208 3PH question

What's that Lassie? You say that Bruce L. Bergman fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Tue, 27 Jan 2009 23:31:55 -0800:

It is, and I did. 15A loaded 10A un-loaded.

Hell, 220V scares me so much, I've never been bit by it. 110V stings plenty, thank you. If I had known it was 460v I might not have bothered taking a reading. But there was plenty of room in the control panel and the line in wires were easy to get the clamp around.

I thought so too. When it wasn't, I thought I should ask here.

Yep. That seems to be the consensus. I'm going to estimate high by assuming nameplate FLA. That and the duty cycle should be close enough.

Thanks.

Dan, You do understand that 240 volts ( in the USA) is erally only two 120 volt circuits? Touching either wire, only gives you 120 volts, to ground.

480 volts, is really 277 volts to ground for any one of the three wires. 480 volts between any two wires.

Now, 277 volts will not be anything I ever want to experience!

Dan, You do understand that 240 volts ( in the USA) is erally only two 120 volt circuits? Touching either wire, only gives you 120 volts, to ground.

480 volts, is really 277 volts to ground for any one of the three wires. 480 volts between any two wires.

Now, 277 volts will not be anything I ever want to experience!

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Are you sure that is true for all 480v systems in the US?

I think all three of my phases measure 480 to ground, and 480 phase to phase.

Not physically (as in physics) (or electrically) possible. To give you a geometric analogy, what you are saying is equivalent to.

Take a piece of paper, put 3 dots on it, that are all exactly the same distance from a common 4th dot, and that same distance from each other. YOu can do it with two dots,[They make an equilateral triangle] but not 3 dots in a flat plane.

jk

I suppose you /could/ wire the secondaries on the service transformer (transformers plural if you use three single-phase cans on an old style rack) corner-grounded, but nobody does - the ONLY place I've seen corner-ground service is a 240V 3Ph well service.

Imagine your triangle made up of the three transformer secondaries in a ring, the three points of the corner are where you attach the 3 motor phases. You run the power to the well pump contactor through three fuses, too.

But you take one corner and also attach the local earth ground, and when it gets to the well panel you bond it to ground there too. Suddenly you have two leads 240V to ground and one 0V to ground - but still 240V phase-to-phase.

It's not very popular, because IMNSHO they aren't safe to allow untrained ranch hands around - people see it's Grounded and simply don't stop to think it can also be a current carrying conductor.

I don't install 'em, I just fix 'em. And I put a Big Warning Note on both the outside and inside of the cover in permanent paint marker, in case one of those untrained persons starts poking around inside - then they can't say I didn't warn them.

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What's that Lassie? You say that Half-Nutz fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Thu, 29 Jan 2009 17:15:41 -0800 (PST):

YEp, got that.

Me neither.

That 277V to ground is only a certainty if they use a Wye connection secondary and ground the center point.

If they have Delta connection and the ground is floating, or it's corner grounded, or other odd stuff - all bets are off.

That's why I spent a Sawbuck on a set of lineman gloves, liners and gauntlets.

I'll work on it hot only as far as opening the door and carefully diagnosing what's wrong, I am NOT going to try any hot repairs.

Discretion is the better part of going home at quitting time.

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Just double checked. My system show 480 phase to ground on two phases, and 0 on the third. All phases measure 480 phase to phase.

So then what you have is a corner grounded delta. Unusual, but not unknown. It ias also possible you have an ungrounded delta, with a ground fault on one leg. [Almost the same difference really]

jk

IIRC, my system is preferred for motor loads and other such high amp equipment, and the 277 flavor was more useful if a LOT of 277v lighting was required.