Industrial Engineer · phase 2 of 16 · noun
Normally Open / Normally Closed
Contact state defined with the field device in its normal, unactuated, and de-energized condition.
The Explain card
- Plain English
- Normally open and normally closed describe a contact with nothing acting on it. Normally open is open until something pushes it closed, and normally closed is closed until something pushes it open.
- Example
- A stop button is wired normally closed. The circuit is live while nobody touches it, and pressing the button breaks it.
- Why it matters
- A stop wired normally closed also stops the machine if the wire breaks, which is why safety circuits use it. Normal always means de-energized and unpressed, never the state the machine spends most of its time in.
- Hook
- Normal is what the contact does when nobody is home.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
A Normally Open auxiliary contact on the motor starter closes when the coil energizes, sending a run-status signal to the PLC input.
Why these words
- normally English normal plus the adverb-forming suffix -ly sets the customary reference condition for the phrase
- open Old English open, not closed supplies the state word paired in memory with closed
Where it came from
- Origin
- English technical compound, from normally and open, ultimately drawing normal from Latin normalis and open from Old English open
- Entered the language
- 20th century
- What changed
- Normal developed from a geometric sense involving a carpenter's square to customary or standard, while open acquired specialized use in electrical terminology.
How it is spelled
- Pattern
- Normally keeps both l letters when normal combines with the suffix -ly.
- Pattern
- Open retains its final silent e.
Spelled like
- formally
- finally
- reopen
Broken into chunks
-
normal
- norm
- normalize
- normative
-
-ly
- formally
- locally
- usually
-
open
- opening
- reopen
- openness
What it sits beside
Same subject
- Normally Closed
- auxiliary contact
- PLC input
- limit switch
- motor starter
Same shape
- Normally Closed
- normally energized
- normally de-energized
contact-state terms
- Normally Open
- Normally Closed
contact devices
- pushbutton
- limit switch
- auxiliary contact
Where it sits in the deck
Phase 2: PLC I/O and Field Signals
Where the controller meets the machine: discrete and analog signals, the wiring conventions behind them, and the field devices that send them.
