How do I test a ground?

July 25, 2007 1:36 PM

How can I test whether something (like a cold water pipe) is a ground?

I've assembled a very simple, battery-powered, transistor radio using my Maxitronix 500-in-1 lab... all except for one last step. The instructions state to connect a wire to a known ground (such as a cold water pipe).

The problem is that I have no idea how to test whether something is a ground or not (despite lots of googling). Could someone tell an electronics newbie how to test for this?

I would mainly like to know just for the sake of knowing. I have a multimeter (in case it's relevant).

Thanks!

posted by blisterpack to home & garden (7 comments total)

This article explains it pretty well
posted by zeoslap at 1:41 PM on July 25, 2007

I should have googled "ground testing". Thanks for the quick answer.
posted by blisterpack at 2:04 PM on July 25, 2007

The electrical wiring FAQ also has an entry: Testing grounding conductors and grounding electrodes. I would only go there with great care (they call the safer method "moderately safe")..
posted by Chuckles at 9:58 PM on July 25, 2007

Also worth noting, all these tests are talking about safety ground, which is not relevant to your project. I'm not exactly sure what the project is trying to accomplish - lots of radios work just fine without a ground connection - but it is related to radio reception and noise considerations.

What does the project use for an antenna? Try testing a few different grounding and antenna combinations..
posted by Chuckles at 10:28 PM on July 25, 2007

Thanks Chuckles. Yes, I think I will avoid the "spraying molten copper" route, but may look into the safer one.

The project: the radio uses a long wire as an antenna and another long wire for the ground. I'm sure it's not a safety ground because the radio uses a few AA batteries. Perhaps it is to help reduce static? I've played around with the wires as you mentioned, but since it's an extremely basic project, I don't expect it to work very well. It's really just a learning project.

More importantly, when I read multimeter instructions, they frequently mention connecting the negative terminal to a known ground. Since, I would like to become familiar with my multimeter, having a known ground seems important.
posted by blisterpack at 12:34 AM on July 26, 2007

the radio uses a long wire as an antenna and another long wire for the ground.

Which is the most basic antenna design, a dipole. Or, more likely, a half-wave dipole. Connecting to ground allows you to eliminate the ground length, making a quarter wave antenna.

Now multimeters needing a ground connection.. Err.. In basic electronics - no safety issues, no radio frequency issues - the notion of ground is just a convenience. Voltages are relative, measured across components, from one node to another, or from one probe to another, not unlike distance. You can't say it is 2500 miles to Los Angeles, that is the distance from New York to Los Angeles. Though arbitrary, choosing a ground simplifies calculations, measurements, and design in general.
posted by Chuckles at 11:58 AM on July 26, 2007

Thanks Chuckles. That clears things up quite a bit.
posted by blisterpack at 3:06 PM on July 26, 2007