Interested to Buy Any Domain ? << Click Here >> for more details...
what is the difference between Ith & Iu rating in MCCB.
Particularly on SACE ABB Circuit Breaker?
- 2 Answers
- 18074 Views
- Siemens, I also Faced
- E-Mail Answers
Answer Posted / 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
__________________
| Is This Answer Correct ? | 1 Yes | 0 No |
Post New Answer View All Answers
solar energy light efficiency & disadvantages?
Which type of transformer is used for lighting loads?
difine electrical ballast in HPSVL
State angle criterion.
In all analog voltmeters or ammeter showing some small size symbols. as well as a star and in star 2no. digit, resister symbol,and other. what is that's meaning ?
what happens if earth of 33kv cable is not connected to earthing pits? please send this query's answer to ngrm.sudha249@gmail.com
what is the prinsiple of dc motor and construction and working ,application of dc motor.
how to calculate
Stator of 3-phase IM has 3 slots per pole per phase. If supply frequency is 50 Hz, calculate the speed of rotating stator flux A 1000 rpm B 500 rpm C 1500 rpm D 1440 rpm
How shall i select the value of capacitor or inductor in a system?
What happen to generator if i have unbalanced load?
IN electrical field, WHAT ALL THINGS THE CUSTOMER WILL ASK WHILE ORDERING FOR LT PANEL (ALL TYPES OF LOW TENSION PANEL)
What Should be the value of Vector Surge angle at Tripping and how to calculate it?
what is the difference between earth leakage and earth fault?
what is the main parts of transformer? how it is functioning? pls giv the ans briefly.
