Twayne wrote:

A "Class 2" xfmr is simply a double-insulated transformer without an earth
ground on its plug, nor a polarized plug.
A "Class 1" xfmr requires a third wire, the earth ground pin on its plug.
The "Class of xfmr is a UL/CSA et al classification which approves the xfmr
and nothing else as safety approved.

The primary characteristic of class 1, 2, and 3 power sources is that
they are power limited. There is a specified maximum voltage, current
and power you can get from the source. For a class 2 24V transformer the
max current is 8A - the maximum current you get if you short circuit the
transformer.

Because the power is limited, the downstream circuit does not have to
meet the general wiring requirements of the NEC. Article 725 is used
instead.

Secondary ckts attached to the output
of a xfmr are not subject to UL/CSA et al safety testing unless a voltage in
it equals or is more than 42VDC or 42V ac p-p. The original spec, UL1459
(now superceded but not changed in this area) is online for those who wish
to read it. I -think- the CSA spec was CS-03.
Whatever class 1 & 2 means ckt-wise, I don't know; it's not a UL/CSA et
al type spec but might be NEC, NFPA or otherwise.

HTH,

Twayne`