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Metric IEC
Introduction
The International Electrotechnical
Commission (IEC) is a European-based organization that publishes and
promotes worldwide mechanical and electrical standards for motors,
among other things. In simple terms, it can be said that IEC is the
international counterpart to the National Electrical Manufacturers
Association (NEMA), which publishes the motor standards most commonly
used throughout North America.
Dimensionally, IEC standards are
expressed in metric units.
IEC Enclosure Protection Indexes
Like NEMA, IEC has designations indicating the
protection provided by a motor's enclosure. However, where NEMA designation are in words, such
as Open Drip Proof or Totally Enclosed Fan Cooled, IEC uses a two-digit Index of protection
(IP) designations. The first digit indicates how well protected the motor is against the entry
of solid objects, the second digit refers to water entry.
By way of general comparison, an IP22 motor relates to Open
Drip Proof, IP54 to totally enclosed.
Protection Against Solid Objects
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#
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Definition
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0
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No protection. |
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1
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Protected against solid objects of over 50mm (e.g. accidental hand contact).
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2
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Protected against solid objects of over 12mm (e.g. finger). |
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3
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Protected against solid objects of over 2.5mm (e.g. tools, wire). |
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4
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Protected against solid objects of over 1mm (e.g. thin wire). |
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5
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Protected against dust. |
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6
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Totally protected against dust. Does not involve rotating machines. |
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Protection Against Liquids
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#
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Definition
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0
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No protection. |
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1
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Protected against water vertically dripping (condensation).
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2
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Protected against water dripping up to 15º from the vertical. |
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3
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Protected against rain falling at up to 60º from the vertical. |
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4
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Protected against water splashes from all directions. |
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5
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Protected against jets of water from all directions. |
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6
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Protected against jets of water comparable to heavy seas. |
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7
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Protected against the effects of immersion to depths of between
0.15 and 1.0 m. |
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8
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Protected against the effects of prolonged immersion at depth.
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IEC Cooling
IEC has additional designations indicating how a motor is
cooled (two-digit IC codes). For most practical purposes, IC 01 relates to a NEMA open design,
IC 40 Totally Enclosed Non-Ventilated (TENV), IC 41 to Totally Enclosed Fan Cooled (TEFC), and
IC 48 to Totally Enclosed Over (TEAO).
IEC winding insulation classes parallel those of NEMA and
in all but very rare cases use the same letter designations.
Duty cycles are, however, different. Where NEMA commonly
designates either continuous, intermittent, or special duty (typically expressed in minutes),
IEC uses eight duty cycle designations.
S1 - Continuous duty. The motor works at a constant load for enough time to reach temperature equilibrium.
S2 - Short-time duty. The motor works at a constant load, but not long enough to reach temperature equilibrium, and the rest periods are long enough for the motor to reach ambient temperature.
S3 - Intermittent periodic duty. Sequential, identical run and rest cycles with constant load. Temperature equilibrium is never reached. Starting current has little effect on temperature rise.
S4 - Intermittent periodic duty with starting.Sequential, identical start, run and rest cycles with constant load. Temperature equilibrium is not reached, but starting current affects temperature rise.
S5 - Intermittent periodic duty with electric braking.Sequential, identical cycles of starting, running at constant load and running with no load. No rest periods.
S6 - Continuous operation with intermittent load. Sequential, identical cycles of running with constant load and running with no load. No rest periods.
S7 - Continuous operation with electric braking. Sequential identical cycles of starting, running at constant load and electric braking. No rest periods.
S8 - Continuous operation with periodic changes in load and speed. Sequential, identical duty cycles run at constant load and given speed, then run at other constant loads and speeds. No rest periods.
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IEC Design Types
The electrical performance characteristics of IEC Design N
motors in general mirror those of NEMA Design B - the most common type of motor for industrial
applications. By the same token, the characteristics of IEC Design H are nearly identical to
those of NEMA Design C. There is no specific IEC equivalent to NEMA Design D.
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