ISO Viscosity Grades

Through the years, lubricant users have been treated to a number of ways to designate viscosity grades of the lubricants used in manufacturing. There are SAE (Society of Automotive Engineers) grades for gear oils and crankcases (engines), AGMA (American Gear Manufacturers Association) grades for gear oils, SUS (Saybolt Universal Seconds), cSt (kinematic viscosity in centistokes), and absolute viscosity. To add to the confusion, two measures of temperature (Fahrenheit and Celsius) can be applied to most of these, not to mention that viscosity might be presented at either 40°C (104°F) or 100°C (212°F).
While all of these have served useful purposes to one degree or another, most lubrication practitioners settle on and use one method as a basis for selecting products. To the new entrant into the lubrication field, the number of options can be confusing, particularly if the primary lubricant supplier does not associate one of the prominent viscosity systems to the product label. To complicate matters, machinery designers must define the lubricant viscosity in such a way that the equipment user understands clearly what is needed without having to consult outside advice.
This points to the need for a universally accepted viscosity designation - one that can be used by lubrication practitioners, lubricant suppliers and machinery design engineers simultaneously with minimal confusion.
In 1975, the International Standards Organization (ISO), in unison with American Society for Testing and Materials (ASTM), Society for Tribologists and Lubrication Engineers (STLE), British Standards Institute (BSI), and Deutsches Institute for Normung (DIN) settled upon an approach to minimize the confusion. It is known as the International Standards Organization Viscosity Grade, ISO VG for short.
You don’t have to listen very long in this field before someone says that viscosity is the most important physical property of a fluid when determining lubrication requirements. So, what is viscosity?
Viscosity is the measure of the oil’s resistance to flow (shear stress) under certain conditions. To simplify, the oil’s viscosity represents the measure for which the oil wants to stay put when pushed (sheared) by moving mechanical components.
Think of a water-skier cutting through the water. Water has a viscosity measured in centistokes of 1. That is at the bottom of the cSt scale. We can see how much water a professional skier displaces when he runs through a ski course. If the skier was skiing on a lake of SAE 90/ISO 220 gear oil and all of the other conditions were exactly the same, then the amount of spray generated would be considerably less because the fluid would resist the force of the ski to a much greater degree.
There are two viewpoints of the resistance to flow that the machine designer is interested in. One is the measure of how the fluid behaves under pressure, such as a pressurized hydraulic line. This property is called absolute viscosity (also known as dynamic viscosity) and is measured in centipoises (cP). The other consideration is how the fluid behaves only under the force of gravity. This is called centistokes, which we have already noted. The two are related through the specific gravity of the fluid. To determine the centipoise of a fluid it is necessary to multiply the viscosity of the fluid times the specific gravity of the fluid, or measure it directly using an absolute viscometer. For the practitioner of industrial lubrication, the centistoke is the measure that will occupy most of our attention.
On a side note, if you are using in-service oils, it is probably worth measuring the viscosity in absolute units. The measure in centistokes can be misleading because the specific gravity of lubricants changes with age, generally moving up. It is possible to find yourself exceeding an absolute viscosity limit for a machine but still have a kinematic measure that indicates you are OK.
So, viscosity is a measure of the fluid’s resistance to flow. Water has a low viscosity of 1 cSt and honey has a very high viscosity, lets say 1,000 cSt. If a machine is heavily loaded then the machine designer will use a lubricant that resists being pushed around, which would be heavy like honey. If the machine runs very fast then the machine designer will specify a lubricant that can get out of the way, and back into the way just as quickly. Generally, machines will have either one or the other to be concerned about; sometimes both at the same time.
Viscosities are defined or assigned using a laboratory device called a viscometer. For lubricating oils, viscometers tend to operate by gravity rather than pressure. Think of a kinematic viscometer as a long glass tube that holds a volume of oil. The measure of the fluid’s viscosity is the measure of the amount of time that it takes for the designated amount of oil to flow through the tube under very specific conditions. Because the conditions are repeatable, it is now possible to measure the amount of time that it takes for the fluid to flow through the tube, and it should be nearly the same each time. This is similar to the amount of time it takes a specific volume of fluid at a specific temperature to drain through a funnel. As the fluid gets thicker - a function of its increasing resistance to flow - then it takes progressively longer to move through the tube (funnel). Water goes through in one second. The same amount of honey takes a thousand seconds (hypothetically).
We know that if we raise and lower the temperature of a fluid, there is often a correlating change in the fluid’s resistance to flow. The fluid gets thicker at lower temperatures and it gets thinner at higher temperatures.
Given all of these variables and details, several organizations decided to come up with a way to characterize lubricating oils so that members of their respective organizations would have a uniform and simple way to communicate, educate and ultimately protect their interests.
The purpose of the ISO system of classifying viscosity grades is to establish a viscosity measurement method so that lubricant suppliers, equipment designers and users will have a common (standardized) basis for designating or selecting industrial liquid lubricants.
Different approaches were thoroughly considered before the ISO Technical Committee (TC23) settled on an approach that is logical and easy to use. There were a few important criteria to keep in mind from the beginning, such as:
  • Referencing the lubricants at a nominal temperature for industrial systems.
  • Using a pattern that conforms to uncertainties imposed by dimensional manufacturing tolerances.
  • Using a pattern that had some sense of repeatability up and down the scale.
  • Using a pattern that used a small, easily manageable number of viscosity grades.
The reference temperature for the classification should be reasonably close to average industrial service experience. It should also relate closely to other selected temperatures used to define properties such as viscosity index (VI), which can aid in defining a lubricant. A study of possible temperatures indicated that 40ºC (104ºF) was suitable for the industrial-lubricant classification as well as for the lubricant-definition properties mentioned above. This ISO viscosity classification is consequently based on kinematic viscosity at 40ºC (104ºF).
For the classification to be used directly in engineering design calculations in which the kinematic viscosity of the lubricant is only one of the parameters, it was necessary that the viscosity grade width (range of tolerance) be no more than 10 percent on either side of the nominal value. This would reflect an order of (center point) uncertainty in calculations similar to that imposed by dimensional manufacturing tolerances. This limitation, coupled with the requirement that the number of viscosity grades should not be too large, led to the adoption of a system with gaps between the viscosity grades.
This classification defines 20 viscosity grades in the range of 2 to 3200 square millimeters per second (1 mm2/s = equals 1 cSt) at 40ºC (104ºF). For petroleum-based liquids, this covers approximately the range from kerosene to cylinder oils.
Each viscosity grade is designated by the nearest whole number to its midpoint kinematic viscosity in mm2/s at 40ºC (104ºF), and a range of +/- 10 percent of this value is permitted. The 20 viscosity grades with the limits appropriate to each are listed in Table 1.



The classification is based on the principle that the midpoint (nominal) kinematic viscosity of each grade should be approximately 50 percent greater than that of the preceding one. The division of each decade into six equal logarithmic steps provides such a system and permits a uniform progression from decade to decade. The logarithmic series has been rounded off for the sake of simplicity. Even so, the maximum deviation for the midpoint viscosities from the logarithmic series is 2.2 percent.



Table 2 pulls together some popular viscosity measurement methods into one table. If the practitioner is comfortable with one particular measure but would like to see the correlating viscosity range in another measure, all he must to do is place a straight horizontal line through his chosen viscosity type and see its correlation within the other types of measures.
While it is true that some viscosity grades will be left out of the mix as companies move toward adopting the ISO designation, it is not necessary that the users of those products have to move away from them. Further, there is no intention to offer quality definition of lubricants with this scale. That a product has an ISO VG number associated with it has no bearing on its performance characteristics.
The ISO designation has been under development since 1975. The most recent release in 1992 (ISO 3448) contains 20 gradients. This covers nearly every type of application that the lubricant practitioner can expect to encounter. The lubricant manufacturing community has accepted the recommended ISO gradients and has devoted appreciable effort and energy to conform to the new grading approach with old and new products.
It is unlikely that all of us who learned about the use of oil from our mentors or friends under the hood of a car will ever abandon the SAE grading system. We don’t have to. At least for automotive oils, we can expect to continue to see the 10- 20- 30- 40- 50- values used. It is likely, however, that in the industrial lubrication world there will be more ISO dependence in the future.



Class of insulation

The main component for electric motor is a stator. What is stator? Basically stators are wound with insulated windings made from cooper wire. The insulation materials for winding of stator such as polyester, poly vinyl formal, polyurethane etc.
The main purpose of insulation is to protect the windings in the slots of the stator lamination and layer between winding coils. The insulation class is durability factor depend on whole of insulation condition.
According from IEEE regulation, the classification of insulation electric motor have a deference rating for maximum temperature that insulation winding can operate. We can see the insulation class at  motor nameplate. Please refer the table below for insulation class rating temperature.
Classification of insulation for electric motor:


Electric motor manufactures design the winding insulation class depend on technical aspect and user application. For good grade of insulation, the cost is higher. So the engineer selects the electric motor based on applications and working area temperature characteristics.
The temperature for electric motor is depending on the fans performance and design. Manufacture normally design the cooling fan according to the duty, type of application and load on the motor. Theoretically the load on motor affected the temperature of motor.
The conclusion is, when we selected the class of insulation for electric motor, several factor must be consider are:
§  Type of load ( pump, turbine, compressor)
§  Working area ambient temperature
§  Application of motor

§  Room condition

MCB/MCCB/ ELCB /RCBO/ RCCB

MCB (Miniature Circuit Breaker)

  • Rated current not more than 100 A.
  • Trip characteristics normally not adjustable.
  • Thermal or thermal-magnetic operation.

MCCB (Moulded Case Circuit Breaker):

  • Rated current up to 1000 A.
  • Trip current may be adjustable.
  • Thermal or thermal-magnetic operation.

Air Circuit Breaker:

  • Rated current up to 10,000 A.
  • Trip characteristics often fully adjustable including configurable trip thresholds and delays.
  • Usually electronically controlled—some models are microprocessor controlled.
  • Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance.

Vacuum Circuit Breaker:

  • With rated current up to 3000 A,
  • These breakers interrupt the arc in a vacuum bottle.
  • These can also be applied at up to 35,000 V. Vacuum breakers tend to have longer life expectancies between overhaul than do air circuit breakers.

RCD (Residual Current Device) / RCCB( Residual Current Circuit Breaker) :

  • Phase (line) and Neutral both wires connected through RCD.
  • It trips the circuit when there is earth fault current.
  • The amount of current flows through the phase (line) should return through neutral .
  • It detects by RCD. any mismatch between two currents flowing through phase and neutral detect by RCD and trip the circuit within 30Miliseconed.
  • If a house has an earth system connected to an earth rod and not the main incoming cable, then it must have all circuits protected by an RCD (because u mite not be able to get enough fault current to trip a MCB)
  • The most widely used are 30 mA (milliamp) and 100 mA devices. A current flow of 30 mA (or 0.03 amps) is sufficiently small that it makes it very difficult to receive a dangerous shock. Even 100 mA is a relatively small figure when compared to the current that may flow in an earth fault without such protection (hundred of amps)
  • A 300/500 mA RCCB may be used where only fire protection is required. eg., on lighting circuits, where the risk of electric shock is small
  • RCDs are an extremely effective form of shock protection

Limitation of RCCB:

  • Standard electromechanical RCCBs are designed to operate on normal supply waveforms and cannot be guaranteed to operate where none standard waveforms are generated by loads. The most common is the half wave rectified waveform sometimes called pulsating dc generated by speed control devices, semi conductors, computers and even dimmers.
  • Specially modified RCCBs are available which will operate on normal ac and pulsating dc.
  • RCDs don’t offer protection against current overloads: RCDs detect an imbalance in the live and neutral currents. A current overload, however large, cannot be detected. It is a frequent cause of problems with novices to replace an MCB in a fuse box with an RCD. This may be done in an attempt to increase shock protection. If a live-neutral fault occurs (a short circuit, or an overload), the RCD won’t trip, and may be damaged. In practice, the main MCB for the premises will probably trip, or the service fuse, so the situation is unlikely to lead to catastrophe; but it may be inconvenient.
  • It is now possible to get an MCB and and RCD in a single unit, called an RCBO (see below). Replacing an MCB with an RCBO of the same rating is generally safe.
  • Nuisance tripping of RCCB: Sudden changes in electrical load can cause a small, brief current flow to earth, especially in old appliances. RCDs are very sensitive and operate very quickly; they may well trip when the motor of an old freezer switches off. Some equipment is notoriously `leaky’, that is, generate a small, constant current flow to earth. Some types of computer equipment, and large television sets, are widely reported to cause problems.
  • RCD will not protect against a socket outlet being wired with its live and neutral terminals the wrong way round.
  • RCD will not protect against the overheating that results when conductors are not properly screwed into their terminals.
  • RCD will not protect against live-neutral shocks, because the current in the live and neutral is balanced. So if you touch live and neutral conductors at the same time (e.g., both terminals of a light fitting), you may still get a nasty shock.

ELCB (Earth Leakage Circuit Breaker):

  • Phase (line), Neutral and Earth wire connected through ELCB.
  • ELCB is working based on Earth leakage current.
  • Operating Time of ELCB:
  • The safest limit of Current which Human Body can withstand is 30ma sec.
  • Suppose Human Body Resistance is 500Ω and Voltage to ground is 230 Volt.
  • The Body current will be 500/230=460mA.
  • Hence ELCB must be operated in  30maSec/460mA = 0.65msec

RCBO (Residual Circuit Breaker with OverLoad):

  • It is possible to get a combined MCB and RCCB in one device (Residual Current Breaker with Overload RCBO), the principals are the same, but more styles of disconnection are fitted into one package

Difference between ELCB and RCCB.

  • ELCB is the old name and often refers to voltage operated devices that are no longer available and it is advised you replace them if you find one.
  • RCCB or RCD is the new name that specifies current operated (hence the new name to distinguish from voltage operated).
  • The new RCCB is best because it will detect any earth fault. The voltage type only detects earth faults that flow back through the main earth wire so this is why they stopped being used.
  • The easy way to tell an old voltage operated trip is to look for the main earth wire connected through it.
  • RCCB will only have the line and neutral connections.
  • ELCB is working based on Earth leakage current. But RCCB is not having sensing or connectivity of Earth, because fundamentally Phase current is equal to the neutral current in single phase. That’s why RCCB can trip when the both currents are deferent and it withstand up to both the currents are same. Both the neutral and phase currents are different that means current is flowing through the Earth.
  • Finally both are working for same, but the thing is connectivity is difference.
  • RCD does not necessarily require an earth connection itself (it monitors only the live and neutral).In addition it detects current flows to earth even in equipment without an earth of its own.
  • This means that an RCD will continue to give shock protection in equipment that has a faulty earth. It is these properties that have made the RCD more popular than its rivals. For example, earth-leakage circuit breakers (ELCBs) were widely used about ten years ago. These devices measured the voltage on the earth conductor; if this voltage was not zero this indicated a current leakage to earth. The problem is that ELCBs need a sound earth connection, as does the equipment it protects. As a result, the use of ELCBs is no longer recommended.

MCB Selection:

  • The first characteristic is the overload which is intended to prevent the accidental overloading of the cable in a no fault situation. The speed of the MCB tripping will vary with the degree of the overload. This is usually achieved by the use of a thermal device in the MCB.
  • The second characteristic is the magnetic fault protection, which is intended to operate when the fault reaches a predetermined level and to trip the MCB within one tenth of a second. The level of this magnetic trip gives the MCB its type characteristic as follows: – ·
  • Type               Tripping Current                                      Operating Time
  • Type B            3 To 5 time full load current                    0.04 To 13 Sec
  • Type C             5 To 10 times full load current               0.04 To 5 Sec
  • Type D            10 To 20 times full load current              0.04 To 3 Sec
  • The third characteristic is the short circuit protection, which is intended to protect against heavy faults maybe in thousands of amps caused by short circuit faults.
  • The capability of the MCB to operate under these conditions gives its short circuit rating in Kilo amps (KA). In general for consumer units a 6KA fault level is adequate whereas for industrial boards 10KA fault capabilities or above may be required.

Fuse and MCB characteristics

  • Fuses and MCBs are rated in amps. The amp rating given on the fuse or MCB body is the amount of current it will pass continuously. This is normally called the rated current or nominal current.
  • Many people think that if the current exceeds the nominal current, the device will trip, instantly. So if the rating is 30 amps, a current of 30.00001 amps will trip it, right? This is not true.
  • The fuse and the MCB, even though their nominal currents are similar, have very different  properties.
  • For example, For 32Amp MCB and 30 Amp Fuse, to be sure of tripping in 0.1 seconds, the MCB requires a current of 128 amps, while the fuse requires 300 amps.
  • The fuse clearly requires more current to blow it in that time, but notice how much bigger both these currents are than the `30 amps’ marked current rating.
  • There is a small likelihood that in the course of, say, a month, a 30-amp fuse will trip when carrying 30 amps. If the fuse has had a couple of overloads before (which may not even have been noticed) this is much more likely. This explains why fuses can sometimes `blow’ for no obvious reason
  • If the fuse is marked `30 amps’, but it will actually stand 40 amps for over an hour, how can we justify calling it a `30 amp’ fuse? The answer is that the overload characteristics of fuses are designed to match the properties of modern cables. For example, a modern PVC-insulated cable will stand a 50% overload for an hour, so it seems reasonable that the fuse should as well.

Typical methods of provision of the main earthing terminal:

Supply type code : TN-S
  • Supplier provides a separate earth connection, usually direct from the distribution station and via the metal sheath of the supply cable.
Supply type code : TN-C-S
  • Supplier provides a combined earth/neutral connection; your main earth terminal is connected to their neutral
Supply type code : TT
  • Supplier provides no earth; you have an earth spike near your premises.

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