Most of the time, this run is unused and has no other equipment on it. Seems like a waste of a relatively clean run ...

Since a lot of our US domestic 220v lines are created by doubling 110v lines, is it possible to tap into one of the individual 110v lines for a separate 110v outlet?

It really isn't that way at all. The secondary of the utility power transformer is a single phase 240Vac winding with a center tap. It is a split phase 120/240Vac or you could call it a 120V 0V 120V balanced power system.

Three power wires enter your house from the utility power transformer.
2 Hot ungrounded conductors. Called Line 1 (L1) and Line 2 (L2)
1 grounded conductor, the neutral. (N)
From Hot to Hot the voltage measures 240Vac nominal.
From either Hot to the neutral the voltage measures 120Vac nominal.

however one wall of my room is adjacent to the laundry room wall with the 220v run for the dryer. Most of the time, this run is unused and has no other equipment on it. Seems like a waste of a relatively clean run ...

Are you talking about building a power cord that will lay on the floor? Will the cord have a plug that will plug into the dryer Receptacle? On the end of the power cord you will install a box and install a 120V 20 amp duplex in the box? Is that what you are thinking of doing?

For the moment lets say that is what you are thinking of doing.

First is the electric dryer receptacle an old 3 wire receptacle or a 4 wire receptacle?
If 3 wire, then No forget about it.

If it is a 4 wire then you might build something that would meet NEC, (National Electrical Code), and possibly city local electrical code.

First problem you have is the breaker at the electrical panel is 30 amp. The breaker needed for a 120V 20 amp duplex receptacle has to be 20 amp per NEC code. 30 amp is too big...

I'll stop here...



 

[jpm]

Thanks for all of the input folks!

If it is a 4 wire then you might build something that would meet NEC, (National Electrical Code), and possibly city local electrical code.

First problem you have is the breaker at the electrical panel is 30 amp. The breaker needed for a 120V 20 amp duplex receptacle has to be 20 amp per NEC code. 30 amp is too big...

I'll stop here...

The dryer plug is 4 pin, the breaker I'll check tomorrow.  In my uninformed mind, I imagined potentially wiring two separate outlets in their own recessed drywall boxes, one from each 120v run. It's quite literally on the opposite side of a shared interior wall.

[jea48]

Thanks for all of the input folks!

The dryer plug is 4 pin, the breaker I'll check tomorrow.  In my uninformed mind, I imagined potentially wiring two separate outlets in their own recessed drywall boxes, one from each 120v run. It's quite literally on the opposite side of a shared interior wall.

You are talking about a multi wire branch circuit consisting of L1, L2, and a shared neutral. Not good for audio equipment connected together by ICs.
 Both 120V separate circuits must be connected to a 2 pole 20 amp breaker per code. What you would have to do is install a small sub panel in the laundry room, not above the washer or dryer, or any fix item deeper than 8" from the wall. You may end up having to install the sub panel on the other side of the wall. the panel would be fed from the 30 amp dryer branch circuit wiring.

Here is how a split phase secondary winding of a power transformer works.

https://www.youtube.com/watch?v=eVamt9IdQd8

Yes, if both L1 to neutral 120V loads and L2 to neutral 120V loads were equal in the main electrical panel in your home, zero amps would return on the service neutral conductor back to the utility power transformer. Only the imbalanced load returns to the source on the neutral conductor.
The balanced 120V loads are in series with each other. 

Exactly the same thing happens on a multi wire branch circuit.