Using 240V Dryer Power for Garage Power

Reply

  #1  
Old 12-07-06, 02:29 PM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 571
Using 240V Dryer Power for Garage Power

I have an unused 240V receptacle in my washer room. I have a gas dryer. The wall into which the receptacle is mounted separates the washer room from the garage.

I want to route the power from the receptacle, through the wall into a panel mounted on the other side of that wall. Inside the panel I want a switch that can be used to route the 240VAC either back to the dryer receptacle or to other breakers in the panel. Those other breakers will be used for power tools running at 120VAC.


Questions:

1. What could I use as a dual-pole, dual-throw switch?

2. Could I mount such a switch in the same panel that will house the CBs for the garage?
 
Sponsored Links
  #2  
Old 12-07-06, 02:47 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Do not do this.

First, and most important, the wire to the dryer would need to be FOUR wire. It may or may not be.

Second, this type of setup is ill advised.

Any job worth doing is worth doing properly. Do the right thing. Run a cable from the main panel to the garage where you can put your panel.

At the very least (but only if the cable is FOUR wire, and I don't like this idea either), use this cable for a sub panel in the garage. Install a breaker in the sub panel for the dryer.
 
  #3  
Old 12-07-06, 02:59 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,342
The dryer circuit may only be used as a subpanel feeder if it has 4 wires. Most dryer feeds have only 3 wires. Additionally, many dryer circuits use aluminum wire which is very problematic for extending or reusing.

If the dryer circuit does have four wires, it can be used to feed a garage subpanel or the dryer but not both. If you installed the subpanel, you could then feed the dryer from the new garage subpanel. However, the dryer would use 100% of the panel capacity, so using a tool while the dryer was running would cause the breaker to trip.
 
  #4  
Old 12-07-06, 10:08 PM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 571
'Fraid I have to agree with both of you - my idea seemed pretty hokey to me, but I thought I'd ask. My service entrance is at one corner of the house and the garage is at the opposite corner. I'd need to run underneath a 50-foot long wooden deck, then along a brick wall for another 30 feet to get into the garage. Guess I'll have to bite the bullet and do it come Spring.
 
  #5  
Old 12-15-06, 08:54 AM
Member
Join Date: May 2006
Posts: 7
I have the same thing., but with 4 wires. does this mean i can use it for a subpanal . what type of amp. would it be just a 30amp. or doesit mean a 60 amp panal.
 
  #6  
Old 12-15-06, 09:03 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
smurfy,

You are asking the wrong question.

The panel can be any size panel.

However, assuming normal 10 gage wiring for a dryer receptacle, the panel can only be fed with a 30 amp breaker. This would be the already in place 30 amp dryer breaker.
 
  #7  
Old 12-15-06, 09:40 AM
Pendragon's Avatar
Member
Join Date: Jul 2002
Location: USA
Posts: 1,835
Originally Posted by ibpooks View Post
then feed the dryer from the new garage subpanel. However, the dryer would use 100% of the panel capacity, so using a tool while the dryer was running would cause the breaker to trip.
Just FWIW, he said it's a gas dryer, so it probably not pulling more than a few amps.

Why not just plug the dryer into the same outlet as the washer, since they are both 120v plugs?

Still, it would be better to just do it right, copper is expensive, but at least you only have to buy it once.
 
  #8  
Old 12-15-06, 03:04 PM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 571
Originally Posted by Pendragon View Post
Just FWIW, he said it's a gas dryer, so it probably not pulling more than a few amps.

Why not just plug the dryer into the same outlet as the washer, since they are both 120v plugs?

Still, it would be better to just do it right, copper is expensive, but at least you only have to buy it once.
Yes, it's plugged into 120VAC with the washer. That's why I thought I'd maybe bypass the dryer receptacle altogether and route the power to a garage box. I want enough 120VAC current to run a 15-amp table saw simultaneously with a 15-amp shop vac (for sawdust pickup).
 
  #9  
Old 12-16-06, 03:23 PM
Member
Join Date: Oct 2006
Location: Now in Sun City, AZ
Posts: 134
Very Similar Question - unused circuit

I have a 3 wire unused Dryer hookup going to the garage. This is failry heavy aluminium wire, currently unhooked and laying in the Service panel. ( Another dryer outlet was installed in another location.)
The Neutral and grounds share the same "bars" in the mian panel box (1970's build, Sun City AZ, Aluminium Wiring).

I would like to use the wiring to power a "subpanel" in the garage with 2 circuit breakers to power outlets around the perimeter of the garage for power tools. Would only be running 1 tool at a time - so was thinking of 2 circuits, one each side of the garage.

Anyway - Would it be remotely possible to put a grounding pole / rod/ - driven into the ground - outside the garage, and ground the subpanel circuits this way? Cross tie into the cold water copper plumbing in the garage ? Any chance of making this worK?
 
  #10  
Old 12-16-06, 05:37 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
No. You need a four wire circuit.
 
  #11  
Old 12-16-06, 08:48 PM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 571
I'm not disputing the 4-wire requirement, but I would like to know the reason for it. I assume the 1st wire is phase 0, the 2nd is phase 180, the 3rd is phase 0 common, the 4th is phase 180 common, and 2 commons are needed to carry the current that each hot wire could together carry. Right? Or is it something else? Like motors, power factors, and other such that is 'way beyond my limited knowledge?
 
  #12  
Old 12-16-06, 10:23 PM
Member
Join Date: May 2003
Location: EASTERN US
Posts: 99
Originally Posted by Pipsisiwah View Post
I'm not disputing the 4-wire requirement, but I would like to know the reason for it. I assume the 1st wire is phase 0, the 2nd is phase 180, the 3rd is phase 0 common, the 4th is phase 180 common, and 2 commons are needed to carry the current that each hot wire could together carry. Right? Or is it something else? Like motors, power factors, and other such that is 'way beyond my limited knowledge?
You want to add a subpannel right? Well you need four wires to do this. You need 2 hot, a neutral, and a ground. On a dryer outlet you don't need a neutral. . The outlets you run from your subpannel need a neutral.
 
  #13  
Old 12-16-06, 10:59 PM
rdn2113's Avatar
Member
Join Date: Oct 2002
Location: Wally World
Posts: 451
The four wires are two hots, one common, and one ground. You need a neutral conductor to provide a current return path for 120 volt circuits.

Like Racraft pointed out earlier, however, it's likely that you have only 10 AWG, so 30 amp is the max for the circuit. Check the power rating information on your tools and equipment to make sure you don't exceed the amp limit and you should be OK.
 
  #14  
Old 12-17-06, 07:40 AM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 571
About your tag line: truer words were never spoken. While I sit and contemplate how fast time passes, another week has gone...

Anyway, I understand the use of the 4-wires for a dryer outlet now.

If anybody reading this can suggest a code book (not the $100 NEC book) that basically describes all one would need to know from where the wires enter into the service entry to a residential home, maybe they could post the book name here??
 
  #15  
Old 12-17-06, 09:55 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,342
Wiring Simplified (skip the chapters about farms)
Black and Decker's Guide to Home Wiring
Wiring a House (by Rex Cauldwell I think)

Lowes, Home Depot, et. al have a pretty good selection of books; go flip through some and find the style you like. Some have lots of how-to pictures and diagrams, some have more explainations of theory and code.
 
  #16  
Old 12-17-06, 10:43 AM
Member
Join Date: Oct 2006
Location: Now in Sun City, AZ
Posts: 134
Neutral q?

If the return wire is White - neutral, Why couldn't I add a "local" ground, and also tie that ground to the copper pipes.

The current available wiring I have to use to the garage is really thick stranded aluminium - not sure of actual gauge, but it's heafty. I'll have to check the gauge when I'm back down there.

I could possibly run a 4th wire through the attic back to the main panel for the ground wire if really necessary, but it would tie in to the same shared Neutral / Ground 'tie bars" ( I hope that's what you'd call them ) a the main panel.

The main panel does have a grounding wire clamped to the house water line.

Thanks All! Merry Christmas.
 
  #17  
Old 12-17-06, 02:04 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
In a single dwelling you have ONE and ONLY ONE ground. This connect to your main panel. All other panels in your building are sub panels from this panel and must be fed with a four wire connection, and at those panels the ground and neutral are separate.
 
  #18  
Old 12-17-06, 02:38 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,342
> Why couldn't I add a "local" ground, and also tie that ground to the
> copper pipes.

This is a code issue that related directly to occupant safety. The reason you do not want the water pipes to act as a ground from more than one panel throughout the house is that it creates the situation where electricity can flow on the pipes. This means that anyone using a faucet, tub, or shower in certain situations risks lethal exposure to electric shock. It is very important from a safety point of view that subpanel grounding be done properly with a 4 conductor feeder.
 
  #19  
Old 12-17-06, 10:10 PM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 571
If I run a #12 wire from phase 1 at the breaker box to an outlet that feeds say a 120V, 15-amp table saw motor, and I run a second #12 wire from phase 2 at the breaker box to another 120V, 15-amp motor (dust collector), and my return wire back to the breaker box is a single #12 wire, aren't there going to be conditions when that #12 return will be inadequate to carry the current back to the breaker box? Like when the dust collector is running and I start up or bog down the table saw??

I thought each hot wire from a circuit breaker must be accompanied by a return wire...
 

Last edited by Pipsisiwah; 12-17-06 at 10:12 PM. Reason: add clarification
  #20  
Old 12-18-06, 04:33 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Pipsisiwah,

First a correction in terms. They are not phases. While the two 120 volt lines into a house are 180 degrees out of phase, they are from the same phase of the utility company electricity. They are properly identified as legs, not phases.

The answer to your question is no. When you have a multi-wire circuit (which is the proper term for what you are describing) the current on the neutral wire is the difference between the current on each hot wire. Therefor it cannot be more than the value on any one hot wire.
 

Last edited by racraft; 12-18-06 at 09:24 AM.
  #21  
Old 12-18-06, 08:34 AM
Member
Join Date: Oct 2006
Location: Now in Sun City, AZ
Posts: 134
Thanks for the clarification on the grounding issue

A follow-up question/thought - Can I run a Separate Ground wire from the proposed sub-panel to the main panel, so long as the neutral and ground are separated in the sub-panel?

Does it matter how/where I run that new ground, so long as it "gets there"?

Should it, could it, be about 2 guages smaller than the hot wires?
 
  #22  
Old 12-18-06, 09:04 AM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 571
Originally Posted by racraft View Post
Pipsisiwah,

First a correction in terms. They are not phases.
I appreciate the clarification, as well as the help you have given me both now and in the past.

Wish I could return the favors...
 
  #23  
Old 12-19-06, 07:45 AM
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
"180 degrees out-of-phase" is a misconception when applied to a single-phase power source. The mis-conception is based on using "instantaneous" voltage and polarity values.

Connect the Negative terminal of a 100 volt battery to the Positive terminal of a 2nd 100 volt battery. We will refer to this connection as "N", for "Neutral"

We have a power-source with 3 connection-points--- "Positive", "N", & "Negative ". We can connect a 100 volt load to either "Positive" & "N" , or "Negative" & "N". We can connect a 200 volt load to "Positive" & "Negative".

There are 3 "reference" points for voltage readings, the 3 connection-points. Using "Negative" as the voltage reference-point, we read "+100" volts between "Negative" & "N", and "+200" volts between "Negative" & "Positive".

Using "Positive" as the voltage reference point, the two readings are "-100" and "-200".

Using "N" as the VRP, we read "+100" and "-100" . To conclude that these two readings are "180 degrees out-of-phase" because they are equal and opposite is erroneous, because "phase" has no application because the voltages remain constant in value and polarity.

Using the "Neutral" in a single-phase 3-wire transformer as the VRP, there can be two "instantaneous" voltages equal in voltage-value,and opposite in polarity, but they are not "out-of phase".

"Phase", as applied to A.C circuits, indicates a time -displacement. A capacitor-start induction Motor connected to a single-phase voltage source resembles a 2-phase motor because there is a time-interval between when the "peak" voltage across the starting winding occurs, and when the peak voltage across the running winding occurs. The result is a "rotating" magnetic field in the windings which causes the rotor to rotate.Without the time-element,or "phase-difference" between the two windings, the motor would not start.
 
  #24  
Old 12-19-06, 07:49 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
pat,

When you look at the sine waves on an oscilloscope of both legs of the service, they are 180 degrees out of phase with each other.

You are correct that that they are not technically out of phase because of how they are derived, but you cannot tell this based on the oscilloscope.

Your comparison to a battery may also confuse people. Since a battery is DC, there is nothing to be out of phase.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'