|Treatment of Lines for Mobile Devices and Appliances - Course: Basic skills and knowledge of electrical engineering. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 21 p.)|
|3. Connection of Lines to Mobile Devices and Appliances|
- Before a cable is put in and connected to a mobile device or appliance, this cable has to be stripped according to the requirements and prepared for connection.
- With the stripping length, the arrangement of the connections in the device or appliance has to be taken into consideration.
After putting the cable into the place of connection, a protective measure with protective conductor has to be taken and the external conductors have to be cut in such way that the protective conductor is the longest connecting core.
Figure 21 Collar coupler plug
1 protective conductor,
2 tension relieving
Why shall the protective conductor be the longest connecting core in the place of connection of the device or appliance?
- The covering of the cable must project into the device or appliance for approximately 3 mm.
By putting in the covered cables, the conductor insulation cannot be damaged by perhaps sharp edges of the device or appliance and sources of faults are avoided.
- The core insulation must end 1 mm in front of the connecting point.
Figure 22 Connection points with correctly removed core insulation
Securing under terminals of the core insulation would put the functioning of the connection at risk. Too long stripping could lead to short circuits.
- Conductors equipped with eyes must only be connected in the direction of rotation of the terminal screw. (In doing so, make sure that the eye rests evenly on the junction block, because otherwise it may come to a deficiency of contact.)
- If several conductors are connected to one connecting bolt, pay attention that each conductor is followed by one washer and that - at least after every third conductor - one spring ring is inserted.
- If and when cable thimble and eye are connected to one connection bolt, the eye has to be connected separately.
Figure 23 Connection to a connection bolt
1 cable eyes, 2 conductor with eyes, 3 connection bolt, 4 washers, 5 spring ring
- With the connection of protective conductor and middle wire, only one conductor per connecting point is permissible.
- To cap-screws without clamping bow or conductor holding fixture, three conductors which may differ by two cross-section steps at the most are allowed to be connected only if one washer is placed between the conductors, each.
Figure 24 Connection by a cap-screw without clamping bow and holding fixture to a connection strap
1 connection strap,
- To cap-screws with clamping bow only one conductor is allowed to be connected on either side of the bow. The conductors to be connected may differ by one step in cross-section.
Figure 25 Connection to a cap-screw with clamping bow
1 clamping bow
- To cap-screws with conductor holding fixtures only one conductor is allowed to be connected to each holding fixture. The conductors to be connected must have the same cross-sections.
Figure 26 Connection to cap-screw with holding fixture
1 free disk, 2 conductor holding fixture
The washers used for the connection of conductors to screws or bolts must cover at least 2/3 of the conductor.
Screw slots must not be damaged by using wrong or defective screw drivers.
- To terminal blocks for sequencing two conductors are allowed to be connected to each terminal point, if they are soldered together at the connecting points and equipped with conductor end sleeves.
- When connecting conductors with end sleeves or eyes, make sure that
. the clip of each respective contact is sufficiently fastened, so that the conductor cannot the sleeve or eye,
. if the conductor end sleeve might be shifted on the conductor when it is put in the clip - for instance with cables that are put in from above - the sleeve should be slightly pressed on with the help of a suitable tool such as round-nose pliers or side cutting pliers.
Why is tension relieving required with mobile devices and appliances?
- Tension relieve is possible inside and outside the connection space of mobile equipment.
- Tension relieve must act immediately on one cable and not on intermediate layers.
- Mostly, tension relieve consists of one pressure clip with two fastening points. (See Figure 21).
- If tension relieve cannot be given within the connection space, it must be done outside at the casing or construction part of the device or appliance. However, the protective system of the device or appliance must thereby not be reduced.
Figure 27 Tension relieving within the connection space of a protective contact flexible cable
1 protective contact connection, 2 external conductor, 3 tension relieving, 4 protection against buckling
Figure 28 Tension relieving at an engine cable
1 clamping box, 2 cable entry,
3 tension relieving clip,
4 bow for tension relieving,
5 engine cable
Figure 29 Trumpet-shaped entry at an explosion-proof lamp which is mobile to a certain extent
1 lamp casing, 2 trumpet-shaped entry, 3 tension relieving clip. 4 supply line, 5 screw with triangular heads
What is the importance of protection against buckling at device and/or appliance entries and exits?
Boltings which only serve the observance of the protective system or degree of protection of the device or appliance must not be used for tension relieving.
- The order of plug and socket and/or coupler socket in the circuit is determined by the direction of the power flow.
- Plug and socket and/or coupler socket must be arranged in such a way that, under no circumstances, the plug pins are alive as long as they are not plugged in.
Figure 30 Direction of a power flow
1 socket, 2 plug, 3 appliance plug-socket, 4 appliance coupler, 5 cable
- For the supply of a number of devices or appliances fixed multiple sockets with earthing contact or mobile multiple sockets with earthing contact are preferred.
- It is not permissible to use plug-in devices in connection with lampholders and of free distributing plugs, even with shock protection.
- To a plug, a coupler socket or an appliance coupler only one mobile cable is allowed to be connected.
Figure 31 Correct installation of a mobile appliance connecting cable
1 plug, 2 coupling
In addition to the cables for connecting mobile devices and appliances, there are pilot-wire circuits consisting of multiwire or thin-wire conductors.
Especially this is the case in plants which, during operation, are exposed to great mechanical strain and vibration.
If in such plants conductors are combined to bank cables, this is called bundled wiring and the manufacture of preformed cables presents itself.
In connection with the manufacture of preformed cables also use the handbook of "Manufacture of Preformed Cable".
Figure 32 Manufacture of shaped cables on a matrix
Manufacture of a preformed cable
- Manufacturing of a model according to the individual conductor connections.
- Testing the cables as to continuity, unwinding them and cutting them to length.
- Combining them to bank cables.
If possible, use punched tape to tie them up with plastic string or cord.
Figure 33 Binding material
1 grit tape, 2 punched tape,
3 binding by punched tape
- Fastening of the bank cables in the place where it shall be connected.
Access to the connections and free connecting and disconnecting must be guaranteed.
- Testing and marking of the cables according to their respective purpose.
Marking the conductors by notches
This is the simplest and safest method of marking conductors.
- Suitable tools for notching are electrician's knives and side cutting pliers.
- The notches have to be started on the cable cross section at the end of the conductor and are continued away from there.
- Roman figures should be used for marking. (A correspondingly stripped piece of conductor is to be seen in Figure 34; it is equivalent to number 100.)
Figure 34 Notch marking by Roman figures
When notching, make sure that the marking remains legible even after a longer period of time and that also other people are able to read it.
What could be the consequences of mixed up connections in a plant?