Simple Electrical System Z-0

[Mich48041]

Below is an electrical drawing of a simple aircraft electrical system. The main feature is a fuse block that receives power at each end. If one current path opens, current can still flow into the fuse block from the other end. Some Bussman fuse blocks can be disassembled and another screw terminal added at the opposite end.
Joe Gores

Available as pdf download: https://drive.google.com/file/d/0B7Z...it?usp=sharing Click FILE, DOWNLOAD or CTRL-S

[az_gila]

It looks like you have added an extra relay in the system to allow for a possible failure of the master contactor.

Perhaps it's just adding another possible failure point?

[Mich48041]

Perhaps it's just adding another possible failure point?

True. But if it fails open, there is no danger. I would be as if it were never installed. Good workmanship will prevent shorts to ground. Some of Bob Nuckolls' designs have a similar relay. I think the danger of the master contactor circuit opening is greater than the danger of the relay circuit shorting to ground. A redundant circuit might have prevented an accident like this one: http://tinyurl.com/myzgxkv
No design is impervious to pilot error.
Joe Gores

[akarmy]

Looks nice and simple for sure. That WayTech is rated at 40amps so that looks good as well. Guess the question is, what are you protecting yourself from? What's your mission? The Article you linked to is not really applicable unless you have electric retracts, a full IFR electrical system etc. The thing to think about is if you are very concerned about the master contractor failing, why not the alternator or battery? Those could fail just as easily, or maybe some might say even more easily.

If you have an electrically dependent plane, then maybe adding more redundancy would make sense. If not and you are ok without your electronics then your design seems good with a bit of dual feed redundancy.

[Mich48041]

what are you protecting yourself from?

It has been my experience that the majority of electrical failures are due to bad connections. Z-0 provides another current path to the bus if a connection fails, not necessarily the master contactor, but any connection.

What's your mission?

My mission is to offer another wiring option to home-builders. Some builders may choose to use Z-0 for very important electrical loads. Modern AGM batteries are unlikely to fail suddenly. But the alternator could. When it does, the pilot can shut off the #1 master switch, thus removing power from the alternator field and from the master contactor. Doing that will conserve battery energy. A relay uses much less energy than a contactor.
Some aircraft builders do not see a need for a separate E-Bus. They can shut off a few unneeded loads individually if desired. Z-0 provides the redundancy of an E-Bus with the simplicity of a single bus. Z-0 takes the simple electrical system of a factory built airplane and adds redundancy for little additional cost or weight.
For hard IFR or long flights over hostile terrain, Bob Nuckolls' Z-13/8 is the best.
The Lancair 235 crashed because there was no electrical power on the main bus to run the fuel pumps. No electrical system is safe if not maintained in good working order.
Joe Gores

[akarmy]

oops, by mission I was just meaning IFR or VFR, long distance or local fly about, etc.

In the case of the Lancair, I would add more than just two master feeds if I had and electrically dependent engine. That's where these designs need to take into account the systems you have in the plane and design accordingly.

Thanks for putting out this design as another idea!

[chris mitchell]

Interesting, simple and not dissimilar to the system I am planning. I have two perhaps very naive questions ( I subscribe to the notion that electrics is all about keeping the smoke inside).

1. Why use a relay rather than a suitably rated switch?

2. Why have a starter contactor as well as the starter solenoid? Sky tech show a suitable contactorless wiring scheme on their website. Always looking for ways to simplify!

I once had my alternator die just as I was landing in Northern France after 1.5 hours airborne and 60 miles over water. No chance of quick replacement and I really didn't want to leave the plane, take the ferry home and then go back to France at a later date. In the end I opted to fly back with Dynon and GPS on it's back up batteries, minimal use of radio and had enough power left at the end to run the trim and flaps. If I had had an e-bus system I could have saved the amps needed to keep the master contactor closed.

Thanks for putting this diagram up.

Cheers

Chris

[Mich48041]

1. Why use a relay rather than a suitably rated switch?

A relay is used for two reasons:
1. A relay can handle lots of current, i.e., 40 amps, so that a small switch can be used.
2. Remote control. A switch inside of the cockpit can shut off the circuit at the source near the battery. This is good feature to have in case of smoke in the cockpit or an imminent forced landing.

2. Why have a starter contactor as well as the starter solenoid?

The starter contactor is optional. Bob Nuckolls diagrams have a starter contactor so I copied it. If the heavy starter cable or the starter itself shorts to ground, nothing bad will happen until the next time the starter contactor is energized while safely on the ground. The starter contactor does increase the complexity, cost, and weight. On the other hand, it eliminates an always hot cable that is subject to engine vibration and heat. Like I said, it is optional.
Joe Gores