digatrip 510
- Thread starter jimbo123
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You are asking a loaded questions. Please advise as to why you are asking the question. There has to more to it.
dresseslady539
New member
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- grdgr
zog
Senior Member
- Location
- Charlotte, NC
The tables have limits on available fault current, not the breakers AIC rating.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
NO.
The kAIC rating of a device depends on its physical construction.
While you can impact the amount of available fault current, there is nothing you can do to change the AIC rating of a device.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Yep, two totally different issues.
A breaker's interrupt rating, the "kAIC" rating, is what it is, you cannot change that.
You also cannot lower the Available Fault Current with a circuit breaker either, it is what it is as well.
You can however theoretically lower the "Incident Energy" with regards to Arc Flash in equipment down stream of a digital breaker by lowering the trip threshold . This is at the same time going to mess up your coordination and expose you to nuisance tripping of the Main or feeder it is applied to. For that reason, some of the CB Mfrs are releasing new versions of their Electronic Trip Units that have what is called a "Maintenance Mode", a TEMPORARY way to lower the trip threshold via a switch input and lower the downstream incident energy while someone is working hot on the equipment DOWNSTREAM of the breaker that has the MM option. A common misconception is that an MM breaker makes working on THAT BREAKER safer, it does not, it does nothing for an Arc Flash that may happen on the line side.
zog
Senior Member
- Location
- Charlotte, NC
He is using the table method from the sounds of it.
Jimbo, if your available fault current, or clearing time, is outside the limits of the table notes you need to do an arc flash study. The tables cannot be used in that case.
Jimbo, if your available fault current, or clearing time, is outside the limits of the table notes you need to do an arc flash study. The tables cannot be used in that case.
My manager told us to dress at level 4 ppe because working on equipment was a hrc4 according to the tables . Now [our equipment]the bus has 100,000scca rating the cb has 85,000 scca [as posted on equipment label]. Maybe i am wrong but the tables list 35,000 scca limits[ for the tasks] and if our cb is rated for 85,000 it sounds like we are operating out side the parameters. Now how can someone use the tables if they don't know the parameters of the system?. I was using the breakers label listing , which you guys say is wrong.
Every section of the tables use a limit [parameter] if outside you must do a arc flash analysis.
So for every or any task listed you must do a arc flash analysis or not use the parameter and just use the hrc .
Also told manager about working energized but it did not seem to matter, his answer was to use contractors.
I come across to him as not being a team player, when i am trying to do the work safe.
Thanks for all the replys.
Every section of the tables use a limit [parameter] if outside you must do a arc flash analysis.
So for every or any task listed you must do a arc flash analysis or not use the parameter and just use the hrc .
Also told manager about working energized but it did not seem to matter, his answer was to use contractors.
I come across to him as not being a team player, when i am trying to do the work safe.
Thanks for all the replys.
Last edited:
zog
Senior Member
- Location
- Charlotte, NC
Possible, it depends on the equipment you are working on, different types of equipment lists different max fault current limits. Ideally your breakers AIC rating should be greater than your available fault current and in some cases the fault current is much lower than the AIC rating. But what usualy disqualifies the tables from being used is the OCPD clearing time.
You can't, simple as that.
The contractors have to follow the same rules as you.
You have made it clear many times your manager is a tool.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
The listings on the labels have only to do with what the breaker CAN withstand, it has nothing whatsoever to do with what EXISTS in the system. You can ASSUME, at best, that whoever selected the equipment did so based on the Available Fault Current being LESS that the ratings of the devices, but that could be ANY amount less. So if all you are looking at is the fact that you have a breaker rated for 85kAIC, that is not telling you anything useful with regards to the PPE requirements. If the guy who is responsible says use PPE4, you have to use PPE4.
It has to be noted that the KAIC rating of a breaker is pretty much what it's withstand rating may be. I'm not aware of a breaker having a withstand rating other than it would be basically what it's (kaic) interupting rating is. Isn't the withstand rating commonly limited to non-automatic devices?
I know breakers need to interupt should they experience anything close to what their withstand rating may be to protect themselves. As such withstand ratings for a breaker is not of much value.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I guess it was a poor choice of words on my part, I should know better. I meant "Interrupt", but I was mainly trying to get the message across that the label on the breaker is not meant to indicate the AVAILABLE fault current in the system.
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