I'm considering setting up a 240 volt appliance in my garage and I need to
determine whether it is being supplied with 220-240 volt service. The
breaker box in the garage has three wires coming in from elsewhere in the
building, one white wired to the neutral bus bar and two black wired to a 70
amp double pole breaker.
1. multimeter shows ~116 volts from hot to neutral for each of the two poles
on the main breaker
2. multimeter shows 0 volts from hot to hot between the two poles on the
3. multimeter shows 0 ohms resistance between from hot to hot between the
two poles on the main breaker
Am I not testing this properly, or is it possible that my garage is not
wired for "three wire single phase" as I suppose electricians prefer to call
it? My understanding would lead me to believe that the two hot wires are
connected upstream to the same half of my building's electrical supply, so
I'm only getting 120 in my garage despite the two hot wires.
Any ideas? Are there any other tests I can perform to verify or invalidate
my conclusions? Thanks for any help you may provide...
I agree with your diagnosis. I used to run into this when I was
repairing dryers, people had the supply installed by a "handyman" or did
it themselves and wondered why the dryer didn't dry.
James P. Javery wrote:
Also, the breaker box in the garage should have 4 wires coming into it,
since it's being fed as a subpanel from another panel elsewhere in the
building. If it were a detached garage, you could use the grounded wire
as a neutral and make a new ground.
In your case, with only 3 wires, you need to tape the ends of the wire
green and you don't have a neutral. It would be best not to have a
breaker box in the garage (and just hardwire the appliance) if you do
this, because someday someone will want to hook up a 120V circuit and
try to use thata ground for a neutral connection.
Are you allowed to re-identify a wire as an equipment grounding
The question I would ask, what type of cable is feeding the subpanel,
is it AC or is it all EMT, since he mentions no specific ground.
As for the 0 volts accross both ungrounded bars, I'm sensing this was
a 'home owner' installation, and caution needs to be taken by this
homeowner in trouble shooting and fixing to get 240 volt properly
tom @ FreelancingProjects.com
On Tue, 23 Nov 2004 05:56:59 GMT, "James P. Javery"
Sounds like your double pole breaker feeding the garage needs to be
moved one position. It is apparently connected to the same phase on
both sides. Some panels will let that happen, some are keyed so it
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.