Clamp tester

[John Dirks Jr]

I got a clamp tester today at home depot. I clamped it on a line in my main box that runs a dedicated service to an appliance that is listed to draw 14 amps. The tester read 11.6 amps. Where does the variance come from. The appliance rating or the tester or both? The tester is a Sperry DSA500.

[hausdok]

That's what the appliance was using at the time.

The rating is it's maximum allowed rating, not what it will normally run at. Think of it this way - you're car uses the most gas when it's under load, less when it isn't. It's the same with electricity. Put the appliance under less load and it will draw less amperage; put it under mor load and it draws more.

ONE TEAM - ONE FIGHT!!!

Mike

[John Dirks Jr]

Ok great, I would rather hear that answer. I mean, I know this particular tester is a cheapo ($49) one. Do you think it will serve me ok?

[Jim Katen]

Originally posted by AHI

Ok great, I would rather hear that answer. I mean, I know this particular tester is a cheapo ($49) one. Do you think it will serve me ok?

It's fine. Plenty good enough for home inspection work. You'll find that it's very accurate. It's cheap because it's less durable than the expensive ones. Don't drop it.

If your tester told you that the device was drawing 11.6 amps, then the device was probably drawing 11.6 amps. Remember that the amperage that an appliance draws will vary in response to the voltage (including any voltage drop) and, if there's a motor, the load that the motor is resisting.

Try measuring the amp-draw of a Skilsaw while it's running without a load, under a load, and in the moment just before it stalls. Tell us what you get.

Then try the same thing with the Skilsaw plugged into a 100-ft, #14 extension cord. Tell us what you get.

Here's another fun one. Measure the amp-draw of your vacuum cleaner, then measure it again while your hand is blocking the vacuum cleaner's intake opening.

What happens to the amp draw?

Why?

How do these amp measurements compare with the dataplate on the vacuum cleaner?

- Jim Katen, Oregon

[John Dirks Jr]

Thanks Jim,

Without performing any tests you mention I understand the different levels of draw that will occur under different circumstances. A long extinsion cord will cause a higher draw due to energy loss in the length of transfer. The appliance at the end of the line will still be demanding a certian load. So that load combined with whatever amps are needed to make up the loss in the line would give a higher reading. Correct?

Many other types of electrical items require a greater load at startup then settle down to an operating load.

Obviousley a free wheeling saw is going to draw fewer amps than one under load.

I am glad that this cheapo clamp tester will at least get me started. My goal in this thread was to determine if I could trust its readings. At least you think it will serve me well so thats good.

Now just curious about this question. My central AC unit was drawing just under 12amps at 220v. Does that sound like an energy hogging unit? Thats just the AC unit outside though. That reading does not include the blower in the furnace portion inside.

[John Dirks Jr]

More questions. Since the wires inside a main panel can be close together it can sometimes be difficult to get the clamp tester around a particular wire. Rather than sticking ones fingers in there, what is a safer way to spread the wires to provide clearance for the clamp? Shutting off the main I am sure is one way. What other safe ways are there without shutting off the main, if any? Is there a suitable tool available or something else makeshift?

[Brian G]

Originally posted by AHI

Rather than sticking ones fingers in there, what is a safer way to spread the wires to provide clearance for the clamp?

You can buy insulated electrical tools like pliers or screwdrivers that should work well, but I'm not sure what you're going to be amp-clamping in a panel. The only place I ever do that is at the AC disconnect, where the clamping is usually much easier (others will vary on that). I carry a long, thin insulated screwdriver just for poking around in main panels, trying to see how things are done around sloppy wiring (Klien 601-8 INS). You should get really, really comfortable with your knowledge of electrical before you consider messing around inside panels.

Shutting off the main I am sure is one way.

I would never shut off the main unless there was a serious and immediate problem. It may not come back on when you're done, you might screw up someone's computer, clocks will be flashing all over, etc.

Is there a suitable tool available or something else makeshift?

Anything totally non-conductive could work, like a short wooden dowel.

Brian G.

Clamping Down On Lousy Wiring [^]

[fqp25]

Instead of trying to stick the Clamp Meter inside a panel, I would purchase an AC Line Separator (I Think That's What They Are Called).

You simply plug the separator into the outlet and it will separate the hot & neutral. Then you'll get an amp reading between the outlet & appliance instead of trying to spread the wires inside of a panel. (Especially those panels which look like a spaghetti factory)

[Jim Katen]

Originally posted by AHI

More questions. Since the wires inside a main panel can be close together it can sometimes be difficult to get the clamp tester around a particular wire. Rather than sticking ones fingers in there, what is a safer way to spread the wires to provide clearance for the clamp? Shutting off the main I am sure is one way. What other safe ways are there without shutting off the main, if any? Is there a suitable tool available or something else makeshift?

I carry a fuse puller for just such occasions.

- Jim Katen, Oregon

[Jim Katen]

Originally posted by AHI

Thanks Jim,

Without performing any tests you mention I understand the different levels of draw that will occur under different circumstances. A long extinsion cord will cause a higher draw due to energy loss in the length of transfer. The appliance at the end of the line will still be demanding a certian load. So that load combined with whatever amps are needed to make up the loss in the line would give a higher reading. Correct?

Yes.

Ok, Mr. Smartypants, how about the vacuum cleaner?

. . . Now just curious about this question. My central AC unit was drawing just under 12amps at 220v. Does that sound like an energy hogging unit? Thats just the AC unit outside though. That reading does not include the blower in the furnace portion inside.

That doesn't sound like a particular energy hog. How does that amp reading compare with the various amp listings on the dataplate?

- Jim Katen, Oregon

[John Dirks Jr]

If you choke the vacuum suction hose you will increase the load on the motor and the amp draw will increase. Why? By doing this you are preventing the motor from doing what it wants to do, move air. With the sorce of incomming air blocked the impeller will be creating a significant low pressure on the suction side which actually has an effect of wanting to pull the impeller the otherway. The motor is working very hard to try and reverse the effect since it is designed to rotate at a fixed rate. Is that technical enough for you?

The rating on the tag is about 15.6 amps compressor and fan combined. My Dad put this AC unit in at least 30 years ago. Its a Sears unit. I replaced a capacitor in it once and thats it. Last year I cleaned the condenser core for the first time. That really increased its output. This little unit is slightly too small for this house. It cranks its little heart out and has been doing it for 30+ years. This thing is friggin awsome.

Heres a pic of it

http://home.comcast.net/~mailmanusa/AC.JPG

[Jim Katen]

Originally posted by AHI

If you choke the vacuum suction hose you will increase the load on the motor and the amp draw will increase. Why? By doing this you are preventing the motor from doing what it wants to do, move air. With the sorce of incomming air blocked the impeller will be creating a significant low pressure on the suction side which actually has an effect of wanting to pull the impeller the otherway. The motor is working very hard to try and reverse the effect since it is designed to rotate at a fixed rate. Is that technical enough for you?

Very technical indeed. But wrong.

Try it.

Hint: When you load a skilsaw, the motor slows down and the amp draw goes up. When you choke a vacuum cleaner, the motor . . .

The rating on the tag is about 15.6 amps compressor and fan combined. My Dad put this AC unit in at least 30 years ago. Its a Sears unit. I replaced a capacitor in it once and thats it. Last year I cleaned the condenser core for the first time. That really increased its output. This little unit is slightly too small for this house. It cranks its little heart out and has been doing it for 30+ years. This thing is friggin awsome.

Very cool.

The amazing thing is that that sucker might keep running for another ten years.

What makes you think it's too small? One of the things that might have contributed to its longevity is that it isn't too large. That means fewer, longer cycles.

- Jim Katen, Oregon

[John Dirks Jr]

Ok I will do the choked vacuum test and report back. You have a good point on the fewer longer cycles attributing longevity of the AC unit. I suspect that over all it uses less energy than a larger unit even though it may run longer.

[Chad Fabry]

Yeah, what Katen said: Reducing area on the input side of a pump reduces the possible work load. Closing off the input side entirely allows the motor to run at close to zero load.

[John Dirks Jr]

I stand corrected.

7.9amps unchoked...

6.4amps choked...

I know if you choke it too long the motor will overheat. Thats why I assumed it was extra amperage that would heat the motor up. So in re-thinking that, is it the lack of air flowing through that makes the motor overheat?

[Jim Katen]

Originally posted by AHI

I stand corrected.

7.9amps unchoked...

6.4amps choked...

I know if you choke it too long the motor will overheat. Thats why I assumed it was extra amperage that would heat the motor up. So in re-thinking that, is it the lack of air flowing through that makes the motor overheat?

That's helping. Also, the bearings may not be intended for the faster rpm.

Another fun thing to try with a clamp-on amp-meter is to check the grounding electrode conductors on the homes you inspect. Every so often, you find current flowing on them.

- Jim Katen, Oregon

[John Dirks Jr]

Current in the GEC? Not good. Can you list some conditions that would cause that? Would one be damaged wire insulation due to staples hammered in too tight? Any others?

[Jim Katen]

Originally posted by AHI

Current in the GEC? Not good. Can you list some conditions that would cause that? Would one be damaged wire insulation due to staples hammered in too tight? Any others?

If you damaged the wire insulation with staples, the current might leak to the equipment grounding wires, but not the grounding electrode wire.

I think that the most likely cause of current on the GEC would be a problem with the service neutral.

- Jim Katen, Oregon

[jon_ran]

How many inspectors actually check the amperage draw of a circuit. I only look at the wire size to determine rating and compare to disconnect size. Seems to me that this is going way above and beyond (which I am all for when it makes sense) because the new owner will use the home in a different manner than the current owner. This may become a future liability issue.

A circuit that is currently only drawing 2.6 amps because the only current load is an alarm clock will change drastically when the computer, monitor, printer, big screen tv with satellite receiver, dvd player and surround sound is added.

If the circuit is drawing more than the wores are capable of, it will be evident without testing the current load.

[Jim Katen]

Originally posted by jon_ran

How many inspectors actually check the amperage draw of a circuit. I only look at the wire size to determine rating and compare to disconnect size. Seems to me that this is going way above and beyond (which I am all for when it makes sense) because the new owner will use the home in a different manner than the current owner. This may become a future liability issue.

A circuit that is currently only drawing 2.6 amps because the only current load is an alarm clock will change drastically when the computer, monitor, printer, big screen tv with satellite receiver, dvd player and surround sound is added.

If the circuit is drawing more than the wores are capable of, it will be evident without testing the current load.

I only use mine for electric furnaces and heat pumps which I see a lot of.

Some inspectors use them to evaluate air conditioning compressors.

- Jim Katen, Oregon

[John Dirks Jr]

Jim, so what does an inspector look for when using a clamp tester on heat pumps, elec furnaces, or ac compressors? Would it be, check for amp draw and compare it to manufacturers tag for load rating? What is good/not good to find?

[Jim Katen]

Originally posted by AHI

Jim, so what does an inspector look for when using a clamp tester on heat pumps, elec furnaces, or ac compressors? Would it be, check for amp draw and compare it to manufacturers tag for load rating? What is good/not good to find?

With a heat pump or an electric furnace, I like to open the furnace's electrical compartment and, one at a time, clamp around the lead to each heating element. Then, when I turn on the furnace, I can see that the elements come on in sequence and go off in sequence.

Sometimes I'll find that one or more elements doesn't fire. In that case I try to determine if the element or relay is bad or if the system is holding that element back on purpose, usually in response to input from an outdoor thermostat.

I don't use a clamp on meter for air conditioners but others here do. They simply use it to measure the amp draw of the AC compressor and compare it to the data plate numbers.

- Jim Katen, Oregon