Fuses in place of motor "heaters"? (induction motor protection)

[DaveC]

Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that doesn't
include use of a contactor. I appreciate the need for precise current limit
(LRA) that a branch breaker can't provide.

So, I choose to not have a contactor but instead, this, which provides the
power-fail protection:

http://www.amazon.com/Woodstock-D4160-110-Volt-Paddle-
Switch/dp/B005W17HYY/ref=pd_sim_hi_1/191-4569239-2528519

This has a relay (rated 1/2 hp) that drops out on power fail, and has
external connections for additional e-stop mushroom switch. But no provision
for motor protection.

Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be
sufficient to protect this motor?

Thanks.

[Mike Marlow]

Look at that switch again - it's a 110v switch, not a 220v switch. Hate to
see you order the wrong one. You could fuse the circuit behind the switch
but you'd have no way to ensure that both legs will drop out at the same
time the way that a breaker does. You would not want to find yourself in a
situation where one leg drops out but the other does not.

What is the application for this motor that requires so much more precision
than the circuit protection that a breaker would provide?

--

-Mike-
mmarlo...@windstream.net

[Jim Wilkins]

"DaveC" <inv...@invalid.net> wrote in message
news:0001HW.CF08B756...@news.eternal-september.org...

Why do you need two fuses for a single-phase motor?

Do you know the motor's actual i-squared-t overcurrent limit
requirement?

http://www.copleycontrols.com/motion/pdf/IsqT.pdf

When I ran a lab at Mitre an engineer kept asking me to buy him more
and more Polaroid film for his scope camera. I finally asked him why
and found that he was trying to discover the principles of how a fuse
blows. He looked really sheepish and subdued when I handed him a
Littelfuse pamphlet of current vs time curves.
http://www.littelfuse.com/~/media/files/littelfuse/technical%20resources/documents/product%20catalogs/autofuseology.pdf

jsw

[Mike Marlow]

Jim Wilkins wrote:

>
> Why do you need two fuses for a single-phase motor?
>

He's running single phase 220v Jim.


--

-Mike-
mmarlo...@windstream.net

[William Sommerwerck]

"Jim Wilkins" wrote in message news:lc0deb$mat$1...@dont-email.me...

> When I ran a lab at Mitre an engineer kept asking me to buy him more and
> more Polaroid film for his scope camera. I finally asked him why and found
> that he was trying to discover the principles of how a fuse blows. He looked
> really sheepish and subdued when I handed him a Littelfuse pamphlet of
> current vs time curves.
http://www.littelfuse.com/~/media/files/littelfuse/technical%20resources/documents/product%20catalogs/autofuseology.pdf

When I worked one Summer at Bell Labs, one of the engineers told me he was
trying to figure out how much detail the eye could see in color. What he
didn't know (and I'd forgotten that I knew) was that this information was part
of the design of the NTSC system.

[Jim Wilkins]

"William Sommerwerck" <grizzle...@comcast.net> wrote in message
news:lc0ev7$u8p$1...@dont-email.me...

As a chemistry student I was expected to learn a lot of practical
detail and hands-on procedure that I later noticed new electrical (and
some mechanical) engineers often lacked.
jsw

[Jasen Betts]

qOn 2014-01-25, Jim Wilkins <murat...@gmail.com> wrote:
> "DaveC" <inv...@invalid.net> wrote in message

> Why do you need two fuses for a single-phase motor?

because it's got two live inputs, and either could develop a short to ground.


--
For a good time: install ntp

--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---

[Jim Wilkins]

"Jasen Betts" <ja...@xnet.co.nz> wrote in message
news:lc1923$74k$1...@gonzo.reversiblemaps.ath.cx...

> qOn 2014-01-25, Jim Wilkins <murat...@gmail.com> wrote:
>> "DaveC" <inv...@invalid.net> wrote in message
>
>> Why do you need two fuses for a single-phase motor?
>
> because it's got two live inputs, and either could develop a short
> to ground.

> For a good time: install ntp
> --- news://freenews.netfront.net/ - complaints:
> ne...@netfront.net ---

The panel circuit breakers protect the wiring from that. The separate
fusing is for a motor overload condition.

[Ignoramus8074]

On 2014-01-25, Jim Wilkins <murat...@gmail.com> wrote:
> "Jasen Betts" <ja...@xnet.co.nz> wrote in message

>> qOn 2014-01-25, Jim Wilkins <murat...@gmail.com> wrote:
>>> "DaveC" <inv...@invalid.net> wrote in message
>>> Why do you need two fuses for a single-phase motor?
>> because it's got two live inputs, and either could develop a short
>> to ground.
>

> The panel circuit breakers protect the wiring from that. The
> separate fusing is for a motor overload condition.

Fuses ARE heaters. They have thermal action and the slow ones are
meant for motors. I would say that fuses are "overload heaters for the
poor".

I spent some effort when replacnig electricals on my three phase
bandsaw, and finally found a contactor with the exact heaters that the
motor needed. Very happy about it.

i

[Phil Allison]

"Jim Wilkins"

>
> Why do you need two fuses for a single-phase motor?

** Cos the AC supply is two phase.

The OP is an American.

They have spit phase power where 240VAC is split into a pair of 120V lines
with a common neutral.

While 120V appliances use one or the other, some ( usually high powered )
ones are rated at 220 /240 and connect across the pair.


..... Phil

[DoN. Nichols]

On 2014-01-25, Jim Wilkins <murat...@gmail.com> wrote:

> "DaveC" <inv...@invalid.net> wrote in message
> news:0001HW.CF08B756...@news.eternal-september.org...
>> Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that
>> doesn't
>> include use of a contactor. I appreciate the need for precise
>> current limit
>> (LRA) that a branch breaker can't provide.

[ ... ]

>> Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses
>> be
>> sufficient to protect this motor?
>>
>> Thanks.
>
> Why do you need two fuses for a single-phase motor?

In the UK, you don't, because 240 VAC comes with one side
grounded. However, in the USA, 240 VAC is normally supplied with a
grounded center tap, so if you have only one fuse -- or have two but
only one blows, you still have 120 VAC live in the motor's housing, and
potentially available for contact and personal zapping. :-)

> Do you know the motor's actual i-squared-t overcurrent limit
> requirement?
>
> http://www.copleycontrols.com/motion/pdf/IsqT.pdf
>
> When I ran a lab at Mitre an engineer kept asking me to buy him more
> and more Polaroid film for his scope camera. I finally asked him why
> and found that he was trying to discover the principles of how a fuse
> blows. He looked really sheepish and subdued when I handed him a
> Littelfuse pamphlet of current vs time curves.

:-)

> http://www.littelfuse.com/~/media/files/littelfuse/technical%20resources/documents/product%20catalogs/autofuseology.pdf

And I'm not sure why he feels the need for precision current
limiting on the motor. Most motors will handle a fairly wide range of
time vs overcurrent exposures. (An exception is a permanent magnet DC
servo motor which can be partially demagnetized by a sort spike over the
rated current limit.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: <BPdnic...@d-and-d.com> | (KV4PH) Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

[bud--]

On 1/25/2014 7:10 AM, Mike Marlow wrote:
> DaveC wrote:
>> Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that
>> doesn't include use of a contactor. I appreciate the need for precise
>> current limit (LRA) that a branch breaker can't provide.
>>
>> So, I choose to not have a contactor but instead, this, which
>> provides the power-fail protection:
>>
>> http://www.amazon.com/Woodstock-D4160-110-Volt-Paddle-
>> Switch/dp/B005W17HYY/ref=pd_sim_hi_1/191-4569239-2528519
>>
>> This has a relay (rated 1/2 hp) that drops out on power fail, and has
>> external connections for additional e-stop mushroom switch. But no
>> provision for motor protection.
>>
>> Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be
>> sufficient to protect this motor?

May or may not, depending on the fuse characteristics. The fuse has to
be slow-blow enough to not open when the motor starts (starting current
is about 6x running current). But it has to open within the i-squared-t
rating of the motor (as in Jim's post).

The "overloads" in motor starters are matched to motor starting. And the
settings in are much finer steps (or are continuous) compared to fuses.

Many 1/2HP motors have internal overload protection ("thermally protected").

>
> Look at that switch again - it's a 110v switch, not a 220v switch. Hate to
> see you order the wrong one. You could fuse the circuit behind the switch
> but you'd have no way to ensure that both legs will drop out at the same
> time the way that a breaker does. You would not want to find yourself in a
> situation where one leg drops out but the other does not.

In the US, using the NEC, fuses are allowed. And a "controller" only has
to open one of the supply wires. (You are right about the 110V rating on
the amazon switch.) A "disconnect" has to open all the live supply
conductors.

>
> What is the application for this motor that requires so much more precision
> than the circuit protection that a breaker would provide?
>

Application is important. But a breaker provides little overload
protection for a motor. For a hard-wired motor circuit (like central air
conditioning) the breaker does not usually provide overload protection
(that is provided at the motor). The breaker can be significantly larger
than the rating of the wires, and provides short circuit protection. A
breaker is large so it does not trip on the motor starting current.

[Phil Allison]

"bud--"

> May or may not, depending on the fuse characteristics. The fuse has to be
> slow-blow enough to not open when the motor starts (starting current is
> about 6x running current). But it has to open within the i-squared-t
> rating of the motor (as in Jim's post).

** Think you will have poor luck with a HRC fuse taking 6 time rated every
time the motor starts or stalls and not nuisance blowing.

A "motor start" circuit breaker is what is normally used.

Slow, thermal characteristic at up to 6 times and then a very fast magnetic
action at about 10 times.



.... Phil

[Jim Wilkins]

"DoN. Nichols" <BPdnic...@d-and-d.com> wrote in message
news:slrnle97cu.5k...@Katana.d-and-d.com...

> On 2014-01-25, Jim Wilkins <murat...@gmail.com> wrote:
>>
>> Why do you need two fuses for a single-phase motor?
>
> In the UK, you don't, because 240 VAC comes with one side
> grounded. However, in the USA, 240 VAC is normally supplied with a
> grounded center tap, so if you have only one fuse -- or have two but
> only one blows, you still have 120 VAC live in the motor's housing,
> and
> potentially available for contact and personal zapping. :-)
>

I assumed it was wired with a 20A double-pole breaker at the panel
protecting from shorts and a smaller fuse sized (how?) to blow before
the motor burned out.

jsw

[Bob Engelhardt]

On 1/26/2014 2:18 AM, bud-- wrote:
> ... The breaker can be significantly larger

> than the rating of the wires, and provides short circuit protection.

...

I don't think so! The breaker is there to protect the wires. If there
is a load on the circuit greater than what the wires can handle, the
breaker opens. You do not want the wires overheating and it doesn't
take a short to do it.

Bob

[bud--]

On 1/26/2014 1:47 AM, Phil Allison wrote:
> "bud--"
>
>> May or may not, depending on the fuse characteristics. The fuse has to be
>> slow-blow enough to not open when the motor starts (starting current is
>> about 6x running current). But it has to open within the i-squared-t
>> rating of the motor (as in Jim's post).
>
> ** Think you will have poor luck with a HRC fuse taking 6 time rated every
> time the motor starts or stalls and not nuisance blowing.

Fuses are not usually used for motor overload protection in the US.
There aren't enough fuse ratings to match to the motor running current
except for relatively small motors.

>
> A "motor start" circuit breaker is what is normally used.
>
> Slow, thermal characteristic at up to 6 times and then a very fast magnetic
> action at about 10 times.
>
>
>
> .... Phil

Time delay breakers can be up to 175% of the motor running current in
the US. They often are used for short circuit protection of a motor
circuit, but not for overload protection. There are even fewer sizes of
breakers than fuses.

[bud--]

Under the US NEC the wires have to be 115% of the motor run current. A
time delay breaker can be 175% of the motor run current. (Breakers that
don't have a time delay can be even larger.) As stated, for a motor
circuit, the breaker provides _short circuit protection_. Breakers can
be large so they don't trip on normal motor starts. (I have seen an
example for something like a 1/2HP motor where the breaker was twice the
wire rating.)

_Overload protection_ is usually at the motor (at the load end of the
circuit). One common method is a motor starter with an 'overload' unit
that is closely matched to the run current. Another is an internal
thermal protector that disconnects the motor when it overheats. An
internal thermal protector may be wired to drop out a motor starter.


For welder circuits, the breaker can be even larger with respect to the
wire rating. That can happen if the welder has a low "duty cycle".

[Bob Engelhardt]

On 1/26/2014 12:15 PM, bud-- wrote:
> On 1/26/2014 9:27 AM, Bob Engelhardt wrote:
>> On 1/26/2014 2:18 AM, bud-- wrote:
>> > ... The breaker can be significantly larger
>> > than the rating of the wires, and provides short circuit protection.
>> ...
>>

>> I don't think so! The breaker is there to protect the wires. ...

> ... for a motor circuit, ...

Ah ... my mindset was residential branch circuit.

[Maynard A. Philbrook Jr.]

In article <lc45c...@news6.newsguy.com>, BobEng...@comcast.net
says...

For readers that are not acquainted with the term "Motor Heaters"
in the subject line, this could be confusing..

Heaters in this context is referred to as the overload protection
device that drives the motor. Heater coils surround the release latches
and when they get hot enough, will allow the protection to activate.

These heater elements are electrically in series with each phase going
to the motor.

Inrush currents for non inverter driven AC motors when starting can be
quite high and the slow response from the heaters for the latches allow
for a delay trip.

It's customary to select the proper heater element so that it's close
to the full load amps of the motor. This way after a short period from
start up the coils will then remain warm and not too far from the trip
point. This means the motor should trip the overload quickly
if it experiences an excessive short inrush problem.

Have a good f'ing day

Jamie

[Phil Allison]

"bud--"

> Phil Allison wrote:
>> "bud--"
>>
>>> May or may not, depending on the fuse characteristics. The fuse has to
>>> be
>>> slow-blow enough to not open when the motor starts (starting current is
>>> about 6x running current). But it has to open within the i-squared-t
>>> rating of the motor (as in Jim's post).
>>
>> ** Think you will have poor luck with a HRC fuse taking 6 time rated
>> every
>> time the motor starts or stalls and not nuisance blowing.
>
> Fuses are not usually used for motor overload protection in the US. There
> aren't enough fuse ratings to match to the motor running current except
> for relatively small motors.
>
>>
>> A "motor start" circuit breaker is what is normally used.
>>
>> Slow, thermal characteristic at up to 6 times and then a very fast
>> magnetic
>> action at about 10 times.
>>
>>

> Time delay breakers can be up to 175% of the motor running current in the
> US.

** Blah, blah, blah...

> They often are used for short circuit protection of a motor circuit, but
> not for overload protection.

** Horse manure !!!!!!!!!!

Overload protection is EXACTLY what circuit breakers are there for.

You cab size them to protect a stalled or overloaded motor or just the
supply cables.



.... Phil

[DoN. Nichols]

On 2014-01-26, bud-- <nu...@void.com> wrote:
> On 1/25/2014 7:10 AM, Mike Marlow wrote:
>> DaveC wrote:
>>> Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that
>>> doesn't include use of a contactor. I appreciate the need for precise
>>> current limit (LRA) that a branch breaker can't provide.

[ ... ]

>>> Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be
>>> sufficient to protect this motor?

To the 1/4 A out of what rating? 1/4 A out of a 1/4 A fuse is
a pretty big error. 1/4 A out of a 50 A fuse is a lot less.

In other words, what kind of percentage? And the curves for
fuses don't say *when* it will blow, they simply say that it must
tolerate full load amps for N hours, and for each increment above that,
they have to blow within a certain time. They can be quicker, but not
slower.

How are you going to find fuses that precisely matched? You
can't really *know* that they are that precisely matched until you have
tested them -- by which time they are now blown, and thus useless,
except perhaps as a poor insulator. :-)

> May or may not, depending on the fuse characteristics. The fuse has to
> be slow-blow enough to not open when the motor starts (starting current
> is about 6x running current). But it has to open within the i-squared-t
> rating of the motor (as in Jim's post).
>
> The "overloads" in motor starters are matched to motor starting. And the
> settings in are much finer steps (or are continuous) compared to fuses.
>
> Many 1/2HP motors have internal overload protection ("thermally protected").

Some of those are thermal fuses (cooked off by the heat in the
windings) buried in the windings. When that goes, you can't access it
to replace it -- except by re-winding the motor. They don't re-set on
their own.

[bud--]

The step between circuit breaker ratings is far too large to provide
overload protection for motors. What I described is exactly what is in
the US NEC and what practice is in the US.

Must be another alwayswrong sock puppet.

[Phil Allison]

"boob = bullshit artist "

>>
> Phil Allison wrote:

>>
>>>>
>>>> A "motor start" circuit breaker is what is normally used.
>>>>
>>>> Slow, thermal characteristic at up to 6 times and then a very fast
>>>> magnetic action at about 10 times.
>>>>
>>>>
>>> Time delay breakers can be up to 175% of the motor running current in
>>> the
>>> US.
>>
>> ** Blah, blah, blah...
>>
>>> They often are used for short circuit protection of a motor circuit, but
>>> not for overload protection.
>>
>> ** Horse manure !!!!!!!!!!
>>
>> Overload protection is EXACTLY what circuit breakers are there for.
>>
>> You cab size them to protect a stalled or overloaded motor or just the
>> supply cables.
>>
>
> The step between circuit breaker ratings is far too large to provide
> overload protection for motors.

** FFS - asshole try LEARNING TO READ

Thermal breakers come in any almost size you like and you fit them between
the AC outlet and the load.

Thermal/ magnetic breakers are not simply for "short circuit protection".

They provide cable overload ( overtemp) protection.

Fucking moron.


.... Phil

[bud--]

On 1/27/2014 4:58 PM, Phil Allison wrote:
> "boob = bullshit artist"
>>>
>> Phil Allison wrote:
>
>>>
>>>>>
>>>>> A "motor start" circuit breaker is what is normally used.
>>>>>
>>>>> Slow, thermal characteristic at up to 6 times and then a very fast
>>>>> magnetic action at about 10 times.
>>>>>
>>>>>
>>>> Time delay breakers can be up to 175% of the motor running current in
>>>> the
>>>> US.
>>>
>>> ** Blah, blah, blah...
>>>
>>>> They often are used for short circuit protection of a motor circuit, but
>>>> not for overload protection.
>>>
>>> ** Horse manure !!!!!!!!!!
>>>
>>> Overload protection is EXACTLY what circuit breakers are there for.
>>>
>>> You cab size them to protect a stalled or overloaded motor or just the
>>> supply cables.
>>>
>>
>> The step between circuit breaker ratings is far too large to provide
>> overload protection for motors.
>
> ** FFS - asshole try LEARNING TO READ

Perhaps you could read. US NEC sizes breakers up to 175% of motor run
current. Wire is 115% of motor run current.

>
> Thermal breakers come in any almost size you like and you fit them between
> the AC outlet and the load.

What breaker would you use for overload protection for a motor with a
run current of 16.3A. Breaker must be UL listed, able to withstand motor
starting currents, and suitable for use as motor protection.

>
> Thermal/ magnetic breakers are not simply for "short circuit protection".
>
> They provide cable overload ( overtemp) protection.

Not in the US NEC. And not the practice in the US.

>
> Fucking moron.

You have such compelling arguments.

[Phil Allison]

"boob = bullshit artist"

>>>>> They often are used for short circuit protection of a motor circuit,
>>>>> but
>>>>> not for overload protection.
>>>>
>>>> ** Horse manure !!!!!!!!!!
>>>>
>>>> Overload protection is EXACTLY what circuit breakers are there for.
>>>>
>>>> You cab size them to protect a stalled or overloaded motor or just the
>>>> supply cables.
>>>>
>>>
>>> The step between circuit breaker ratings is far too large to provide
>>> overload protection for motors.
>>
>> ** FFS - asshole try LEARNING TO READ
>>

>> Thermal breakers come in any almost size you like and you fit them
>> between
>> the AC outlet and the load.
>

>> Thermal/ magnetic breakers are not simply for "short circuit protection".
>>
>> They provide cable overload ( overtemp) protection.
>
> Not in the US NEC. And not the practice in the US.

** You are one stupid, lying ass.

WTF do you think AC supply circuit breakers are fucking for?
--------------------------------------------------------------------

> You have such compelling arguments.

** While you have posted NONE at ALL !!!!!!!!

Fuck off - you crazy fucking nut case.



.... Phil

[bud--]

On 1/28/2014 5:41 PM, Phil Allison wrote:
> "boob = bullshit artist"
>
>>>>>> They often are used for short circuit protection of a motor circuit,
>>>>>> but
>>>>>> not for overload protection.
>>>>>
>>>>> ** Horse manure !!!!!!!!!!
>>>>>
>>>>> Overload protection is EXACTLY what circuit breakers are there for.
>>>>>
>>>>> You cab size them to protect a stalled or overloaded motor or just the
>>>>> supply cables.
>>>>>
>>>>
>>>> The step between circuit breaker ratings is far too large to provide
>>>> overload protection for motors.
>>>
>>> ** FFS - asshole try LEARNING TO READ
>>>
>>> Thermal breakers come in any almost size you like and you fit them
>>> between
>>> the AC outlet and the load.
>>
>>> Thermal/ magnetic breakers are not simply for "short circuit protection".
>>> They provide cable overload ( overtemp) protection.
>>
>> Not in the US NEC. And not the practice in the US.
>
> ** You are one stupid, lying ass.

More of the famous Allison logic.

>
> WTF do you think AC supply circuit breakers are fucking for?

You forgot to to answer the question. Maybe because you deleted it.
"What [AC supply circuit] breaker would you use for overload protection

for a motor with a run current of 16.3A. Breaker must be UL listed, able
to withstand motor starting currents, and suitable for use as motor
protection."

That should be a trivial you.

>
>> You have such compelling arguments.
>
>
> ** While you have posted NONE at ALL !!!!!!!!

Only if you can't read !!!!!!!!

>
> Fuck off - you crazy fucking nut case.

Does you mommy approve of your language?

[Michael A. Terrell]

bud-- wrote:
>
> Must be another alwayswrong sock puppet.

No, this is a different character. A psychotic Aussie.

[gregz]

Fred Abse <excret...@invalid.invalid> wrote:

> Panel breakers are there to protect the upstream wiring from excessive
> load current, not to protect the load.
>
> Matching the I-squared-t of a breaker, or fuse, to startup and running
> conditions of a motor is not trivial. Motors are subject to starting
> inrush currents sometimes tens of times the rated full-load current. Be
> guided by the data published by reputable manufacturers. There's plenty of
> it.


My ac compressor unit says, use 20 amp breaker. The wiring said nothing.

Greg

[bud--]

The manufacturer tells you what size breaker will withstand the starting
current and provide protection from manor failures.

Overload protection is very likely a thermal trip on the compressor.
Small fans are "impedance" protected.

[josephkk]

For real horror to think he eats with that mouth.

?-)