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

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Discussion Overview

The discussion centers around measuring the current draw of a 120V AC device, exploring methods and tools suitable for this task. Participants share their experiences and suggest various approaches, including the use of multimeters and clamp meters.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant inquires about measuring AC current with a multimeter and whether it is safe or feasible to probe the plug spades directly.
  • Another participant explains that a conventional multimeter requires being connected in series, which involves cutting the power cord, and suggests using a clamp meter instead for convenience and safety.
  • Some participants express concerns about the safety and practicality of cutting the power cord to measure current, highlighting that a multimeter may not handle high currents well.
  • There is a mention of the potential issues with measuring current from highly inductive loads, such as electric motors, which could lead to inaccurate readings or damage to the meter.
  • Participants discuss the availability and affordability of clamp meters, with one noting they found options online for around $50.
  • One participant shares their experience with an extension cord designed for easy clamp-on testing of 120V loads.

Areas of Agreement / Disagreement

Participants generally agree that using a clamp meter is a safer and more convenient method for measuring AC current, but there is no consensus on the use of multimeters in this context, with some cautioning against it.

Contextual Notes

Participants mention limitations regarding the current ratings of multimeters and the potential risks associated with measuring current in inductive loads, but these points remain unresolved.

Who May Find This Useful

This discussion may be useful for individuals looking to measure AC current in household devices, particularly those new to working with AC circuits or considering the purchase of measurement tools.

eberg
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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
 
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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?
 
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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.
 
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.
 
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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.
 
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.
 
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.
 

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