Darned Charlie , I had to think back on this one. I was trying to wait a bit with the hope that someone else would hop on this one. But I'm sure someone else will after I submit my post.
I dug around and I can't find info on Class 1 regarding CTs, PTs, or WHMs.
This is what I am referring to:
You have to consider the ANSI Metering Accuracy of a specific CT. Accuracy's are related to burdens such as B-0.1,0.2, and 0.5.
For example, the ratio of a 5a/60hz CT that has a burden designation of
B-0.1 will have an impedance of .1 at 2.5a, .9pf.
My metering and Instrument transformer Application guide shows
Now, the
0.3% accuracy refers to that B-0.1 metering class CT being accurate within .3% as long as the CT burden rating in not exceeded. At 100% rated current a 0.3 accuracy class will be accurate .997min to 1.003 max and .994-1.006at 10% rated current.
More info at:
http://www.netaworld.org/files/ItemFilea830.pdf
Of course PTs have their accuracy ratings also. They have burden designations with the letters W, X, Y, Z, and ZZ and
accuracy classes of 1.2, .6, and .3 which relates to the limits of the transformer correction factor and the limits of power factor More info at: load.
http://www.netaworld.org/files/ItemFileA336.pdf
So what this all means is that you won't remember this stuff but to appreciate that there is a bit more to applying CTs and PTs that meets the eye. If you aren't qualified it's best to have someone who understands the package to specify the parts.
All watthour meters have a class designation (marked on the Nameplate) which indicates their overload capacity. Again a "Class" Designation such as
Class 10, 20, 60, 100, 200, 320.
My reference shows a
"class 10" 2.5 amp meter with a 400% overload capability and a
"class 100" 15a meter with a 666-2/3% overload capacity.
Not being a metering expert I'm not sure of the newer electronic/digital meters bring more metering accuracy to the party of not.
Dave
8)
