Previous in Forum: MCCB Maximum Measured Earth Fault Loop   Next in Forum: Short Circuit Connection
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
6 comments
Rate Comments: Nested
Dalton
Associate

Join Date: Nov 2009
Posts: 42

Difference Between Iu & Ith

05/02/2010 11:15 AM

Can you help me guys know the difference between Ith & Iu rating in MCCB?

I have an MCCB with the rating of Ue = 660 volts & Iu = 1250 Amps

It as a rating also of Ith = 800 amps max @ 45 deg C & Ir = 6300.

I have a motor for my chiller which requires a MCCB with min. ampacity rating of 911 amps. tthe voltage is 380 volts, 3 phase 60 hz. can i use this MCCB with a rating of Iu = 1250 Amps and Ith = 800 A max at 45 degree C.
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Anonymous Poster
#1

Re: Difference Between Iu & Ith

05/02/2010 9:01 PM

Noope!

53 2E 4D 2E
Register to Reply Score 1 for Good Answer
No more "Almost" Good Answers.
tooz
Commentator
Australia - Member - New Member Engineering Fields - Electrical Engineering - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Jan 2008
Location: Mount Gambier, South Australia
Posts: 56
#2

Re: Difference Between Iu & Ith

05/03/2010 5:45 AM

Having a Ith = 800A max, whereas you need a min of 911A so it is a little under size.

__________________
 tooz
Register to Reply
Anonymous Poster
#3

Re: Difference Between Iu & Ith

05/03/2010 7:39 AM

So far I know ,Ith is the thermal current of circuit breaker in air.For this value circuit breaker will trip.The more circuit breaker current than Ith circuit breaker will trip more faster.On the other hand,Iu is the uninterruptable current.So circuit breaker can carry it without tripping.

In your MCCB ,Iu is higher than Ith.How?

I think you should choose a MCCB ,Iu rating more than 911A.

Thanks

Fakrul
Register to Reply
Dalton
Associate

Join Date: Nov 2009
Posts: 42
#4
In reply to #3

Re: Difference Between Iu & Ith

05/03/2010 8:39 AM

Yup ur right. That's why I find it strange too. Iu is 1250 A while Ith is 800 A max. That's why i wonder what the use of Iu 1250 amps when @ 800 A it will trip already. Thanks guy for your help.

Anyway the MCCB is made of ABB SACE model SN1250.
Register to Reply Score 1 for Good Answer
Go to Next "Almost" Good Answer
Andrei_V_Kiselyov
Member

Join Date: Sep 2009
Location: Ukraine
Posts: 5
#5
In reply to #4

Re: Difference Between Iu & Ith

05/13/2010 8:23 AM

Why wouldn't go to ABB catalogs to verify.
Register to Reply
Anonymous Poster
#6

Re: Difference Between Iu & Ith

06/09/2010 6:03 AM

See page 10

http://www.gil-lec.co.uk/custom/upload/pdfs/circuit%20protection/Hager_Isolators_Switches.pdf
Register to Reply
Register to Reply
Have a Different Question?
6 comments

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

Andrei_V_Kiselyov (1); Anonymous Poster (3); Dalton (1); tooz (1)

Previous in Forum: MCCB Maximum Measured Earth Fault Loop   Next in Forum: Short Circuit Connection

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (51 right now)
Show Members
Advertisement