Electrical Power Distribution (2024)

Electrical power distribution provides battery power to the electrical and electronic systems. See Fig. 3.1 for power distribution component locations.

The following components make up the power distribution system:

MEGA Fuse Junction Block (MFJB), EPA07 only

Powertrain Power Distribution Module (PT-PDM)

Electrical Power Distribution (1)

  • 1. SAM Cab
  • 2. Powertrain PDM (PT-PDM)
  • 3. Powernet Distribution Box (PNDB)
  • 4. SAM Chassis
  • 5. Main Ground Junction Block
  • 6. MEGA Fuse Junction Block
  • 7. Cab Load Disconnect Switch (optional location)
  • 8. Cab Load Disconnect Switch (optional location)
  • 9. Trailer PDM

Fig. 3.1, Component Locations

Powernet Distribution Box (PNDB), EPA10 and newer

Cab Load Disconnect Switch

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 Fig. 3.2 .

Electrical Power Distribution (2)

  • 1. MEGA Fuse Junction Block
  • 2. Main Ground Junction Block

Fig. 3.2, EPA07 MEGA Fuse Junction Block

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 .

Electrical Power Distribution (3)

  • 1. Powertrain PDM (PT-PDM)
  • 2. Inline Fuse, Auxiliary PDM
  • 3. SAM Chassis
  • 4. Powernet Distribution Box (PNDB)

Fig. 3.3, Engine Compartment Power Distribution Components

Power Distribution Modules

Powertrain PDM

The powertrain PDM contains fuses and relays that provide battery and ignition power to the engine, aftertreatment device, transmission, and other powertrain-related circuits. It is mounted in the engine compartment, above the driver-side inner fender.

Auxiliary PDM

The optional auxiliary PDM is used when additional circuit protection is needed for optional features. 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 supplies control signals to the relays in the trailer PDM.


The SAM cab is located behind the glove box inside the vehicle cab. See Fig. 3.4 . The SAM cab contains fuses and relays in addition to solid state circuit protection devices that will trip when a circuit is overloaded.

Refer to Chapter 25 for fuse and relay locations.

Electrical Power Distribution (4)

Fig. 3.4, SAM Cab Location

SAM Chassis

The SAM Chassis is located in the engine compartment on the driver-side frontwall. See Fig. 3.3 . The SAM chassis contains fuses and relays in addition to solid state circuit protection devices that will trip when a circuit is overloaded.

Refer to Chapter 25 for fuse and relay locations.

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 temperature 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 handling a self-resetting circuit breakers, which can reach extremely high temperatures. Failure to use appropriate heat protection can lead to serious injury.


Self-resetting circuit breakers can be permanently damaged if improperly handled. Use the guidelines below to handle them safely.

Disconnect the batteries before removing a self-resetting circuit breaker.

Use a circuit breaker removal tool to remove a self-resetting circuit breaker. See Fig. 3.5 . Use of any other tool, including pliers, may damage the circuit breaker.

Electrical Power Distribution (5)

  • 1. Circuit Breaker Removal Tool
  • 2. Self-Resetting Circuit Breaker

Fig. 3.5, Self-Resetting Circuit Breaker Removal

Never attempt to probe a self-resetting circuit breaker while installed on the SAM Cab or SAM Chassis. Remove the circuit breaker first, or use a non-contact infrared thermometer to measure temperature.

Cab Load Disconnect Switch


Turning the cab load disconnect switch (CLDS) to the off position does not disconnect the connection between the battery and the starter. To work on the vehicle safely, the negative leads must be disconnected from the battery.

IMPORTANT: The ignition should be turned off before turning the CLDS to on or off.

The CLDS is used to avoid excessive draw on the battery when the vehicle is parked for an extended period of time by disconnecting (or opening) the connection between the battery and the most of the vehicle electrical system.

The CLDS may be mounted:

inside the cab on the outboard side of the driver's seat;

at the battery box;

outboard on the left frame rail.

See Fig. 3.6 for an EPA07 CLDS; see Fig. 3.7 for an EPA10 and newer switch.

Electrical Power Distribution (6)

Fig. 3.6, Cab Load Disconnect Switch, EPA07

Electrical Power Distribution (7)

Fig. 3.7, Cab Load Disconnect Switch, EPA10 and Newer

If the CLDS is turned to the off position while the vehicle is running, the emergency power system will activate. The powertrain PDM will receive power from the emergency power feed, but the batteries will not be charging. See the Emergency Power Supply heading below for details.

Electrical Power Distribution (2024)


Electrical Power Distribution? ›

A distribution system originates at a distribution substation and includes the lines, poles, transformers and other equipment needed to deliver electric power to the customer at the required voltages. Customers are classed as: Industrial Customer. Commercial Customer. Residential Customer.

What is distribution in an electrical power system? ›

A distribution system originates at a distribution substation and includes the lines, poles, transformers and other equipment needed to deliver electric power to the customer at the required voltages. Customers are classed as: Industrial Customer. Commercial Customer. Residential Customer.

What are the four types of power distribution systems? ›

  • Radial. Many distribution systems operate using a radial feeder system. ...
  • Parallel feeders. A greater level of reliability at a higher cost is achieved with a parallel feeder. ...
  • Ring main. A similar level of system reliability to that of the parallel arrangement can be achieved by using ring main feeders. ...
  • Meshed systems.
Jul 22, 2019

How does electrical power distribution work? ›

Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kV and 33 kV with the use of transformers. Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises.

What are the three methods of power distribution? ›

Radial, Loop, & Network Systems.

What are the requirements of an electrical distribution system? ›

Requirements of a good distribution system are : proper voltage, availability of power on demand and reliability. due to the variation of load on the system. Low voltage causes loss of revenue, inefficient lighting and possible burning out of motors.

Are distribution power lines AC or DC? ›

A transmission grid is a network of power stations, transmission lines, and substations. Energy is usually transmitted within a grid with three-phase AC. Single-phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors.

What is the primary distribution system in electrical? ›

The primary distribution system consists of the feeders emanating from the substation and supplying power to 1 or more secondary distribution systems. Such feeders are usually 3-phase circuits.

What are the two types of electrical distribution lines? ›

Distribution lines consist of "overhead distribution lines" (power lines hung on utility poles) and "underground distribution lines" (cables buried in the ground).

What are the standard electrical distribution voltages? ›

Primary lines have voltages ranging from 2,300 to 39,000 volts. Common primary line voltages are 2,300, 4,160, 12,470, 13,800, 25,000 and 34,500 volts depending on which distribution voltages a utility uses. Common secondary line voltages are 120, 208, 240, 277 and 480 volts.

Who controls the distribution of electricity? ›

Q: How is electricity regulated? A: The Federal government, through the Federal Energy Regulatory Commission , regulates interstate power sales and service. State governments, through their public utility commissions or equivalent, regulate retail electric service as well as facility planning and siting.

What are the three wires from pole to house? ›

The three wires used to carry electricity from one place to another are:
  • Live wire (L)
  • Neutral wire (N)
  • Earth wire (E)
Jul 3, 2022

How is electricity distributed in a house? ›

Every home has a service panel that distributes electricity to switches, outlets, and appliances. The service panel is usually found in the basem*nt, garage, or utility area.

What is the basic electrical distribution system? ›

The primary purpose of an electricity distribution system is to meet the customer's demands for energy after receiving the bulk electrical energy from transmission or subtransmission substation. There are basically two major types of distribution substations: primary substation and customer substation.

What voltage are residential power lines? ›

You generally talk about household electrical service as single-phase, 120-volt AC service.

What are the steps of power distribution? ›

The power goes from the transformer to the distribution bus. The bus distributes power to local distribution lines. The bus has its own transformers that can also step down or step up voltage according to local energy needs. At the bus, there may be two separate sets of distribution lines at two different voltages.

What do you mean by distribution of power? ›

The distribution of power refers to how power is delegated in the government of a society. This is often expressed in the creation of separate independent branches of government such as the judicial, executive, and legislative branches common to many republican systems today.

What is the distribution of power function? ›

Power-function (PF) distribution is a flexible and simple lifetime model that may offer and exhibit a better fit to some sets of failure data. The PF distribution is often employed in the assessment of semiconductor devices and electrical component reliability [1].

What is distribution flow in power system? ›

The idea of distributed power flow is to solve local power flow problems within each subsystem, independently of each other, and to find consensus on the physical values of the exchanged power between the subsystems, see Fig.

What is a distribution panel in electrical system? ›

A distribution board (also known as panelboard, breaker panel, electric panel, fuse box or DB box) is a component of an electricity supply system that divides an electrical power feed into subsidiary circuits while providing a protective fuse or circuit breaker for each circuit in a common enclosure.

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