MCB (Miniature Circuit Breaker) is very common protection device (Such as fuse) used in domestic and industrial wiring and application and most of us have tried to buy MCB. It is very important device, which is to be procured with care.
But when we use to visit shops or take
advice of our “expert” electrician then in most of time, without any
technical consideration they advise for a particular brand. For us,
especially who is not from electrical background, it is very tough to
understand technical points of MCB.
We just see the MCB rating
and buy it. It is really a wrong practice. Your electrician or
shopkeeper may be suggesting you the right product but you also should
know about it while purchasing. Deciding MCB is very simple. Most of the data is generally printed on a MCB. Only few local companies hide information and you can easily ignore them. We would like to tell you about printed information of MCB.
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Model Number.: All reputed manufacturer has a
particular code of each device type. It will be very easy to communicate
with seller or manufacturer, if you quote the model no., in case of any
service complaint.
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MCB Current and Curve Rating: As shown in example it
is mentioned D125.First letter is showing is characteristics curve.
There are three characteristics curves (In common use) available- B C
& D. B curve indicates that short circuit rating of device is in range of 3-5 times of standard rated current. C curve indicates it to be 5-10 times and D curve indicates
it to be 10-20 times. Be very careful while selecting this. On a
resistive load (say heater, normal lighting load) it will B Curve, for
inductive load (Like pump, Motors etc.) it will be C curve and for
highly inductive or capacitive load it will be D curve. The numeral part
indicates rating of MCB in Ampere. In the given example it is 20A. MCB
rating is very important and be very precise about it.
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Operating Voltage: It is in Volts and is the
operational voltage for which current rating is said. In three phase it
is usually 400V or 415 V. For single phase it is 230V or 240V. Choose as
per your application only.
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MCB Breaking Capacity: Breaking capacity can be
defined as the maximum level of fault current which can be safely
cleared. It is written as in numerals like in in example it is 10000. It
means it 10000A = 10kA. Choose breaking capacity as per your fault
level possible. Since it is the parameter which may increase or decrease
the cost, so it should be properly decided. Breaking capacity should be
higher than the possible fault level. For domestic application where
fault level cannot be calculated easily, it advisable that go for a
standard breaking capacity of 10kA which is easily available. Please
note that this rating is mentioned as per testing made on basis of IS
60898. If it is for IEC60947-2 then it need to be mentioned separately.
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Energy Class: MCB normally work on current limiting
feature. It means that it does not allow fault to get it’s peak and trip
before that. But since there is some time consumed in tripping, fault
current will create some energy which will exist in system. This energy
is termed as let through energy. For efficient MCB operation it should
be limited. On basis of amount of energy it is classified in class 1,
class 2 and class 3. Here Class 3 is best which allows maximum 1.5L
joule/second. This is being tested as per IS 60898.
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Status Indicator: It shows the ON-Off Indication
while in operation. Never buy an MCB which don’t have clear status
indicator because serious damage may be occurred with ON-OFF confusion
of the device.
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Operation Symbol: This is always printed by any good manufacturer. This shows operation mechanism of MCB.
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Additional Relevant Information : Information like
Impulse voltage, ISI marking etc are usually printed on side of MCB.
However there are many parameters on which quality of MCB should be
judged but aim of this blog is to make you aware of printed information
on MCB.
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Catalog No: Most of the MCB manufactures put the catalog number of the MCB products. This code provide the overall information on the manufacture website such as MCB specification and Datasheet ect.
Below is the typical MCB nameplate rating data which shows the most important information printed on it.
These are generally:
- Product Modal No
- Max Current Rating
(6, 10, 16, 20, 25, 32, 40, 60, 63 etc) - Operation Symbol
- Breaking Capacity Type
- Breaking Capacity (Max Short Circuit Current)
- Operating Voltage(230V, 400V, 440V)
- Tripping Curve Type
- Energy Class
- ON-OFF Indication
- Catalog No
P.S:
Printing of MCB data may be placed as per the convenience of
manufacturer. Model No. of every manufacturers are of different style.
No standard definition format used but translated in easy words for easy
understanding. for proper and more information related to MCB rating nameplate, use the provided Datasheet by the manufacturer of that MCB(s).
