Discovering How to Measure AC Current for a 120V Device | Tips and Tricks

[eberg]

Hi Everyone,

I'm new to the forum, this is a great place to dig around and do some reading.

My first question is:
I want to read the current draw (amps) of a 120V AC device (standard wall plug). I've worked with DC quite a bit but rarely with AC. Can I just probe the plug spades with a multimeter to read the current in an AC circuit, or how could I test this?

Thanks

 

[Jimmy]

What kind of device are you talking about? It would be inconvenient to use a conventional multimeter to measure the current of a device since the multimeter would have to be connected in series with the device.

You would have to cut one wire of the cord and insert the meter in series at the break.

A clamp meter would be useful in this case. This is a meter that will take current readings without the need to break the circuit. It clamps on the wire and uses electromagnetic induction to measure the current. Fluke makes good clamp meters. Of course, fluke makes nice meters in general.

http://www.fluke.com/products/specifications.asp?SID=0&AGID=0&PID=30405

Are there any ratings on the device you want to take a reading from?

 

[eberg]

That sounds a little easier than using a multimeter, I wasn't even sure if AC could be measured with a multimeter in the way you described. It's not convenient or real safe, but it's nice to know it can be done that way.

Thanks for the advice on the clamp meter, that would be the best. I don't own one, but may be able to get one from work that I could borrow.

I would like to use it like on a drill for example, where as the load increases I could measure it quantitatively using the increase in amperage.

 

[Jimmy]

Glad to be of help. I definitely wouldn't recommend cutting your power cord to measure current. Who would want to anyway? .

Besides, a typical multimeter might not be able to handle the current depending on what you are measuring. The one I have here is only rated up to 10A.

 

[wimms]

If you have highly inductive load like powerful electric motor, then handheld Meter in series can a) fail, b) give bs readouts. Be careful.
Clamp meter could even give more precise measurement besides being both more convenient and safe.

 

[eberg]

Thanks a lot guys. I found some clamp meters online for fairly cheap. I'll check out some local stores, looks like I should be able to pick one up for around 50 bucks that is still decent quality.

 

[russ_watters]

Originally posted by wimms
Clamp meter could even give more precise measurement besides being both more convenient and safe.

That's the best option. I have an extension cord with the wires separated for easy clamp-on for testing 120v loads.