Connectors or not

[cdeerinck]

I really hope this doesn't become a "primer wars" type of conversation. I'm also hoping that people can provided their reasoning and not just reply with an "I used ...", as I am always most interested in learning reasoning, so I can adapt that knowledge accordingly.

Background:

While doing my wiring, I caught an error that I had made, and had to remove my fuel pumps (EFII system) to redo the wiring. The connectors on the fuel pumps are ring terminals. I still don't have the top of the fuselage on yet, but it was still difficult to disconnect everything, given how buried the wiring to them is in my situation. So I disconnected the fuel lines, the entire pump assembly, and then the wires.

I shuddered to think how "near impossible" it would have been if the top was on. I would not have been able to access it through the luggage hatch, and going under the panel would have been an exercise in advanced yoga and patience.

I considered putting some connectors here to facilitate potential maintenance in the future, but I also realize that any single connector introduces three new failure points.

I have a similar situation in one other location as well.

My question is this: How does one best weigh the decision of introducing a connector, especially in an electrically critical situation, and if a connector is used, what type is the most reliable for 14 and 16 awg wire?

As a follow up question, in aviation wiring, when should a ring terminal be used vs. spade or fork terminals?

[Mike S]

OK, to try to explain the "why" of things---------

I use these knife splice terminals for the simple reason they are designed to be separated and re attached when you need to do so.

http://www.steinair.com/product/red-knife-splice/

More in this thread. http://www.vansairforce.com/communit...ighlight=deans

They do need to be insulated, but shrink tube not only provides electrical insulation, but also a mechanical backup to the friction fit that keeps the two units together.

I also have had success using Deans Connectors for wiring that I foresee being separated in the future---again, they are designed to be separated and re attached when you need to do so. They are electrically insulated, but I use lacing cord or shrink tube to make a mechanical safety so they cant come apart accidentally.

http://wsdeans.com/products/plugs/index.html

More here. http://www.vansairforce.com/communit...13&postcount=6

I am making the assumption you want to use pigtails on the pump to make removal easier, with connectors that can be separated without having to work down in some dark, close quarters.

[BobTurner]

RV is too new to comment. However, after owning a 182 for 25 years I would say that plugs were as often as not the source of electrical trouble. I avoid them as much as possible. If necessary to remove something just cut the wire, re-install with a good quality crimp connector. If you end up with more than a couple crimps, then replace the wire.

[sblack]

Have a look at what a biz jet or airliner uses. I think they have plugs on everything so that techs can swap stuff out quickly. That is to me the only way to go. If good plugs are well installed, secured from vibrating and protected from the elements they will likely last longer than the thing they are connecting. Theoretically terminal strips and connectors add weight and failure points, but they make the airplane far more practical to maintain and I think operators of large civilian and military aircraft follow the same practice.

I bet there are lots of people on here with military and commercial civil maintenance or fabrication experience on this list. They would know better than me. How about it guys? Are any electrical components hard wired in place? Pumps, generators, regulators etc etc?

[snopercod]

I agree with BobTurner: Avoid connectors whenever possible because the vibration in an aircraft can work them loose. You can do like Bob said and cut and re-splice the wires if you have to. More importantly, try and locate all equipment where it can be reached for maintenance. Pumps of all kinds will probably need to be changed in 12 years or so. During construction, it's smart to plan ahead for how you're going to gain access. Ask me how I know

[N941WR]

I used blade connectors on the fuel pump and flap motor. I put a male plug and a female blade on the pump and flap motor wires. The power and ground leads received matching male and female blades & pugs on their wires. That way, if I ever removed one for maintenance, and I have, I couldn't wire them backwards.

They are also colored black and red but that wouldn't stop someone from connecting them wrong, the plugs do that.

[Canadian_JOY]

Sorry folks but I've got to weigh in. I've worked on everything from little puddle jumpers to fast attack aircraft to heavy rotary wing aircraft to all but the newest widebody airliners. Connectors are to the maintainer what cash is to a banker. You just can't live without 'em, and only a fool would try.

As for connector reliability, THE single largest driver of connector failure is.... HUMAN ERROR. Connectors themselves are often simple mechanical devices with inherently high reliability. How we assemble them, crimp wires in place, strain relieve those wires, then accidentally snag a wire bundle with a wrench when we're doing maintenance, or remove a component and let it dangle by its wire harness - THAT's what kills connectors and introduces lower reliability.

With respect to vibration loosening connectors, that may be true of cheap ones, but it sure ain't true for the better connectors. Ask any Air Force flight line maintainer why they have Cannon plug pliers in their tool kit!

I'll be totally honest and say one of the most perplexing issues I have ever worked was on a Bell 212 where the firewall connector pin carrying field current to the starter/generator pushed out and touched the backshell of the connector from time to time. That was a tough one to find. What wasn't tough to see were the ugly, ugly tool marks that had been left on the connector at some earlier date by a less-than-competent maintenance person.

If you are going to install connectors, install the best you can afford, using proper tooling. For most light GA applications, the Amp CPC series of connectors (now stocked by Aircraft Spruce) are quite adequate, and very reasonably priced. Get the right crimper and extraction tools and you're set. I've maintained a fleet of MD500 helicopters where our auxiliary payload equipment was built using the Amp CPC connectors. These were exposed to brutal conditions in West Africa - heat, humidity, vibration, sand, you name it. And they performed beautifully, flying 40+ hours per week, every week, for years on end.

For simple "power ground and control" connections like those found on a boost pump, the previous suggestion of using knife connectors is an excellent one. To aid in ensuring proper polarity, stagger the knife connectors - cut the power wire something like 6" from the pump, the ground wire 8" from the pump and the control wire 10" from the pump. This staggering of knife connectors is an effective way to ensure wires never get crossed, and that they can't short together in the event somebody slides the heatshrink tubing up the wire to expose the connector. Oh yeah, one other suggestion for knife connectors which are more likely to be removed in service. Put heatshrink on the airframe side of the wires and only shrink the first 1/2" or so, then slide the heatshrink over the knife connectors and tie the other end in place using lacing cord. It will never come off unless you cut off the lacing cord, and yet you will always be able to cut the cord, slide the heatshrink up the wire, unfasten the connection, then slide the shrink back down over the exposed knife connector so as to prevent sparks should somebody flip the power on while you've got the connection broken open.

Be not afraid of connectors - be vigilant in their installation and maintenance and they will serve you well.

[Walt]

Originally Posted by BobTurner

RV is too new to comment. However, after owning a 182 for 25 years I would say that plugs were as often as not the source of electrical trouble. I avoid them as much as possible. If necessary to remove something just cut the wire, re-install with a good quality crimp connector. If you end up with more than a couple crimps, then replace the wire.

I agree, for our RV's crimp splices are cheap, easy to install and 100% reliable when installed with the correct tools.

[Jesse]

I have the same recommendation as Canadian Joy. The CPC connectors are excellent. I only use the good gold-plated connectors. It adds cost and time, but for wing roots and wing tips and things like that, they are excellent. For low power things, like trims, I use free-hanging Dsub connectors, also with the good machined barrel crimp connectors.

I use some butt splice crime connectors, but I have started using a lot more solder splices. These are great for making permanent connections of a couple of wires, or for joining 3 or mores wires together, like splitting the 5V excite circuit from an engine monitor or splitting an RS232 output from a GPS serving multiple devices.

Running continuous wires is always the cheapest and most reliable option, but if you must use a connector, these are what I recommend.

[cdeerinck]

Very solid advice, thank you very much.

So in my situation, not only will I put in CPC connectors, but I was thinking on replacing a few Molex connectors with CPC's as well, especially in the wing roots. Some of those wires are 12awg (15 amp peak Pitot heat).

I managed to find a crimper on eBay for about $80 (they are running $400-800 for a new crimper)

For the 14-18 awg wire, I think I need these:

CPC Series 1
Pins are Type II, Screw Machined Crimp, Contact Size 16
16-18awg 200336-1 and 200333-1
14awg 201570-1 and 201568-1

For the 12 awg I think I need a Series 3 CPC.

They all seem kind of expensive at about $20 per full connector (minus the pins), and I will deal with that. But surely there has to be a source of the pins less than $2 to $4 each? One even as high as $13 per pin?

Aircraftspruce seems to only sell the signal size pins. So can anyone point me at a source that has them at a reasonable price?