Final answer:
The ignition switch check is typically made at the idle RPM of a reciprocating engine to ensure the spark plugs are firing correctly at idle speed.
Step-by-step explanation:
In a reciprocating engine, the ignition switch check is typically made at a specific RPM known as the idle RPM. This is the RPM at which the engine is running at its lowest speed without stalling. The purpose of checking the ignition switch at idle RPM is to ensure that the spark plugs are firing correctly when the engine is operating at its normal idle speed.
For example, in a car with a gasoline engine, the ignition switch check is usually performed at around 600-800 RPM. This allows the engine to run smoothly at idle while the ignition system is being checked.
It's important to perform the ignition switch check at idle RPM because at higher RPMs, the engine is running faster and the ignition system may behave differently. Checking the ignition switch at idle RPM provides a more accurate assessment of the ignition system's performance.