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M7 Electrical essay > Bonding, Grounding, And Continuity > Flashcards

Bonding, Grounding, And Continuity Flashcards

1
Q

Why would bonding be done?

A 
To minimise radio and radar interference
To minimise lightning damage
Minimise fire hazard from sparks
To provide a low resistance return path in single wire systems
To aid in shielding effectiveness
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2
Q

What else can the return path from bonding be used for?

A

Aid shielding

Provide means to ground the aircraft

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3
Q

What can be done to keep resistance low on bonding wires?

A

Remove anodising films and non-conductive paint at terminal points

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4
Q

How low could the bonding resistance get and where would required values be dictated?

A

0.025 ohms

Values can be found in the AMM

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5
Q

What is grounding?

A

Connecting the single wire systems and shields to the aircrafts structure at certain points

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6
Q

What are the three conditions for grounding?

A

Grounds must be separate (AC, DC, shields)
4 terminals max on each stud
Dual grounds only at fuel vapour areas

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7
Q

Why does the wire have to be long enough for grounding?

A

To allow for fault current, without generating heat

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8
Q

How is a ground terminal measured, and what does the resistance have to be lower than?

A

A bonding meter is used to measure the resistance which must be less than 0.0025 ohms

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9
Q

When are grounding measurements usually taken?

A

After:
Modification of ground stud or wires
Removal of ground stud nut

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10
Q

How is the insulation resistance measured?

A

Wire to wire

Wire to ground

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11
Q

What is the typical voltages for the insulation resistance check?

A

240 or 500 volts

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12
Q

Can an insulation resistance check be carried out when disconnected from the system?

A

Yes, this is the only time it should be done

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13
Q

When is the ideal time to carry out an insulation resistance check?

A

Before installation

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14
Q

What is the resistance values for wires for accessories?

A 
2 miliohms (cowlings, landing gear, etc.)
5 miliohms (galleys, lighting, service systems)
10 miliohms (other service systems)
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15
Q

What is the resistance values for wires without contacts/connectors?

A 
100 miliohms (between terminals)
200 miliohms (between terminal and ground)
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16
Q

What is the resistance value for systems such as instruments and computers?

A

5 miliohms

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17
Q

What is continuity testing?

A

The use of a ohmmeter or multimeter to determine if a circuit has a complete current path.
Done when power is off

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18
Q

What is bonding?

A

The electrical interconnection of metallic parts for safe distribution of charge and current

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19
Q

Is an aircraft earthed when on the ground? If so, then how?

A

It’s is through the landing gear and the electrically conductive compound impregnated into the tyres

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20
Q

What is bonding used to protect against?

A

Charges from build up of static, electrostatic induction, etc.
Electric shocks
Can also reduce interference on essential services

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21
Q

What could be used to bond moving parts?

A

Braided copper or aluminium cords with connecting tags or lug on the ends.

22
Q

What is bonding?

A

The electrical interconnection of metallic parts for safe distribution of charge and current

23
Q

Is an aircraft earthed when on the ground? If so, then how?

A

It’s is through the landing gear and the electrically conductive compound impregnated into the tyres

24
Q

What is bonding used to protect against?

A

Charges from build up of static, electrostatic induction, etc.
Electric shocks
Can also reduce interference on essential services

25
Q

What could be used to bond moving/vibrating parts?

A

Braided copper or aluminium cords with connecting tags or lug on the ends.

26
Q

What could happen if bonding jumpers aren’t attached properly and why is it a problem?

A

The contact between parts could become intermittent due to the vibration.
Intermittent contact is worse than none at all (need context)

27
Q

What should be made sure when installing bonding cables/wire?

A

Does not interfere with nearby/associate equipment
Not too tight or slack
Insulating materials removed before installation

28
Q

What joins are self bonding?

A

Metal to metal held by threaded devices or rivets
Most cowling fasteners, locking and latching mechanisms
Metal to metal door and hinges
Metal to metal bearings

29
Q

What are the two classes of bonding?

A

Primary and secondary

30
Q

When would the manufacturer dictate the maximum resistance of a primary bond?

A

Between extremities of fixed non-metal/composite construction

31
Q

At what times would the max resistance of a bond be 0.05 ohms as dictated by the CAA

A

Between fixed extremities of metallic construction

Between bonded components and portions of main earth system they are connected to

32
Q

What bonding scenario would have a max resistance 0.5 megaohms or 100,000 ohms per square foot of surface area?

A

Between isolated conducting parts which may be subject to electrostatic charging and the main earth system

33
Q

What would the max resistance be for metallic parts in contact with flammable fluids?

A

1 ohms

34
Q

What is the maximum resistance for any other secondary bonds, and what are they?

A

Equipment supplied from the unearthed system- 1 ohm

Between equipment with circuits of 50 volts or more - 1 ohm

35
Q

What are the lengths and number of spikes on the cables used for bond testing?

A

60 feet, single spike

6 feet, double spike

36
Q

What does a commonly used bond test equipment consist of?

A

Ohmmeter operating on current ratio principle, single 1.2 volt nickel-alkaline cell in wooden carry case

37
Q

What should be checked before doing any bonding tests?

A

Full scale deflection of meter when twin spikes are shorted

Meter reads zero when both cable spike are used to short each other

38
Q

How is the first bond test method carried out?

A

60 foot cable connected to earth
6 foot cable used to check resistance between selected points
Bond resistance will be shown in ohms on meter

39
Q

What should be done for the first bond testing method on large aircraft with multiple main earth points?

A

Check the resistance values between main earth points before any testing begins

40
Q

How would the four terminal bond test method be carried out?

A

Use appropriate milliohmmeter
Test current supplied by internal batteries through resistance via cables c1 and c2
The voltage drop along the resistance is measured, compared with the current flow

41
Q

What is the other form for the four terminal methods test equipment?

A

Duplex spikes

42
Q

What should be done for excessive resistance across bonding jumpers?

A

Remove connecting lugs or tags
Clean the contacts with slight abrasive, removal all abrasive traces afterwards
Seal connecting area and treat with anti-oxidant as specified in manuals
Do the same as above for holding bolts

43
Q

What should be done in cases of excessive resistance when required bond value cannot be obtained at the aircrafts structure?

A

Seek manufacturers advice

44
Q

What is continuity testing used to find?

A

Concealed breaks in cable cores

45
Q

What does a typical continuity tester consist of?

A

Low-voltage battery
Test lamp
Low reading volt meter

46
Q

What preparations should be carried out before testing continuity?

A

Disconnect or switch off power
Check fuses are intact
Check appropriate cbs are closed to complete the circuit

47
Q

What methodology should be used when continuity testing a circuit?

A

Work progressively through the circuit, from fuse or CB to the test equipment

48
Q

What should be done when testing large circuits with multiple paths?

A

Work down each path systematically, breaking down at plugs as little as possible

49
Q

When is the millivolt drop test recommended?

A

Excessive resistance in high current carrying circuits- faults such as loose terminals and poorly swaged lead ends

50
Q

What current is best to use for continuously rated circuits?

A

Normal operating current with power derived form external source

51
Q

What current should be used for short rated circuits?

A

The current should be scaled down with a dummy load or suitable resistance instead of normal load.

52
Q

How is the millivolt drop test carried out?

A

The meter is connected to either side of the suspected joint and a note of the volt drop is indicated

M7 Electrical essay (3 decks)

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