Industrial Engineer · phase 9 of 16 · noun
Derating
Required reduction in drive output capability for conditions such as high temperature, altitude, switching frequency, or unusual load duty.
The Explain card
- Plain English
- Derating is the reduction in what a drive can deliver when it is used outside the conditions its rating assumes. High ambient, high altitude, high carrier frequency and unusual duty all cost capacity.
- Example
- A drive rated 40 amps at 40 degrees and 1000 meters is installed in Denver at 1600 meters with the carrier frequency raised for a quiet motor. The manual's curves take it down to about 32 amps.
- Why it matters
- A derated drive that was sized on its nameplate number runs at the edge and fails in the conditions that caused the derate, which is exactly when you need it. Read the derating curves before the order goes in.
- Hook
- The rating on the box is for the box's ideal day.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
During commissioning, the engineer applied derating before entering the motor current limit in the VFD parameter set.
How it is built
- de- prefix down or away from a stated level
- rate root assign a specified operating level or capacity
- -ing suffix the action or process
Where it came from
- Origin
- English technical formation from derate, built from de- and rate, with the noun-forming suffix -ing
- Entered the language
- 20th century
- What changed
- Rate developed a technical sense tied to assigned equipment limits; derate expressed lowering that assigned level, and derating became the process noun.
How it is spelled
- Pattern
- The final silent e in derate is dropped before -ing: derate becomes derating.
- Pattern
- The prefix de- joins directly to the base without a hyphen.
Spelled like
- rating
- abating
- operating
Broken into chunks
-
de-
- devalue
- declassify
-
rate
- rated
- rating
-
-ing
- commissioning
- wiring
What it sits beside
Same subject
- nameplate rating
- switching frequency
- motor current limit
- overload protection
Same shape
- derated
- derates
- rating
drive sizing terms
- continuous current
- overload current
- service factor
equipment rating changes
- derating
- uprating
Where it sits in the deck
Phase 9: VFD Ratings, Sizing, and Motor Data
Nameplate arithmetic, where the currents, voltages and duty ratings decide whether a drive can actually run the motor you bolted it to.
