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3 Answers

What is a crossfeed electrical bus?

Asked by: 8302 views Aircraft Systems

What exactly does the crossfeed bus do? For the C172SP, it says it powers the alternator field and the warning systems, which I understand. But why must those things be on the crossfeed bus and when would the crossfeed bus become inoperative?

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3 Answers

  1. Best Answer


    jeff on Apr 08, 2015

    A crossfeed bus does exactly what the name implies. Many aircraft split the main electrical bus into a left and right hand bus. The manufacturer/designer then splits the electrical demands and will put various components on either the left or right hand bus (for instance, the pilots avionics on the left bus and the co pilots on the right. There may be systems which are not redundant that exist on only one bus, for instance, an aircraft with one hydraulic pump or one alternator, may be on either the left or right bus. They do this in general to split the load. But what happens if you have an electrical problem on the left sided bus? You would loose all equipment tied to that bus. Think of the crossover bus as a connection between the two main buses, so if you were to loose the left bus, the right side bus can still power all the equipment that was on the left bus. You should always have at least basic understanding of the electrical system of any aircraft you fly. In addition to knowing where the circuit breakers are (left or right panel), a knowledge of systems is important in understanding emergency procedures related to the various systems. Becomes more and more important as the aircraft get more complex.

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  2. Drew on Apr 08, 2015

    Thank you, Jeff.

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  3. crossaint on Sep 12, 2016

    An aircraft electrical system is split into busses, not to split the loads, but to be able to switch arts of the system off if it malfunctions (e.g. gets a short circuit).

    A cross-feed bus is connected to more than one electrical bus to be get current by any of them, which is very useful if you have devices on board that MUST run.

    In a Cessna 172R, the cross feed bus is connected using diodes to the two main busses, and it’s feeding not that much: the alternator, the warning annunciator, and the instrument lights.
    (Interesting enough: the two main busses are fed from the same battery and alternator, the third buss could simply have used the third circuit breaker in the power distribution box and bypass the other busses completely)

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