What are the different Mounting Positions of Electrical Motors ?

    Proper motor installation and mounting position is essential in obtaining top-quality operation, efficient performance, and maximum reliability.Here are the different type of common mounting positions as follows.

What is Dead Front in Electrical Panel ?

An electric panel will generally have one or two covers. Panels with two covers have an outer cover (which will open to the side or upwards) and an inner cover, called a “Dead Front”. The dead front cover normally has the slots / knockouts for the breakers to fit into.

It is called a “Dead Front” for a reason

When the “Dead Front” is missing, the wiring, breakers and the bus bar is exposed. This is very dangerous. If a person comes into contact with or touches the live bus bar, a serious shock or injury could occur. Even death. That is how the name “Dead Front” came about.

Replacing the “Dead Front”

When the “Dead Front” is missing it is wise to replace it as soon as possible. Also, the main cover should be locked and tagged until the Dead Front is properly in place. A number of manufactures have replacement covers for their panels.

What does NFPA 70e stand for?

NFPA 70e stand Standard for Electrical Safety

NFPA 70E, titled Standard for Electrical Safety in the Workplace, is a standard of the National Fire Protection Association (NFPA). The document covers electrical safety requirements for employees. The NFPA is best known for publishing the National Electrical Code (NFPA 70)

What is Festoon Cable ?

Let’s start with the name — ‘festoon’ is a word that often refers to something suspended in a curve between two points.Simply put, festoon cable is a flat portable cord. 

This may help in remembering common applications for festoon cables; they are typically used in cranes, hoists, and other suspension applications.

What is the construction of festoon cable?

Festoon cable is made of finely stranded bare copper conductors at its very core. The size of this cable ranges from 4/0 AWG to 16 AWG, and features either PVC insulation and jacket or neoprene insulation and jacket. The PVC version of this cable comes in black or yellow, while the neoprene is only available in black.

The neoprene version is more flexible than PVC because its conductors can have a higher strand count, meaning it can be used in continuous flexing applications.

Even though these versions vary slightly, they’re still similar. They both have small bending radii, contributing to each cable’s flexibility, and these cables still have many of the same applications.

What is the recommended Insulation Class and Temperature for Induction Motor ?

(1 Min Read)

• Class F insulation with Class B temperature rise is the most commonly required insulation system for industrial motors i.e., max. temperature rise of 80 °C above ambient temperature.
• The use of Class F insulation (ambient temperature 40 °C + Max. permissible temperature rise 105 °C + Hotspot temperature margin 10 °C ) with Class B (ambient temperature 40 °C + Max. permissible temperature rise 80 °C + Hotspot temperature margin 10 °C ) temperature rise gives motors a 25 °C safety margin. This can be used to increase the loading of the motor for limited periods, to operate at higher ambient temperatures or altitudes or with greater voltage and frequency tolerances. It will help to extend insulation life.
• Hence a Class F Motor's insulation can go up to to a max temperature of 40+80+10 = 130°C is the recommended limit by most of the manufacturers.

Why Single Stranded Wires are not used for Domestic Wirings ?

(2 Min Read)

• In Domestic wiring circuits, Conduits (Pipe protecting electrical wiring) have large number of bends and turns with smaller dia.
• Single stranded wire is not  flexible, hence cable won't go through easily inside the conduits and also increase the chances of metal fatigue and the wire breaking as a result. Because of this, single stranded wires are best suited for products that won’t encounter much space restrictions and bends.
• Multi-Strand wiring is more flexible and less susceptible to cracking and metal fatigue(weakness) than single stranded conductors. This makes it the preferable solution for domestic wiring.

Domestic Wiring Conduits & Junction Box

What is the Direction of Rotation of Induction Motor if we Connect R, Y, B in U, V, W ?

(1 Min Read)

    When the mains supply is R, Y, B is connected to stator terminals marked U, V, and W respectively then the motor will Rotate Clockwise, as viewed from the D-end. The direction of rotation can be reversed by interchanging any two of the three conductors connected to a starter switch or motor.

What are the IEC Standards for Induction Motors ?

(5 Min Read) 

    The following guide serve as reference lists for Electrical and Mechanical IEC Standards that apply to most Low Voltage Induction Motors. In this context, Low Voltage refers to Motors that operate at voltages less than 1000 V and produce a maximum power of 1000kW. 

    IEC 60034 is an International Standard by International Electrotechnical Commission(IEC)  for rotating electrical machinery.

    A Standard is a specifications document established as a result of consensus between international technical experts working for a standards organization such as the International Electrotechnical Commission (IEC), the European Committee for Electrotechnical Standardization (EN), or a national standards organization (NEMA in the US, DKE in Germany).

                                              

Electrical Standards:

• IEC 60034-1 - Rating and performance
• IEC 60034-2-1 - Standard methods for determining losses and efficiency from tests (excluding machines for traction vehicles)
• IEC 60034-2-2 - Specific methods for determining separate losses of large machines from tests – Supplement to IEC 60034-2-1
• IEC 60034-8 - Terminal markings and direction of rotation
• IEC 60034-11 - Thermal protection
• IEC 60034-12 - Starting performance of single-speed three-phase cage induction motors
• IEC 60034-17 - Cage induction motors when fed from converters – Application guide
• IEC 60034-25 - Guidance for the design and performance of AC motors specifically designed for converter supply
• IEC 60034-26 - Effects of unbalanced voltages on the performance of three-phase cage induction motors
• IEC 60034-30 - Efficiency classes of single-speed three-phase cage induction motors(IE-Code)
• IEC 60034-31 - Selection of energy-efficient motors including variable speed applications – Application guide
• IEC 60038 - Standard voltages
• IEC 60050-411 - International electrotechnical vocabulary – Chapter 411: Rotating machines

Mechanical Standards:

• IEC 60034-5 - Degrees of Protection provided by the integral design of rotating electrical machine (IP code)
• IEC 60034-6 - Methods of cooling (IC code)
• IEC 60034-7 - Classification of types of construction, mounting arrangements and terminal box position (IM Code)
• IEC 60034-9 - Noise limits
• IEC 60034-14 - Mechanical vibration - Measurement, evaluation and limits of vibration severity
• IEC 60072-1 - Dimensions and output series for rotating electrical machines Part 1: Frame sizes 56 to 400 and flange numbers 55 to 1080
• IEC 60529 - Degree of protection provided by enclosure (IP Code)

What does the AC1 and AC3 terms mean in Power Contactors ?

           The duty of electrical contractor is categorized by the types of electrical loads used such as inductive, or resistive or capacitive and duty cycle such as plugging or runtime breaking, short circuit breaking etc. 

           Let’s see the different types of contactor duties are used in electrical distribution system. Below mentioned duties are categorized by IEC (International Electrotechnical Commission). Generally, these rating are normally mentioned on the contactor Refer the picture.

AC duty (Alternating Current) for Contactors:

AC-1: Such duty contactors are used in resistive loads such as heaters and electrical furnace. Non-inductive or slightly inductive loads are included which means the power factor of the load lie between 0.95 to 1.

AC-2: These are used in Slip-ring motors starters such as Switching on and switching off the motor. They mostly prefer for high Torque current application.

AC-3: These type of contactors are generally preferred for starting of Squirrel-cage motors, and switches off motor during running time which means the contactor can withstand of high current continuously. Example. Lifts, elevators, fans etc.On closing, the contactor makes the inrush current, which is about 5 to 7 times the rated full load current of the motor. On opening, the contactor breaks the rated full load current of the motor.

         Image above represents the Air Break Power Contactor from Siemens, with mentioning AC1 ratings of 30A while AC3 rating of 16A, Usually AC3 ratings are lesser than AC1 ratings because breaking the arc in resistive circuits(AC1) remains easy with minimal arcing and contact wear. 

AC-4: Frequently on/off on Squirrel-cage motors such contactors are used. They have ability to break high starting current starting such as plugging and inching operation. Example: Cranes

AC-5a: These type of contactor is used in discharge lamps such as mercury vapor and sodium vapor lamps and Auxiliary Control circuit.

AC-5b: Switching of incandescent lamps

AC-6a: Transformers ON/OFF

AC-6b: These type of contactor is used in capacitor banks switching.

AC-7a: Small Inductive loads on house hold such as TV, mixers, drilling machine etc.

AC-7b: Rotating machines on households such as fans, central vacuum cleaners, washing machines etc.

AC-8a: Hermetic refrigerant compressor motor control with manual resetting on O/L.

AC-8b: Hermetic refrigerant compressor motor control with automatic resetting overloads

AC11: Auxiliary (control) circuits i.e. they don’t have power contacts such as NO (Normally open) and NC (Normally closed)

AC-12: Electronics switching using solid state devices on resistive loads

AC-13: Control of Resistive Load & Solid State Load with Transformer Isolation

AC-14: Control of small electromagnetic loads less than 72VA

AC-15: Control of A.C. electromagnetic loads greater than 72VA

AC-20: Connecting and disconnecting under no-load conditions

AC-21: Switching of resistive loads, including moderate overloads

AC-22: Switching of inductive loads as well resistive loads (Mixed)

AC-23: Switching of motor loads or other highly inductive loads

A: Protection of circuits, with no rated short-time withstand current

B: Protection of circuits, with a rated short-time withstand current

Direct Current Duties DC1, DC3, DC5:

DC-1: Non Inductive or slightly inductive loads, resistance furnaces, heaters

DC-3: Shunt-motors, starting, plugging (1), inching(2), dynamic braking of motors

DC-5: Series-motors, starting, plugging (1), inching(2), dynamic braking of motors

DC-6: Switching of incandescent lamps

DC-12: Control of resistive loads and solid state loads with opto-coupler isolation

DC-13: Control of D.C. electromagnetics

DC-14: Control of D.C. electromagnetic loads having economy resistors in the circuit

DC-20: Connecting and disconnecting under no-load conditions

DC-21: Switching of resistive loads, including moderate overloads

DC-22: Switching of mixed resistive and inductive loads, including moderate overloads (i.e. shunt motors)

DC-23: Switching of highly inductive loads (i.e. series motors)

However mostly in industries, AC1 and AC3 contactors are preferred

Difference between AC1 and AC3 contactors is AC1 contactor are used for less inductive loads such as resistive loads (the power factor of the load is near about 1) but AC3 duty contactors are used for high inductive, squirrel cage motors which will be off during the motor is running condition.

Example for AC1: Heaters, Electric Furnace

Example for AC3: All squirrel cage motors such as industrial fans, lifts, escalators, conveyors, bucket elevators, compressors, pumps, mixers, air conditioning units