'blowing out' phases on motor protection breaker? 2

[robbm]

Just wondering if anyone has come across this. We have a basic motor control panel for a 7.5HP motor (460VAC, 3phase). The protection is a motor protection circuit breaker, rated/sized according to the motor. We tested it without issue and the customer is now claiming that they are 'blowing out 1phase of it' about once a week, and need to replace the breaker each time (and that's all they can provide for info). Still trying to get more info from them, but if anyone has any suggestions, by all means...My guess would be that motor may be the culprit if a single phase is causing the breaker to trip or even be damaged beyond just tripping, but thoughts/comments are welcome...

thanks in advance.

 

[rbulsara]

How about gathering some facts rather than guessing? Saves everyone time and effort.

Rafiq Bulsara

http://www.srengineersct.com

 

[robbm]

those are the only facts the customer can give us. that's why i was looking for any possible hypotheses some could offer.

 

[rbulsara]

Well, you may have to go to the site. I would guess, you are getting paid..

You can always stay tuned for guesses from others, however. It is always fun to read.

Rafiq Bulsara

http://www.srengineersct.com

 

[robbm]

our company doesnt just fly anywhere that a customer has a problem, so automatically going to the site without trying to work through possible solutions isn't feasible or practical.

 

[rbulsara]

Good luck!

Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

Have the customer return a breaker for inspection.
By the way, the ABS light came on on my vehicle. What's wrong? I keep replacing the same sensor but the light still comes back. Please help. Get the idea?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[robbm]

I've already suggested that. My thoughts are that the same device won't continually fail/be bad if there isn't another culprit...

 

[whippee2]

I would ASSUME that as well. I would say that the motor needs to have an IR test performed. So you definelty have to go to the site to peform this.

 

[Zogzog]

You can't troubleshoot without any data. Get some real info and post it, until then this is nonesense.

 

[jraef]

"Blowing out 1 phase" is an official descriptor of a failure precipitated by the thingamajiggy contacting the whachamacallit without the whozis being engaged.

As mentioned above, there is really not much to go on here. But I assume you are the provider of said breaker? Remembering that you are on an international forum, can you please describe this better for us? The term "motor protection breaker" is too vague and can mean different things in different countries. We (as a group) tend to go off half cocked with misinterpretations.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[robbm]

very true, i've been working on getting info from the end user more than the initial description i was given. the breaker is an AllenBradley 140M series 3phase motor protection circuit breaker. We use them with an AB 100C series contactor to make a TypeE self-protected combination motor controller. Like i said above, i'm not looking for an end-all solution. I was looking more for suggestions of possible things to check that could be causing the breaker to trip from single-phasing.

 

[idontgetanyofthat]

Could be wrong type of breaker not motor rated. Why is the breaker not connected to the other 2 breakers? I can only think you talking about fuses and not MCB's? Is the motor connected correctly? Star or Delta?

Any way this long distance stuff is easy, get some one to do a video with a camerafone or the like of the problem and put it on you tube or send it directly to you if you can receive files that big.

 

[robbm]

There are motor rated breakers, this isn't the first time we've used them, and yes, they are breakers, not fuses.

 

[waross]

Is there a disconnect switch ahead of the breaker? How is the power interupted in order to change the breaker?
Have you checked a failed breaker?
I have encountered a few failed breakers over the years. The most common cause mode of failure is soft O/Ls. The breaker trips on progressively less current. Some fail due to heat damage caused by loose connections either to the bus or the outgoing cable. A failed pole is rare. Very rare. It doesn't happen often and when it does it usually happens over a period of time. BUT, as a pole deteriorates, the heat generated usually causes a premature trip and the breaker is replaced due to "Soft O/Ls" long before a pole actually fails open.
Three breakers all failed open on one pole in a short period of time with no other cause? To mis-state some foot ball jargon, "Gotta throw the bull ship flag on this one".

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[robbm]

this is a single motor system, so the circuit breaker is the local disconnect switch. the building's breaker panel is where the supply is coming from, and that's what is shut down when they need to swap out the breaker that keeps failing.
the heat damage caused by a loose connection on the motor circuit breaker seems quite possible, because the breaker isn't just tripping, it's actually unusable when it finally fails.

 

[starkopete]

In your original post you state 'blowing out 1phase of it', is it the same phase on all of the failed breakers?

 

[rasevskii]

for robbm:

There is no way that you will get around the need to go to the site, or send a good electrician there. It may be only a loose, therefore resulting overheated connection that is causing the repeats. Just change out the whole equipment with new and check out the installation, and measure the currents.
An IR check of the motor windings (ground fault?) is needed.

What is the application-is this a pumping station (submersibles?) where water may have gotten in- We are not clairvoyants here... What sort of environment..wet, dry, indoor, outdoor, rainwater... ? If your client is important to you then some site effort is indicated ASAP...

rasevskii

 

[jraef]

Ah, the semantics issues rears it's ugly head.

The A-B Bul. 140 is not a "circuit breaker" by North American definition, it is what is called a "Motor Protection Switch", a.k.a. "Manual Motor Starter", a.k.a. "Motor Starter Protector" etc. etc., but we generally don't use the term "circuit breaker" here because that implies a specific set of design criteria (reserved for MCCBs) that those devices do not possess, chiefly UL489 listing or recognition.

These devices include the OL protection as an adjustable dial, the same as on bi-metal IEC overload relays. It also possesses a fixed Instantaneous Magnetic Trip function and a disconnecting means. So one of these devices + a contactor constitutes a complete "Type E Combination Starter" listed under UL508.

These are not particularly robust devices compared to older traditional Combination Motor Starters that use an MCCB as the protection device. A short circuit, even if the device interrupts it successfully, is likely to damage it. They are essentially a "one shot" protective device; the official term is "self protected", meaning they will sacrifice themselves in the line of duty, but don't expect them to be reusable (something expected of an MCCB).

So it's entirely possible that you have something in the circuit that is giving you an intermittent dead short to ground or a bolted fault, and that little device is "throwing itself on the grenade" to prevent a fire.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Impressive Jeff. LPS

Bill
--------------------
"Why not the best?"
Jimmy Carter