Circuit Voltage

8/13/2019 Circuit Voltage

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Systems Operation - FundamentalsElectrical System for All Caterpillar Products

Circuit Voltage

SMCS -1400; 1450

Circuit Faults

The following information will describe the circuit malfunctions of series, parallel, and series parallelcircuits.

Circuit Malfunctions

There are several ways that a circuit can malfunction. Most electrical malfunctions are caused by thefollowing conditions: opens, shorts, grounds, high resistance, or intermittents.

OpensAn open in any part of a circuit is an extremely high resistance that results in no current flow in the circuit.An open can be caused by any of the following components that have failed:

Switch

Fuse

Broken wire

Connector

Component (load)

The physical location of the open determines how the circuit will react. In a series circuit, any openconnection will result in no current flow in the circuit. Illustration 1 shows an open in a series circuit. Theswitch acts as an open. Therefore, no current will flow through the two loads when the switch is open.

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Troubleshooting an open circuit is easily accomplished by using a multimeter and by measuring the sourcevoltage. If source voltage is available at the connection ahead of the switch and not available on the loadside of the switch, the switch contacts are open. If voltage is available on the load side it would be necessaryto continue checking the circuit until the open is identified.

In a parallel circuit, identifying an open depends on where the open occurs. If the open occurs in the mainline, none of the loads or components will work. All parallel branches will not operate. Additionally, anopen in the return ground path would have the same effect as an open in the main line. An open in the returnground path is referred to as an open ground.

If the open occurs in any of the branches below the main line, only the load on that specific branch isaffected. All other branch loads will operate normally. Illustration 2 shows an example of an open in themain line and in a parallel branch.

Illustration 1 g01070634




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When you are troubleshooting or diagnosing an open in a circuit, the result is normally a component thatfails to operate or to function. Since most circuits are protected with some type of a fuse or circuit protectiondevice, it is recommended that the fuse or device be checked visually. If a visual check does not reveal anopen condition, remove the device and perform a continuity check in order to ensure that the device isfunctional. The next most probable place to check for an open is at the component. Using a multimeter and a

electrical schematic, determine if the system voltage or source voltage is available. If voltage is not presentat the component, the next step is to determine what other electrical devices, such as switches or connectors,are in the circuit path. Eliminate those devices, starting at the easiest location and working back toward thevoltage source.

Shorts

A short in a circuit is a direct electrical connection between two points. There is usually a very lowresistance or opposition to current flow. A short in a circuit often describes an unwanted or an incorrectelectrical connection. This may draw higher than expected current. In describing malfunctions that arecaused by electrical shorts, the types of shorts are usually identified as a short to ground or a short to power.

A short to ground occurs when current flow is grounded before it was intended to be. This usually happenswhen wire insulation breaks and the conductor actually comes in contact with the machine ground. Theeffect of a short to ground depends on the design of the circuit and on the location in relationship to othercircuit components (protection devices, switches, loads).





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Illustration 3 shows the short occurring after the protection device and the switch, but before the circuit load(lamp). In this example, a low resistance path to ground occurs whenever the switch is turned on and thesource voltage is available. The result of this unwanted path will result in a blown fuse when the switch isturned on.

Illustration 4 shows the short to ground occurring before the switch. This condition is often referred to as adead short. In this situation, the fuse will blow anytime that the circuit voltage is applied.





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A short to power occurs when one circuit is shorted to another circuit. The symptoms of a short to powerdepends on the location of the short. The result of this of condition generally causes one or both circuits tooperate improperly. A component that is being energized when it is not supposed to be is an example. Theroot cause of this condition is caused by worn electrical wiring or frayed electrical wiring. Also, this

condition seldom causes protection devices to open or cause damage to other components.

Illustration 5 shows the short to power occurring before the controlling devices (switches). This conditionallows both switches to control the two loads.





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Illustration 6 shows the short to power that occurrs after the load in one branch, and before the load in theother. In this case, if the switch that controlls circuit no. 2 is turned on, the load does illuminate, but if theswitch that controls circuit no. 1 is turned on, a direct short to ground occurs resulting in the fuse blowing.





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Grounds

A grounded circuit usually results in a component that fails to operate. A grounded condition indicates thatthe circuit has an unwanted path to the machine frame. The effect on the circuit is determined by where theground occurs.

High Resistance

Circuit malfunctions also occur when resistance levels become too high. The circuit effect usually results inthe component failing to operate or the component does not operate according to specification. The cause ofhigh resistance is a build up of corrosion on connections, or dirt on connections and on contacts.

Intermittent

An intermittent condition occurs when contacts or connections become loose or when internal componentparts break. These problems usually results in lights flickering, or in components working intermittently.This problem usually appears as the result of vibrations or machines moving. These problems are not easilydiagnosed because the condition corrects itself when the machine is stopped.


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Circuit Voltage