I can't figure out what I'm doing wrong. I'm currently trying to add an oulet for 4800 watt construction heater in my shop. I've run 10/3 wire to the outlet, added a 2-pole 30amp breaker to the sub-panel, and installed a 6-30 plug by connecting the black and red wires to the blades on the plug, and the bare wire ground to the box 1st and then to the ground on the outlet. The white wire is capped off and not being used. When I plug in the heater it will not turn on. Breaker does not trip.
I get 120v on each side of the plug with my voltmeter. I even was able to test the voltage in the heater and there is 120v going to each input inside the heater. I replaced the heater with a brand new one, and also replace the outlet and get the same results.
uh? just the red & black? Where's the nuetral connected? You gotta have a return circuit. if you've got 10/3 then you've to red, black, white, ground right? Am I missing something here or just don't know what I'm talking about.
That's not the problem. If it's wired correctly (and as he describes it, it is) the unit will work without the ground at all. Won't be safe, but it will work.
Could've used 10/2, since it's a pure 240V load, but that's just FYI, and unrelated to the problem.
What do you get between the two hot legs? Here's my guess: measure that at the outlet, and you'll see ZERO.
Possible explanations:
1) You don't have the breaker for this circuit wired correctly. I doubt that's the case, though, since you seem to have done everything else right.
2) I've heard of, but never actually seen, panels in which adjacent lugs are on the *same* leg of the service, instead of on opposite legs (opposite legs being on opposite sides). You may have such a panel. But I doubt it. If they exist at all, I'm sure they're very rare.
3) You said you installed the new breaker in a subpanel. Have you verified that there's actually 240V coming into the subpanel? I bet there's not. Put a voltmeter across the two main breakers (or lugs) in the subpanel, and you'll probably see 0V. I suspect that the subpanel is wired incorrectly at the main panel, and nobody ever noticed before because nobody ever installed a 240V circuit in the sub before.
Some panels will only accept 2 pole breakers in certain slots. I haven't looked into why that is, but maybe because of this. Look to see if your box has such a condition, and if you are doing it properly.
I've encountered this as well. Look closely at the buss bar in the center of the box and make sure that your 220v breaker is really connecting to alternating buss lugs. Some boxes only have 220v capability on the first few lugs of the buss bar and then everything below that point is 110v.
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.
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. :-)
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!
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.
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