How to Installation of Electric motors | How to mount a motor | Electrical installation of machines.
This questions are arise when we have electrical motor to install in proper way we need know about foundations ,suitable starter ,cables connected to motor, vibrations, atmosphere around motor ,class of motor .
Where the final connection is made with flexible conduit, the tube must not be relied upon to provide a continuous earth path and a separate circuit protective conductor (CPC) must be run either inside or outside the flexible conduit.
All motors over 0.37 kW rating must be connected to the source of supply through a suitable starter which incorporates overload protection and a device which prevents dangerous restarting of the motor following a mains failure
At the supply end, the motor circuit will be protected by a fuse or miniature circuit breaker (MCB). The supply protection must be capable of withstanding the motor starting current while providing adequate over current protection. There must also be discrimination so that the over current device in the motor starter operates first in the event of an excessive motor current.
Most motors are ‘ continuously rated ’ . This is the load at which the motor may be operated continuously without overheating.
Many standard motors have class A insulation which is suitable for operating in ambient temperatures up to about 55°C. If a class A motor is to be operated in a higher ambient temperature, the continuous rating may need to be reduced to prevent damage to the motor.
The motor and its enclosure must be suitable for the installed conditions and must additionally prevent anyone coming into contact with the internal live or moving parts. Many different enclosures are used, depending upon the atmosphere in which the motor is situated.
Clean air, damp conditions, dust particles in the atmosphere, chemical or explosive vapors will determine the type of motor enclosure. In high ambient temperatures it may be necessary to provide additional ventilation to keep the motor cool and prevent the lubricating oil thinning.
The following motor enclosures are examples of those to be found in industry.
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| fig, 01 |
- Screen protected enclosures prevent access to the internal live and moving parts by covering openings in the motor casing with metal screens of perforated metal or wire mesh. Air ? ow for cooling is not restricted and is usually assisted by a fan mounted internally on the machine shaft. This type of enclosure is shown in Fig 1
- Totally enclosed enclosure is one in which the air inside the machine casing has no connection with the air in the room in which it is installed, but it is not necessarily airtight. A fan on the motor shaft inside the casing circulates the air through the windings and cooling is by conduction through the motor casing. To increase the surface area and assist cooling, the casing is surrounded by fins, and an externally mounted fan can increase the ? ow of air over these fins. This type of enclosure is shown in Fig. 1
- A duct ventilated enclosure is used when the air in the room in which the motor is situated is unsuitable for passing through the motor for cooling – for example, when the atmosphere contains dust particles or chemical vapor. In these cases the air is drawn from a clean air zone outside the room in which the machine is installed, as shown in Fig.1 .
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| Fig 02 |
- A flameproof enclosure requires that further modifications be made to the totally enclosed casing to prevent inflammable gases coming into contact with sparks or arcing inside the motor. To ensure that the motor meets the stringent regulations for flameproof enclosures the shaft is usually enclosed in special bearings and the motor connections contained by a wide flange junction box
- When a motor is connected to a load, either by direct coupling or by a vee belt, it is important that the shafts or pulleys are exactly in line. This is usually best achieved by placing a straight edge or steel rule across the flange coupling of a direct drive or across the ? at faces of a pair of pulleys, as shown in Fig.02
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| Fig 03 |
Since pulley belts stretch in use it is also important to have some means of adjusting the tension of the vee belt. This is usually achieved by mounting the motor on a pair of slide rails as shown in Fig. 03.
Adjustment is carried out by loosening the motor fixing bolts, screwing in the adjusting bolts which push the motor back, and when the correct belt tension has been achieved the motor fixing bolts are tightened
Adjustment is carried out by loosening the motor fixing bolts, screwing in the adjusting bolts which push the motor back, and when the correct belt tension has been achieved the motor fixing bolts are tightened
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