question on siemens senetron breaker

[tonyou812]

I went to a plumbing supply store today to pick up some stuff for my bath remodle and when I got there all the power was out. They told me its been happening for about 6 weeks.
I went there in my personal vehicle so I didnt have any tools or meters but the guy remembered me and said oh your that electrician that came in last week. Would you mind taking a look?
So being the sporting type I went to the back and had a look.
The power company had some power analyzing equipment set up and when I scrolled throgh some of the stats nothing really seemed to jump out at me.
I was curious as to why the three trip settings were all set to max..? I was also curious as to why they would have installed a 300 amp JXD6 style breaker. From what I understand these are designed to be able to be fed from either side, load or line..? THis is a plumbing supply store with a big wearhouse and store front. And the breaker that was replaced looked almost brand new..?
I understand that I havent provided much technical info but I was hoping someone could have a similar story to share. And what they found to be the problem.
Thanks

 

[tonyou812]

Heeelllooooooooo, heeeeelllooooooo, heeeellloooooo, ..........:-? no takers huh......wow do i smell or something.

 

[ron]

The overcurrent characteristic adjustments were probably set a max, because nobody did a selective coordination study. They are typically set a max by the person that didn't get settings from an EC or engineer, or sometimes set at minimum because that's the way it comes from the factory as default.
Line/Load capabilities should have anything to do with whether it falsely trips or not.

 

[zog]

I am failing to see the question. and yes, you smell like a Klingon.

 

[steve66]

I've seen a condensing unit that was going bad trip a 800A breaker several times. Although it and a MCC were the initial suspects, it took a couple of days to confirm that it was the condensing unit.

Turns out, without anyone else knowing, one of the maintenance guys reset an overload inside the condensing unit a couple of times without anyone else knowing.

I think it was probably a 40 amp unit, with something like a 125A branch breaker. And no, the branch breaker never tripped.

So I could see a smaller condensing unit taking out your 300A breaker.

 

[LarryFine]

Heeelllooooooooo, heeeeelllooooooo, heeeellloooooo, ..........:-? no takers huh......wow do i smell or something.

From whom were you expecting a response in an hour and 15 minutes?

Patience, my friend, patience. (And, take a shower if you need one. :grin

 

[Jraef]

I went to a plumbing supply store today to pick up some stuff for my bath remodle and when I got there all the power was out. They told me its been happening for about 6 weeks.
I went there in my personal vehicle so I didnt have any tools or meters but the guy remembered me and said oh your that electrician that came in last week. Would you mind taking a look?
So being the sporting type I went to the back and had a look.
The power company had some power analyzing equipment set up and when I scrolled throgh some of the stats nothing really seemed to jump out at me.
I was curious as to why the three trip settings were all set to max..? I was also curious as to why they would have installed a 300 amp JXD6 style breaker. From what I understand these are designed to be able to be fed from either side, load or line..? THis is a plumbing supply store with a big wearhouse and store front. And the breaker that was replaced looked almost brand new..?
I understand that I havent provided much technical info but I was hoping someone could have a similar story to share. And what they found to be the problem.
Thanks

I guess your question is a "why" question, and that is not easy to answer. As Don said, most likely it's just someone being lazy and not doing the homework it takes to set the trip values correctly. But another possibility is that they have been having troubles with loading and the breaker is tripping on over current, so someone has been trying to "tweak" it to prevent that. But a JXD breaker has a fixed thermal trip, so adjusting the mag trips will have no effect if that's the problem. Unfortunately, a lot of lay people (and a few Electricians) have no idea what that setting means and think they are "turning it up" when in fact they are just increasing their risk of damage.

As to why a 300A breaker? Probably because they have a load that needs it? No way to answer that from here.

 

[tonyou812]

From whom were you expecting a response in an hour and 15 minutes?

Patience, my friend, patience. (And, take a shower if you need one. :grin

Yea I know....LOL sorry LOL .... i got ants in my pants...

 

[tonyou812]

I would absolutly love it and really appreciate it if someone could show me the math on how and why a failing condensor can trip a main breaker. Its been a long time for me when it comes to industrial stuff so I am very rusty on the calculations. But I really enjoy the learning non the less.

I can remember one time when we were demoing am office space someone accidently trip a 277 lighting circut and it wound up tripping the main for the floor. I can also remember when my buddy shorted out a HID light in a parking lot and it tripped the main all the way back in another building. Why does this happen. Any insight would be lovely..

 

[72.5kv]

when that happens the system is not coordinated, basically the time currect curve of the breakers are overlapping

 

[tonyou812]

when that happens the system is not coordinated, basically the time currect curve of the breakers are overlapping

See thats what I want to understand better. As well as fault current calcs. I guess Ill look them up in the archives.

 

[Doug S.]

I'll save the math for those who present it better than myself...

If your 300 amp breaker is pulling 200 amps (for example), and a medium sized condenser (again for example) is shorting out causing a spike of lets say 200a (very reasonable) it may be able to fold over your main, prior to tripping it's upstream OCPD.

So some one (smarter than me) examines the breakers, feeder sizes and lengths, (normally just feeds the data into a computer) allowing for "coordination". So a load only will trip it's OCPD and NOT the OCPD's upstream.

Not the best presentation, but simple enough?

FWIW, I do smell... 90 deg. in W. MI today. That's HOT.

Doug S.

 

[tonyou812]

thanks Doug. I acually really appreciate your insight. That makes sense about plugging the numbers into a computer. I didnt really present much info in the problem which is probably why no one is really chimming in. I asked this same question on another forum but no results. I really need to take a industrial refresher course.

 

[Doug S.]

Well I'm glad I could offer some insight.

Some of the simple nature of my "insight" is due to the fact that an in depth analysis isn't always needed. The situation you describe could very well be complex, but a little time with a clamp and a DVM may be all you need to nail down a seemingly complex problem.

Good Luck,
Doug S.