AC-Only or AC/DC Clamp Ammeter?

(Rerun) Get the right clamp meter for testing your RV electrical systems…

Dear Mike,

I really enjoy your entries in the RV Travel newsletter. They are very informative. Some time ago I think I recall you making a recommendation of a clamp meter for RVers. I would like one that measures DC current in 12-volt systems. Can I bother you for a recommendation? —Bill

Hey Bill,

Most certainly…. As some of you may already know, an AC clamp amp-meter uses a tiny current transformer in its jaws to measure amperage.

However, transformers only pass Alternating Current (AC), so that technology can’t measure DC amperage. That’s why an AC clamp meter is only useful for measuring AC current. And that’s a problem if you want to measure things like DC charging current for your RV battery system.

Enter the Hall Effect Sensor

More expensive clamp meteres use a Hall Effect Sensor instead of a current transformer. This semiconductor device can measure either AC or DC current, so you can get a clamp meter that will measure both 120-volt AC shore power amperage, as well as 12-volt DC amperage in your RV’s battery system.

Expect to pay a little more for a clamp ammeter with a Hall Effect Sensor that performs both AC and DC current measurements, but the flexibility of having a tool that will work for both AC and DC troubleshooting in your RV is well worth it.

I use a Southwire 21550T in my seminars and webcasts

Here’s my go-to clamp ammeter for RV electrical testing. The Southwire 21550T does AC or DC amperage clamp testing as well as voltage and resistance measurements. It can also do diode and capacitor testing, plus temperature measurements with a thermocouple probe.

In addition, this is a True RMS meter, which means it can perform accurate voltage and amperage measurements of distorted (non-sinusoidal) waveforms. And it includes a Non-Contact Voltage Tester function, which can be used for hot-skin voltage testing.

And if you do residential and RV air conditioner maintenance checks there’s an optional Pipe Clamp Temperature Probe.

I’ll be covering these advanced testing functions in several RV technician training videos in early 2025, which I can repost here for RV owners as well. Stay tuned!

The Southwire 21550T is a great clamp meter that’s reasonably priced and available at Lowe’s stores or on Amazon HERE.