On 2014-01-13, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
"DoN. Nichols" fired this volley in
:
It is at least a *possible* one.
Don, I'm not picking on your answer... I had to respond to someone's, and
yours got the prize...
O.K. I won't take it personally. :-)
This is the dumbest discussion I've ever heard (short of all the
political spew on here).
Even half-quality garbage plastic switches from China are NOT prone to
accidentally 'switching on' from accumulations of dust or swarf.
Though some which are made to mount behind a trim plate in the
wall (typical home light switch) may be more open to a buildup of swarf
inside it. I've seen various failures in home electrical hardware which
I would not have expected.
Among those, there was an outlet which failed during a
nearby lightning strike. The form of the failure was a breakdown in the
hole into which a drive screw went to hold the ground strap which mounts
it to the outlet box. It was *supposed* to be a blind hole, but they
had used a slightly too long drive screw, or a chip was under it, and
there was a little of the inside surface which broke away.
Still -- normally not a problem. However, the lightning strike
introduced a high enough voltage so the gap to the nearby hot lead was
bridged, and the subsequent arc, both partially melted the "hot" inside
the socket, and welded it to what was plugged into it (one of those
duplex to six outlet plates) -- *and* filled the vicinity with carbon
dust.
When I got home from work and discovered the power loss in the
living room, I went downstairs and switched on the breaker. Five second
delay and BZZZZTTT-CLICK. A repeat got the same results. I then walked
around the house (old wiring, given breakers showed up in a lot of
outlets around the house.
I then walked around the house, until I smelled the burnt
Bakelite. Of course the outlet was behind a bookcase which I had to
empty and move to get to it. Then I discovered that the multi-outlet
adaptor would not unplug until I applied a lot of force, and that left
one pin of the adaptor in the socket.
I then removed the socket, and replaced it with a new one -- and
just had to take it apart to see what had happened.
If the Bakelite had not flaked around the drive screw, it would
not have broken down -- and the failure would have been somewhere else
at an even higher voltage -- or maybe not.
So -- I don't *depend* on any commercial electrical hardware for
the home to do what it should do.
And -- once I needed a toggle switch which did not introduce
vibration when it was operated to put in the mounting plate for a
turntable, so I could cue a record, and then switch on the motor at the
appropriate time. At that time, you could get "silent" light switches
which contained a puck of mercury in glass and metal end caps. It was
designed to work in a vertical orientation, but it was possible to take
the switch mounting plate off, and file different notches into the
toggle handle so it would hold the puck for horizontal operation. Now,
that switch was *not* designed to keep swarf out, so it would have to
depend on the decorative plate which goes over it. Granted, no normal
person would mount it as I did -- and I never had swarf near the
turntable, so it was no problem. But I do remember that switch, and how
easy it would be for swarf or sawdust to work its way in. Sawdust would
just make it take a bit more force to operate. Metal swarf would bridge
the ends of the puck and leave it on full time.
Granted -- most of the horizontal/vertical bandsaws use a normal
bat-handle toggle switch, but there are variations in quality there.
The best have a seal around the ball on which the bat rotate, and have
sealed wire entrance on the back. Cheap ones either have terminals on
the back (which you screw, solder wires to, or tabs for (hopefully)
insulated push-on crimp terminals -- but still metal swarf could bridge
that to the frame.
That it's a remote possibility, I won't deny. But such switches typically
serve for years to decades without a malfunction in the dusty, dirty,
swarf-filled environments in which we use them, and it's dumb to think of
the average home craftsman's going to the trouble to re-wire, retrofit,
and otherwise jigger-up his equipment with low voltage contactors and
safety circuits. That some would or even could is beside the question.
Given that he is already "jiggering up" the bandsaw -- replacing
the single phase 120 VAC motor with a higher horsepower single phase 240
VAC motor, you introduce another problem. Ideally (given USA wiring,
where 240 VAC is really two 120 VAC wires 180 degrees out of phase, so
they produce 240 VAC between them), you want a switch which interrupts
both sides of the power -- so a winding failure in the motor does not
leave some part of the system perhaps floating at 120 VAC instead of
near ground as it should be. Now, -- in the UK you don't normally have
240 VAC with a grounded center tap. Instead, one side of the 240 VAC is
grounded.
This discussion should be turned to "What's the best-quality switch I can
buy affordably that will suit the safety needs of the application." For
that, I recommend a good industrial-quality safety-style switch that
requires a simple swipe of the hand to turn off, and a positive 'de-
locking' action to turn on.
*And* -- one which interrupts both sides of the line, since he
is putting in a 240 VAC motor.
My old (1970s) Shopsmith came with one. When I finally wore it out in
the 1990s, I replaced it with the same-quality switch from a US maker
(IIRC it was a Square-D safety switch, specifically for table saws). You
could knock it off easily, but had to pull the bat out manually to turn
it back on -- heavy-duty thing. It lasted more than 20 years of nearly
daily use, and the replacement is still on the machine, still working.
Good enough. Remember that the motor is being changed here, so
at least some change in the switch is called for.
For special switches, somewhere I still have a switch designed
for reversing a single phase motor. It runs in either direction
(reversing two of the three circuits), but it enforces a pause when
switching from one direction to the other -- since running single phase
motors can't be instantly reversed just by swapping two wires. They
have to be allowed to slow down enough to come to a near halt (enough so
the centrifugal switch closes to enable the start winding for the
reversal.)
So -- yes with the right switches -- no problem. However, if
you want the weight of the arm of a horizontal/vertical bandsaw to
switch it off (at least he 4x6" ones) -- you want a switch with not much
operating force -- which is less likely to be capable of switching both
sides of the line for the 240 VAC motor. (I'm still not sure why he
feels the need for a larger motor -- perhaps it was one of those Chinese
import motors which are almost all empty housing, and very little frame,
made to *look* like a bigger motor, but bound to burn out with any
serious use. My 4x6 HV bandsaw came from MSC, and apparently they
spec'd a better quality motor -- and that one is still running, and does
not get hand-burning hot with a long cut. :-) So perhaps all he needs is
a motor which really is the nameplate horsepower on what he had -- and
for that, a 120 VAC motor should be sufficient and the original switch
might even do well. (I'll have to look under the base of mine to see
what the switch looks like there. :-)
Enjoy,
DoN.
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