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Old 10-14-2012, 06:57 PM   #1
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Newcomer with a couple of simple Questions


In a conventionally wired all-electric home built in 1970 (to code), does the presence of three wires at each of the main switch junctions mean that I could draw 240V from that circuit? (if within the 30A circuit load rating)

I pulled a switch set and replaced the switches. I notice that my whole house is wired with a heavy grade of Romex (all circuits are 30 and 40 amp)

The wires are black, white, copper.

CanI create 240 off that type of feed if properly wired? I need to move an air conditioner unit down a hallway from an attic installation - and would like to keep the built-in whole house fan that is part of that unit.

My thought is to pull 240V off the light circuit in the back bedroom by using the existing switch junction box, as it is 30 amp, the same amps as the 240V AC circuit now in use. I have an adjoining bedroom circuit that I would then wire to power both bedrooms - the original system has 30 amps to each bedroom separately. Dad didn't like interruptions to Johnny Carson.

Is this possible? As long as the main romex is heavy enough, can I convert any junction that has three-wire romex from 120 to 240 by using all three wires?

I'm 53 years old and I feel so ignorant on this.


Last edited by imautoparts; 10-14-2012 at 07:15 PM.
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Old 10-14-2012, 07:25 PM   #2
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Newcomer with a couple of simple Questions


30 and 40 amp general purpose circuits are not code compliant with the NEC.

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Old 10-14-2012, 07:33 PM   #3
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You are either seeing it wrong, describing it wrong or worst of all....
IT'S JUST PLAN WRONG!!!

You are NOT allowed 30 amp general lighting or outlet circuits in a residence. What color are these wires?
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Old 10-14-2012, 07:35 PM   #4
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Newcomer with a couple of simple Questions


I was wrong. 20A circuits for all the bedrooms and misc light/outlet circuits downstairs.

I had mixed up the two boxes on my circuit list. We have a bunch of circuits at 30amp or higher, as explained below. The bedroom circuits are all 20 amp, as are the circuits for the outlets downstairs.


This house was a "Reddy Kilowatt" demonstration home. My Father was the builder. It has commercial grade wiring and water systems.

Thus, I amend my question. If the romex in the walls is heavy enough, can I upgrade an existing 20A 120V circuit to 240V without pulling new wires from the box (es).


Last edited by imautoparts; 10-14-2012 at 07:54 PM.
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Old 10-14-2012, 08:16 PM   #5
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Generally 120 volt circuits can be repurposed for 240 volts. It's unlikely that gnereal purpose circuits in a completely wired home could be modified this way and maitain the integrity of home compliancy.
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Old 10-14-2012, 08:26 PM   #6
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In that case I have to be very careful when I look at my wires.

In your opinion, what is the most accurate way to determine the gauge and current capacity (if that's the right term) of the wall outlet romex? I am familiar with correct procedures to open up the CB boxes and replace or change breakers - I had an unused 40A in the box for an old outdoor grill that I repurposed to feed one of the water heaters (it had a faulty 40A breaker).
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Old 10-14-2012, 08:41 PM   #7
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Take a look at your breakers. What amperage are they? And I'm surprised that your water heater was 40 amp. 99% are 30 amp.
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Old 10-14-2012, 08:44 PM   #8
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The problem with switching the circuit to 240 is that all of the circuit changes over, not just one receptacle. This would mean that you would have no places to plug in lamps or TVs etc on the circuit.
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Old 10-14-2012, 08:54 PM   #9
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The problem with switching the circuit to 240 is that all of the circuit changes over, not just one receptacle. This would mean that you would have no places to plug in lamps or TVs etc on the circuit.
I had not thought of that. How about this plan:

I would draw power for the overhead from an adjoining bedroom on a shared wall, pulling from the switch on the common wall with that room. That bedroom also has its own 20A circuit. I could also keep one outlet live in the new AC/Mechanical room by pulling through a shared wall from the same circuit. Thus I'd have the overhead light and one 120V outlet. The other two outlets would be unneeded and I could nut the wires and cover them with blank outlet covers.

The closet is going to be converted into the new AC unit's home - and if my 20A circuit wiring is heavy enough, I won't need to run any new romex from the boxes. I can just upgrade to a 30A breaker and wire in the new 240V box to the romex in the wall.

This new AC install is 60+ feet from the CB boxes - literally on the opposite corner of the house. I really don't want to pull wire.
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Old 10-14-2012, 09:04 PM   #10
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I seriously doubt that your home has #10 wiring run to the receptacles.

You can check the wiring size against a piece of a known gauge or use wire strippers.
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Old 10-14-2012, 09:30 PM   #11
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The existing wire is 42 years old, and we have no idea how many splices/connections exist.

I would run a new circuit.

Does this ac unit have an outdoor condenser . You might need another 240v circuit for it.

My recommendation would be to hire an electrician.
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Old 10-14-2012, 10:17 PM   #12
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The existing wire is 42 years old, and we have no idea how many splices/connections exist.

I would run a new circuit.

Does this ac unit have an outdoor condenser . You might need another 240v circuit for it.

My recommendation would be to hire an electrician.
I think you're right. The existing AC was a site-built attic unit with the condenser and evaporator sharing the same chassis. A huge tube connects the condenser waste air to a large passive airbox on the roof.

I have not yet found a modern replacement that will integrate into the airbox ducting (which is also the ceiling of the hallway - it is 4" lower than the adjoining rooms).

I know several reputable electricians locally.

I'd say you've done a great job teaching me some basics about house systems. Thanks for your patience everybody.

Fortunately the downstairs unit is a standard-style installation.
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Old 10-15-2012, 11:57 AM   #13
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In almost all cases the same wiring that is now a 120 volt circuit can be repurposed as a 240 volt circuit with the same number of amperes, for example a 14 gauge circuit can handle 240 volts at 15 amps.

You do need to be sure that all 120 volt receptacles in the daisy chain are removed or replaced with 240 volt receptacles, and all hard wired (120 volt) lights are disconnected from the circuit.

Rarely the wire is not rated for 240 volts; Romex cable used nowadays is rated for 250 or 600 volts.

And to comply with code the room needs enough 120 volt receptacles remaining with the appropriate maximum 12 foot spacing between them and 6 foot maximum from a doorway and a wall section between two doorways at least 2 feet wide having a receptacle.
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Old 10-15-2012, 08:23 PM   #14
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Quote:
Originally Posted by imautoparts View Post
In a conventionally wired all-electric home built in 1970 (to code), does the presence of three wires at each of the main switch junctions mean that I could draw 240V from that circuit? (if within the 30A circuit load rating)

I pulled a switch set and replaced the switches. I notice that my whole house is wired with a heavy grade of Romex (all circuits are 30 and 40 amp)

The wires are black, white, copper.

CanI create 240 off that type of feed if properly wired? I need to move an air conditioner unit down a hallway from an attic installation - and would like to keep the built-in whole house fan that is part of that unit.

My thought is to pull 240V off the light circuit in the back bedroom by using the existing switch junction box, as it is 30 amp, the same amps as the 240V AC circuit now in use. I have an adjoining bedroom circuit that I would then wire to power both bedrooms - the original system has 30 amps to each bedroom separately. Dad didn't like interruptions to Johnny Carson.

Is this possible? As long as the main romex is heavy enough, can I convert any junction that has three-wire romex from 120 to 240 by using all three wires?

I'm 53 years old and I feel so ignorant on this.
Code wise ! If the wires are white , black , and bare copper,
Then it should be a 120v circuit !
If its a 220v circuit it should be black / red / bare copper.

How ever I would check with a meter to be 100%.
Because not everybody always follow code !

Dont be afraid to ask if you dont know,
For this is how you learn !
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Old 10-15-2012, 08:45 PM   #15
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Well, I'm convinced that when the conversion occurs, I will establish new feeds for the AC air handler and the outside unit.

However, as I researched all this, I found the following diagram on the Dept of Energy's website. Apparently, the layout of my system is exactly what they say they recommend. I haven't even SEEN a similar system locally.

Here's their diagram:


Here's my house:
[IMG][/IMG]

Anybody know if that ceiling mounted AC system can be replaced with a more modern unit? The old one sounds like someone is shunting freight cars in the attic. I think they got the solenoids from Studebaker.

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