Breaker/motor starter

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sportster

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I got a guy that wants to use a 3 phase breaker as the only control for a 40 HP. 3 phase motor 230 V.for a conveyer. He is going to open the door an a panel box push the breaker to on and shut the panel door. Where I work we have flash protection/touchless motor starters, ect. What he is attempting don't sound right to me, but I need some input form you guys on code sections or safety standards that I can talk him out of this.
Maybe I live in an overly safe environment.
Thanks
 
Re: Breaker/motor starter

Circuit breakers are permitted for use as both a disconnecting means and as a controller for all motors. See sections 430.83(A)(2) and 430.111
 
Re: Breaker/motor starter

sportster,
As bphgravity said they are allowed. The breaker will work just fine.
However, how about the "rest of the Story."
By simply providing an answer to your question may not be entirely correct.
You never described the entire installation which would imply that our answer is bases upon the very limited information that you had provided us.
Is the breaker being used because it is in a convenient location and that there is adequate motor overload and short circuit protection at the motor?
 
Re: Breaker/motor starter

He wants to run from his generator set in to a box with his feeders to this breaker and out to the motor. That's the total installation.
 
Re: Breaker/motor starter

Then he has no overload protection for the motors unless by some odd chance that there is thermal protection that is integral to the motor.
This does not appear to be an acceptable arrangement in that he's selected to overlook and/or avoid the cost of motor protection.
What one would like to see is a motor starter at each motor where the OLR heaters are coordinated with the motor. The actual starter control could be wired such that it energizes and closes when the breaker is closed and drops out when the breaker is opened. Should the motor be overloaded the OLR will detect it and drop out the contactor to protect the motor from damage. Most OLRs can be set for either manual or automatic reset.
 
Re: Breaker/motor starter

see 430.32. overload protection for 1 hp and up is a code requirement for continous duty motors.A circuit breaker is ok if its not continous but I would NEVER use it as the sole device on a motor this large. Cicuit breakers are really meant to break a load under overloaded and/or shorted-grounded conditions. You may want to use a long 2x4 to close this breaker if you are the one that has to close it. Just my 2c worth from many years of experience. Joe The defintion of continous is only 3 hrs and I would thnk a conveyoer would probably be turned on and left on for long periods no?

[ February 18, 2005, 07:03 PM: Message edited by: stew ]
 
Re: Breaker/motor starter

The definition of continuous duty as applied to article 430 is in the notes to Table 430.22A

"Note: Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use. "NEC


Charlie
 
Re: Breaker/motor starter

Stew, A breaker will have no problem controlling the motor load. The thought of needing in 2x4 to operate the breaker is on old wives tale. The statement
Cicuit breakers are really meant to break a load under overloaded and/or shorted-grounded conditions.
Click to expand...
is not entirely true. NEC table 430.150 shows the FLA of a 40hp, 230v 3ph motor to be 104a. UL489 test in part state that a 225a frame breaker endurance test require 4000FL operations and 4000 NL operations at 5 operations per minute. This is a brief part of the tests which also include overload, dielectric withstand, repeated short circuit and calibration tests.
Controlling a 40HP, 230v 3ph motor is a piece of cake.
A circuit breaker is not the wimpy device you may think it is when applied within its voltage and interrupting ratings.
 
Re: Breaker/motor starter

templdl

Hello! That CB may be set at 300 A. 125% of 104A and selecting the next size higher 430.52 If The motor is not heavily loaded the LRC Table 430.251 05 NEC spec's 641A inrush. If the motor is under load the stress on the breaker would appear to be slightly or greatly?? more significant. What information might you glean and share concerning that aspect and the impact of UL 489??


Thanks Charlie
 
Re: Breaker/motor starter

Does anybody thing that any circuit breaker is designed to withstand 1,000,000 on and off switching? You can end up with one burned contact and then the motor itself.

Yes the NEC may be is permitting that. But is it a good prctice?
 
Re: Breaker/motor starter

Hi Charlie.
104a x 125%=300a??
Anyway, the breaker will operate well. No problem. Expect to get at least 4000 operations from a 225a frame breaker.

oliver100,
No, one would be foolish to expect a breaker to have the mechanical life of a contactor which is device designed to control motors.
Never the less breakers are allowed and will function just fine.
Should life be an issue then the breaker used as a control may not a good choice. However, it appears as though you are making 1,000,000 operations an issue when there is a good possibility it isn't and issue in this application.
He wants to run from his generator set in to a box with his feeders to this breaker and out to the motor. That's the total installation.
Click to expand...
Does this imply that type of duty cycle? Do you think he may be operating the breaker more than 4000 times?
If the breaker were to be closed and opened once a day expect it to have a life expectancy of about 10 years or more. As such is 1,000,000 operations an issue?
 
Re: Breaker/motor starter

i give igive. but I still would not do it and he still needs overloads in my opinion. A contactor close imn my opinion much faster than a breaker and thus the arcing associated with the hi inrush is minimized.
My interpretation of continousy loaded is the definition given in definitions of 3 hrs. I always size my motor loads as continous unless I absolutly know that they are intermittent. Joe

[ February 18, 2005, 09:25 PM: Message edited by: stew ]
 
Re: Breaker/motor starter

I agree Joe that it's not the best way to do it. As you also picked up on the subject of how motor overload protection has been addressed appears to have been avoided as breakers do not provide motor overload protect.
As I stated in my first post simply providing a yes or now answer to the breaker issue may not be entirely correct as it is not all that unusual for questions to be posed in a way to get an answer which they want to hear.
Dave
 
Re: Breaker/motor starter

The short answer is the best way to handle this, regardless of what you might be able to code justify, is with a motor starter and overloads.
 
Re: Breaker/motor starter

templdl
Thanks for pointing out the error 104 x 1.25= 130A :(

The next size up would be 150A x 5= 750A Thats even closer to the 650LRC .

I do not get a warm fuzzy but I see the discussion has advanced in that direction already.

Charlie P
 
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