HOT BUS definition
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Well, hot bus is a bus that is constantly energized with power from any source, i.e. battery or generator, when the rest of the system is "locked out" from the power source.
In my airplane as an example, emergency power is available when turning on the emergency power switch independent of the battery switch is in the on/off position. Emergency power is taken from the Battery Hot Bus (or known as the Battery Direct Bus).
Fuelling panel, stairs and emergency annunciator lights is typically powered from a Hot Bus.
In my airplane as an example, emergency power is available when turning on the emergency power switch independent of the battery switch is in the on/off position. Emergency power is taken from the Battery Hot Bus (or known as the Battery Direct Bus).
Fuelling panel, stairs and emergency annunciator lights is typically powered from a Hot Bus.
Last edited by MD80rookie; 6th Sep 2010 at 16:27. Reason: spelling
Think of it as what's still powered when you shut everything down. I don't know how many oral exams have started, "You walk out to a cold, dark airplane. What's powered?" On Boeings, engine fuel shutoff valves, APU controller and (for glass planes) the DC side of the IRUs are pretty good answers. Some add the engine and APU fire bottles.
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Can someone with english as his first language please give me the definition of HOT BUS?
A hot bus is a powered bus, but the term is generally used to describe specifically a bus that can't be powered down, or shut down as other normal busses (but still employs circuit breaker protection). If the aircraft battery master switch is shut off while sitting on the ground on battery power, for example, causing the entire aircraft's electrical system to be shut down, the only bus remaining powered is generally the hot battery bus.
Some airplanes put certain critical items on the hot battery bus, or items which are needed when the rest of the system isn't powered. Door latch motors, for example, may be one such item. In some aircraft, pitot heat comes off the hot battery bus. What's specifically on the hot battery bus depends on the airplane under discussion.
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A grouping of services that have power available to their protective devices regardless of cockpit switch positions.
The only way to remove power from a hot bus is to remove all power sources and physically disconnect the battery (or cause it to become flat
).
It can include services that are critical, services that are a final back-up and/or services that are usefull for ground servicing eg the refueling pannel, some lights etc.
In the simplest terms;
A Bus is simply a grouping of services.
A hot bus is a grouping of services that constantly has power.
So another definition could be- a grouping of services that can not be load-shed.
The only way to remove power from a hot bus is to remove all power sources and physically disconnect the battery (or cause it to become flat
).It can include services that are critical, services that are a final back-up and/or services that are usefull for ground servicing eg the refueling pannel, some lights etc.
In the simplest terms;
A Bus is simply a grouping of services.
A hot bus is a grouping of services that constantly has power.
So another definition could be- a grouping of services that can not be load-shed.
Last edited by DFC; 7th Sep 2010 at 08:46.
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Hot bus items can be load-shed; while the bus can't be interrupted with a switch in most cases (some, it can, but these are the exception).
An installation feature of all electrical circuits is a requirement for circuit breaker protection (not to protect the component, but to protect the wiring). Where resettable circuit breakers are provided, the hot battery bus items can be disconnected. Many hot battery bus items are controllable by switch, as well.
The bus isn't usually controllable by switch, but the specific items on the bus generally are, and can thus be interrupted.
An installation feature of all electrical circuits is a requirement for circuit breaker protection (not to protect the component, but to protect the wiring). Where resettable circuit breakers are provided, the hot battery bus items can be disconnected. Many hot battery bus items are controllable by switch, as well.
The bus isn't usually controllable by switch, but the specific items on the bus generally are, and can thus be interrupted.
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The bus isn't usually controllable by switch, but the specific items on the bus generally are, and can thus be interrupted.
Otherwise there would be a great business in recharging flat batteries!!!
Cunning Artificer
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I incorrectly assumed that everyone would know that all services fed from the hot bus can be interupted
On the B767 nose gear are a set of lights that show the status of the parking brake. That is either Brake On and Pressure available or Brake Off. Thus, at least one of these is always illuminated, even on a "dead" aircraft. In addition, one of the anti-skid system control relays is energised any time the gear is down. For parking the aircraft for more than 24 hours the parking brake and anti-skid circuit breakers must be opened.
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Sorry. I incorrectly assumed that everyone would know that all services fed from the hot bus can be interupted eg fuel panel deactivated by a microswitch operated by the door opening/closing etc etc etc.
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In common electricians language, a "Hot Bus", or indeed any "hot" electrical circuit is simply a circuit that has power on it.
In aviation, it's come to mean a 'bus' that still has power on it, even when just about everything has been shut down.
Exactly like your car... you turn off the ignition and take the key out, but a few items will remain on a "hot bus", like the electrical door locks and the clock.
CJ
