1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be
replaced quite often; maybe more often than once a year. The replacement
is always rated at 250V, 15A. The switches have been from RS and Rapid
(not all the same batch then). The mode of failure is mechanical: the
toggle springs back to the ON position when switched towards OFF.
Sometimes once the faulty switch has been removed it then works
perfectly! It's as if simply being fixed into the panel is stressing it
in some way. The switch body doesn't touch the panel. Other switches on
the panel never fail, including one that does exactly the same job but
supplies a different PC. I'm puzzled. Chance?

Bill

williamwright wrote:
1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

I have a drawer in my 'bits' collection with a random collection of
those (plus the smaller ones for pots etc.).

--
Chris Green
·

On 14 Nov 2020 at 19:15:35 GMT, "williamwright"
wrote:

1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be
replaced quite often; maybe more often than once a year. The replacement
is always rated at 250V, 15A. The switches have been from RS and Rapid
(not all the same batch then). The mode of failure is mechanical: the
toggle springs back to the ON position when switched towards OFF.
Sometimes once the faulty switch has been removed it then works
perfectly! It's as if simply being fixed into the panel is stressing it
in some way. The switch body doesn't touch the panel. Other switches on
the panel never fail, including one that does exactly the same job but
supplies a different PC. I'm puzzled. Chance?

Bill

The only thing I can think of is an inductive load causing the contacts to arc
and fuse. The monitors aren't ancient very large CRT ones I suppose?

--
Roger Hayter

On 14/11/2020 22:23, Roger Hayter wrote:


The only thing I can think of is an inductive load causing the contacts to arc
and fuse. The monitors aren't ancient very large CRT ones I suppose?


No, new Samsung ones.

I mean, the weird thing is that some of the faulty switches have come
alright once they're removed from the panel. But I have to throw them
away, obviously. I have one in my hands now. It doesn't seem to be
caused by stress on the 1/4" connectors.

Bill

williamwright wrote:
On 14/11/2020 22:23, Roger Hayter wrote:


The only thing I can think of is an inductive load causing the
contacts to arc
and fuse. The monitors aren't ancient very large CRT ones I suppose?


No, new Samsung ones.

I mean, the weird thing is that some of the faulty switches have come
alright once they're removed from the panel. But I have to throw them
away, obviously. I have one in my hands now. It doesn't seem to be
caused by stress on the 1/4" connectors.

Bill

Inrush on a PC supply is 40A to 80A for a couple of 50Hz cycles.

OK, what kind of switch likes that.

I had a switch on a computer we designed at work, disintegrate
in my fingers one day while switching on. The switch was
destroyed by inrush. Switch contact rating was 10 amps continuous.
It took about 200 switch operations, to destroy it (one year, daily usage).

The senior manager in the group decided "he wanted this problem gone".
The senior manager and junior managers "owned" the chassis, because
there was a lot of interaction with the factory regarding the
computer chassis, so they owned that design and handled it themselves
without any help. None of the regular engineer talent was to
know what they were up to.

The switch was replaced with a switch plus a relay. The relay had
contacts rated at 40 amps. And it also happened to make a nice
quality "clunk" at startup. You could tell the machine meant
business, when you pushed the (ordinary) switch on the front
and you'd hear that "clunk" from inside the housing. The housing
for the computer was made from welded steel members. You could
drive a Ford F150 over it and not leave a mark.

I haven't seen a computer since, built like the tank that thing was.
I gather there'd been some complaints about the previous model
being "fragile" :-)

But, the electrical issue was fixed, and no more degraded
broken or fried switches were heard of.

The inrush limiter on PC power supplies is many things:

1) Protects rectifiers on front end.
2) Prevents I^2T issues with breaker panel at customer premises.
3) Does *not* solve all inrush issues!

Neat, eh. (3) is biting you on the ass. There isn't
enough inrush to kill the rectifiers, but there is
enough inrush to ruin your switch.

Now, don't ask me "how much switch is big enough switch".
Is it a 40 amp switch ? Is it a 10 amp switch ? Who knows.

You should do a post mortem on the switch and
look for carbon deposits (where the contacts close).
And now you have to tell the difference between
"normal" carbon deposits and "infrastructure destroying"
carbon deposits. Everything in the general area
is likely to have heat marks.

You can also alter the order of switch operation.

Turn off the PC at the back.
Turn off the "switch".
..... time passes
Turn on the "switch". No inrush, because PC is still switched off.
Turn on the PC at the back. (The PC switch eats the inrush.)

*******

NTCR1 is an example of an inrush limiter. This is an old design,
but the schematic nicely gets across some of the general principles
of ATX supply design.

http://www.pavouk.org/hw/en_atxps.html

The lower left is supervisor power. It provides power so the
"soft" power switch on the front of the PC works. It also
provides standby power for the RAM sticks in auto-refresh
while the PC sleeps. The upper right are the normal power
outputs, used in S0 ("Run") state. The fans spin, when the
upper right stuff is powered.

You might notice that design doesn't have a switch for mains
either. Unlike modern supplies, many of which have a switch
for mains. Some modern machines (like Apple) use a relay for
mains and sequence power to the supply. You hear a "click"
rather than a "clunk" when the power cord is plugged in.

Paul

Paul wrote:
williamwright wrote:
On 14/11/2020 22:23, Roger Hayter wrote:


The only thing I can think of is an inductive load causing the
contacts to arc
and fuse. The monitors aren't ancient very large CRT ones I suppose?


No, new Samsung ones.

I mean, the weird thing is that some of the faulty switches have come
alright once they're removed from the panel. But I have to throw them
away, obviously. I have one in my hands now. It doesn't seem to be
caused by stress on the 1/4" connectors.

Bill

Inrush on a PC supply is 40A to 80A for a couple of 50Hz cycles.

OK, what kind of switch likes that.

Yes, I don't think it's even for as long as "couple of 50Hz cycles", I
think it's simply the mains rated capacitor that is fequently
connected directly across the incoming supply.

When I plug my laptop's power supply in there is often a noticeable
'crack' and there are lots of burn marks on the plug as a consequence.
I assume the randomness of it happening is simply down to what part of
the mains cycle it gets plugged in.

--
Chris Green
·

On 14/11/2020 19:15, williamwright wrote:
1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be
replaced quite often; maybe more often than once a year. The replacement
is always rated at 250V, 15A. The switches have been from RS and Rapid
(not all the same batch then). The mode of failure is mechanical: the
toggle springs back to the ON position when switched towards OFF.
Sometimes once the faulty switch has been removed it then works
perfectly! It's as if simply being fixed into the panel is stressing it
in some way. The switch body doesn't touch the panel. Other switches on
the panel never fail, including one that does exactly the same job but
supplies a different PC. I'm puzzled. Chance?

Probably as others have said the switch can't cope with the high inrush
current at switch on and fuses the contacts.

The act of taking it out may be enough to free the spot welded contacts
so that when you later test it on the bench it is no fault found.

FWIW my suggestion would be to use a mains toggle switch rated for 20A
and see if it lasts any longer- a 20A rated DPDT with the contacts used
in parallel might be your best bet as a more robust solution.

If that still fails then a mains relay to switch the load would be my
next suggestion. BTW Rapid are usually cheaper than RS.

--
Regards,
Martin Brown

williamwright wrote:
1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be
replaced quite often; maybe more often than once a year. The replacement
is always rated at 250V, 15A. The switches have been from RS and Rapid
(not all the same batch then). The mode of failure is mechanical: the
toggle springs back to the ON position when switched towards OFF.
Sometimes once the faulty switch has been removed it then works
perfectly! It's as if simply being fixed into the panel is stressing it
in some way. The switch body doesn't touch the panel. Other switches on
the panel never fail, including one that does exactly the same job but
supplies a different PC. I'm puzzled. Chance?


Ive come across similar issues with cord pull switches for lights and
showers. Work perfectly in your hand, screw them to the ceiling and they
stop latching. Never could work out why.

Tim

--
Please don't feed the trolls

Does seem odd, I have a bulgin one from maybe 20 years ago on a light which
was a replacement for the useless rocker it did have and its never had a
problem, Its true these days, only my cleaner uses it, but nonetheless the
toggle is metal and the thread is metal but the back is plastic.

I used to fit these in a hole with either a flat or a spigot so it could
not turn, clamped between two nuts with a shakeproof washer on the inside
one. If you bolted them down to the body, then the plastic could bend and
suffer intermittencies etc.
I suspect modern switches are nowhere near as substantial.

The ones I used to buy in Tandy all those years ago, made in Mexico were
really very well built.
Brian

--

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"williamwright" wrote in message
...
1. I only realised today that normal toggle switches that need a nominally
half-inch hole have (at least) two incompatible threads and sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be replaced
quite often; maybe more often than once a year. The replacement is always
rated at 250V, 15A. The switches have been from RS and Rapid (not all the
same batch then). The mode of failure is mechanical: the toggle springs
back to the ON position when switched towards OFF. Sometimes once the
faulty switch has been removed it then works perfectly! It's as if simply
being fixed into the panel is stressing it in some way. The switch body
doesn't touch the panel. Other switches on the panel never fail, including
one that does exactly the same job but supplies a different PC. I'm
puzzled. Chance?

Bill

Any use shoving some wd 40 into them, or did that not make any difference.
Toggle mechanisms are pretty simple devices, , a bit like the mechanical
version of a Schmidt Trigger, they have hysteresis in other words, so
anything that pushes the bias too much in one direction can make them be
stuck, but I'd have thought this was going to remain when removed unless
there is something physically moving its position when bolted down.
Brian

--

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Note this Signature is meaningless.!
"williamwright" wrote in message
...
On 14/11/2020 22:23, Roger Hayter wrote:


The only thing I can think of is an inductive load causing the contacts
to arc
and fuse. The monitors aren't ancient very large CRT ones I suppose?


No, new Samsung ones.

I mean, the weird thing is that some of the faulty switches have come
alright once they're removed from the panel. But I have to throw them
away, obviously. I have one in my hands now. It doesn't seem to be caused
by stress on the 1/4" connectors.

Bill

Not sure about this though, as its not a new idea to have capacitors across
the mains for filtering etc.
I just think possibly that a bit of wear and tear, could be heat related if
its all made of plastic, has somehow pushed the bias of the switch too close
to one direction . When the stress changes after removal its just enough to
work again. Could be as simple as a hole elongated where the spring seats
at one end.
Brian

--

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Note this Signature is meaningless.!
"Chris Green" wrote in message
...
Paul wrote:
williamwright wrote:
On 14/11/2020 22:23, Roger Hayter wrote:


The only thing I can think of is an inductive load causing the
contacts to arc
and fuse. The monitors aren't ancient very large CRT ones I suppose?


No, new Samsung ones.

I mean, the weird thing is that some of the faulty switches have come
alright once they're removed from the panel. But I have to throw them
away, obviously. I have one in my hands now. It doesn't seem to be
caused by stress on the 1/4" connectors.

Bill

Inrush on a PC supply is 40A to 80A for a couple of 50Hz cycles.

OK, what kind of switch likes that.

Yes, I don't think it's even for as long as "couple of 50Hz cycles", I
think it's simply the mains rated capacitor that is fequently
connected directly across the incoming supply.

When I plug my laptop's power supply in there is often a noticeable
'crack' and there are lots of burn marks on the plug as a consequence.
I assume the randomness of it happening is simply down to what part of
the mains cycle it gets plugged in.

--
Chris Green
·

I had one push switch on an akai tape recorder that stopped latching. It was
the mains switch. They sent me a new one and it worked for six months and
the same thing happened. After looking at the old one there was a kind of
metal finger and a metal piece biased one way that it slid along and it was
supposed to spring at a point stopping it from going back until a second
press. All that was wrong was the little metal slider was jamming on its
pivot due to too much friction and or poor spring. I respran the spring a
bit, a sod to get back on but then it worked flawlessly until the deck
itself wore out. Odd how a very competent piece of engineering can be let
down by minor things outside of the makers control.
Brian

--

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Note this Signature is meaningless.!
"Tim+" wrote in message
...
williamwright wrote:
1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be
replaced quite often; maybe more often than once a year. The replacement
is always rated at 250V, 15A. The switches have been from RS and Rapid
(not all the same batch then). The mode of failure is mechanical: the
toggle springs back to the ON position when switched towards OFF.
Sometimes once the faulty switch has been removed it then works
perfectly! It's as if simply being fixed into the panel is stressing it
in some way. The switch body doesn't touch the panel. Other switches on
the panel never fail, including one that does exactly the same job but
supplies a different PC. I'm puzzled. Chance?


I've come across similar issues with cord pull switches for lights and
showers. Work perfectly in your hand, screw them to the ceiling and they
stop latching. Never could work out why.

Tim

--
Please don't feed the trolls

In article
,
Tim+ wrote:
williamwright wrote:
1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be
replaced quite often; maybe more often than once a year. The replacement
is always rated at 250V, 15A. The switches have been from RS and Rapid
(not all the same batch then). The mode of failure is mechanical: the
toggle springs back to the ON position when switched towards OFF.
Sometimes once the faulty switch has been removed it then works
perfectly! It's as if simply being fixed into the panel is stressing it
in some way. The switch body doesn't touch the panel. Other switches on
the panel never fail, including one that does exactly the same job but
supplies a different PC. I'm puzzled. Chance?


I‘ve come across similar issues with cord pull switches for lights and
showers. Work perfectly in your hand, screw them to the ceiling and they
stop latching. Never could work out why.

A spring isn't strong enough to counter the effect of gravity?

--

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On 15 Nov 2020 10:12:06 GMT, Tim+ wrote:

williamwright wrote:
1. I only realised today that normal toggle switches that need a
nominally half-inch hole have (at least) two incompatible threads and
sizes of nut.

2. I have a panel that includes a toggle switch that controls the mains
supply to a row of sockets, to which are connected a desk PC and two
monitors. (Other peripherals (scanner, printers, etc) are on a different
circuit). This switch is only operated twice a day. It has to be
replaced quite often; maybe more often than once a year. The replacement
is always rated at 250V, 15A. The switches have been from RS and Rapid
(not all the same batch then). The mode of failure is mechanical: the
toggle springs back to the ON position when switched towards OFF.
Sometimes once the faulty switch has been removed it then works
perfectly! It's as if simply being fixed into the panel is stressing it
in some way. The switch body doesn't touch the panel. Other switches on
the panel never fail, including one that does exactly the same job but
supplies a different PC. I'm puzzled. Chance?


I¢ve come across similar issues with cord pull switches for lights and
showers. Work perfectly in your hand, screw them to the ceiling and they
stop latching. Never could work out why.

Tim

Possibly something to do with String Theory?
--
Peter.
The gods will stay away
whilst religions hold sway