rockstar.esq

Electrical trouble from multi-headed terminal bolts

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I just recently repaired a cabinet full of burnt wiring and welded contactors.  Everything had worked for three years before the client noticed an operational problem.  Long story short, the bolts on the contactor lugs weren't tight.  Given enough time and opportunity, an insufficiently tightened lug will start arcing, burning, etc. In this particular case, it got so bad that some of the contactor terminals burnt apart, others welded, wires were scorched, just not good.

I suspect I know the root cause of this situation.  The bolts on the contactor lugs are multi-headed to accept phillips or straight bladed screwdrivers.  Cordless drills are very common and phillips bits are the obvious choice because they're self-centering.  Unfortunately, many electrical equipment manufacturers use soft steel for these bolts.  Between the natural cam-out function of the phillips design, and the soft steel used, it's very common to strip the bolt head well before proper torque is applied to the fastener. Also, there are terminals with an insulated recess containing two square washers on a central bolt.  If the manufacturing tolerances aren't very good, the top washer can rotate sufficiently that two corners bind against the plastic of the insulated recess. Tightening the bolt doesn't draw the washer down on the conductor because the washer is digging into the device housing.  All of this is much harder to see if you're using a cordless drill.

The solution is to use a manual straight bladed screwdriver that's ground to precisely fit the slot.  It's certainly slower than a power tool, but the screwdriver gives tactile feedback.  A wire being compressed feels different than when the washer is binding.  Another advantage of the screwdriver is that you have better visibility of the conductor getting terminated.  Many electricians use a "wobble" or "crank" type screwdriver to rapidly take up slack in the terminal before switching to the straight blade screwdriver for final torque. 

One final comment, there are a lot of cordless tools on the market that can deliver much higher torque than a given fastener will tolerate.  I've seen electrical devices that cracked in two when their terminals were over-tightened. 

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2 hours ago, rockstar.esq said:

The solution is to use a manual straight bladed screwdriver that's ground to precisely fit the slot.

You made a good point regarding a precise blade-to-slot fit. I wrote and published an article several years ago in an automotive restoration magazine about the advantages of hollow-ground screwdrivers over tapered-blade screwdrivers and how to fit hollow-ground screwdrivers to slotted-head (aka, slotted-drive) screws. Since the portion of the hollow-ground blade that fits into the slot is parallel to the sides of the slot and not tapered, there is no tendency for 'cam-out' or other damage to the screw slot as long as the screwdriver is held in alignment with the screw, and the width and thickness of the blade are appropriate for the geometry of the slot. I never use an ordinary tapered-blade screwdriver on a slotted-head screw except in an emergency.

Gunsmithing catalogs usually have interchangeable-bit hollow-ground screwdriver sets that contain many different blade widths and thicknesses. The last time I checked, Brownells had a set that included 58 different hollow-ground screwdriver bits/blades. If you have a complete set, you can "almost" always find a nice close match between a blade and a screw slot without having to custom grind the blade. 

That said, there might be some exceptions among watchmakers, who seem to argue the relative merits of tapered vs. hollow-ground screwdrivers, possibly in part because of the difficulty of finding or making hollow-ground blades to precisely fit such tiny screws, but I'm no horologist/watchmaker, so I'll let them battle it out among themselves. For my own purposes at least, a properly-fitted hollow-ground blade beats a tapered blade, hands down.

Al (Steamboat)

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Steamboat,

It's actually a little bit impressive that nobody has thought to make a combi-bit for those fasteners.  The phillips part would keep the bit centered, and the hollow ground straight bit would provide better torque.

About fifteen years ago I bought a set of straight bits that had a spring-loaded collar on them.  The collar would keep the bit from sliding off the screw until the head was flush.  They were particularly nice to use with the little cordless screwdrivers we had at the time.  Over the years I've broken and lost all of them.  I haven't been able to find replacements since.

 

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Rockstar, check out this video of a Wiha #2 Xeno driver. I think it fits the bill for the comb-bit that you mentioned.

https://www.dailymotion.com/video/x5sff2x

I like Wiha tools, but they don't give them away.

Being kind of a tool junkie, I've picked up a myriad of gadgets over the years and I might even have one or two of the self-centering screwdrivers with a spring-loaded sleeve that you described. I'll have to take a look around and see if I can find them.

Al (Steamboat)

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Just a good tip. A little dab of fine valve grinding compound on the screwdriver tip really helps to avoid the cam out effect and prevents the screwdriver tip from becoming polished. Does not make up for an improper tip size though!

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That's an interesting suggestion, Frozenforge. It does seem reasonable that some valve grinding compound could help the grip, most particularly when using a tapered-blade screwdriver. A lot of new tapered-blade screwdrivers come from the factory with a roughened blade for a better grip in the slot, which seems closely related to what you suggested. And even when using a properly-sized hollow-ground screwdriver, perhaps a bit of grit might improve the grip when the slot in a screw has been rounded off a bit from usage.

Of course, I think we'd all agree that valve grinding compound (or any other grit-bearing substance) should NOT be used on screws where some stray grit could cause problems, such as screws used for electrical connections, applications where the torque is critical, mechanisms that must be kept very clean, etc.

Al (Steamboat)

 

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That tip dates WAYYYY back to when valve grinding compound was a common garage item.  I haven't used any since small engine class back around 1970...They just don't make car engines like they used to---thanks to a beneficent deity!

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When I did my first car engine overhaul (the venerable 235-inch six in a 1953 Chev) at age 13 back in the 1960s, I remember lapping the valves with compound for hours, since I didn't own any electric valve or seat grinding tools and couldn't afford to have it done out of my lawn mowing money. I still have the manual valve-lapping tool somewhere that would rotate the valves back and forth as you cranked the handle. It did produce a good seal, though, and the engine ran great afterwards, so I quickly sold that car to move on to the next car project, which involved an upgraded three-angle valve job.

I still like a lot of the old iron from those days. I'm a big fan of Ford/Mercury flathead V8s, despite their idiosyncrasies, and my current restoration project, a 1954 Dodge M37 military cargo truck, has some surprises that one might not expect in engines of that vintage, such as the original forged high-carbon steel crankshaft and hardened alloy exhaust valve seats.

We seem to have strayed off topic a bit.

Getting back to Rockstar's original topic, I think that he brings attention to the fact that dealing with something that "seems" to be as simple as an electrical terminal screw can be more complex and demanding than one might think, and worthy of some careful thought and research to avoid potentially dangerous or destructive outcomes.

Al (Steamboat)

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Steamboat,  Thank you so much for telling me about those Wiha screwdrivers.  I just googled it and found that they also make a driver bit with that head!  

Speaking of historical anachronisms, I typically carry a modern version of the "Yankee" screwdriver that accepts hex bits in my tool bag.  It uses an Archimedes screw like a push drill to spin the bits.  I've found that it's pretty much the ideal tool for removing panel covers on my own.  It supplies sufficient speed and torque to get things done without damage, while still fitting in my leg pocket.  Much like the manual screwdriver, it provides a lot of feel so I can tell if a bolt is wanting to cross thread on me.  As a bonus, it really freaks out the younger apprentices who've never seen a "cordless" screwdriver that can keep up with their power tools.  

Frozenforge, I like your tip but it's probably better for non-electrical stuff.  It does remind me of a "cheat" for getting a too-small slotted screwdriver to work.  Take a wide rubber band and lay it so one side is covering the screw slot.  Push the screwdriver into the rubber band so the rubber is between the blade and the screw slot.  

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Another anachronistic oddity I love to use is  a bit for my Brace & Bits that drives 1/2" drive sockets.  (It even has the pyramidal end on the shank end.) Lots of speed and torque---I once won a race to see who could put in a bunch of lag bolts fastest, Me with the brace & bit or a friend with his cordless driver.  He was faster getting them started but really slowed down driving them "home" and I didn't run out of battery...

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I run out of steam sometimes.....   

I remember when every respectable carpenter had a brace-and-bit and a Yankee screwdriver. Now I think that most of them (the tools, that is) are collecting dust and rust in barns and basements, although I did see quite a load of cleaned and oiled ones stacked on the shelves at my favorite used-tool store when I was up there about a week ago. However, they weren't exactly flying out the door. On the other hand, small hand-crank drills may be coming back into vogue, since their supply was almost completely sold out. Somewhere in some neglected box or bin in our basement or garage I may still have some of the above-mentioned ancient mechanisms.

Rockstar, I'm glad the link about the screwdriver was helpful.

Al (Steamboat)

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I give all my grandkids an eggbeater drill; there are some really nice ones out there for very reasonable fleamarket rates...

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I think that tools make great gifts for kids!

Generally speaking, I would rather see kids spend more time using what I call "real" (physical) tools and less time glued to their smartphones. I'm not anti-smartphone, per se (I've used them since the first 'brick' analog phones came out), but I'd like to see more kids doing more in the way of building, designing, fixing, and modifying tangible things, which would provide a broad range of learning experiences and a greater appreciation for the whole spectrum of human endeavor, IMHO.

Al (Steamboat)

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I've looked at the "toy" tools and decided that *real* tools would be better for kids.  I have done things like cut down a wood saw blade with my shear and then rasp down the handle to fit my Daughter's hand.  I'm restoring a small draw knife to go to my grandkids I gave a froe to last Christmas and I found a small carpenter's square to go to them too.  I fully expect a lot of the early tool gifts will get trashed as they learn on them.  Not a problem; Grandpa can find *more*!  (Still looking for "Baby's First Chainsaw"...)

I remember when I was a kid and would take anything thrown out and take it apart and see what it looked like inside; harder to do today.

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I think we're on the same wavelength, Thomas.

By the way, when I said "real" physical tools, I was just differentiating between physical tools and the software apps (which might include some software tools among the entertainment stuff) that could be found on a smartphone. I wasn't suggesting that the eggbeater drill was a toy tool, just in case you might have interpreted it that way.

I also used to dismantle things whenever possible when I was a kid, and after a while I got so I could start putting them back together again. And yes, it's harder to do that today with so much digital and microprocessor stuff, not to mention the continuing reduction of removable fasteners in favor of molded/welded/riveted assemblies that are not meant to be taken apart, but simply replaced as a unit or tossed in a recycle bin.

Al (Steamboat)

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Heating and cooling wires also loosen electrical connections.  When I worked at Jelly Belly we had an outside contractor come in that did thermal scans for insurance purposes. they would scan all of the electrical items in the plant like motor control panels, breaker boxes, disconnects, machine controls, etc Loose connections show up as hot spots. We would tighten them as he went along.

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