Electrical Power Distribution; Circuit Protection Features - freightliner cascadia Driver Manual

Electrical System

Electrical Power Distribution

Electrical power distribution provides battery power to
the electrical and electronic systems. See
power distribution component locations.
The following components make up the power distri-
bution system:
•
MEGA Fuse Junction Block (MFJB), EPA07
only
•
Powertrain Power Distribution Module
(PT-PDM)
•
Powernet Distribution Box (PNDB), EPA10 and
newer
•
Cab Load Disconnect Switch
•
Auxiliary PDM
MEGA Fuse Junction Block, EPA07
On EPA07 vehicles, the MFJB distributes battery
power to the alternator, SAM cab, SAM chassis, and
powertrain PDM. Battery power may also be routed
to an inverter and a trailer PDM. The MFJB houses
up to five MEGA fuses, and is located on the left
frame rail in front of the batteries. See
Powernet Distribution Box, EPA10
and Newer
The PNDB distributes battery power to the SAM cab,
SAM chassis, powertrain PDM, and other keep-alive
circuits.
The PNDB is mounted in the engine compartment on
the frontwall near the steering column. The label on
the PNDB fuse cover identifies typical circuits. See
Fig. 3.3.
Power Distribution Modules
Powertrain PDM
The powertrain PDM contains fuses and relays that
provide battery and ignition power to the engine, af-
tertreatment device, transmission, and other
powertrain-related circuits. It is mounted in the en-
gine compartment, above the driver-side inner
fender.
3.1
Auxiliary PDM
The optional auxiliary PDM is used when additional
circuit protection is needed for optional features. For
Fig. 3.1 for
example, if a beacon light is added to the Cascadia,
it may require an auxiliary PDM. The auxiliary PDM
may contain fuses and relays for these devices. It is
mounted in the cab, behind the doghouse cover.
Trailer PDM
The optional trailer PDM, mounted on the frame rail,
is used to supply trailer power to the chassis-
mounted trailer receptacles. The SAM chassis sup-
plies control signals to the relays in the trailer PDM.
SAM Cab
The SAM cab is located behind the glove box inside
the vehicle cab. See
fuses and relays in addition to solid state circuit pro-
tection devices that will trip when a circuit is over-
loaded.
Refer to
SAM Chassis
The SAM Chassis is located in the engine compart-
Fig. 3.2.
ment on the driver-side frontwall. See
SAM chassis contains fuses and relays in addition to
solid state circuit protection devices that will trip
when a circuit is overloaded.
Refer to

Circuit Protection Features

The SAM chassis and SAM cab may be equipped
with self-resetting circuit breakers instead of fuses.
Self-resetting circuit breakers are tripped when they
reach 170°F (77°C), then self-reset once the tem-
perature drops sufficiently. When the circuit overload
is removed, this circuit protection will self-reset.
Some of these circuits require the ignition switch to
be cycled off then back on again for the self-reset to
occur.
Some ECU's are equipped with a self-resetting circuit
breaker removal tool.
Always wear heat-protective gloves when han-
dling a self-resetting circuit breakers, which can
Fig. 3.4. The SAM cab contains
Chapter 25 for fuse and relay locations.
Chapter 25 for fuse and relay locations.
WARNING
Fig. 3.3. The