Brian,
The short answer is that a "Class 2 Power Unit" is what we would
normally call a "wall wart" or a "brick" power supply.
Clause 1.1 of UL 1310 (August 21, 1992) says:
"These requirements cover (1) direct plug-in Class 2 power units
intended for connection to a 15-ampere nominal 120- or 240-volt ac
branch circuit, and (2) cord-connected Class 2 power units intended for
connection to a 15- or 20-ampere ac branch circuit with a potential of
150 volts or less to ground. These products utilize an isolating
transformer and may incorporate rectifiers and other components to
provide a source of alternating- or direct-current supply. These
products provide Class 2 power levels in accordance with the National
Electrical Code, and are intended primarily to provide power to low
voltage, electrically operated devices."
Other clauses in the Scope say that UL 1310 does not cover:
* Products whose input power could exceed 660W.
* Battery chargers for charging engine-starting batteries.
* Power supplies for toys.
* Products with other than Class 2 outputs.
* Battery chargers to charge batteries for wheelchairs and other
mobility aids.
* Class 2 transformers intended for field connection (i.e. bell
transformers).
Section 725 of the National Electrical Code (NEC) covers Class 1, Class
2, and Class 3 Remote-Control, Signalling, and Power-Limited Circuits.
The Scope in 725-1 says that (these) "are not an integral part of a
device or appliance." The Definition in 725-2 says "Due to its power
limitations, a Class 2 circuit considers safety from a fire initiation
standpoint and provides acceptable protection from electric shock."
Chapter 9, Tables 11(a) and 11(b) of the NEC show:
* Class 2 ac source is limited to:
- For 0 to 20V output, < 8A output under any load conditions, with
a nameplate rating < 5*Vmax volt-amps and < 5.0 Amps.
- For 20 to 30V output, < 8A output under any load conditions, with
a nameplate rating < 100 volt-amps and < 100/Vmax Amps.
- For 30 to 150V output, < 0.005A output under any load conditions,
with a nameplate rating < 0.005*Vmax volt-amps and < 0.005 Amps.
* Class 2 dc source is limited to:
- For 0 to 20V output, < 8A output under any load conditions, with
a nameplate rating < 5*Vmax volt-amps and < 5.0 Amps.
- For 20 to 30V output, < 8A output under any load conditions, with
a nameplate rating < 100 volt-amps and < 100/Vmax Amps.
- For 30 to 60V output, < 150/Vmax output under any load conditions,
with a nameplate rating < 100 volt-amps and < 100/Vmax Amps.
John Barnes
dBi Corporation
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