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Posted By Topic: Type A MCB?

Mar 13 2018 21:25

I've always been familiar with MCBs with type B, C and D tripping curves.

Question. Was there ever a Type A MCB and if so what was it, what did its trip at, and what happened to it?

I was asked this by one of our an Apprentices yesterday and had aboslutely no idea!

I said I'd get back to him later as I was too busy... So if you know the answer please let me know.

That way I can get back to him tomorrow and maintain my reputation as the fountain of all knowledge.

Thanks, Paul.

Mar 13 2018 22:02

I checked an old IEC 60898:2004 standard that I have and at the point in time (2004) there was only typers B, C and D.

There ws a major change in the ways of rating MCBs operting charistics back in the 1960s; Close and coarse protection to the old timers like myself.

What happen to type A (if one ever existed) is a unknown.

I assume that it was a another rating factor which has fallwn out of use due to different ways of rating the maximum temperature of cable conductor under high short circuit flowing conditions which the MCB as the circuit protection device must operate before permanent damge is done to the cable insulation.

Mar 14 2018 07:04

Thanks for the response Pluto.

When asked it seamed a very obvious and good question.

Evidently the answer lays lost in time.

Thanks again, Paul.

Mar 14 2018 07:41

I remember a tutor having an answer for this at tech as being along the lines of type A MCBS were susceptible to nusance tripping especially in parts of the world with humidity, so they fell out of favour.

Not sure how true this is but thats what I remember.

Mar 14 2018 07:44

I'm not sure how you manages to confuse Pluto with this one?

Type A is the type that we use in NZ. They comply with AS/NZS3190 and AS/NZS 61008.1

Take a look at which lists some of the types of RCD

Mar 14 2018 08:01

Sorry, too early in the morning for me..

You're asking about MCBs, not RCDs

Mar 14 2018 21:35

All good Doug

It seems such a simple question on the face of it but after ten mins of googling I found nothing.



Mar 15 2018 00:14

According to the BEAMA Guide to Low Voltage Circuit-breakers Standards in accordance
with BS EN 60898-1, BS EN 60898-2 and BS EN 60947-2

"Note: There is no Type A instantaneous tripping characteristic to avoid confusion with the A abbreviation for amperes."

Mar 16 2018 07:25

Thanks everybody. I can gnow go into my weekend with the A-type MCB mystery solved!