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MCB Switching off curve

This topic originated from the How to page called Miniature circuit breakers (MCBs)
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chris911sc

from Ireland

Joined: 18 Mar 2005
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PostPosted: Mon May 30, 2005 12:40 pm Reply with quote

Could somebody explain to me the difference between MCB switching off curves A, B & C?
Thanks
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plugwash

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PostPosted: Mon May 30, 2005 12:50 pm Reply with quote

afaict there is no type A

basically a mcb has two parts

the thermal trip is the same between a B a C and a D of the same rating and deals with relatively small but sustained overloads.

the magnetic trip is designed to take out short cuircuits and it either trips or it doesn't. If the magnitic trip point is hit the breaker will trip extremely fast (0.1 sec is the standard iirc but some manufacturers claim even faster). The type of the breaker determines how many times the rated current is needed to take out the magnetic trip

B is 3-5 times C is 5-10 times and D is 10-20 times.

A lower fast trip point makes cuircuit design to meet earth fault loop requirements easier but can cause nusense tripping with some loads (b6 breakers on lighting cuircuits are well known for this issue).
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ban-all-sheds

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PostPosted: Mon May 30, 2005 6:00 pm Reply with quote

As Breezer says, it's amazing what info you can find in the For Reference topic....

http://www.diynot.com/forums/viewtopic.php?p=76467#76467
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Senarathne

from Sri Lanka

Joined: 30 Aug 2006
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PostPosted: Wed Aug 30, 2006 10:29 am Reply with quote

What are the advantages and disadvantages of minature circuit breakers?
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JohnD

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PostPosted: Wed Aug 30, 2006 11:07 am Reply with quote

Compared to a chocolate cake, an MCB doesn't taste so good (disadvantage) but is better at cutting electrical overloads or short circuits (advantage)
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securespark

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PostPosted: Wed Aug 30, 2006 2:37 pm Reply with quote

JohnD wrote:
Compared to a chocolate cake, an MCB doesn't taste so good (disadvantage) but is better at cutting electrical overloads or short circuits (advantage)


I find victoria sponge better at cutting overloads than a choccy cake...must be the jam...
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ban-all-sheds

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PostPosted: Wed Aug 30, 2006 5:19 pm Reply with quote

Surely currant buns are the best for that purpose?
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RF Lighting

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PostPosted: Wed Aug 30, 2006 5:22 pm Reply with quote

ban-all-sheds wrote:
Surely currant buns are the best for that purpose?


shouldn't that be a current bun? icon_wink.gif
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TheGaffersSon

from United Kingdom

Joined: 29 Aug 2006
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Location: Manchester,
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PostPosted: Wed Aug 30, 2006 5:47 pm Reply with quote

RF Lighting wrote:
ban-all-sheds wrote:
Surely currant buns are the best for that purpose?


shouldn't that be a current bun? icon_wink.gif


That's a shocking joke icon_lol.gif

I'll just get me' coat...
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ban-all-sheds

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PostPosted: Wed Aug 30, 2006 6:13 pm Reply with quote

RF Lighting wrote:
ban-all-sheds wrote:
Surely currant buns are the best for that purpose?


shouldn't that be a current bun? icon_wink.gif

No - it's a homophonic pun.
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JohnD

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PostPosted: Wed Aug 30, 2006 6:18 pm Reply with quote

homophonic bun, you mean.
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RF Lighting

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PostPosted: Wed Aug 30, 2006 6:26 pm Reply with quote

ban-all-sheds wrote:
No - it's a homophonic pun.


Sorry I don't know what that word means.
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JohnD

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PostPosted: Wed Aug 30, 2006 6:29 pm Reply with quote

A pun is a humerous wordplay with words that sound the same.

"Homophonic" means sounds the same.
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ban-all-sheds

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PostPosted: Wed Aug 30, 2006 8:12 pm Reply with quote

But are spelled differently.

Can also be homographic - same spelling, different meanings, e.g. "Being in politics is just like playing golf: you are trapped in one bad lie after another."
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