**ON A/C 051-099,
The EMER EXIT LT switch 4WL on the overhead panel 25VU controls the emergency lighting system. Self-monitoring circuit breakers 1WL, 2WL and 3WL protect the system from too much current flow. The EMER EXIT LT switch 4WL has three positions, OFF, ARM and ON. Each of these positions gives a discrete ground signal to all EPSUs and power supply units. The EPSUs monitor the correct voltage of the AC and DC busbars. The power supply units monitor the correct voltage of the DC busbars. When the voltage on these busbars falls below a specified level, the emergency lighting automatically comes on. This is when the EMER EXIT LT switch 4WL is in the ARM position. When only the AC normal busbar fails:
-
the 28VDC essential busbar supplies the emergency lighting system through the 28VDC/6VDC converter in each EPSU,
-
the marking system of the emergency escape path stays in the off
condition.
When the 28VDC essential busbar fails:
-
the internal batteries in the EPSUs and the power supply units supply the emergency lighting system,
-
the marking system of the emergency escape path is in the on condition.
When the EMER EXIT LT switch 4WL is in the ON position:
-
the converters or the internal batteries in the EPSUs and the power supply units supply the emergency lighting system.
When the LIGHT EMER pushbutton switch and its integral light on the forward attendant panel 120RH are on:
-
the converters or the internal batteries in the EPSUs and the power supply units supply the emergency lighting system.
An open or short circuit in the related control lines causes the emergency lighting to come on. The internal test program in the EPSUs finds defects in the load circuits.
R **ON A/C 106-149, 401-499,
The EMER EXIT LT switch 4WL on the overhead panel 25VU controls the emergency lighting system. Self-monitoring circuit breakers 1WL, 2WL and 3WL protect the system from too much current flow. The EMER EXIT LT switch 4WL has three positions, OFF, ARM and ON. Each of these positions gives a discrete ground signal to all EPSUs. The EPSUs also monitor the correct
R 1EFF : 001-049, 051-099, 101-149, 151-158, 1 33-51-00Page A3 1201-209, 401-499, 1Aug 01/05 1 1 1CES 1
voltage of the AC and DC busbars. When the voltage on these busbars falls
below a specified level, the emergency lighting automatically comes on. This
is when the EMER EXIT LT switch 4WL is in the ARM position.
When only the AC normal busbar fails:
-
the 28VDC essential busbar supplies the emergency lighting system through
the 28VDC/6VDC converter in each EPSU.
When the 28VDC essential busbar fails:
-
the internal batteries in the EPSUs supply the emergency lighting system.
When the EMER EXIT LT switch 4WL is in the ON position:
-
the converters or the internal batteries in the EPSUs supply the emergency lighting system.
When the EMER pushbutton switch and its integral light on the flight
attendant panel 120RH are on:
-
the converters or the internal batteries in the EPSUs supply the emergency lighting system.
An open or short circuit in the control lines causes the emergency lighting to come on. The internal test program in the EPSUs finds defects in the load circuits.
**ON A/C 301-302,
The EMER EXIT LT switch 4WL on the overhead panel 25VU controls the emergency lighting system. Self-monitoring circuit breakers 1WL, 2WL and 3WL protect the system from too much current flow. The EMER EXIT LT switch 4WL has three positions, OFF, ARM and ON. Each of these positions gives a discrete ground signal to all EPSUs. The EPSUs also monitor the correct voltage of the AC and DC busbars. When the voltage on these busbars falls below a specified level, the emergency lighting automatically comes on. This is when the EMER EXIT LT switch 4WL is in the ARM position. When only the AC normal busbar fails:
-
the 28VDC essential busbar supplies the emergency lighting system through the 28VDC/6VDC converter in each EPSU and the marking system of the emergency escape path through the 28VDC/115VDC converter in the EPSUs.
When the 28VDC essential busbar fails:
-
the internal batteries in the EPSUs supply the emergency lighting system and the marking system of the emergency escape path.
When the EMER EXIT LT switch 4WL is in the ON position:
-
the converters or the internal batteries in the EPSUs supply the emergency lighting system.
When the LIGHT EMER pushbutton switch and its integral light on the forward attendant panel 120RH are on:
R 1EFF : 106-149, 301-302, 401-499, 1 33-51-00Page A4 1 1 Aug 01/05 1 1 1CES 1
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