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B&C Voltage Regulator Screw Security

mfleming

Well Known Member
Patron
-7 wiring in progress :D

Following the B&C manual for mounting the LR3D regulator, mines on the pilot side of the firewall. All the wires were ready to attach to the regulator when I noticed that the screws are very short and do not come with a lock washer. There is a sort of ridged landing pad that might act as a locking device when all is snugged down.

My question is for those who have gone before me: Did you use what B&C supplied and called it good, or did you do something different?

Here's a photo just for grins.
 

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MS35333-37 (Type A), Available from Spruce and others.

And use TE PIDG Ring Terminals for the wire terminations...
 

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Dont understand why

I dont understand the need to use lock washers on these terminals. Lock washers keep the threads engaged during vibration when parts may “gap”. With these terminals, there is little mass to cause gapping; the terminals should stay tight under the most severe vibration.

However if the wires tend to move a little, or the threads are lubricated, then the screws can loosen. There are two other solutions: one is to stake the screw heads with ec2216, or use locktite.

It is important to secure the wires close to the terminals for many reasons.

Removing these screws to add lockwashers is fine if the screws are long enough still for full engagement of the threads and the part is outside the airplane. But if the terminal screws are short, or the part is already inside the airplane, it is fraught with problem trying to remove to add lock washers.

A way to check full thread engagement is to back out the screw until it is not screwing out anymore. Then turn the screw in. It should turn in 4 turns. Or conversely from tight should back out four turns before it is free.
 
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Any single sided fastener (if you can’t torque for either side) must have a locking feature or safety installed. This screw would qualify as/need such unless you put a nut on the back side. If not specified, then it is good practice and cheap insurance.
 
I've worked on dozens of aircraft that had terminal strips installed for various wiring functions, B&C regulators included. I've never found one loose. I'm only one mechanic, so take that for what it's worth. The problem I've found is overtightening, leading to broken screws when I try to remove them.

Terminal strip designs, which usually included a serrated surface and/or a serrated screw, tend to be very secure. My own RV-7 also has several, and two B&C regulators. Never had a loosening problem in over 1000 hours.
 
can't speak to issues with these screws, but I can say that lock washers don't always work in this situation. I chased an over voltage issue for several weeks until I finally found a loose connection on the alt field breaker. These breakers all had lock washers on the screws and ALL of them were loose enough to require re-tightening. The loose screw was creating resistance and lower the sensed voltage for the regulator, raising the output voltage.

Larry
 
I've never seen these come loose. I don't think there is a need for a lockwasher.

Vic

I put lock washers on screws that aren't held in place with a nylock nut, MS21043 nut, nut plate, or similar retention device.

Klixon 7277 CBs have split lock washers, and they are installed in the same environment -- good enough for them...
 

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B&C

Anyone ask B&C Tech Support. They have equipment all over the Expimental and Certified market. Seems like they would know best.
 
Factory extras

Anyone ask B&C Tech Support. They have equipment all over the Expimental and Certified market. Seems like they would know best.

Of course you are right. My previous comments were meant for those who decide to change the factory recommendations and add a lockwasher. Of course if the terminals come with lockwashers, by all means use them.
 
Anyone ask B&C Tech Support. They have equipment all over the Expimental and Certified market. Seems like they would know best.

My first thought exactly but it was the weekend and I wanted to put this job behind me.

Since B&C does not provide a locking device, I'm assuming they don't think it needs one. Vic, who sees so many of these, doesn't think they need one either.

Although I'm not normally a belt and suspenders builder, I think a star type lock washer can't hurt here.
 
Screw lengths

My first thought exactly but it was the weekend and I wanted to put this job behind me.

Since B&C does not provide a locking device, I'm assuming they don't think it needs one. Vic, who sees so many of these, doesn't think they need one either.

Although I'm not normally a belt and suspenders builder, I think a star type lock washer can't hurt here.
Just make sure the screws are long enough with the lockwasher, otherwise good to go.
 
I've installed 5 of the B&C LR-2/LR-3 in 5 different homebuilts without using locks washers. Over 5,500 hours aggregate flight time, and never a loose connection. If I were inclined to use a lockwasher (and I'm not), I'd use the internal tooth variety.
 
It doesn’t have to be a lock washer, safety wire, etc. If one of the surfaces has “locking teeth” or similar, that complies. I’ll state again, if a fastener can’t be torqued from either side (inserted into a blind hole like a terminal strip), some type of locking hardware is required. One could lawyer around the regs and find ways. If the OEMs drawings (here B&Cs) call out a specific fastener stack, one would technically be in compliance. The next inspection should flag the installation if said drawing couldn’t be referenced. A similar circumstance would be installing a bolt thread side up. Orientation should be changed unless specified in some released documentation (drawing). Not trying to start an argument. Hopefully the reasoning behind the position is obvious to most. These types of installations are fine, until they aren’t. Build/fly safe.
 
I’ll state again, if a fastener can’t be torqued from either side (inserted into a blind hole like a terminal strip), some type of locking hardware is required. One could lawyer around the regs and find ways.

What regs are you referring to?

Erich
 
They all run together on me these days. The strictest I’ve dealt with were for NASA. Those were the first I had to utilize and probably the most strict. Those specs were actually derived from the old North American Aviation (later Rockwell) standards. Am told the FAA specs were derived from those as well but citation is needed. BTW bolts utilizing nut plates aren’t generally considered a blind install. NPs act as a female fastener. The threads are not part of the material “stack”. If you want an example that most are familiar with, the bolt that sets and secures most alternator belt tension is a blind (one sided) fastener installation. It should be safety wired or should incorporate a lock washer. The source isn’t as important as the reasoning. I’m aware that the subject terminations aren’t structural but there are consequences if the connection is lost. Most any spec in any industry allows for deviation if the proper calcs, due diligence, etc are done. For that reason, it is assumed that OEM have done such and their released documentation can override such. If I have time to try and find any docs, I’ll do so. Sorry for any consternation. Vans does a good job of applying techniques that make it easy for builders. The techniques and reasoning go well beyond their releases and associated following.
 
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