Burden Ratings on ANSI Voltage Transformers for Metering 1

[SSLA]

Folks:

ANSI has defined a number of standard burdens (W,X,Y,Z,ZZ and sometimes M). Usually a VT nameplate will list all that it can support e.g. 0.3WXY for a 75 VA unit and 0.3WXYZ for a 200 VA unit.

But what does it mean if the name plate on a VT with one secondary lists only one value, e.g. 0.3Z? I have always assumed that meant it was also passed factory tests at all of the lesser burdens, i.e. 0.3Z would mean 0.3 class accuracy at W,X and Y burdens as well.

Am I right? Or can accuracy at the lesser burdens exceed the limits of the 0.3 (in this case) class?

I've had a look in the ANSI, IEEE standards and Handbook for Electricity Metering but cannot find a clear reference to what the single rating means.

Can anyone help?

 

[scottf]

The correct way to list it would be 0.3 WXYZ, but 0.3Z means the same thing, i.e. 0.3 for burdens up to Z (200 VA).