M7.7 EWIS Cat-B V7.01

What method of testing is typically carried out after the bonding test and prior to the insulation test?

• Visual inspection

• Continuity testing

• Insulation resistance testing

What should be ensured when using a digital multimeter for continuity testing?

• It should be set to 'volts'

• It should be set to 'amps'

• It should be set to 'ohms'

Answer explanation

As we are checking the conductivity between the 2 test points we need to measure the resistance. Therefore we will need to set the Digital MultiMeter (DMM) to Ohms

What is the purpose of insulation testing?

• To measure the resistance within wires and motor windings

• To identify current leakage and faulty insulation

• To measure the voltage drop across wires

Answer explanation

Insulation Testing

Purpose of Insulation Tester

Insulation testers use a high voltage, low current DC charge to measure the resistance within wires and motor windings to identify current leakage and faulty or damaged insulation, which can lead to arc faults, blown circuits, and risk of electrical shock or fire.

What type of bonding ensures that components within an aircraft system have the same potential to ground?

• Equipment bonding

• Metallic surface bonding

• Static bonding

Answer explanation

Equipment Bonding

Low-impedance paths to aircraft structure are normally required for electronic equipment to provide radio frequency return circuits, and for most electrical equipment to facilitate a reduction in Electro Magnetic Interference (EMI).

The cases of components that produce electromagnetic energy must be grounded to the structure. To ensure the proper operation of electronic equipment, it is particularly important to conform to the system’s installation specification when interconnection, bonding, and grounding are being accomplished.

Metallic Surface Bonding

All conducting objects on the exterior of the airframe must be electrically connected to the airframe through mechanical joints, conductive hinges, or bond straps capable of conducting static charges and lightning strikes. Exceptions can be necessary for some objects such as antenna elements, whose function requires them to be electrically isolated from the airframe. Such items must be provided with an alternative means to conduct static charges and/or lightning currents, as appropriate.

Static Bonding

All isolated conducting parts inside and outside the aircraft, having an area greater than 3 in² and a linear dimension over 3 in, are subjected to appreciable electrostatic charging due to precipitation, fluid, or air in motion. They must have a mechanically secure electrical connection to the aircraft structure of sufficient conductivity to dissipate possible static charges.

A resistance of less than 1 ohm when clean and dry generally ensures such dissipation on larger objects. Higher resistances are permissible in connecting smaller objects to the airframe structures.

Which class of electrical bonds protects against RF potentials?

• Class A

• Class R

• Class S

Answer explanation

Industry standards for the installation and repair of aircraft electrical systems describe six different classes of electrical bonds:

• Class A refers to antenna installation. The resistance of Class A bonds must be less than 2.5 mΩ.

• Class C describes the current path return. This ensures no excessive voltage drop is drawn by the loads.

• Class H refers to shock hazard. Class H bonds protect against shock hazard. The resistance of this type of bond must be less than 100 mΩ.

• Class L describes lightning protection. This type of bond must be less than 0.05 Ω.

• Class R refers to RF potential. This must ensure that there is a low-impedance path (less than 2.5 mΩ) from the equipment to the aircraft structure.

• Class S describes a static discharge. The resistance of Class S bonds must be less than 1.0 Ω.

What precautions are taken before conducting an insulation test?

Select all correct answers

• isolate a circuit

• circuit breakers are pulled and gagged

• LRUs/components are removed

• LRUs/components are installed

• the isolation is clean to ensure good contact with the test lead.

Answer explanation

A non-isolated circuit can damage the meter and/or injure personnel when using an insulation resistance tester.

• Always isolate a circuit when using an insulation resistance tester.

• Ensure circuit breakers are pulled and gagged and that other trades are briefed on what is being tested.

• Ensure that all LRUs/components are removed.

What must been done immediately after an successful insulation test

• Function checks on all the services subjected to the test

• Re-instate the electric circuit and complete the work card

• Complete the work card to declare the system serviceable

• Ground the test equipment to remove any residual voltage.

What process ensures that all components, modules, or LRU fitted within an aircraft system or circuit have the same potential (or resistance) to ground?

• Bonding
• Grounding
• Connecting
• Isolating

Which of these methods are part of a wiring check?

Select all correct answers

• • Visual inspection

• • Continuity testing

• • Insulation resistance testing

• • Bonding testing

• Termination inspection