I recently move to a new home. One plug in the garage wasn't wired with an outlet yet. It appeared on the panel as "Heater" and has two breakers. I think it's what they call a 208 volt heater plug (why 208?) Are these common? Can I use it as a 220 instead (Table Saw)? There doesn't appear to be a neutral only two hots. I'm guessing 12 gauge wire. Thx.
I'm surprised that there would be a 208 volt service in a residential area. The utility that serves your area would provide 220v and half of that is the
110v that is standard in the US. For you to have anything different would require a step-up or step-down transformer (in your case) somewhere in the circuit. Check around your circuit breaker panel for a transformer on the wires that run to the plug you mentioned. If there isn't any transformer than you probably don't have 208v. However, you may want an electrician check it out. Circuit breakers won't step-down the voltage. Hope this helps.
And it is entirely possible that some newer residential environments (especially multifamily homes) will have 208 service (which is _NOT_ the same as 220).
Don't post if you don't know.
scott
By the chart it's a 2 pole 3 wire 250V (two 15 amp breakers) thx. So it's for a heater, right?
It's two, 110~120's 15amps each and a ground.What's it for. Can I use it for a 220 table saw? Why no neutral? Thx.
Because you don't need one. 220V is two 110 legs....180 degrees out of phase. If you measured the voltage between either leg and neutral it would be 110V, but between both hot legs, it is 220V. Some appliances (like a dryer) require a neutral because some functions of the appliance (like the light) run on 110V. On the inside, a dryer is really a hybrid device.
Basic motors and heater are not hybrids; they don't need 110, therefore do not need a neutral.
Steve
Table saw don't ordinarily need a neutral, though the magnetic switch on mine does.(don't ask...) Two 120v wires can mean either 240v or 208v.
It would be very unusual to have 208v in a home, so it is probably 240v and is probably okay; but if it really is 208v you could burn the motor out. It is prudent to test it with a voltmeter and/or check with your utility to make certain.
It will need a neutral if it also has a 110V device (such as a light bulb, for example).
Also I read somewhere that some new regs require 4-conductor wiring for all
220V outlets. However, I do not have a reliable source for that statement (nor do I know if it applied to just outlets or devices as well), take it as a rumor I suppose.
It tests around 115 on each side therefore not 208. Someone I know called it a 208, they were wrong. Thx.
You can have true 208V single phase without 3 phase power being supplied. Line-to-Line is 208 V and Line to Neutral is 120 V.
However, in my experience, it is highly unusual to have 3 phase power supplied to a residence. The most common US residential service is 120/240.
Does it matter that the breakers are both on the left hand side of the panel? Not one on the left and one on the right? Does that mean both lines are coming in to the plug on the same phase? And not 180 degrees out?
No. That is correct. A two pole breaker is designed to be installed that way. The breaker should be a single 2-pole breaker, and not two 1-pole breakers.
No by being stacked on each other they ARE on different phases. If they were side by side you would have an issue.
Typically a house is supplied with a single 240volt phase center tapped. Neutral is connected to this center tap and thus pole to pole voltage is
240 and pole to centertap is 120. 208 volt service is derived from 120 volt three phase "wye" power where one pole from each phase is tied together. Neutral is connected to this junction which yields 120 volts pole to neutral and 208 volts pole to pole. The difference is that the 208 is derived from two phases that are 120 degrees apart. 120 volts * sin(pi/3) * 2 = 207.6 volts.Some utility companies just tap into two phases to give the 208 to a residential unit, though this is rare. Usually they step a single 7200 volt or so single phase line into center tapped 240.
-Bruce
That is not adequate; 208a will test about 115v to ground on each also. You have to test hot to hot.
208v has two 120v hots 120 degrees out of phase. Between them they are 208v. 240v has two 120v hots 180 degrees out of phase. Between them they are 240v. (strictly speaking they are not out of phase, but it is close enough to the truth for this purpose.)
Correct, that is what I said.
Actually it is the other way around. 120V single phase is derrived from a
208V 3 phase Y connected transformer.In any case, the rest of what you said is correct as well.
You only need 4 wires (3 conductors and a ground) if you have something that actually needs the neutral; such as a table saw with a 120v light bulb (?). Otherwise you only need 3 wires.
My dryer puts 7a into the ground (technically an "uninsulated neutral") which is a little spooky, but I have never heard of anyone having a problem; which could result if the neutral connection broke somehow and energized the case.
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