Contemporary Control Systems BAScontrol20 User Manual - Manual (Page 12)

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3 Installation
The BASC20 is intended to panel-mounted with screws (not provided).
3.1 Power Supply
The power source for the internal supply is applied via the two terminals labelled HI
and COM. COM is for the power source return and also serves as the common
ground connection. Primary 24 VAC/VDC (± 10%) power is applied to HI and COM.
HI connects to a diode accomplishes half-wave rectified power
— while providing
reverse input voltage protection. The recommended power conductor size s 16 –18
AWG (solid or stranded). Ground is directly connected to zero volts. Input
connections are reverse-polarity protected.
WARNING: Powering devices can present hazards. Read the next two sections carefully.
3.1.1 Power Supply Precautions
Internally, the BASC20 utilizes a half-wave rectifier and therefore can share the
same AC power source with other half-wave rectified devices. Sharing a common
DC power source is also possible. Sharing AC power with full-wave rectified devices
is NOT recommended. Full-wave rectified devices usually require a dedicated AC
power source that has a secondary elevated above ground. Both secondary
connections are considered HOT. AC power sources that power several half-wave
devices have a common secondary connection called COMMON, LO, or GROUND.
This connection might be tied to earth. The other side of the secondary is
considered the HOT or HI side of the connection. Connect the HOT side of the
secondary to the HI input on the BASC20 and the LO side to COM on the BASC20.
All other half-wave devices sharing the same AC power source need to follow the
same convention. When using a DC power source, connect its positive terminal to
the HI input on the BASC20 and the negative terminal to COM on the BASC20.
Reversing polarity to the BASC20 will not damage the BASC20.
WARNING: Devices powered from a common AC source could be damaged if a mix
of half-wave and full-wave rectified devices exist. If you are not sure of the type of
rectifier used by another device, do not share the AC source with it.
3.1.2 Limited Power Sources
The BASC20 should be powered by a limited power source complying with the
requirements of the National Electric Code (NEC) article 725 or other international
codes meeting the same intent of limiting the amount of power of the source. Under
NEC article 725, a Class 2 circuit is that portion of the wiring system between the
load side of a Class 2 power source and the connected equipment. For AC or DC
voltages up to 30 volts, the power rating of a Class 2 power source is limited to 100
VA. The transformer or power supply complying with the Class 2 rating must carry a
corresponding listing from a regulatory agency such as Underwriters Laboratories (UL).