Something is strange. If I follow your link I see where they say:
Part #: 3343-0-30ACA (That part number implies a 0 to 30 Amp meter range) and they also mention Meter, analog. Meter movement: 0-10VAC. Scale reads: 0-30 AC Amps. Needs external transformer.
However the image clearly shows a 0 to 20 Amp. Now a 20 amp part number would be 3343-0-20ACA and if I Google that I end up with this:
https://www.electronicsurplus.com/I...10VAC METER Scale_0-20AMPS AC - 3343-0-20ACA/
Seeing no image available?
Now for that line of meters this is the data sheet:
https://www.electro-tech-online.com/custompdfs/2012/01/ruggedseal_datasheet-1.pdf
Discounting digital scalable meters all the analog meters I have worked with were scaled for an input of 0 to 5 Amps AC. So if you uses a 50:5 CT the CT secondary went directly to the meter movement and the meter had a 0 to 50 AAC scale on the face.
Also, the forum seems to have lost its link buttons?
More Later
Ron