Our delema: Changed a 3 phase motor to a 4 hp single phase. Bought a
standard Unisaw switch for single phase, 220 volts. We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? And/or does a 4 hp motor
require a different breaker. We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. The wiring from breaker to socket
seems to be ok. When we plug the saw into the socket, the breaker
trips. The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

Sonny

On 5/18/2012 5:09 PM, Sonny wrote:
Our delema: Changed a 3 phase motor to a 4 hp single phase. Bought a
standard Unisaw switch for single phase, 220 volts. We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? And/or does a 4 hp motor
require a different breaker. We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. The wiring from breaker to socket
seems to be ok. When we plug the saw into the socket, the breaker
trips. The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

Sonny


I think you will need a starter for a 4 HP motor. Perhaps an
electrician will help out on this. If I recall, anything bigger than 1
/12- 2 HP needs a magnetic starter.

Here is some information:
http://www.emsco.net/faq.htm
http://www.southlandelectric.com/mot...hart_for_s.htm



--


___________________________________

Keep the whole world singing . . .
Dan G
remove the seven

On 5/18/2012 5:09 PM, Sonny wrote:
Our delema: Changed a 3 phase motor to a 4 hp single phase. Bought a
standard Unisaw switch for single phase, 220 volts. We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? And/or does a 4 hp motor
require a different breaker. We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. The wiring from breaker to socket
seems to be ok. When we plug the saw into the socket, the breaker
trips. The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

See if this helps:

http://media.ptg-online.com/media/dm...2-04-01-04.pdf

--
www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)
http://gplus.to/eWoodShop

In article ,
Sonny wrote:
Our delema: Changed a 3 phase motor to a 4 hp single phase. Bought a
standard Unisaw switch for single phase, 220 volts. We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? And/or does a 4 hp motor
require a different breaker. We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. The wiring from breaker to socket
seems to be ok. When we plug the saw into the socket, the breaker
trips. The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

If the breaker trips *immediately* when you plug the saw in, with the saw
switched _off_, you obviously have something wired VERY WRONG.

A 4hp single-phase motor on a 20A 220v circuit is 'iffy', at best.

The running power consumption is within the limits for a 'plug in' device
on a 20A circuit, but 'start-up' power draw is -much- higher.

A 30 A circuit, with 10 ga (minimum!!) wiring is recommended.

FURTHER, check the power rating _on_the_switch_. It should state the
maximum number of amps, _and_ the max. horsepower rating of a motor,
that it can be used to control. DO NOT EXCEED those ratings -- if you
do, the device may NOT TURN OFF when you turn the switch 'off'.

Thanks Dan. We probably should put a LVC on it, to be safe. I had
always understood an LVC was required for commercial use, but a
private saw didn't have to have one. I really don't know, though.
I've never had this problem.

I suspect this 4 ph mptor needs a larger breaker, like 40 amps.
Leeson motor, Cat# 120998.00, model - C145K34FB16D. This model motor
may be discontinued, as it is not listed on the Leeson website. There
is a model C145K34FB16E, though (same Cat#)..... only difference is
the last letter - D & E.

We were hoping to get this thing fixed and running today/this
weekend. We may have to wait until Monday, when electricians are
available, for help.

*Oh, no matter if the saw switch is turned on or off, with the saw
plugged into the socket and then the breaker is turned on, it trips.

Sonny

On May 18, 6:08*pm, (Robert Bonomi) wrote:
In article ,





Sonny wrote:
Our delema: *Changed a 3 phase motor to a 4 hp single phase. *Bought a
standard Unisaw switch for single phase, 220 volts. *We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? * And/or does a 4 hp motor
require a different breaker. *We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. *The wiring from breaker to socket
seems to be ok. *When we plug the saw into the socket, the breaker
trips. *The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

If the breaker trips *immediately* when you plug the saw in, with the saw
switched _off_, you obviously have something wired VERY WRONG.

A 4hp single-phase motor on a 20A 220v circuit is 'iffy', at best.

The running power consumption is within the limits for a 'plug in' device
on a 20A circuit, but 'start-up' power draw is -much- higher.

A 30 A circuit, with 10 ga (minimum!!) wiring is recommended.

FURTHER, check the power rating _on_the_switch_. *It should state the
maximum number of amps, _and_ the max. horsepower rating of a motor,
that it can be used to control. *DO NOT EXCEED those ratings -- if you
do, the device may NOT TURN OFF when you turn the switch 'off'.- Hide quoted text -

- Show quoted text -

Okay, our problem may, in part, be some of these issues.

We did read the switch load and compare it to the motor. It does
appear the switch may be too weak. I'll double check that tomorrow.

We did wire it with 12-2 wire, not 10 guage wire.

We probably wired it incorrectly, anyway. I think we need to call in
an expert. This is definitely not my or my friend's field.

On May 18, 6:07*pm, Swingman wrote:
On 5/18/2012 5:09 PM, Sonny wrote:





Our delema: *Changed a 3 phase motor to a 4 hp single phase. *Bought a
standard Unisaw switch for single phase, 220 volts. *We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? * And/or does a 4 hp motor
require a different breaker. *We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. *The wiring from breaker to socket
seems to be ok. *When we plug the saw into the socket, the breaker
trips. *The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

See if this helps:

http://media.ptg-online.com/media/dm...0331153155_En4...

--www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)http://gplus.to/eWoodShop- Hide quoted text -

- Show quoted text -


Thanks Karl. I glanced at that earlier. today. Those wiring diagrams
were Greek to me.

Too late, now, to mess with that, anyway. I've been invited to go eat
and watch the baseball game.

Sonny

Sonny wrote:
Thanks Dan. We probably should put a LVC on it, to be safe. I had
always understood an LVC was required for commercial use, but a
private saw didn't have to have one. I really don't know, though.
I've never had this problem.


What is this LVC you speak of?

I suspect this 4 ph mptor needs a larger breaker, like 40 amps.

No way. I have not done the math, but at first blush - 20A might be just
fine. Certainly NOT 40A.

Leeson motor, Cat# 120998.00, model - C145K34FB16D. This model motor
may be discontinued, as it is not listed on the Leeson website. There
is a model C145K34FB16E, though (same Cat#)..... only difference is
the last letter - D & E.

We were hoping to get this thing fixed and running today/this
weekend. We may have to wait until Monday, when electricians are
available, for help.

*Oh, no matter if the saw switch is turned on or off, with the saw
plugged into the socket and then the breaker is turned on, it trips.

You have wired your switch/motor wrong.

You should have two hots (black and red or black and white) and a ground
going to the outlet. Look at the wiring diagram in the motor to see which
terminals to hook to coming out of your switch. Your plug/wire should go to
the switch, and both legs should hit the switch. Then, from the switch, on
to the appropriate spades on the motor.

If you are tripping the breaker as soon as you plug it in, your wiring to
the switch is hosed.

--

-Mike-

Robert Bonomi wrote:


A 4hp single-phase motor on a 20A 220v circuit is 'iffy', at best.


I don't think so. It actually should be plenty of protection for a 4hp
motor.

The running power consumption is within the limits for a 'plug in'
device
on a 20A circuit, but 'start-up' power draw is -much- higher.

Not as much higher as people think. Unloaders greatly reduce the startup
power requirements.


A 30 A circuit, with 10 ga (minimum!!) wiring is recommended.


I believe that is overkill for a 4hp compressor.

--

-Mike-

Sonny wrote:


Okay, our problem may, in part, be some of these issues.

We did read the switch load and compare it to the motor. It does
appear the switch may be too weak. I'll double check that tomorrow.

We did wire it with 12-2 wire, not 10 guage wire.

That may not be a problem for you Sonny. Again - I have not verified this,
but I believe you are well within the capabilities of 12ga/20A.


We probably wired it incorrectly, anyway.

The fact that you trip the breaker immediately upon plugging it in,
regardless of the switch position is an absolute assurance that you wired it
wrong. That's where you have to focus.

I think we need to call in
an expert. This is definitely not my or my friend's field.

It's really not rocket science, but if it doesn't make sense to you, then
you're best to let someone else do the hook up for you. That way you simply
get to enjoy the tool.

--

-Mike-

On 5/18/2012 6:02 PM, Mike Marlow wrote:
Robert Bonomi wrote:


A 4hp single-phase motor on a 20A 220v circuit is 'iffy', at best.


I don't think so. It actually should be plenty of protection for a 4hp
motor.

The running power consumption is within the limits for a 'plug in'
device
on a 20A circuit, but 'start-up' power draw is -much- higher.

Not as much higher as people think. Unloaders greatly reduce the startup
power requirements.


A 30 A circuit, with 10 ga (minimum!!) wiring is recommended.


I believe that is overkill for a 4hp compressor.


It depends on the supply and the run. If the supply to the breaker
is "iffy" (too long and of inadequate size) and the distance from the
saw to the receptacle is "long", even #10 ain't gonna solve the problem.
(You probably know that but I thought I would make that clarification) ;-)

Max

On 5/18/2012 6:25 PM, Sonny wrote:
On May 18, 6:07 pm, wrote:
On 5/18/2012 5:09 PM, Sonny wrote:





Our delema: Changed a 3 phase motor to a 4 hp single phase. Bought a
standard Unisaw switch for single phase, 220 volts. We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? And/or does a 4 hp motor
require a different breaker. We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. The wiring from breaker to socket
seems to be ok. When we plug the saw into the socket, the breaker
trips. The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

See if this helps:

http://media.ptg-online.com/media/dm...0331153155_En4...

--www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)http://gplus.to/eWoodShop- Hide quoted text -

- Show quoted text -


Thanks Karl. I glanced at that earlier. today. Those wiring diagrams
were Greek to me.

Too late, now, to mess with that, anyway. I've been invited to go eat
and watch the baseball game.

LOL ... therein lies your problem.

IME, magnetic switches require a good deal of head scratching
understanding to install properly, and you normally must match the motor
size to the switch. First check out that the switch indeed corresponds
to motor size/horsepower ... Delta sells both a 3 HP and 6 HP Unisaw
and, while I'd bet those switches are NOT interchangeable, you might
want to DAGS that.

I agree, as Robert has indicated, that you would do well to consider a
40A circuit/#10 wire for this motor, as I believe you will find that 20A
will be marginal for the task, if not totally underpeckered.

I do know that, without doubt, a 220v/40A circuit is a requirement for
all 5 HP saws I've dealt with, and your close to that spec ... besides,
it won't hurt to run your 4hp motor on that higher amperage circuit in
any event.

--
www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)
http://gplus.to/eWoodShop

On 5/18/2012 8:54 PM, Swingman wrote:
On 5/18/2012 6:25 PM, Sonny wrote:
On May 18, 6:07 pm, wrote:
On 5/18/2012 5:09 PM, Sonny wrote:





Our delema: Changed a 3 phase motor to a 4 hp single phase. Bought a
standard Unisaw switch for single phase, 220 volts. We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? And/or does a 4 hp motor
require a different breaker. We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. The wiring from breaker to socket
seems to be ok. When we plug the saw into the socket, the breaker
trips. The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

See if this helps:

http://media.ptg-online.com/media/dm...0331153155_En4...

--www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)http://gplus.to/eWoodShop- Hide quoted
text -

- Show quoted text -


Thanks Karl. I glanced at that earlier. today. Those wiring diagrams
were Greek to me.

Too late, now, to mess with that, anyway. I've been invited to go eat
and watch the baseball game.

LOL ... therein lies your problem.

IME, magnetic switches require a good deal of head scratching
understanding to install properly, and you normally must match the motor
size to the switch. First check out that the switch indeed corresponds
to motor size/horsepower ... Delta sells both a 3 HP and 6 HP Unisaw

Typo ... "5" HP, NOT 6.


--
www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)
http://gplus.to/eWoodShop

Max wrote:


It depends on the supply and the run. If the supply to the breaker
is "iffy" (too long and of inadequate size) and the distance from the
saw to the receptacle is "long", even #10 ain't gonna solve the
problem. (You probably know that but I thought I would make that
clarification) ;-)

Yeahbut - one can go to any length with the Iffy stuff. If the power
company, if the, if the, if the. If the supply to the breaker is
inadequate, then the wire run to the device is not an issue. As far as the
run goes - you have to go a very long way to worry about that run.
Granted - it is a consideration at some point, but that is brought up here
way more than it really is a factor.


--

-Mike-

Swingman wrote:

I agree, as Robert has indicated, that you would do well to consider a
40A circuit/#10 wire for this motor, as I believe you will find that
20A will be marginal for the task, if not totally underpeckered.

#10 would be underpeckered for a 40A circuit as well.


I do know that, without doubt, a 220v/40A circuit is a requirement for
all 5 HP saws I've dealt with, and your close to that spec ...
besides, it won't hurt to run your 4hp motor on that higher amperage
circuit in any event.

That would be a couple of times the current draw of that motor. Who spec'd
that? 5HP doesn't come close to drawing 40A.

--

-Mike-

This saw, recently purchased used, is in my friends shop. The
subpanel to the shop is fed by a 60 amp breaker from his house panel,
75' away. The run from the saw to the subpanel is 30', at most, and
the saw's power cord is maybe 10' long. He impressed to me he knew
some wiring and we both thought we could manage this switch wiring,
but apparently not.

I had guessed, as to what size breaker was needed for a 4 hp motor,
interpolating from this link's chart, which doesn't have a breaker
size listed for a 4 hp motor.
http://www.groverelectric.com/howto/...c%20Motors.pdf
This chart's figures may be a generalization and, apparently (?), an
actual breaker size needed may be dependent on a variety of one's
individual circumstances, also.

I had tried Googling for help before asking here. At least we can
speak to the electrician with a bit more knowledge, now, than before,
too. I'll give an update when it's all figured out.

Sonny

Sonny wrote in
:


Okay, our problem may, in part, be some of these issues.

We did read the switch load and compare it to the motor. It does
appear the switch may be too weak. I'll double check that tomorrow.

We did wire it with 12-2 wire, not 10 guage wire.

We probably wired it incorrectly, anyway. I think we need to call in
an expert. This is definitely not my or my friend's field.

A friend of mine referred to calling in the professionals early as "keeping
the repair bill small." If you're not sure, call in the expert early so he
doesn't have to fix what you screwed up.

Puckdropper
--
Make it to fit, don't make it fit.

On Fri, 18 May 2012 16:16:47 -0700 (PDT), Sonny
wrote:

Thanks Dan. We probably should put a LVC on it, to be safe. I had
always understood an LVC was required for commercial use, but a
private saw didn't have to have one. I really don't know, though.
I've never had this problem.

I suspect this 4 ph mptor needs a larger breaker, like 40 amps.
Leeson motor, Cat# 120998.00, model - C145K34FB16D. This model motor
may be discontinued, as it is not listed on the Leeson website. There
is a model C145K34FB16E, though (same Cat#)..... only difference is
the last letter - D & E.

This particular Leeson is nameplated at 17.6A, but 4hp@230v gives a
nominal 12.8A draw. You might need to go to a heavier breaker, but I
doubt it. Then again, the engineering toolbox rule of thumb is 7 amps
per horse at single-phase 230v.


We were hoping to get this thing fixed and running today/this
weekend. We may have to wait until Monday, when electricians are
available, for help.

*Oh, no matter if the saw switch is turned on or off, with the saw
plugged into the socket and then the breaker is turned on, it trips.

You have -definitely- wired it incorrectly, Sonny. With the switch
off, it shouldn't EVER be able to blow the breaker.

Did you ground the saw and motor, then wire the two 120v phase leads
through the switch so -both- interrupt when it's off? It's a DPST (or
DPDT) switch, right?

Have you ohmed it out yet? That will show you where your trouble is
if you understand a VOM and the circuit.

--
The reasonable man adapts himself to the world; the unreasonable
one persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man.
-- George Bernard Shaw

You have -definitely- wired it incorrectly, Sonny. *With the switch
off, it shouldn't EVER be able to blow the breaker.

Yep, I am now sure we wired something wrong. But there may be
something else amiss....

Did you ground the saw and motor, then wire the two 120v phase leads
through the switch so -both- interrupt when it's off? *It's a DPST (or
DPDT) switch, right?

I didn't do the actual wiring, but Jonas was sure he had done so
correctly. He did comment that the wires may be positioned to make
the saw turn backwards, so that would be tested and reversed if need
be. Also, he thought maybe he had wired the "on" button as actually
"off", and 'off' to 'on', but said this shouldn't have made the
breaker trip.

Have you ohmed it out yet? *That will show you where your trouble is
if you understand a VOM and the circuit.

We have an ohm meter. I don't know how to operate an ohm meter, but
Jonas seems to know. I don't know what all Jonas may have ohmed or
why. I am confident in wiring a 220 outlet, but not a switch, as
this.

There may (unlikely?) be another reason for our problem. The motor
(discontinued model, maybe?) was recently purchased via Amazon, so it
is new. It came with a cord already wired into it, whether this cord
would go directly to the switch or to an LVC box, first. Since there
is no LVC box on the saw, Jonas ran this cord to the switch. If Jonas
did wire the switch correctly, then this motor's cord may be (the
unlikely aspect?) incorrectly wired inside the motor. He was
confident his wiring of the power cord (from the switch to the plug/
outlet) was correct. I don't know if he tested all of this with the
ohm meter.... at this stage of our unknowing, I was searching online
trying to troubleshoot the issue.

We may play with it again today. Yesterday, we spent most of the day
working on the whole of the saw, so some fatigue, late in the day, may
have played some role in whatever is screwed up. We may be a little
more clear-headed today. I vote to have an electrician check it out,
though.

This has been a good learning experience for me.
Sonny

On Sat, 19 May 2012 05:58:13 -0700 (PDT), Sonny
wrote:


You have -definitely- wired it incorrectly, Sonny. *With the switch
off, it shouldn't EVER be able to blow the breaker.

Yep, I am now sure we wired something wrong. But there may be
something else amiss....

Did you ground the saw and motor, then wire the two 120v phase leads
through the switch so -both- interrupt when it's off? *It's a DPST (or
DPDT) switch, right?

I didn't do the actual wiring, but Jonas was sure he had done so
correctly. He did comment that the wires may be positioned to make
the saw turn backwards, so that would be tested and reversed if need
be. Also, he thought maybe he had wired the "on" button as actually
"off", and 'off' to 'on', but said this shouldn't have made the
breaker trip.

Are you certain it's a single-phase motor, not 3-phase?


Have you ohmed it out yet? *That will show you where your trouble is
if you understand a VOM and the circuit.

We have an ohm meter. I don't know how to operate an ohm meter, but
Jonas seems to know. I don't know what all Jonas may have ohmed or
why. I am confident in wiring a 220 outlet, but not a switch, as
this.

If I didn't know how to use a VOM, I wouldn't feel comfortable wiring
anything, be it switch, outlet, or motor. It's a very good time to
learn how to read and use one, Sonny. It could save your life.


There may (unlikely?) be another reason for our problem. The motor
(discontinued model, maybe?) was recently purchased via Amazon, so it
is new. It came with a cord already wired into it, whether this cord
would go directly to the switch or to an LVC box, first. Since there
is no LVC box on the saw, Jonas ran this cord to the switch. If Jonas
did wire the switch correctly, then this motor's cord may be (the
unlikely aspect?) incorrectly wired inside the motor. He was
confident his wiring of the power cord (from the switch to the plug/
outlet) was correct. I don't know if he tested all of this with the
ohm meter.... at this stage of our unknowing, I was searching online
trying to troubleshoot the issue.

He should have opened the little cover to see exactly how the motor
was wired. I hope you find an electrician. The stuff you two are
toying with can kill ya.


We may play with it again today. Yesterday, we spent most of the day
working on the whole of the saw, so some fatigue, late in the day, may
have played some role in whatever is screwed up. We may be a little
more clear-headed today. I vote to have an electrician check it out,
though.

Excellent idea. Dead shorts which blow 40A of breaker are dangerous.


This has been a good learning experience for me.

Good. Keep learning and stay very careful, please.

--
The reasonable man adapts himself to the world; the unreasonable
one persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man.
-- George Bernard Shaw

In article ,
Mike Marlow wrote:
Robert Bonomi wrote:


A 4hp single-phase motor on a 20A 220v circuit is 'iffy', at best.


I don't think so. It actually should be plenty of protection for a 4hp
motor.

And you don't know the NEC. grin

The OP has since posted that the moter is plated at 17.6 A.

For 'plug' items, you are limited, by NEC to 80% of the breaker
capacity. 80% of 20A is 16A. 17.6 A definitely exceeds the 'legal'
limit.

The running power consumption is within the limits for a 'plug in'
device
on a 20A circuit, but 'start-up' power draw is -much- higher.

Not as much higher as people think. Unloaders greatly reduce the startup
power requirements.

An 'unloader' on a _table_saw_?? *snort*

I've measured transient start-up current draw of motors, under no load, at
well over 2x the rated 'full load" draw.

A 30 A circuit, with 10 ga (minimum!!) wiring is recommended.

I believe that is overkill for a 4hp compressor.

Your 'belief' doesn't change the reality of the situation.

First off, we're not dealing with a compressor.

Second, you admit you haven't done the math. You should have. Using
'real world' efficiency numbers, not 'theoretical' 100% efficiency
conversions. For a 'plug in' device, the 'legal limit' on a 20 A circuit
is 3-3.5 HP.

Lastly, 12 ga _is_ sufficient for the load, BARELY. Running the saw as a
'plug in' device requires _more_ than a 20 A breaker, however -- because it
has a 'plate' draw that is more than the allowable 80% of the breaker rating.
The next larger standard breaker is a 30A one. Or you can pay through
the nose for a 25 A one. Either way, you have to upgrade to 10 ga wiring
though -- because 12 ga, in conduit, is not rated for even 25A. And the
wiring must be of a size sufficient for the rated breaker ampacity.

Now, if this was a 'permanently wired' device, you'd be 'legal' with
12 ga wiring on a 20 A breaker. BUT, the start-up draw would still be
a potential issue. It depends tremendously on the 'small overload'
characteristics of the breaker -- how quickly it trips at what level
over rated ampacity.

On 5/18/2012 9:56 PM, Sonny wrote:
This saw, recently purchased used, is in my friends shop. The
subpanel to the shop is fed by a 60 amp breaker from his house panel,
75' away. The run from the saw to the subpanel is 30', at most, and
the saw's power cord is maybe 10' long. He impressed to me he knew
some wiring and we both thought we could manage this switch wiring,
but apparently not.

I had guessed, as to what size breaker was needed for a 4 hp motor,
interpolating from this link's chart, which doesn't have a breaker
size listed for a 4 hp motor.
http://www.groverelectric.com/howto/...c%20Motors.pdf
This chart's figures may be a generalization and, apparently (?), an
actual breaker size needed may be dependent on a variety of one's
individual circumstances, also.

I had tried Googling for help before asking here. At least we can
speak to the electrician with a bit more knowledge, now, than before,
too. I'll give an update when it's all figured out.

Be careful because IME you're getting some bad information above on the
two components for a motor circuit: the ampacity of the branch circuit,
and wire size of that branch circuit.

This is not a cut and dried situation when you take into account a motor
with a starter and thermal overload protection on a branch circuit that
will most likely be classed as "continuous duty" by any inspector that
comes along, which an electrician, or anyone else doing the work, is
going to have to take into account to size the circuit properly (and in
many cases, I wouldn't even bet that a journeyman electrician is going
to be up to speed on the many issues and requirements)

In short, just be aware that motor calculations are very different than
other types of loads ... you can't just look at the Amp on the motor
nameplate and look it up in table to determine the correct branch
circuit wiring, which is pretty obviously the basis of the advice you've
received thus far on the issue.

--
www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)
http://gplus.to/eWoodShop

As long as he has the wiring in the saw and wall to support 40A.

If not 40A won't trip before there is a serious problem.

On 5/18/2012 9:54 PM, Swingman wrote:
On 5/18/2012 6:25 PM, Sonny wrote:
On May 18, 6:07 pm, wrote:
On 5/18/2012 5:09 PM, Sonny wrote:





Our delema: Changed a 3 phase motor to a 4 hp single phase. Bought a
standard Unisaw switch for single phase, 220 volts. We either have
something wired wrong or the 4 hp motor requires a different switch.
Too late to call out an electrician for help.

Do 4 hp motors require a different switch? And/or does a 4 hp motor
require a different breaker. We have a 20 amp breaker.

Otherwise, I think we wired the switch wrong.

There is no LVC box on this saw. The wiring from breaker to socket
seems to be ok. When we plug the saw into the socket, the breaker
trips. The motor came wired, but not to the switch, since there was
no switch.

Any comments are welcome.

See if this helps:

http://media.ptg-online.com/media/dm...0331153155_En4...

--www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)http://gplus.to/eWoodShop- Hide quoted
text -

- Show quoted text -


Thanks Karl. I glanced at that earlier. today. Those wiring diagrams
were Greek to me.

Too late, now, to mess with that, anyway. I've been invited to go eat
and watch the baseball game.

LOL ... therein lies your problem.

IME, magnetic switches require a good deal of head scratching
understanding to install properly, and you normally must match the motor
size to the switch. First check out that the switch indeed corresponds
to motor size/horsepower ... Delta sells both a 3 HP and 6 HP Unisaw
and, while I'd bet those switches are NOT interchangeable, you might
want to DAGS that.

I agree, as Robert has indicated, that you would do well to consider a
40A circuit/#10 wire for this motor, as I believe you will find that 20A
will be marginal for the task, if not totally underpeckered.

I do know that, without doubt, a 220v/40A circuit is a requirement for
all 5 HP saws I've dealt with, and your close to that spec ... besides,
it won't hurt to run your 4hp motor on that higher amperage circuit in
any event.

On 5/19/2012 9:37 AM, tiredofspam wrote:

As long as he has the wiring in the saw and wall to support 40A.

If not 40A won't trip before there is a serious problem.

A "serious problem" where"?

_If_ pigs had wings - (for a dedicated motor circuit you will find that
you can indeed run higher breaker sizes for a specified wire size ...
the motor is considered to have its own thermal protection, so the c'bkr
will be dealing with a 'short to ground' fault with be a very high current)

Remember, the c'brk is there to protect the wiring, not the equipment.

And, the motor used in a table saw generally has its own thermal
protection, which guarantees any thermal overload protection from a
c'bkr to be a moot point.

On 5/18/2012 9:54 PM, Swingman wrote:

I do know that, without doubt, a 220v/40A circuit is a requirement for
all 5 HP saws I've dealt with, and your close to that spec ... besides,
it won't hurt to run your 4hp motor on that higher amperage circuit in
any event.

If this was not what you're talking about, chalk it up to being another
problem with top posting ... making it damned difficult to tell what
you're taking exception to.

--
www.eWoodShop.com
Last update: 4/15/2010
KarlCaillouet@ (the obvious)
http://gplus.to/eWoodShop

Robert Bonomi wrote:
In article ,
Mike Marlow wrote:
Robert Bonomi wrote:


A 4hp single-phase motor on a 20A 220v circuit is 'iffy', at best.


I don't think so. It actually should be plenty of protection for a 4hp
motor.

And you don't know the NEC. grin

The OP has since posted that the moter is plated at 17.6 A.

For 'plug' items, you are limited, by NEC to 80% of the breaker
capacity. 80% of 20A is 16A. 17.6 A definitely exceeds the 'legal'
limit.

The running power consumption is within the limits for a 'plug in'
device
on a 20A circuit, but 'start-up' power draw is -much- higher.

Not as much higher as people think. Unloaders greatly reduce the startup
power requirements.

An 'unloader' on a _table_saw_?? *snort*

I've measured transient start-up current draw of motors, under no load, at
well over 2x the rated 'full load" draw.

A 30 A circuit, with 10 ga (minimum!!) wiring is recommended.

I believe that is overkill for a 4hp compressor.

Your 'belief' doesn't change the reality of the situation.

First off, we're not dealing with a compressor.

Second, you admit you haven't done the math. You should have. Using
'real world' efficiency numbers, not 'theoretical' 100% efficiency
conversions. For a 'plug in' device, the 'legal limit' on a 20 A circuit
is 3-3.5 HP.

Lastly, 12 ga _is_ sufficient for the load, BARELY. Running the saw as a
'plug in' device requires _more_ than a 20 A breaker, however -- because it
has a 'plate' draw that is more than the allowable 80% of the breaker rating.
The next larger standard breaker is a 30A one. Or you can pay through
the nose for a 25 A one. Either way, you have to upgrade to 10 ga wiring
though -- because 12 ga, in conduit, is not rated for even 25A. And the
wiring must be of a size sufficient for the rated breaker ampacity.

Although there are additional considerations, the above is much more
practical advice ... advice that actually reflects many of the realities of
the issues involved.

--
www.ewoodshop.com

Robert Bonomi wrote:
In article ,
Mike Marlow wrote:
Robert Bonomi wrote:


A 4hp single-phase motor on a 20A 220v circuit is 'iffy', at best.


I don't think so. It actually should be plenty of protection for a
4hp motor.

And you don't know the NEC. grin

The OP has since posted that the moter is plated at 17.6 A.

For 'plug' items, you are limited, by NEC to 80% of the breaker
capacity. 80% of 20A is 16A. 17.6 A definitely exceeds the 'legal'
limit.


Yes it does. I'm glad I did not omit that part that said I had not done the
math. Knee jerk on my behalf was that 4hp would be covered by a 20 amp
breaker. It's not so far away - though admitedly, it is over the spec for a
20 plug device. At the time I replied, I don't believe that Sonny had
posted the plate information. Kind of hard to act on that information if
it's not made available. If he had posted it at or before the time I
replied - then I missed that.




An 'unloader' on a _table_saw_?? *snort*

Caught dead to rights. I have no freakin' idea how I got compressors in my
mind. I'd blame it on drinking, but I can't...



--

-Mike-

(Robert Bonomi) wrote in news:0JydnQuWB-
xcommunications:

And you don't know the NEC. grin

Apparently, you don't know it as well as you think you do.

The OP has since posted that the moter is plated at 17.6 A.

For 'plug' items, you are limited, by NEC to 80% of the breaker
capacity.

No, you are not. The 80% limit applies only to "continuous loads", which is defined in the Code
as "a load where the maximum current is expected to continue for 3 hours or more."