Common Cause Failure
It is when two redundant channels fail at the same time because of a single common cause. Overvoltage, excessive temperature, humidity, vibration, or a defect coming from the same production batch can wipe out the protection redundancy provides in one stroke; this risk is assessed with a scoring approach.
Redundancy rests on the assumption that the two channels are independent. Common cause failure refutes that assumption: if the two channels run through the same cable duct, one crushing cuts both; if they run from the same supply, one overvoltage damages both.
The assessment is made by scoring the measures taken, and a certain total score is expected to be exceeded. Typical measures that earn points:
- Physical separation of the channels, routing them along separate paths.
- Diversity: using different technology or components from different manufacturers on the two channels.
- Overvoltage, overcurrent and temperature protection.
- Electromagnetic compatibility measures and correct earthing.
In a crane installation the most concrete expression of this is the cable layout: do not run safety lines through the same duct as the motor cable, leave at least about 20 cm between them, and make unavoidable crossings at right angles.
The context in which this term is used: Wireless Crane Remote Control Selection Guide