Sounds like you are measuring from each leg to ground. Measure the voltage
across the red and black wire. It should be 240 volts. If it is 0 or 120,
check back at the breaker panel. Something is miswired.
Thanks for all your help!
When I get home tonight I'll check the voltage accross for 240v. I
didn't do that. At the main panel I connected the black and red to the
2 pole breaker, ground to ground bus, and white to the neutral bus (not
used). I'm thinking I'll find that I don't have 220v. The sub-panel
is not bonded. Could that have anything to do with it? How will I
know where in the panel I can add 220v breakers and where I can't?
I used the 10/3 so that I can change the configuration should my needs
change in the future.
By which you mean, I hope, that the ground and neutral busses in the subpanel
are not bonded to each other. It's *supposed* to be that way. The *only* place
where they are ever bonded together is in the service entrance panel.
No. The neutral isn't used at all in a pure 240V circuit (and can be omitted
altogether), and the ground isn't used except in the case of a ground fault in
the equipment (i.e. in normal operation, the ground isn't used either). So
nothing involving either the ground or the neutral would have any effect on
the problem you're seeing.
In *most* panels, any place that you can put a double-pole breaker will give
you 240V. Your panel may be an exception, as at least a couple of us have
noted, and the easiest way to tell where you can and can't is to look at the
label on the inside of the panel cover -- that will show the possible
configurations. Another way to tell is to probe between the lug screws on
adjacent breakers (with the breakers on) to see where you measure 240V and
where you get only 120V. Yet another way is to pull the breakers, and look at
the configuration of the bus bars.
But before you do any of that, the *first* thing you should do, in my opinion,
is to measure the voltage between the two main breakers (or lugs) in the
subpanel, and see whether you get 240V or 0V. I think you'll see 0V, because
- assuming that you've described everything accurately - the simplest
explanation for the problem you're seeing is that the subpanel is not wired
correctly at the main. Specifically, I think that if you look in the main
panel at the wires feeding the subpanel, you'll find that when the subpanel
was installed, the black and red wires feeding it were connected to two
separate single-pole breakers (instead of to one double-pole breaker), and
those two breakers are on the same leg of the service.
That's fine -- just wasn't necessary for *this* application. But planning for
the future is always good. :-)
Doug Miller (alphageek at milmac dot com)
ok, I know electronics, but am NOT an electrician. But I don't quite
get why we don't need a nuetral? Where's the return path?
240v comes in and in the main service panel I know the nuetral and
ground are bonded.... never have understood that one. then each leg of
the 240v is one side of the bus bar array in the service panel.
So what am I missing? I'm asking in all seriousness. I "added" a 220
outlet for my wife one day so she could have an electric stove and I
popped the breaker immeaditly when I fired it up because of the nuetral
being tied to ground. So I shrugged said I don't get why its doing
that, read the directions with the receptacle and removed the nuetral.
All was well. I look at my dryer cord and its got 3 wires. I know the
top angled two are "hot" 120vac each and the other is the ground.
I realize that we can take a +12vdc and a -12vdc circuit and using only
2 wires get +24vdc across them and then have to have a chassis ground.
Man its been a long time since I studied electronics!
Doug Miller wrote:
Voltage is a potential difference. The difference between the two
current carrying conductors measures 240v. The difference between
a current carrying conductor and the grounded (aka neutral) conductor
is 120v. This being AC, rather than DC, the concept of a "return path"
doesn't really apply, per se. Note that the grounded conductor is
derived from a center-tap on the distribution transformer.
You don't need a neutral to utilize the 220, in fact doing so negates
it from _being_ 220v. This is 180 degree out of phase AC, not DC.
All you need is a voltage potential and somewhere for it to travel,
for current to flow. This is provided by the two 120v out-of-phase
legs of your typical residential service. Hopefully you do not become
part of the conduction path, and is the primary reason that most
woodworking equipment requires a ground. It is not designed to be a
current carrying conductor.
Great confusion exists among novices as concerns Grounds and Neutrals,
especially when it involves outbuildings. Protection against
electrocution and lightning are two of the main reasons that the
current grounding guidelines/codes exist.
The ground on most 220vac equipment is for safety grounding only.
It is a ground, not a neutral, although they do eventually connect
together in your main panel, but never in an in-house subpanel.
Older stoves and cloths dryers sometimes used a common ground/neutral
to provide 120v for lamps and timer motors, but the new code and all
new appliances require a 4 conductor plug and wiring. Two hots, a
neutral, and a ground. It's a safety thing...
Get a copy of the NEC if you want to read up on how to wire things
safely, and to code. Otherwise, please, call an electrician.
Mistakes can be deadly and cause great property loss.
its been forever since I read any of the electrical code stuff and
OBVIOUSLY don't use it very often hardly. I'll be sure to ask any
questions before I mess with anything other then 120. At least I know
what I'm doing with that.
There isn't a "return path" per se in a 240V circuit. In a 120V circuit, the
hot is at a potential of 120V with respect to ground and neutral. In a 240V
circuit, the potential between the two hots is 240V; each is at a potential of
120V with respect to ground and neutral.
That's to ensure that the neutral is at true earth ground potential.
That's not why you popped the breaker. Not having seen what you did, I can't
say why you *did* pop the breaker, but I can say with certainty that tying
neutral to ground didn't trip the breaker, in and of itself. Unless it was a
Means you had it connected to a hot lead somewhere...
Yep, it's basically the same concept.
Residential electrical supply isn't quite the same animal. There are a number
of books available at any decent library or bookstore, or at most home
centers, if you want to learn more.
Doug Miller (alphageek at milmac dot com)
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.