I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.

But, as I understand it, switches are rated for the current that they
can *break*. My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

Thanks,
Bob

On Tue, 22 Jul 2008 22:29:46 -0400, Bob Engelhardt
wrote:

I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.


So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

I dunno, but if you've got room, these are rated 30A @ 600VAC.

http://www.mcmaster.com/catalog/114/...e/7657kp3l.gif

7657K23
Manual Motor Switch 3 Pole, 3 Ph, Open Frame Enclosure, Toggle
Operator
In stock at $51.36 Each

I've got a bunch of them -- $10 each + shipping if you're interested.
They're new.

--
Ned Simmons

"Bob Engelhardt" wrote in message
...
I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch with
that capacity.

But, as I understand it, switches are rated for the current that they can
*break*. My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2 sets
of contacts will double (more or less) the current capacity.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never break
the current with it, could it carry 21A?

Thanks,
Bob

Grainger 5HA31
http://www.grainger.com/Grainger/items/5HA31

Greg

On 2008-07-23, Bob Engelhardt wrote:
I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.

How about McMaster item 7657K33, open frame DPST, 30 amps at 600 VAC,
3 HP rated, for $24.24? Page 854 of the catalog.

i

But, as I understand it, switches are rated for the current that they
can *break*. My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

Thanks,
Bob

--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
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On Jul 23, 12:29 pm, Bob Engelhardt wrote:
I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.

But, as I understand it, switches are rated for the current that they
can *break*. My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

Thanks,
Bob

Thats a bloody big clothes dryer Bob - 5Kw - and I doubt if an
"ordinary" 240v outlet could handle it - you will need a dedicated
circuit, at least. Whats its origin - ex laundromat?

One alternative is to use a small toggle switch, which controls a big
relay or even better, a SSR (Solid State Relay) which are quite cheap
nowadays...

Andrew VK3BFA.

On Tue, 22 Jul 2008 22:29:46 -0400, with neither quill nor qualm, Bob
Engelhardt quickly quoth:

I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.

But, as I understand it, switches are rated for the current that they
can *break*. My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

Why not use a smaller switch to run the dryer through a 240V relay?

--
Imagination is more important than knowledge...
Albert Einstein (1879 - 1955)

In article , Bob Engelhardt wrote:
I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.

But, as I understand it, switches are rated for the current that they
can *break*.

They are rated for the current they can carry.

My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.

Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

No.

In article ,
Bob Engelhardt wrote:

I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.

But, as I understand it, switches are rated for the current that they
can *break*. My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

Most likely, but will detonate if some fool flips it in use. I used a
15A toggle to switch a 15 amp magnet, with a BIG sign to NEVER flip the
switch unless the magnet was OFF. (I used it to reverse field at truly
tiny currents) Sure enough, some fool flipped the toggle at max current
and it blew up like a hand grenade, only the panel metal saved the fool.
So if you do go that route, package it so the explosion doesent kill
anyone and the mess is easy to clean up. The fool's pants will be
harder to clean

Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/
** Posted from http://www.teranews.com **

Doug Miller wrote:
In article , Bob Engelhardt wrote:

I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.
My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.


Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.

I think you may be misunderstanding Bob's application. Suppose you had
a single 15A switch in line with L1. When you toggle it, it will (obviously)
make or break 15 amps. Now suppose you put *another* 15A switch in parallel
with the first switch. Now if both switches are on, half the current would
flow through each. It's the switches that Bob is thinking of as being in
parallel, not the L1/L2 legs.

Bob, I doubt you can get 30A out of a 15A DP switch this way, though.

Grant Erwin

In article cgFhk.374$DS3.189@trnddc01, Grant Erwin wrote:
Doug Miller wrote:
In article , Bob Engelhardt
wrote:

I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.
My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.


Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.

I think you may be misunderstanding Bob's application.

Not at all. I think you didn't read his post carefully enough.

Suppose you had
a single 15A switch in line with L1. When you toggle it, it will (obviously)
make or break 15 amps.

To clarify: it will make, break, or carry up to 15 amps *safely*. If 21 amps
is applied to it, it will make, break, or carry 21 amps -- until it fails.

Now suppose you put *another* 15A switch in parallel
with the first switch. Now if both switches are on, half the current would
flow through each. It's the switches that Bob is thinking of as being in
parallel, not the L1/L2 legs.

In the part you snipped, he wrote:

"So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?"

He's not even talking about two switches. He's talking about *one* switch,
and thinking that the L1 and L2 legs are in parallel. They are not.

Also, FWIW, using two switches in parallel as you suggest is flatly prohibited
by the National Electrical Code.

Ned Simmons wrote:
http://www.mcmaster.com/catalog/114/...e/7657kp3l.gif

Greg O wrote:
Grainger 5HA31

Ignoramus2245 wrote:
How about McMaster item 7657K33, ...

Duh, well I feel pretty dumb - looked in all the wrong places (Surplus
Center, etc). Thanks for doing my search for me G.

I forgot to mention - I need double throw. Center off would be nice,
too. Doing my own search, I get McMaster-Carr 8001K35. 25A ON-OFF-ON,
toggle style, only $11.27!

Thanks!
Bob

wrote:
Thats a bloody big clothes dryer Bob - 5Kw - and I doubt if an
"ordinary" 240v outlet could handle it - you will need a dedicated
circuit, at least. Whats its origin - ex laundromat?

It's not anything special - 25 year old Sears. It's own circuit,
indeed. I suspect you're not in US, where ordinary circuits are 120v &
240v is only for ranges, ovens, & dryers - all of which have their own
circuits.

One alternative is to use a small toggle switch, which controls a big
relay or even better, a SSR (Solid State Relay) which are quite cheap
nowadays...

Larry Jaques wrote:
Why not use a smaller switch to run the dryer through a 240V relay?


That would be my 2nd choice, but I did find the switch I need.

Thanks,
Bob

nick hull wrote:
Most likely, but will detonate if some fool flips it in use. I used a
15A toggle to switch a 15 amp magnet, with a BIG sign to NEVER flip the
switch unless the magnet was OFF. (I used it to reverse field at truly
tiny currents) Sure enough, some fool flipped the toggle at max current
and it blew up like a hand grenade, ...

Thank you! That's exactly what I wanted to know. Well, I would have
preferred the answer to be "You'll be OK". But a definite answer is
still good G.

My load is strictly resistive (heater), but I'm still going to go with a
rated switch from McMaster. My wife would be VERY annoyed to have the
dryer blow up in her face!!

Thanks!!
Bob

Doug Miller wrote:
Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.


What I mean is paralleling the 2 "poles", i.e., sets of contacts, in the
same switch, so there are 2 sets of contacts carrying & dividing the load:

/
_________/ ___________
| / |
|__/ __|
240 LOAD

_________________________



Grant's reference to 2 switches was just to make it easier to visualize
(to put words in his mouth).

Bob

BTW - the NEC does not apply to wiring inside appliances/devices. Once
you get beyond the "disconnect", anything goes. Unless "Underwriters"
is going to have to its say G

In article ,
Bob Engelhardt wrote:

Ned Simmons wrote:
http://www.mcmaster.com/catalog/114/...e/7657kp3l.gif

Greg O wrote:
Grainger 5HA31

Ignoramus2245 wrote:
How about McMaster item 7657K33, ...

Duh, well I feel pretty dumb - looked in all the wrong places (Surplus
Center, etc). Thanks for doing my search for me G.

I forgot to mention - I need double throw. Center off would be nice,
too. Doing my own search, I get McMaster-Carr 8001K35. 25A ON-OFF-ON,
toggle style, only $11.27!

The Borg does not have such switches, but I had no problem buying such
switches from the local electric supply houses, for small dollars.

Joe Gwinn

In article , Bob Engelhardt wrote:

I forgot to mention - I need double throw. Center off would be nice,
too. Doing my own search, I get McMaster-Carr 8001K35. 25A ON-OFF-ON,
toggle style, only $11.27!

Rated 25A at **125** volts. You're switching 240V.

In article , Bob Engelhardt wrote:
Doug Miller wrote:
Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.


What I mean is paralleling the 2 "poles", i.e., sets of contacts, in the
same switch, so there are 2 sets of contacts carrying & dividing the load:

/
_________/ ___________
| / |
|__/ __|
240 LOAD

_________________________

Think this through a little farther. You don't have one wire carrying 240V as
you illustrated. You have two: L1 and L2.

Finish your drawing -- show where you're going to connect the L1 and L2 leads
to that switch.

(Doug Miller) writes:

"So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?"

He's not even talking about two switches. He's talking about *one* switch,
and thinking that the L1 and L2 legs are in parallel. They are not.

For what its worth, I read that post the same way Bob did: he's not
talking about the two poles of the power, he's talking about the two
poles of the switch.

In article , Joe Pfeiffer wrote:
(Doug Miller) writes:

"So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?"

He's not even talking about two switches. He's talking about *one* switch,
and thinking that the L1 and L2 legs are in parallel. They are not.

For what its worth, I read that post the same way Bob did: he's not
talking about the two poles of the power, he's talking about the two
poles of the switch.

And -- ?? 240V has two legs, L1 and L2. Are you suggesting connecting L1 to
*both* poles of a DPST switch, and leaving L2 unswitched? That would leave
120V applied to the load even with the switch off, not exactly a safe thing to
do.

Doug Miller wrote:
In article , Bob Engelhardt wrote:

Doug Miller wrote:

Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.


What I mean is paralleling the 2 "poles", i.e., sets of contacts, in the
same switch, so there are 2 sets of contacts carrying & dividing the load:

/
_________/ ___________
| / |
|__/ __|
240 LOAD

_________________________



At that power level, a dual circuit breaker might be more appropriate, hmmm?

--

Richard

(remove the X to email)

Doug Miller wrote:
Think this through a little farther. You don't have one wire carrying 240V as
you illustrated. You have two: L1 and L2.

Finish your drawing -- show where you're going to connect the L1 and L2 leads
to that switch.

Sigh:

/
L1 --- _________/ ___________
| / |
|__/ __|
240 LOAD

L2 --- _________________________

In article , Bob Engelhardt wrote:
Doug Miller wrote:
Think this through a little farther. You don't have one wire carrying 240V as

you illustrated. You have two: L1 and L2.

Finish your drawing -- show where you're going to connect the L1 and L2 leads

to that switch.

Sigh:

/
L1 --- _________/ ___________
| / |
|__/ __|
240 LOAD

L2 --- _________________________

Sigh:

So L2 will always be supplying 120V to the load, even when the switch is off.

Does that sound safe, prudent, or wise to you?

(Doug Miller) writes:

In article , Joe Pfeiffer wrote:
(Doug Miller) writes:

"So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?"

He's not even talking about two switches. He's talking about *one* switch,
and thinking that the L1 and L2 legs are in parallel. They are not.

For what its worth, I read that post the same way Bob did: he's not
talking about the two poles of the power, he's talking about the two
poles of the switch.

And -- ?? 240V has two legs, L1 and L2. Are you suggesting connecting L1 to
*both* poles of a DPST switch, and leaving L2 unswitched? That would leave
120V applied to the load even with the switch off, not exactly a safe thing to
do.

I'm not, I think he is.

On Wed, 23 Jul 2008 11:11:34 GMT, (Doug Miller)
wrote:

In article , Bob Engelhardt wrote:
I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.

But, as I understand it, switches are rated for the current that they
can *break*.

They are rated for the current they can carry.

My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.

Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

No.

You are not reading what the OP said. He did NOT say he would switch
both lines. He said he would tie the two sets of contacts together,
back to back (that's parallel) to share the load on ONE WIRE.
As long as there is nothing 110 on the drier, this will work, even if
it is not the right way to do it (he'll still have one line "hot" when
the "powwer" is shut off.

So the short answer is it will work. The not QUITE so short answer is
it is not the right way to do it, and I would recommend you do not.

What's the switch for if the timer will shut it off?

Why not use a "contactor" made for the job, if you need to switch it?

** Posted from http://www.teranews.com **

On Wed, 23 Jul 2008 12:21:52 GMT, (Doug Miller)
wrote:

In article cgFhk.374$DS3.189@trnddc01, Grant Erwin wrote:
Doug Miller wrote:
In article , Bob Engelhardt
wrote:

I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.
My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.


Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.

I think you may be misunderstanding Bob's application.

Not at all. I think you didn't read his post carefully enough.

Suppose you had
a single 15A switch in line with L1. When you toggle it, it will (obviously)
make or break 15 amps.

To clarify: it will make, break, or carry up to 15 amps *safely*. If 21 amps
is applied to it, it will make, break, or carry 21 amps -- until it fails.

Now suppose you put *another* 15A switch in parallel
with the first switch. Now if both switches are on, half the current would
flow through each. It's the switches that Bob is thinking of as being in
parallel, not the L1/L2 legs.

In the part you snipped, he wrote:

"So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?"

He's not even talking about two switches. He's talking about *one* switch,
and thinking that the L1 and L2 legs are in parallel. They are not.

Nope. He's talking about a DPDT switch. That is ONE switch physically,
but 2 electrically.

Also, FWIW, using two switches in parallel as you suggest is flatly prohibited
by the National Electrical Code.

Except it is NOT 2 switches. Relays are used this way all the time.

Still, as I have posted elsewhere, not the best solution - although it
WOULD work.

** Posted from http://www.teranews.com **

clare at snyder dot ontario dot canada wrote:
....
What's the switch for if the timer will shut it off?

To select the "high" thermostat or the "low". It's really an SPDT, but
I simplified the drawing.

Why not use a "contactor" made for the job, if you need to switch it?

Save space, components (cost), & effort. KISS

not switching both sides of the 240v - the other side is switched
elsewhere (a centrifugal switch on the motor). That was irrelevant to
my question, so I simplified.

I got into the classic RCM rabbit hole here by not explaining up front
the entirety of the project, with a complete schematic, the alternatives
I'd considered, and why I was intending to do it this way. I just
wanted to know about paralleling contacts, but it was naive to think
that the thread would focus on that. I should have known better - I'm
not exactly an RCM newbie G.

Thanks,
Bob

Bob Engelhardt wrote:
... It's really an SPDT, ...

Oops - I mean DPDT. Bob

clare at snyder dot ontario dot canada wrote:
... Relays are used this way all the time.

Still, as I have posted elsewhere, not the best solution - although it
WOULD work.

Oh, right - I remember from way, way, way back having relay contacts
paralleled.

Thanks,
Bob

Bob Engelhardt wrote:

clare at snyder dot ontario dot canada wrote:
...
What's the switch for if the timer will shut it off?

To select the "high" thermostat or the "low". It's really an SPDT, but
I simplified the drawing.

Why not use a "contactor" made for the job, if you need to switch it?

Save space, components (cost), & effort. KISS

not switching both sides of the 240v - the other side is switched
elsewhere (a centrifugal switch on the motor). That was irrelevant to
my question, so I simplified.

I got into the classic RCM rabbit hole here by not explaining up front
the entirety of the project, with a complete schematic, the alternatives
I'd considered, and why I was intending to do it this way. I just
wanted to know about paralleling contacts, but it was naive to think
that the thread would focus on that. I should have known better - I'm
not exactly an RCM newbie G.


Do you expect each set of contacts to have the eaxact same resitance?


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Michael A. Terrell wrote:
Do you expect each set of contacts to have the eaxact same resitance?

I don't know, should I? I guess that's an question that might be
answered here. My intuition is that they would be "close enough".

Bob

Bob Engelhardt wrote:

Michael A. Terrell wrote:
Do you expect each set of contacts to have the eaxact same resitance?

I don't know, should I? I guess that's an question that might be
answered here. My intuition is that they would be "close enough".

Bob


If they are not equal, you have different current in each set of
contacts. It might be "Close Enough" in a fresh production switch, but
it will change as the switch ages. At some point the imbalance can be
enough to cause excessive current to flow trough one set of contacts,
welding them, or causing them to overheat and destroy the switch. I've
seen it too many times to ever do it myself. Every time the switch is
used, it expects a small spark to clean the contacts. Always switching
under no load makes them deteriorate even faster. There are two types
of switch contacts. Power and low level signal. The low level
mechanically wipe, or use a pair of knife edges at right angles to apply
a lot of pressure so they don't need any current to stay clean. He
others are simple, flat faces that touch in pairs. The do no open or
close perfectly, and a double pole switch doesn't operate at exactly the
same time, due to mechanical tolerances, and even how squarely you
operate the switch.


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Bob Engelhardt wrote:
I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.

But, as I understand it, switches are rated for the current that they
can *break*. My application will never require the switch to break the
current - that will be done by the dryer's timer.

The current breaking ability of the switch is certainly a big part of the
rating, but the current carrying is certainly in there as well. You can't
push 100 amps through a 1 amp switch. I bet however that you would be
fairly safe pushing 21 amps through the 15 amp switch.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.

So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?

It seems to me that the resistance would be extremely hard to control in
that situation. The resistance is so low, that I strongly suspect you
would get a large imbalance between the two polls. If the alignment of the
contacts is only slightly different in the two polls it seems to me you
could get a 10 to 1 ratio in the resistance. Such as .00001 vs .000001 in
the two contacts and if that's so, you get a 10 to 1 imbalance in the
current. Your wires leading to the switch, and the contact you make in
connecting the wires to the switch all play important factors in
determining the total resistance of each path and in turn control the
current. If you just tighten the screw a little more on one pole and get
twice the surface area for the wires connected to one pole vs the other
because you flattened the wires more on one pole I think it could lead to a
2 to 1 resistance ratio and a matching 2 to 1 current flow. All in all,
it's not safe to assume the resistance would be "close enough" to create a
reasonable balance.

However, because switches that can carry 15 amps have to be a bit
over-rated to be safe, I think it would in practice work just fine for your
21 amp load even with a single pole. And if you put them in parallel, you
would only make it better, no matter how imbalanced the resistance was. So
even if it was as bad as 10 to 1 out of balance with the resistance, it
would still reduce the current to about 19 amps in one pole and 2 amps in
the other bringing it that much closer to the 15 amp rating.

So in practice, I think your solution would work fine - as long as it
doesn't get switched much under load. With the strong magnetic load talked
about in the other post, there's a _HUGE_ back emf voltage spike when you
break the circuit which the switch has to be designed to take or else it
will wear down very quickly. With your resistance only dryer load, that
would not be an issue so at worse.

In practice, I think it would work fine, and at worse, you would see a
reduced life span on the switch. If the switch didn't have to be used
much, it would last even longer in practice.

To be safe however, you of course shouldn't do it. The odds of it melting
down and starting a fire or hurting someone only go up when you play games
like that. It's a good thing you found a switch rated for the task at a
reasonable price...

I feel the need to go wire a few 15 amp switches in parallel and see what
type of current balance I actually get.....

Thanks,
Bob

--
Curt Welch http://CurtWelch.Com/
http://NewsReader.Com/

On Jul 23, 11:03 pm, Bob Engelhardt wrote:
wrote:
Thats a bloody big clothes dryer Bob - 5Kw - and I doubt if an
"ordinary" 240v outlet could handle it - you will need a dedicated
circuit, at least. Whats its origin - ex laundromat?

It's not anything special - 25 year old Sears. It's own circuit,
indeed. I suspect you're not in US, where ordinary circuits are 120v &
240v is only for ranges, ovens, & dryers - all of which have their own
circuits.

One alternative is to use a small toggle switch, which controls a big
relay or even better, a SSR (Solid State Relay) which are quite cheap
nowadays...
Larry Jaques wrote:

Why not use a smaller switch to run the dryer through a 240V relay?

That would be my 2nd choice, but I did find the switch I need.

Thanks,
Bob

Ah - I stand corrected. Your right - our standard wall outlets are
240v which can run just about everything as long as the total circuit
loading is ...(I forget - but I thinks the limit is 10 outlets per
circuit) and your also correct, stoves here have their own dedicated
circuit. And increasingly, big air conditioners. (Stuff the
environment - here, our peak power demand is now in Summer for
cooling, rather than a generation before when Winter heating was peak
load. Thats cool - just build another coal fired power station....)
But a 5Kw drier is a big one - hope YOU got cheap electricity....

Andrew VK3bFA.

On Wed, 23 Jul 2008 17:36:27 -0400, Bob Engelhardt
wrote:

clare at snyder dot ontario dot canada wrote:
...
What's the switch for if the timer will shut it off?

To select the "high" thermostat or the "low". It's really an SPDT, but
I simplified the drawing.

Why not use a "contactor" made for the job, if you need to switch it?

Save space, components (cost), & effort. KISS

not switching both sides of the 240v - the other side is switched
elsewhere (a centrifugal switch on the motor). That was irrelevant to
my question, so I simplified.

I got into the classic RCM rabbit hole here by not explaining up front
the entirety of the project, with a complete schematic, the alternatives
I'd considered, and why I was intending to do it this way. I just
wanted to know about paralleling contacts, but it was naive to think
that the thread would focus on that. I should have known better - I'm
not exactly an RCM newbie G.

Thanks,
Bob
For your application, what you propose will work just fine.
** Posted from http://www.teranews.com **

On Wed, 23 Jul 2008 18:37:58 -0400, "Michael A. Terrell"
wrote:


Bob Engelhardt wrote:

clare at snyder dot ontario dot canada wrote:
...
What's the switch for if the timer will shut it off?

To select the "high" thermostat or the "low". It's really an SPDT, but
I simplified the drawing.

Why not use a "contactor" made for the job, if you need to switch it?

Save space, components (cost), & effort. KISS

not switching both sides of the 240v - the other side is switched
elsewhere (a centrifugal switch on the motor). That was irrelevant to
my question, so I simplified.

I got into the classic RCM rabbit hole here by not explaining up front
the entirety of the project, with a complete schematic, the alternatives
I'd considered, and why I was intending to do it this way. I just
wanted to know about paralleling contacts, but it was naive to think
that the thread would focus on that. I should have known better - I'm
not exactly an RCM newbie G.


Do you expect each set of contacts to have the eaxact same resitance?

It will be close enough. Not good enough to double the capacity, but
150% should be fine . This application is a no-load switch - no making
or breaking contact under load in normal operation.
** Posted from http://www.teranews.com **

On Wed, 23 Jul 2008 18:59:55 -0400, "Michael A. Terrell"
wrote:


Bob Engelhardt wrote:

Michael A. Terrell wrote:
Do you expect each set of contacts to have the eaxact same resitance?

I don't know, should I? I guess that's an question that might be
answered here. My intuition is that they would be "close enough".

Bob


If they are not equal, you have different current in each set of
contacts. It might be "Close Enough" in a fresh production switch, but
it will change as the switch ages. At some point the imbalance can be
enough to cause excessive current to flow trough one set of contacts,
welding them, or causing them to overheat and destroy the switch. I've
seen it too many times to ever do it myself. Every time the switch is
used, it expects a small spark to clean the contacts. Always switching
under no load makes them deteriorate even faster. There are two types
of switch contacts. Power and low level signal. The low level
mechanically wipe, or use a pair of knife edges at right angles to apply
a lot of pressure so they don't need any current to stay clean. He
others are simple, flat faces that touch in pairs. The do no open or
close perfectly, and a double pole switch doesn't operate at exactly the
same time, due to mechanical tolerances, and even how squarely you
operate the switch.
Use a "snap action" switch - like a DC rated switch.
** Posted from http://www.teranews.com **

(Curt Welch) wrote:

I feel the need to go wire a few 15 amp switches in parallel and see what
type of current balance I actually get.....

Couldn't find any switches digging in the basement but I did a quick test
with a little different format just to see what would happen.

I used 4 wires to connect a standard 20 amp electrical outlet. 2 for the
hot, 2 for the neutral, and then wired those two together to create a
parallel power feed to the outlet. I used standard 12 gauge wire for all
paths. I plugged in a 100 W light to the outlet an measured the current
with a magnetic pick up style AC current meter.

The total current was around .81 amps, and the distribution in the two
parallel paths was around .31 amps and .48 amps or about 40% 60% balance of
current.

I suspect with the contacts of a 15 amp switch, the distribution could
easily be less balanced even with a new switch, and would only get worse
over time as one switch would no doubt wear down faster than the other.
But I don't have one handy to find out if this is true or not.

If you got a 40% 60% split like I did in my quick test, that would be 8.4
amps of your load in one contact and 12.6 amps in the other putting it well
within the 15 amp range of that switch. As long as it stayed that good or
better, it would be fine.

But this just demonstrates how parallel low resistance paths don't tend to
split the current evenly because the resistance is never very close to
equal.

People mentioned the idea of wiring relay contacts in parallel. That's
interesting and makes me wonder why they do it because it would be so hard
to balance the current when the contacts are closed. I wonder if it has
more to do with what happens as the circuit is opened and the contacts arc?
The current through two arcs might be better balanced because of the higher
resistance of the arcs and it might help reduce the spacing required to
break each arc?

Or maybe it's done just to improve relay life by creating redundancy? If
the contacts tend to degrade with age and their resistance increase the
redundant contacts will simply keep the circuit working longer because both
contacts will have to degrade to a high level before the relay will fail to
do its job? I doubt that current load balancing is the main reason for
wiring the contacts in parallel.

--
Curt Welch http://CurtWelch.Com/
http://NewsReader.Com/

clare, at, snyder, dot, ontario, dot, canada wrote:

On Wed, 23 Jul 2008 18:59:55 -0400, "Michael A. Terrell"
wrote:


Bob Engelhardt wrote:

Michael A. Terrell wrote:
Do you expect each set of contacts to have the eaxact same resitance?

I don't know, should I? I guess that's an question that might be
answered here. My intuition is that they would be "close enough".

Bob


If they are not equal, you have different current in each set of
contacts. It might be "Close Enough" in a fresh production switch, but
it will change as the switch ages. At some point the imbalance can be
enough to cause excessive current to flow trough one set of contacts,
welding them, or causing them to overheat and destroy the switch. I've
seen it too many times to ever do it myself. Every time the switch is
used, it expects a small spark to clean the contacts. Always switching
under no load makes them deteriorate even faster. There are two types
of switch contacts. Power and low level signal. The low level
mechanically wipe, or use a pair of knife edges at right angles to apply
a lot of pressure so they don't need any current to stay clean. He
others are simple, flat faces that touch in pairs. The do no open or
close perfectly, and a double pole switch doesn't operate at exactly the
same time, due to mechanical tolerances, and even how squarely you
operate the switch.
Use a "snap action" switch - like a DC rated switch.


Do whatever the hell you want. I really don't give a damn. Burn the
shop down, for all I care. Paralleling contacts on switches or relays
is concidered bad engineering practice.


--
http://improve-usenet.org/index.html

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm

Sporadic E is the Earth's aluminum foil beanie for the 'global warming'
sheep.

That setup (one side of 240 line switched) is done all the time in the
internal wiring for a kitchen oven. I'm not defending it as the safest,
just that it is a common way to do it.

Doug Miller wrote:
In article , Bob Engelhardt wrote:
Doug Miller wrote:
Think this through a little farther. You don't have one wire carrying 240V as
you illustrated. You have two: L1 and L2.

Finish your drawing -- show where you're going to connect the L1 and L2 leads
to that switch.
Sigh:

/
L1 --- _________/ ___________
| / |
|__/ __|
240 LOAD

L2 --- _________________________

Sigh:

So L2 will always be supplying 120V to the load, even when the switch is off.

Does that sound safe, prudent, or wise to you?

A dutiful engineer doing suitable tests to investigate and provide
definitive answers to a less than completely constrained situation.

Go for it!!

Curt Welch wrote:
(Curt Welch) wrote:

I feel the need to go wire a few 15 amp switches in parallel and see what
type of current balance I actually get.....

Couldn't find any switches digging in the basement but I did a quick test
with a little different format just to see what would happen.

I used 4 wires to connect a standard 20 amp electrical outlet. 2 for the
hot, 2 for the neutral, and then wired those two together to create a
parallel power feed to the outlet. I used standard 12 gauge wire for all
paths. I plugged in a 100 W light to the outlet an measured the current
with a magnetic pick up style AC current meter.

The total current was around .81 amps, and the distribution in the two
parallel paths was around .31 amps and .48 amps or about 40% 60% balance of
current.

I suspect with the contacts of a 15 amp switch, the distribution could
easily be less balanced even with a new switch, and would only get worse
over time as one switch would no doubt wear down faster than the other.
But I don't have one handy to find out if this is true or not.

If you got a 40% 60% split like I did in my quick test, that would be 8.4
amps of your load in one contact and 12.6 amps in the other putting it well
within the 15 amp range of that switch. As long as it stayed that good or
better, it would be fine.

But this just demonstrates how parallel low resistance paths don't tend to
split the current evenly because the resistance is never very close to
equal.

People mentioned the idea of wiring relay contacts in parallel. That's
interesting and makes me wonder why they do it because it would be so hard
to balance the current when the contacts are closed. I wonder if it has
more to do with what happens as the circuit is opened and the contacts arc?
The current through two arcs might be better balanced because of the higher
resistance of the arcs and it might help reduce the spacing required to
break each arc?

Or maybe it's done just to improve relay life by creating redundancy? If
the contacts tend to degrade with age and their resistance increase the
redundant contacts will simply keep the circuit working longer because both
contacts will have to degrade to a high level before the relay will fail to
do its job? I doubt that current load balancing is the main reason for
wiring the contacts in parallel.