In ,
bud-- typed:
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.

I think you're confused between class definitions for Safety and what the
NEC defines; they are different.

Class 1, 2, and 3 CIRCUITS are classified as remote-control, signaling, and
power-limited circuits in the National Electrical Code (NEC).

Class 1 and 2 Power Supplies determines the insulation PROPERTIES of a power
supply and there is no Class 3. To the layman, they either need the third
ground wire or not (1 & 2 respectively).

The 8 Amp limitation IN NEC has nothing to do with UL/CSA et al
classifications. A transformer can output any current it can be designed for
as long as it meets the insulation and overvoltage/current test
specifications and meet the safety requirements.
Class 1, 2, 3 as used in the NEC as you can see above is quite different.
While saftey is of course a concern, simply limiting an output to 8 amps
would not deem it to be "safe". The NEC is concerned with wiring, and the
Safety is concerned with safety. Two different worlds. A google for UL
1459 might be enlightening for you. You apparently already have some
NEC information, or I'd assume so at least. You know NEC and I know Safety;
perhaps between the two of us, we could purchse/outfit/install equipment for
a homeG.

HTH,

Twayne`

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ac p-p. The original spec, UL1459 (now superceded but not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`