Electrical buses

Let'sgoflying!

Let'sgoflying!

Touchdown! Greaser!
Joined
Feb 23, 2005
Messages
20,316
Location
west Texas
Display Name
Display name:
Dave Taylor
Have a look at the pic below, a small part of the electrics of a small bizjet.
I am trying to figure out what the function is of the 9 buses.
Redundancy and isolation-ability, yes but I need more details.

A) I can see the feed buses being necessary to distribute power from the generators.
B) The CrossFeed bus; needed to provide power to the other side should an engine or generator fail.
C) Why three wires to each Extension bus? One wire too bulky? If one wire or CB fails, the others could handle some load?
D) The Extension buses - I think these are simply because the Feed buses are back at the engine and buses are needed in the cockpit, near the loads.
E) Emergency bus; easy one.
F) The CrossOver buses are the biggest mystery to me. I guess if there is a fault one one side after the Extension buses, that side is not completely dead?



upload_2017-5-11_21-12-19.png
 
It really depends on what the connections to specific gear are past the top of the diagram in the CB panel to guess as to why they used that double-crossover setup. Need to see more of the circuit to figure out the design goal.

You're correct on the three cables... 75A at unknown AC/DC voltage probably needs some fat cables, and if you toast one or pop a breaker, all of them on that side are going to pop at full load... but you can probably load shed and then test individual feeds and get much of either the LH or RH CB panel back.

This diagram seems aimed at showing you how the two panels get fed, but you can't quite tell why there's two panels, nor what would not work if one of them was down.

Also need more info on what triggers the EMER RELAY and the BATT DISABLE RELAY.

Just isn't enough info here to completely figure out what they're trying to accomplish. What's on the two CB panels, and what's on the EMER BUS, and are they dual-fed?
 
The crossover busses are to group system circuit breakers together, like avionics, without having them running off the same power feed. You don't want transponder 1 cb on one side of the cockpit while transponder 2 cb is on the other side. It make it much easier to find them when you know all of the avionics are on the right cb panel and are grouped together on that panel.
 
Last edited:
Let'sgoflying! said:
Have a look at the pic below, a small part of the electrics of a small bizjet.
I am trying to figure out what the function is of the 9 buses.
Redundancy and isolation-ability, yes but I need more details.

A) I can see the feed buses being necessary to distribute power from the generators.
B) The CrossFeed bus; needed to provide power to the other side should an engine or generator fail.
C) Why three wires to each Extension bus? One wire too bulky? If one wire or CB fails, the others could handle some load?
D) The Extension buses - I think these are simply because the Feed buses are back at the engine and buses are needed in the cockpit, near the loads.
E) Emergency bus; easy one.
F) The CrossOver buses are the biggest mystery to me. I guess if there is a fault one one side after the Extension buses, that side is not completely dead?
Click to expand...
A) The "Feed" buses used to be called "Main" buses and are in the tail up in the "Hell Hole" close to the generators between the engines in the main electrical panel.
B) The "Crossfeed" bus was called "Battery Bus" in an earlier iteration, since it's connected directly to the battery through the battery relay. It allows the generators to charge the battery and also make a cross-generator start.
C) The "Extension" bus is in the cockpit, a long way from the "Hell Hole". Makes sense to me from a fire hazard standpoint to have three wires carry smaller loads. Chafing a 240 amp wire could melt a lot of airframe metal.
D) Correct.
E) Comm 1, Nav 2, Copilot's DG, cockpit overhead lights--if this were a Citation II like I flew. Don't know about this one, since all Emer CBs were located on the copilot's panel (no pilot-side Emergency bus).
F) The "Crossover" bus organizes the "systems" and "avionics" to the left and right panels for easier troubleshooting, as mentioned above (quite well) by Plano Pilot. For example, the Pitch Trim circuit is a "system" and is powered from the right side, but the CB is crossed over to the pilot's CB panel. (It's the 4th CB aft in the bottom row, unless moved in a later model, and important to find in a hurry.)

dtuuri
 
Last edited:
Makes a lot more sense once you know the type it is and the location of the stuff.

Neat @dtuuri and @Plano Pilot.

I knew electrically the diagram made no sense to do the crossovers for an electrical reason, so it had to be a physical thing. Grouping the breakers makes sense.
 
You must log in or register to reply here.
Back
Top