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Single phase manual motor starter Tazz 11-05-2006
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Posted by Tazz on November 5, 2006, 10:11 am


I have installed 120v manual motor starters forever.
Also install magnetic 3 phase motor starters forever

I recently bought a 230v motor for a pump for the deerlease and
wanted to install a manual motor starter for it. I sized the overloads
according to the nameplate and Sf etc etc.

But what got me was that the manual motor starter only takes out one
leg of the 230v when it trips on overload.

I think this is a bad thing.
Although the motor wont work on one leg of 115v
Why would anyone engineer it that way?

I thought it was code that you had to open ALL legs to motor when it
trip on overload.

If you have a 3 phase motor on a magnetic there are 3 sets of
overloads that will trip the system.
Any of them that will take out all 3 phases




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Posted by RBM on November 5, 2006, 10:32 am


The idea is to stop the flow of current to the motor before damage occurs,
which it does. You are still required to have a disconnect within site from
the motor, which will disconnect all power to the motor



>I have installed 120v manual motor starters forever.
> Also install magnetic 3 phase motor starters forever
>
> I recently bought a 230v motor for a pump for the deerlease and
> wanted to install a manual motor starter for it. I sized the overloads
> according to the nameplate and Sf etc etc.
>
> But what got me was that the manual motor starter only takes out one
> leg of the 230v when it trips on overload.
>
> I think this is a bad thing.
> Although the motor wont work on one leg of 115v
> Why would anyone engineer it that way?
>
> I thought it was code that you had to open ALL legs to motor when it
> trip on overload.
>
> If you have a 3 phase motor on a magnetic there are 3 sets of
> overloads that will trip the system.
> Any of them that will take out all 3 phases
>
>
>



Posted by Proctologically Violated©® on November 5, 2006, 5:30 pm


I think you are confusing legs w/ phases.
Altho there are, in fact, two legs going to your 230V motor, it's only one
phase (two legs in series), and interrupting either one will do the job.
This is not at all unusual.
Altho, most shut off swtiches will be double pole. Altho, you could get
away w/ a single pole switch as well--just not entirely safe, as parts of
the motor are always then "hot". Sorta like putting a swtich on a lite
fixtrue on the neutral side. <ouch>
In 3 ph, the situation is not so simple, and heaters, etc. are req'd on all
three legs.
Altho I have seen starters where only 2 of the three legs were protected.
:)
--
------
Mr. P.V.'d (formerly Droll Troll), Yonkers, NY

Stop Corruption in Congress & Send the Ultimate Message:
Absolutely Vote, but NOT for a Democrat or a Republican.
Ending Corruption in Congress is the *Single Best Way*
to Materially Improve Your Family's Life.
The Solution is so simple--and inexpensive!

entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie,
all d'numbuhs

>I have installed 120v manual motor starters forever.
> Also install magnetic 3 phase motor starters forever
>
> I recently bought a 230v motor for a pump for the deerlease and
> wanted to install a manual motor starter for it. I sized the overloads
> according to the nameplate and Sf etc etc.
>
> But what got me was that the manual motor starter only takes out one
> leg of the 230v when it trips on overload.
>
> I think this is a bad thing.
> Although the motor wont work on one leg of 115v
> Why would anyone engineer it that way?
>
> I thought it was code that you had to open ALL legs to motor when it
> trip on overload.
>
> If you have a 3 phase motor on a magnetic there are 3 sets of
> overloads that will trip the system.
> Any of them that will take out all 3 phases
>
>
>



Posted by Tazz on November 5, 2006, 5:39 pm



Completely understand that single phase will have two legs.
I just am suprised that is is not against NEC to open all the
conductors ( excluding the ground) for the exact reasons you mentioned
below. There is the potential there of 115v. at the motor that in my
opinion just doesnt need to be there in an overload situation.



Thanks for the reply



On Sun, 5 Nov 2006 17:30:53 -0500, "Proctologically Violated©®"

>I think you are confusing legs w/ phases.
>Altho there are, in fact, two legs going to your 230V motor, it's only one
>phase (two legs in series), and interrupting either one will do the job.
>This is not at all unusual.
>Altho, most shut off swtiches will be double pole. Altho, you could get
>away w/ a single pole switch as well--just not entirely safe, as parts of
>the motor are always then "hot". Sorta like putting a swtich on a lite
>fixtrue on the neutral side. <ouch>
>In 3 ph, the situation is not so simple, and heaters, etc. are req'd on all
>three legs.
>Altho I have seen starters where only 2 of the three legs were protected.
>:)

Posted by RBM on November 5, 2006, 6:15 pm


A 3 phase started needs to monitor all three legs, because the motor will
run, and burn out on single phase. A single phase motor, regardless of
voltage, only needs to disconnect one leg to kill the circuit and protect
the motor. Motor starters are strictly for motor protection, disconnect
switches which disconnect all non grounded legs are for people protection



>I think you are confusing legs w/ phases.
> Altho there are, in fact, two legs going to your 230V motor, it's only one
> phase (two legs in series), and interrupting either one will do the job.
> This is not at all unusual.
> Altho, most shut off swtiches will be double pole. Altho, you could get
> away w/ a single pole switch as well--just not entirely safe, as parts of
> the motor are always then "hot". Sorta like putting a swtich on a lite
> fixtrue on the neutral side. <ouch>
> In 3 ph, the situation is not so simple, and heaters, etc. are req'd on
> all three legs.
> Altho I have seen starters where only 2 of the three legs were protected.
> :)
> --
> ------
> Mr. P.V.'d (formerly Droll Troll), Yonkers, NY
>
> Stop Corruption in Congress & Send the Ultimate Message:
> Absolutely Vote, but NOT for a Democrat or a Republican.
> Ending Corruption in Congress is the *Single Best Way*
> to Materially Improve Your Family's Life.
> The Solution is so simple--and inexpensive!
>
> entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie,
> all d'numbuhs
>
>>I have installed 120v manual motor starters forever.
>> Also install magnetic 3 phase motor starters forever
>>
>> I recently bought a 230v motor for a pump for the deerlease and
>> wanted to install a manual motor starter for it. I sized the overloads
>> according to the nameplate and Sf etc etc.
>>
>> But what got me was that the manual motor starter only takes out one
>> leg of the 230v when it trips on overload.
>>
>> I think this is a bad thing.
>> Although the motor wont work on one leg of 115v
>> Why would anyone engineer it that way?
>>
>> I thought it was code that you had to open ALL legs to motor when it
>> trip on overload.
>>
>> If you have a 3 phase motor on a magnetic there are 3 sets of
>> overloads that will trip the system.
>> Any of them that will take out all 3 phases
>>
>>
>>
>
>



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