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 Topic Title: Type 1, 2, 3 MCBs and max Zs Topic Summary: Created On: 01 September 2013 08:42 PM Status: Read Only Linear : Threading : Single : Branch
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 01 September 2013 08:42 PM Smith249 Posts: 386 Joined: 09 September 2004 Good evening. Could someone explain the older MCB types modern equivalent ?, also the max Zs for them. Many thanks. 01 September 2013 08:53 PM geoffsd Posts: 1783 Joined: 15 June 2010 Page 72 in OSG 02 September 2013 10:12 AM AJJewsbury Posts: 16095 Joined: 13 August 2003 Could someone explain the older MCB types modern equivalent ? Mostly the difference is the magnetic trip rating - B types - 3 to 5x In C types - 5 to 10x In D types - 10 to 20x In where as the old types: type 1 - 2.7 to 4x In type 2 - 4 to 7x In type 3 - 7 to 10x In So you can calculate max Zs using Ohm's Law and the current needed to reliably achieve the upper rating. E.g. a 30A type 2 will guarantee to trip at 7x In = 7x30 = 210A, hence 1.1 Ohms (or 0.8x = 0.88 Ohms if you want it corrected to room temperature using the usual rule of thumb). - Andy. 02 September 2013 11:20 AM Parsley Posts: 1353 Joined: 04 November 2004 here's an example 3871 type 2 5amp MCB Type 2 I.T.C (see table below) = 4 to 7 use 7. Multiply by current rating. Divide into Uo (230V) 7 x 5 = 35 A 230/35= 6.57 ohms (as per AJ use rule of thumb if you want) MCB InstantaneousTrip current Type (0.1-5s) 1 2.7 to 4In B 3.0 to 5In 2 4.0 to 7In C 5.0 to 10In 3 7.0 to 10In 4 10.0 to 50In D 10.0 to 20In Alternatively contact manufacturer especially where you have old type 4's. Regards
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