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Old 04-21-2017, 06:04 AM
humptybump's Avatar
humptybump humptybump is offline
Join Date: Feb 2011
Location: Eastern Shore of Virginia
Posts: 3,014
Default Circuit breakers and fuses - which for what?

With more and more electronics, the complexity of the electrical system grows. For many RVs, things are quite different from when the original kit was designed. A recent "show is your panel" had 46 visible circuit breakers. An RV-1: has just 12 visible fuses.

I've done a few upgrades to my panel over the past 5 years and each time, I ask myself the same questions.
  • Should every single electrical consumer have its own circuit?
  • What electrical consumers could be / should not be combined into a single circuit?
  • Should electrical component 'X' get a circuit breaker or would a fuse be OK?
  • Where to mount the circuit breakers and/or fuse blocks?

Before we get off into the weeds, I understand the circuit breaker / fuse is designed to protect the wire, not the component.

I fly an RV-8. During one significant upgrade I moved the circuit breakers to the panel. I now need the panel real estate and will eventually need to go back to using the right-hand side panel.

I still have not found a good location for the fuse blocks.

I'm interested it the choices other builders have made and how those decisions have worked out.
- Glen, ESVA
RV-8 FP IFR | Track my RV-8 | 53VG

Last edited by humptybump : 04-21-2017 at 06:14 AM.
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Old 04-21-2017, 07:45 AM
Mich48041 Mich48041 is offline
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,578

Ideally, every single load should have its own circuit protection. But airplanes are compromises.

Any important load should be on its own circuit. Before putting two or more loads on one circuit, ask yourself, "if one of these loads shorts out, can I get along without the other loads that share this breaker or fuse?"

Any load that is likely to nuisance trip its circuit protection should be protected by a circuit breaker. Motors and over-voltage protection come to mind. Everything else can be protected by either breakers or fuses.

Loads that are critical to flight safety should have their circuit protection accessible (on the panel) while flying. On the other hand, there should not be any critical electrical loads. Have a backup plan. Assuming that nothing is critical and can wait until safely on the ground before troubleshooting, locate fuses anywhere that they can be easily tested and replaced.

A wise pilot and electrical engineer once said something like this, "this blown fuse or popped breaker just prevented smoke and fire. You want to give it another chance?"

Use fuses to save money, space, and weight. Fly the plane and wait until safely on the ground before troubleshooting.
Joe Gores
RV-12 Flying
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Old 04-21-2017, 08:07 AM
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DanH DanH is offline
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Location: 08A
Posts: 7,443

What Joe said, entirely. I do run the flap motor on a fuse.

One CB for the alternator field. The rest swings down from under the panel...very rarely, like never in flight.

Dan Horton
Barrett IO-390

Last edited by DanH : 04-21-2017 at 09:30 AM.
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Old 04-21-2017, 09:29 AM
rapid_ascent rapid_ascent is online now
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Location: Dublin, CA
Posts: 891

On the topic of combining devices on one circuit I think it comes down to what you are willing to lose if one device fails. If you are not willing to lose a device if another fails then it needs to have its own circuit and protection.
Ray Tonks
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Old 04-21-2017, 10:16 AM
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az_gila az_gila is offline
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Location: 57AZ - NW Tucson area
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Originally Posted by DanH View Post
What Joe said, entirely. I do run the flap motor on a fuse.

One CB for the alternator field. The rest swings down from under the panel...very rarely, like never in flight.
Similar on my -6A, with the only addition being a pullable CB for the autopilot servos as a back-up emergency disconnect.
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
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La Cholla Airpark (57AZ) Tucson AZ
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Old 04-21-2017, 11:03 AM
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Veetail88 Veetail88 is offline
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Location: Hales Corners, WI
Posts: 836

I'm like the others. Breakers for the alternator fields in the cockpit, all the rest on an access door from inside the front baggage compartment. Couldn't get to them inflight if I wanted to.
Jesse Bentley
N229Z - RV-8 - Flying - Livin' the dream!
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Old 04-21-2017, 11:48 AM
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RONSIM RONSIM is offline
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Location: Largo, FL
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Default I like pullable breakers for

"load shedding", in case of need, and to isolate components during testing and trouble-shooting. I use some switch/breakers for avionics and lights. I do not use an "avionics master" -- (been burned, on that one)!

RV-10 Co-built (sold)
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Old 04-21-2017, 02:33 PM
sjhurlbut sjhurlbut is offline
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Posts: 557
Default CB vs fuse

For me anything I may need to reset in cockpit or controls a control surface gets panel mounted CB. Rest are fuses behind panel.

Elec Ignition
Alt field
"Aerodynamics is for people who can't build engines"
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Steve H
Cold Lake, Alberta
RV7A #70015 - C-FZQX - built - sold
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Old 04-22-2017, 10:25 AM
Reformed SeaSnake Reformed SeaSnake is offline
Join Date: Nov 2016
Location: Beaverton
Posts: 21
Default CB vs Fuse and location


I tend to like CB's for the flexibility to pull them if needed to manage loads (like Ron) so I have a number of them. Panel space was an issue for me too, so I have a handful on the panel, and several on each mid-cabin cover organized by function and location relative to the load (to keep the wiring runs reasonable).

If I was doing it over, I would put every load that had a switch on a fuse and all unswithced loads on CBs.

I love Dan's fuse panel solution. If that does not work for you, the forward baggage compartment might work.
Jason Rood
Beaverton Oregon | RV-8A, Very slow QB
No Pithy quote here; just the sincere hope that your day ends better then it began
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Old 04-22-2017, 12:02 PM
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Sparky Sparky is offline
Join Date: Nov 2006
Location: Perham, MN
Posts: 350
Default Circuit Breakers and Fuses


On my RV-7 I installed circuit breakers for things that I like to be able to control, either in flight or on the ground, and for all items that have overvoltage protection devices installed.


1) Electronic ignition (single)
2) EFIS 1 - (For the EFIS screens a C/B works great to cycle power individually during software updates)
3) EFIS 2
4) Autopilot
5) Trim
6) Flaps
7) Carbon Monoxide Detector
8) Alternator Field - (overvoltage protected)
9) Standby Alt Field - (overvoltage protected)
10) External Power Solenoid - (overvoltage & reverse voltage protected)


Everything else

My fuse blocks are installed behind the right EFIS screen. It's easy to remove the AFS-4500 EFIS screen on the ground to gain easy access the fuse blocks, and the screen is shallow enough to leave plenty of room for the fuse blocks to be mounted on the subpanel.
Paul Winkels
RV7 Standard Build - First flight 4/16/2016 - Now Flying!

Last VAF donation - 4/22/2017
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