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Topic Title: MCCBs
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Created On: 23 January 2011 11:03 PM
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 23 January 2011 11:03 PM
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PatHammond

Posts: 213
Joined: 04 December 2008

Can any one clarify when and why one would use an MCCB as opposed to a MCB. I don't think it's just about high capacity distribution circuits because I noted the merlin gerin do them down to 16 amps.

Can I assume that this means 16 amps per phase overcurrent protection with the same time/current disconnection charactersitics of an MCB?

Also; when they state that the MCCB provides earth leakage protection does this mean they have 30mA RCD characteristics like an RCBO.

Thanks for your help

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4.5 day wonder...had to start somewhere
 23 January 2011 11:53 PM
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daveparry1

Posts: 5887
Joined: 04 July 2007

MCCB's have much higher pscc ratings than mcb's and are usually, (not sure whether always) adjustable, that's all I know about them Pat, I don't know whether they ever incorporate an rcd, my work is mainly domestic so I don't come across them,
Dave.
 23 January 2011 11:57 PM
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peteTLM

Posts: 3083
Joined: 31 March 2005

They do them in small sizes so that they can go into main distribution boards in say a plant room without having to go through another level of distribution for things like fire alarms, essential services etc.
You might have a board supplying mainly lifts, large submains etc, and you can stick a 10A in there for the alarm.

P

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 23 January 2011 11:59 PM
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peteTLM

Posts: 3083
Joined: 31 March 2005

i think the manufacturers data needs to be consulted for each case, as i believe they differ between makes.

Wheres JP when you need him?

P

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 24 January 2011 07:26 AM
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Jaymack

Posts: 4480
Joined: 07 April 2004

It's not in the knowing, it's in the knowing where to look!

MCB (Miniature Circuit Breaker) - rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation.

MCCB (Moulded Case Circuit Breaker) - rated current up to 1000 A. Thermal or thermal-magnetic operation. Trip current may be adjustable. Higher fault level withstand than an MCB.

Air Circuit Breaker - Rated current up to 10kA. Trip characteristics are often adjustable including configurable trip thresholds and delays. Usually electronically controlled - some models are microprocessor controlled. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance. Higher fault level withstand than an MCCB.

Regards
 24 January 2011 07:57 AM
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GeoffBlackwell

Posts: 3430
Joined: 18 January 2003

Well down here in the South things have moved on .

MCBs - BS 60898 includes a range up to 125A and a fault rating of up to 25kA - The Crabtree polestar has a rating of 15kA.

MCCBs - example - ABB SACE Isomax S8 MCCB which is available in ratings up to 3200A with a variety of electronic control packs .

or from another ABB range
(sic)
In the range of molded case circuit breakers conforming with the UL 489 and CSA C22.2 Standard, ABB proposes an entire range which covers current ratings between 15 A and 2500 A and interrupting ratings, at 480 V AC, which can reach 150 kA.
The ranges available are as follows:
- circuit breakers for power distribution (fitted with thermomagnetic or electronic trip units starting from 100 A)
- circuit breakers with adjustable magnetic only trip units for motor protection (MCP: Motor Control Protection)
- molded case switches for use as isolators or switching devices for lines, busbars or parts of a plant (MCS:
Molded Case Switch)
With the introduction of the new Tmax UL series, a single-pole circuit breaker with interrupting rating of 18 kA
at 277 V AC is available on the American market for the first time.


Note the 150kA fault rating available on some!

ACBs - try Merlin Gerin Master Pack range - 800A to 6500A - fault capabilities from 65kA to 150 kA .

Regards

Geoff Blackwell
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