The Amp Clamp Mystery

Amp Clamp

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Photo by: Ed Sherman

We received a question the other day about the proper orientation of a DC amp clamp on a conductor that's worth sharing because it can be a bit confusing and could have some real ramifications on your diagnostic capabilities if you get it wrong. The question is which way the amp clamp should be oriented around the wire you are checking. In the photo above you can see the amp clamp I use most of the time now. Its my Blue Sea model 8110. Notice the "plus" sign and the arrow embossed on the jaw of the clamp. This is Blue Sea's way of illustrating the orientation on their tool. The arrow is pointing in the presumed direction of current flow, assuming a flow from positive to negative, the accepted convention in modern electrical work. (Electron flow is actually from negative to positive, but that's a long story we won't tell here.)

I'm not aware of any definative rule in the world of meter manufacturers that dictates that this is the only way to mark these clamps. If I recall, some meters will just have an arrow that may be pointing to the "source" of power.

So, what's the answer here? Assume nothing, read the instructions for your specific meter to be sure on this. What you don't want to do is get this wrong and then think that current is flowing out of you battery when it should be flowing in when the charging system is turned on; as an example of what could go wrong is this gets misapplied.

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