Probing terminal strips

[DaveC]

Whether with scope probe or DMM sticks, I have trouble getting a reliable
connection to terminal strips. With a crimp terminal stuffed under a
round-head screw, and shrink covering the terminal's shank, there's not much
to clip onto, especially with an alligator clip.

I'm tired of re-clipping probes and alligators that pop off with the
slightest touch. How do others do this?

I thought about inventing a small magnetic button probe that would locate
itself firmly on the top of the screw. Unless I can come up with another
solution...

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
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[Jim Miller]

Whether with scope probe or DMM sticks, I have trouble getting a reliable
connection to terminal strips. With a crimp terminal stuffed under a
round-head screw, and shrink covering the terminal's shank, there's not much
to clip onto, especially with an alligator clip.

I'm tired of re-clipping probes and alligators that pop off with the
slightest touch. How do others do this?

I thought about inventing a small magnetic button probe that would locate
itself firmly on the top of the screw. Unless I can come up with another
solution...

Thanks,

A large percentage of terminal strips use nickel plated brass screws.
Sometimes a mini-grabber type hook can get around the terminal between
the screw and the terminal shank.

I think Fluke makes some very good clips, though. My favorite is the
plunger style alligator clips. Sometimes these will even hold onto
the screw itself.

Some terminals are still a problem, where no clip seems to work.
If I can shut the unit off, I sometimes put another terminal with
pigtail under the screw to hook test clips to.

 

[DaveC]

Thus spake Jim Miller:

I think Fluke makes some very good clips, though. My favorite is the plunger
style alligator clips. Sometimes these will even hold onto the screw itself.

Some terminals are still a problem, where no clip seems to work. If I can
shut the unit off, I sometimes put another terminal with pigtail under the
screw to hook test clips to.

Good idea. But with some machines that have rows and rows of these things,
that a lot of pigtails! Powering-down the equipment, unscrewing, screwsing,
powering up, taking readings, adjust, repeat... ugh!

My magnetic idea... someone pointed out that many screws are made from brass!

 

[Wild Bill]

There are several companies that have specialty test probe accessories,
Pamona is a quality manufacturer.
Test equipment usually just includes basic accessories, and users need
to seek more specialized items best suited to their most common tasks.

The easiest solution would be to get some alligators with
insulation-piercing spikes inside the jaws. This isn't the ultimate
solution, and piercing can cause secondary problems in some
applications, but it's simple.
I think I've seen piercing scope probe tips too, but don't remember
where.

Securely grabbing the small area of the sides of screw heads isn't an
easy task. A possible design would include sharp points that are held
with tension, involves points that will stay sharp with a clip that
won't lose it's tension. Add to this design a method of insulating the
clip, and the design gets more complex fairly quickly.
A feature of replaceable points would be a good one, but probably not
economically feasible.

Sometimes the best you can do is find something that's almost suitable,
and modify it yourself. A little filing or reforming of the existing
products might be the best direction.
A Dremel-type tool is handy to have for small projects like this.

Nearly every technician will eventually make custom test leads that
suit their particular test requirements. The main feature will be user
safety.

If someone was often working with equipment that had the same identical
terminal strips, it might be worthwhile to fabricate an insulated
transferrable clip-on device that would attach to the terminal strip
body (or over it), which had accessible test pins incorporated into the
test clip design.
If the terminal strips were located within a steel cabinet, a
magnetically-mounted holder could possibly be utilized to hold the test
interface pin header-type device in place temporarily.

I've been pondering a 2-wire clip-on device that could be attached to 2
soldered pads on circuit boards (on the solder side, instead of
attaching to component leads on the component side). I figure it will
look more like an old spring-tensioned clothespin with sharp points to
dig into the thru-hole soldered lead areas, and stay in place for a
short time without falling off. Too much spring tension would cause the
points to cut (or plow) thru the solder, and the clip would pop off.

 

[Smitty Two]

Whether with scope probe or DMM sticks, I have trouble getting a reliable
connection to terminal strips. With a crimp terminal stuffed under a
round-head screw, and shrink covering the terminal's shank, there's not much
to clip onto, especially with an alligator clip.

I'm tired of re-clipping probes and alligators that pop off with the
slightest touch. How do others do this?

I thought about inventing a small magnetic button probe that would locate
itself firmly on the top of the screw. Unless I can come up with another
solution...

Thanks,

If you're gonna invent something, how about this: Have you seen the
screwdrivers that grab the head of a screw so you can get the screw
started in a recessed area into which you can't reach fingers?

One of the many styles of screwgrabbers for slotted head screws is a
split blade. The two half-blades move in opposite directions,
perpendicular to the slot of the screw. They are thus forced against
opposing inside walls of the slot. Seems like a technique that could be
applied to a test clip.

 

[Michael Kissin]

Whether with scope probe or DMM sticks, I have trouble getting a reliable
connection to terminal strips. With a crimp terminal stuffed under a
round-head screw, and shrink covering the terminal's shank, there's not much
to clip onto, especially with an alligator clip.

I'm tired of re-clipping probes and alligators that pop off with the
slightest touch. How do others do this?

I thought about inventing a small magnetic button probe that would locate
itself firmly on the top of the screw. Unless I can come up with another
solution...

Thanks,

SoanarPlus (formerly PolyKom) makes magnetic connectors that are
essentially a 40mm long piece of 0.65mm diameter wire bonded to a 6mm
diameter button magnet. They might be a bit big though.

Catalog number PP-0050.

- Michael