Spring-Loaded Switch?

[Jones]

Hello, all,

My father's old table saw (240V) used to have a box and wall-style
switch that he wired into it, and if I recall correctly, the switch
seemed to be really hard to throw, and when it did, it seemed to "snap"
really hard and fast.

I think I remember Dad telling me that it was a special switch and that
it had strong springs that were meant to slam the contacts together
very fast and hard to prevent arcing and consequent
corrosion/pitting/degradation of the internal contacts.

Am I remembering this right, and can anyone tell me more about this
type of switch (what it's called, etc.)? Thank-you.

Jones.

 

[bud--]

I don't know exactly what he had, but it may be a manual motor starter,
which is basically a switch designed for the inductive motor load. You can
find them at most suppliers that handle motor controls.

..
From the UL White book: "AC general-use snap switches are tested ...
for motor loads up to 80% of the amp rating of the switch, but not
exceeding 2 hp." These are standard wall switches.

A "manual motor starter" is probably more rugged, would probably last
longer, and I agree it fits the OP's description.

 

[bud--]

There are motor rated "spec grade" switches at the Home Depot but
these are the ones in a box, not the 50 cent ones in the barrel

..
According to the White book the 50 cent ones can be used for motors up
to 80%/2HP if they are "AC general-use" (not AC-DC). One of the hidden
tidbits in the UL standards. (Snap switches, guide category WJQR.)

The 50 cent ones might not be the best choice for what to use.

 

[[email protected]]

10:39 -0600, bud-- <[email protected]>
| wrote:
|
|>According to the White book the 50 cent ones can be used for motors up
|>to 80%/2HP if they are "AC general-use" (not AC-DC). One of the hidden
|>tidbits in the UL standards. (Snap switches, guide category WJQR.)
|>
|>The 50 cent ones might not be the best choice for what to use
|
| Bear in mind U/L is only saying these things won't burn your house
| down when they fail, not that they will actually work for any length
| of time.

Exactly. UL testing is in regards to safety, not efficacy.

 

[Tom Horne]

Bear in mind U/L is only saying these things won't burn your house
down when they fail, not that they will actually work for any length
of time.
Since this is a 240v saw, he already needs the two pole unit and that
eliminates the 50 cent jobs. If he gets the 2 pole, 30 amp device it
will have that heavy duty click he is looking for and it will hold up
to regular use..They have them at most home stores

The man has brought out a very important point here that we ignore at
the peril of our customers dissatisfaction.

A little history is in order here. When the Great Chicago Exposition
was under construction to be a showcase for mans brand new servant
called electricity the closest Chicago fire houses had horses literally
dying from exhaustion because so many fires of electrical origin broke
out. The insurance companies that had insured the exposition saw the
specter of financial ruin staring them in the face. The underwriters
who had purchased a share of the risk in return for a share of the
premiums threatened to withdraw their support and leave the original
insurers with the entire risk. They agreed to continue to underwrite
the risk under specific conditions. One sample of every single item to
be used in the electrical installations was to be delivered to a
laboratory that they hired an engineer to set up in a nearby loft
building. If that engineer didn't approve it for the list of acceptable
components it could not be used without voiding the fire insurance.
That was the birth of the "Underwriters Laboratory" and it's listing
service.

To make it onto the electrical materials list a device has to pass
testing that has nothing to do with service life or fitness for a given
use. The testing is only meant to show that the device will fail safe
in that in failing it will not serve as an ignition source for a fire of
electrical origin. Even the preamble to the National Electrical Code
warns that compliance will produce "an installation that is essentially
free from hazard but not necessarily efficient, convenient, or adequate
for good service or future expansion of electrical use."

When customers demand an installation that is "just whats needed to pass
inspection I have them sign off on a letter that quotes that section and
throws their exact words right back at them. That usually serves as the
beginning of a discussion that leads to a more rational approach to the
job in question. When I asked one fella to sign it he was amazed that I
thought it necessary. When I explained that my intent was only to make
sure he new what he had asked for he allowed as how he didn't know what
to ask for so we went over the prints for his addition together and he
got pricing in advance for what he decided he wanted. Long after the
job was over I found out he is a consumer rights attorney with a great
record of success representing the interest of the buying public in my
state. He is also an adjunct professor at a law school and a friend
told me he uses that letter in class.

Perhaps the basic principal being discussed here can best be explained
by quoting the old Yankee shop keepers warning that "Quality can be
illustrated by the purchase of oats. If you want nice clean fresh oats
you must pay a fair price. If you will be content with oats that have
already been through the horse you may pay slightly less!"
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison

ARTICLE 90 Introduction
90.1 Purpose.
(A) Practical Safeguarding. The purpose of this Code is the practical
safeguarding of persons and property from hazards arising from the use
of electricity.
(B) Adequacy. This Code contains provisions that are considered
necessary for safety. Compliance therewith and proper maintenance will
result in an installation that is essentially free from hazard but not
necessarily efficient, convenient, or adequate for good service or
future expansion of electrical use.

 

[John]

"Jones" wrote

Hello, all,

My father's old table saw (240V) used to have a box and wall-style switch
that he wired into it, and if I recall correctly, the switch seemed to be
really hard to throw, and when it did, it seemed to "snap" really hard and
fast.

I think I remember Dad telling me that it was a special switch and that it
had strong springs that were meant to slam the contacts together very fast
and hard to prevent arcing and consequent corrosion/pitting/degradation of
the internal contacts.

Am I remembering this right, and can anyone tell me more about this type
of switch (what it's called, etc.)? Thank-you.

Sounds like just like a common type of isolator which was common until about
the 1950's/60's. Probably about 6" high by 5" wide by 4" deep and often
silver in colour, and with the switch actuator lever on the right and
designed so as to stop the front cover being opened while in the "on"
position.

Most switches will contain a spring to ensure that they change state very
rapidly to minimise arcing.

 

[bud--]

The man has brought out a very important point here that we ignore at
the peril of our customers dissatisfaction.

A little history is in order here. When the Great Chicago Exposition
was under construction to be a showcase for mans brand new servant
called electricity the closest Chicago fire houses had horses literally
dying from exhaustion because so many fires of electrical origin broke
out. The insurance companies that had insured the exposition saw the
specter of financial ruin staring them in the face. The underwriters
who had purchased a share of the risk in return for a share of the
premiums threatened to withdraw their support and leave the original
insurers with the entire risk. They agreed to continue to underwrite
the risk under specific conditions. One sample of every single item to
be used in the electrical installations was to be delivered to a
laboratory that they hired an engineer to set up in a nearby loft
building. If that engineer didn't approve it for the list of acceptable
components it could not be used without voiding the fire insurance. That
was the birth of the "Underwriters Laboratory" and it's listing service.

..
Interesting. Sounds like the 1893 Fair, which was the first major defeat
for Edison’s DC empire.
..

To make it onto the electrical materials list a device has to pass
testing that has nothing to do with service life or fitness for a given
use. The testing is only meant to show that the device will fail safe
in that in failing it will not serve as an ignition source for a fire of
electrical origin.

..
For some devices, like TVs, it is not possible (or desirable) for UL to
determine if the device is actually useful.

The same is true for industrial control panels. They are investigated
for safety.

I believe fuses and circuit breakers are investigated for “fitness for a
given use” and “service life”.

I expect more complicated devices, like GFCIs and smoke detectors to be
fit for their intended use and have a useful service life. (Both with
testing as required in the listing.)

A lot of other electrical apparatus is tested for more than failing safely.

One of the 3 UL standards I have is a 15 year old one for Snap Switches
- the subject.
For AC only switches the tests include the following - at rated voltage:
10,000 operations at rated current
10,000 operations at rated current and power factor around 0.8
10,000 operations at rated current controlling incandescent loads
as you know, this involves a high inrush current and IMHO
is similar to starting a motor
100 operations at 4.8x rated current and power factor around 0.5
IMHO this is very similar to switching off a stalled motor with
running current 0.8x the switch rating
IMHO this is testing for “service life” and “fitness for use”, and is a
reasonable test for use with on motors.

But I still would use a spec grade switch if using it for a motor load
approaching 0.8x rated switch current.
..

Even the preamble to the National Electrical Code
warns that compliance will produce "an installation that is essentially
free from hazard but not necessarily efficient, convenient, or adequate
for good service or future expansion of electrical use."

..
I have always taken this to be a comment on the code itself. A house
with the minimum circuits required for kitchen, laundry, bath and
general would be safe but probably would not make a buyer happy.