Respironics BiPAP Focus Operator's Manual page 22

Setup
CAUTION: The nurse call station port is intended to connect only to
a SELV (Safety Extra-Low Voltage) and ungrounded system with
basic insulation to ground, in accordance with IEC 60601-1. To
prevent damage to the nurse call circuit, the signal input should not
exceed the maximum rating of 24 VAC (Volts of Alternating Current)
or 36 VDC (Volts of Direct Current) at 500 mA (milliamps), with a
minimum current of 1 mA.
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16 BiPAP Focus™ Noninvasive Ventilator System
1027404 Rev K