Answer / mazed

Extract form appendix K of standard IEC 60947 -2
Voltage
• Ue = Rated operational voltage
• Ui = Rated insulation voltage
• Uimp = Rated impulse withstand voltage
Current
• In = Rated current
• Ith = Conventional free –air thermal current
• Ithe = Conventional enclosed thermal current
Short -Circuit
• Icm = Rated short circuit making capacity
• Icu = Rated ultimate short circuit breaking capacity
• Ics = Rated service short circuit breaking capacity
• Icw = Rated short time withstand current
Trip unit
• Ir = Adjustable overload setting current
• 1.05xIr = Conventional non –tripping current
• 1.30xIr = Conventional tripping current
• Isd = Short time delay tripping setting current
• Ii = Instantaneous tripping setting current

Answer / mazed

CCB Ith & Ir Acronym Meaning
05/02/2010 9:16 AM

We are planning to replace our Chiller with bigger capacity.

The motor rating of old chiller is 375 kw whhle the new one
is 570 kw, all at 380 volts, 3phase , 60 hz. The suppllier
required us to a circuit breaker with minimum ampacity of
911 amps.

our existing Circuit Breaker is SACE ABB, Iu =1250, Ue =660
Volts, 3 poles. Their is a rating of Ith @ 45 deg C of 800
Amps maximum and Ir = 6300 max. My questions are:1. What is
the Ith & Ir means. 2. Can i use ourold MCCB with the rating
of 1250 Amps Iu?

Please all extert here help me.

My best regards to all.
Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments
are added.
Join CR4, The Engineer's Place for News and Discussion!
Comments rated to be Good Answers:
These comments received enough positive ratings to make them
"good answers".

* #4 "Re: What is the Ith & Ir at MCCB stand for?" by
JRaef on 05/02/2010 7:01 PM (score 5)

Tornado
Guru
[Tornado's Picture]
Technical Fields - Technical Writing - New Member
Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Ketchikan, AK, USA
Posts: 11914
Good Answers: 421
[Click to collapse or expand]
#1
[Comment] Re: What is the Ith & Ir at MCCB stand for?
05/02/2010 2:42 PM

Ith is the thermal current rating of the breaker. The more
the motor current exceeds this, the quicker the breaker will
trip. I'm unsure of the other abbreviations, but they may
represent the magnetic trip rating, which is nominally
instantaneous.

If the motor requires 911 A, it is likely to trip this
breaker either 1) right away if the starting current exceeds
6300 A, or 2) in a short time if the running current exceeds
800 A. So I don't think this combination will work.
__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Reply
Dalton
Associate

Join Date: Nov 2009
Posts: 28
[Click to collapse or expand]
#2
In reply to #1
[Comment] Re: What is the Ith & Ir at MCCB stand for?
05/02/2010 2:59 PM

Thanks, but how about the Iu (1250 Amps) which i believed is
the nominal current rating. Our MCCB rating Iu = 1250 Amps &
Ue is 660 volts. then their is anothr rating which is Ith =
800 max @ 45 Deg C. any idea on this Sir?
Reply
Tornado
Guru
[Tornado's Picture]
Technical Fields - Technical Writing - New Member
Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Ketchikan, AK, USA
Posts: 11914
Good Answers: 421
[Click to collapse or expand]
#3
In reply to #2
[Comment] Re: What is the Ith & Ir at MCCB stand for?
05/02/2010 4:15 PM

My idea on that is exactly as before. If the thermal rating
Ith of 800 A is exceeded by the 911 A motor, the breaker
will trip (sooner or later).

However, if the ambient temperature at the breaker is less
than 45°C, the Ith will be somewhat higher. This may get you
by, but it looks really borderline. Reduced-voltage and
unloaded starting will also help.
__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Reply
Anonymous Poster
[Click to collapse or expand]
#5
In reply to #2
[Comment] Re: What is the Ith & Ir at MCCB stand for?
05/03/2010 5:16 AM

ASK ABB for their catalogue on MCCBs select yourself you
will find all inputs required you could download the
catalogue from ABB web site.

good luck

murali

Ex power user
Reply
Dalton
Associate

Join Date: Nov 2009
Posts: 28
[Click to collapse or expand]
#6
In reply to #5
[Comment] Re: What is the Ith & Ir at MCCB stand for?
05/03/2010 8:46 AM

thanks. this an old model MCCB from ABB. SACE SN1250 model.
Installed last 1986 by the German Contractors here in KSA.

All I want to know is if could still use this MCCB. But i
think the best solution now is to buy a new MCCB.

Rgards to all.
Reply
[Rated a 'Good Answer' with a score of 5] 5
JRaef
Guru
[JRaef's Picture]
United States - Member - New Member Engineering Fields -
Power Engineering - New Member

Join Date: Sep 2006
Location: California, USA, where the Godless live next door
to God.
Posts: 3209
Good Answers: 419
[Click to collapse or expand]
#4
[Comment] Re: What is the Ith & Ir at MCCB stand for?
05/02/2010 7:01 PM

Extract form appendix K of standard IEC 60947 -2

Voltage

* Ue = Rated operational voltage
* Ui = Rated insulation voltage
* Uimp = Rated impulse withstand voltage

Current

* In = Rated current
* Ith = Conventional free –air thermal current
* Ithe = Conventional enclosed thermal current

Short -Circuit

* Icm = Rated short circuit making capacity
* Icu = Rated ultimate short circuit breaking capacity
* Ics = Rated service short circuit breaking capacity
* Icw = Rated short time withstand current

Trip unit

* Ir = Adjustable overload setting current
* 1.05xIr = Conventional non –tripping current
* 1.30xIr = Conventional tripping current
* Isd = Short time delay tripping setting current
* Ii = Instantaneous tripping setting current

__________________

how to calculate vfd o/p voltage by frequency

0 Answers   HCL, Orchid,

---

why CT output is always raetd 5.regardsof primery curre.

3 Answers   ABB, BARC,

---

what is difference between di electric and insulator?

2 Answers   Greenko,

---

What is harmonics and how the 1st,2nd,3rd etc harmonic levels

2 Answers  

---

Does increase or decrease of reactive load affects the Voltage.

5 Answers   Nalco,

---

what does the transformer connection symbol YNaod1 mean ?

3 Answers  

---

freuency meter

1 Answers  

---

WE HAVE A PROBLEM THAT THE MAIN DRIVE OF OUR CEMENT MILL HAS AN EARTHING PROBLEM?TWO OF STATOR WINDINGS INSULATION HAS BEEN COLLAPSED DUE TO AGING PROBLEM.THE PHASES HAVE BEEN BYPASSED AND NOW THE LOAD HAS BEEN INCREASED.WE CAN'T REPLACE THE MOTOR.KINDLY HELP ME BY GIVING SUGGESTION THAT HOW TO MAINTAIN THE STARTING TORQUE AND CURRENT FOR HIGH LOADS.

1 Answers   ACC,

---

WHY TRANSFORMER IS MEASURED IN KVA?

10 Answers  

---

what is difference between neutral and ground wire?

2 Answers   TCS,

---

Explen all type electrical protection ? like O/C,E/F,NPS,VOLTAGE UN BLANCE,CURRENT UN BALANCE,NAGETIVE PHASE SEQ,AND ETC...............electrical Protection

6 Answers   Reliance,

---

what does work of electrical technician in industrial

1 Answers  

---