AC AMMETERS

AC Ammeters measure AC Amperes, AC Current...how ever you want to say it. They can measure a fraction of an amp, so we would be measuring milliamperes (mA).  It's just what it says, 1 mA is equal to .001 Amperes (A), and one set further 1 microampere is equal to .000001 A.

There are smaller increments, but these are the ones that will apply to us.  On the other side of the scale the are Kiloamperes (KA), and yes, 1 KA is equal to 1000 A and one set further is Mega Amps…yep one meg is equal to 1,000,000 A (though not very common for us).  So these AC Ammeters cover a wide range of inputs, as you see.

So now we have a range of AC Ammeters, so you can begin to see the variety of part numbers we'll deal with.  Every specific range isn't offered by the manufacturer, that's where we come into play as a "Mod Center."

The most popular is the Current Transformer rated meter.  In order for a panel meter to measure any amperes above, say, 50 ACA, the construction of the meter will no allow the size wire to handle 50 ACA.  Let's say we want to measure 50 ACA.  In order for 50 ACA to travel safely through the meter, the size wire required to handle the amps would be about the thickness of a pencil.  This is why you have different size diameter power cords.  The one to your skill saw is different from your electric razor.  It all depends on the amount of current or amperes that is required to operate it.

So trying to manipulate this size wire through a small meter is difficult.  It varies from mfg to mfg, so in general the maximum most meters will read is around 50 ACA, and we call this a "self contained meter."  In order to read ACA above this, the industry standard is to provide a CT rated meter.  This meter must be used with an external current transformer.  This is common practice through out our industry. 

Let's say we need to measure 100 ACA.  In this case we'll use a CT rated meter that has an input of 5 ACA and a scale of 0-100ACA along with an external CT that is 100 to 5 or 100:5.  The 100 Amps is hooked up to the 100 Amp CT.  It converts it to 5A and this 5 A is hooked to the meter.  When the CT sees the 100 ACA the output of the ct is 5 ACA, the meter sees the 5 ACA and the pointer indicates 100 ACA on the scale...get it?

So, a CT rated meter in combination with a CT is used to measure high amounts of current or amperes.  The meter and CT are in a matched pair.  The meter has a scale of 0-100 ACA and an input of 0-5 ACA and the CT has a primary of 100 ACA and a secondary 5 ACA.

So you want to measure 300 ACA...Meter is a CT rated meter of an input of 0-5 ACA and a scale of 0-300 ACA and the ct will be a 300:5. Man, you're coming right along...so now unlike the voltmeter in the truck you can see how and why the inputs and scales vary from range to range and this will apply throughout all the different ranges and devices we'll discuss.  Now, just as we discussed before, up to approx 50 ACA a meter can measure without an external ct.  Ranges below that can all be "self-contained" and the input, rating, scale, and captions are at the customers’ requests.

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