how do you test a 220V circuit?

[kato]

I know this is absolutely unrelated to audio but I can't find the answer anywhere online and you guys are the only people I know who know about electronics...

How do I test a 220V outlet?
I have a circuit in my house and I want to know if it's live (or if the appliance I'm plugging into is is dead.) It's one or the other - and I suspect I can't just stick a regular 110V outlet tester in there - since i understand 220v circuits carry multiple voltages...
Thanks, Kato

 

[HappyTom]

Don't you have a DMM?

HT

 

[kato]

I do.

But I lack the understanding of what the three wires carry.
I can see that none of them carries ground because there's a 4th ground wire that's not connected to anything.

 

[bcarso]

Typically 220V outlets are three-wire, with either hot side 110V w.r.t. the safety ground. In North America they resemble three-prong 110V outlets except one of the blades is at a 90 degree angle relative to the other.

If you have a four-conductor outlet (odd for a home installation) it may be 208 three-phase. Check at the breaker box to see if you really have three phase coming in. Maybe they wired your house that way for a big A/C compressor.

There are some current and former electricians in here who can tell you what to look for.

 

[kato]

Oh I see - so one of these has to be a ground wire - they just wired it using one of the 3 as ground and left the ground wire dangling.

The colors that are connected are black, white, and red. (and a bare copper wire is disconnected.)

My multimeter is a super-generic one that I've only really used to check continuity:

Can anyone recommend a beginner's mm that's not too expensive, that would be useful for someone whose longterm projects include just building a couple of compressors, preamps - and general household use?

Kato

 

[Butterylicious]

Think of it as the secondary of a center tapped transformer with the center tap grounded, because that's exactly what it is. The round or "L" shaped hole is ground. The 2 straight blades are hot and should read a potential of 120 volts to ground. They should have a potential of 240 volts hot to hot. Be sure and check it hot to hot because it is possible that both of the hots ended up on the same phase or 1/2 of the breaker is off and potential is measuring backwards through the load. I seen clothes dryers that would spin but not heat because of 1/2 tripped breakers.

 

[Butterylicious]

Oh, and red and black are the 2 hots, bare is ground, and white is neutral. The major difference between a neutral and a ground is that a neutral is designated to carry current and a ground is for case bonding to earth. In a 3 wire application, you're really supposed to cap off the neutral and use the ground, but if it's a dedicated clothes dryer recept, the neutral and ground are supposed to be terminated at the same place.