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ballast for mains input

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Physics Junkie

Wed May 22 2013, 07:47PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

After reading my last post again I just confuse myself even more

hehe. Hopefully this clears it up

1369251547 7267 FT153555 Img 20130522 153334 928

Right, so I might have labeled the incoming polarities from the utility transformer wrong, but who cares... all I am trying to understand is how it comes from the 220V 30A breaker, and I think I got that part right. After talking to another tesla coiler in the US who uses a 240V variac, this is how it appears to be wired. Not being knowledgable in EE or how mains AC works in any great detail, it just seemed fishy to me that two HOT wires are connected at the transformer rather than a single 240V and neutral (like over in the UK, I think). But as I understand the two wires being "out of phase" equal 240V rather than cancel out and equal zero. Hope this is right.

HV Enthusiast

Wed May 22 2013, 11:06PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Your 220VAC from your circuit breaker box is simply the full voltage across the utility transformer. When you run a typical 220VAC circuit, you don't use the neutral.
Don't think of it as two (2) 110VAC circuits 180 degrees out of phase. Just think of it as a 220VAC transformer with a center-tap.

If you want to run 220VAC into a variac, you would just run the two wires as you would with any other variac.

Also, the power coming into your house is single phase 220VAC. And that is what you get when you wire a 220VAC outlet. Its only the 110VAC lines which are divided between the two-halves on the utility transformer.

Its probably the fact that the neutral is tied to earth ground that is confusing you.

Physics Junkie

Wed May 22 2013, 11:32PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

EasternVoltageResearch wrote ...

Don't think of it as two (2) 110VAC circuits 180 degrees out of phase. Just think of it as a 220VAC transformer with a center-tap.

thats exactly what I needed to hear! The whole time I was trying to be technical and think of it as wiring two 110's off phase. I know many EE guys hate the term "out of phase" because its not totally true. its just single phase and all that really changes is amplitude. unless you are specifying that one leg of the utility transformer with respect to center tap/neutral/ground is 180 degrees out of phase with the opposite leg with respect to center tap. I think the term "out of phase" was adapted from polyphase terminology (but who cares

)

EasternVoltageResearch wrote ...

If you want to run 220VAC into a variac, you would just run the two wires as you would with any other variac.

Yeah that's the conclusion I came to. I realized this when I looked at two ganged 120V variacs wired together for 240V operation, then it all clicked because it's exactly the same. But in this case its a single 240V variac

EasternVoltageResearch wrote ...

Its probably the fact that the neutral is tied to earth ground that is confusing you.

not really, I knew there is no neutral involved in the wiring of the 240V variac for U.S. besides the fact the ground is connected to the metal enclosure. Mostly confused because the schematic for these variacs say 240V hot and neutral, that's where I was worried it would require a single 240 Hot line rather than two 110/120's. furthermore, what I was unsure of is imposing two HOT lines together. I just dont know enough about AC phase angle in the real world to say 100% "oh thats going to equal 240" or "thats going to equal zero" or "thats going to blow up my house" but after doing the simple math and also looking at it from a trigonometric standpoint (as seen in the top left and bottom left of the attached pic) I can see how it equals 240V, and now it makes more sense. Thanks, I appreciate it.

HV Enthusiast

Thu May 23 2013, 01:10AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Yeah, just look at it from a transformer standpoint as opposed to trigonometric strandpoint. You have 14.4kV on the primary and 220VAC on the secondary.

And don't think of the neutral as safe. Although its tied to ground in household applications, its only tied to ground at the MAINS box coming into the house. If you have a large current flowing through the neutral, the neutral wire at the outlet box can be many volts above ground and quite dangerous.

Also, note that if you have an auxilliary subpanel box, the neutrals in that box are NOT tied to ground in that subpanel.

Physics Junkie

Thu May 23 2013, 01:38AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Good point. Shouldnt have to worry about the neutral though as I am using a 3 wire (two hot one ground) line as opposed to the 4 wire with a neutral.

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