jonball Posted June 20, 2013 Share Posted June 20, 2013 I've recently bought an old analogue MicroPack 2.5 series II dimmer for a bargain price. All 4 channels work fine but one thing is puzzling me. The wording on the front says "max. load per channel = 2.5kW" but then goes on to say "Use only BS1362 7 amp fuses" and indeed 7 amp fuses are fitted. This isn't particularly a problem for me as it is useful for me to be able to dim small heads like 650's but I'd like to understand this apparent contradiction. Why does it say max load 2.5kW per channel when the specified fuse protection effectively limits each channel to about 1.6kW? I'm probably being dense... Jon Link to comment Share on other sites More sharing options...
ianknight Posted June 20, 2013 Share Posted June 20, 2013 The BS for the fuse states that it has to carry at least 1.5 times it's rated current before it blows - 'twas explained to me by Tim Burnham one afternoon at Berkey Colortran in Thetford (many moons ago). At the time, they considered 7a fuses to be relatively easy to get hold of on "the high street" and that the triacs were durable enough to not warrant a fast acting fuse. But this all did happen c1979 so my memory may be a bit hazy... :) Link to comment Share on other sites More sharing options...
Brian Posted June 20, 2013 Share Posted June 20, 2013 The BS for the fuse states that it has to carry at least 1.5 times it's rated current before it blows... Not quite. The non-fusing current is 1.6 times the rated current; the fusing current is 1.9 times the rated current. [source: BS1362. Section 5.6.2] Link to comment Share on other sites More sharing options...
ocfe Posted June 20, 2013 Share Posted June 20, 2013 Wow I used to do some work at a place with Green Ginger dimmers 2k loads and 7amp fuses, it puzzled me too. Thanks for that very useful nugget of information Ian. Link to comment Share on other sites More sharing options...
ianknight Posted June 20, 2013 Share Posted June 20, 2013 The BS for the fuse states that it has to carry at least 1.5 times it's rated current before it blows... Not quite. The non-fusing current is 1.6 times the rated current; the fusing current is 1.9 times the rated current. [source: BS1362. Section 5.6.2] I did say my memory was hazy :P Anyway what's 0.1 between "friends"? Link to comment Share on other sites More sharing options...
PaulDF Posted June 20, 2013 Share Posted June 20, 2013 Won't using them above their rated current for prolonged periods end up with melted fuse holders? Or are the fuse holders different to the normal melty plastic ones? Link to comment Share on other sites More sharing options...
Brian Posted June 20, 2013 Share Posted June 20, 2013 Won't using them above their rated current for prolonged periods end up with melted fuse holders? On most equipment the melty fuse-holders is the over-current protection! Or at least on that equipment where the designer doesn't know how to read a fuse-holder's datasheet. Link to comment Share on other sites More sharing options...
Robin D Posted June 20, 2013 Share Posted June 20, 2013 I have three old UK build Berkey Colortran "6 Pack"s and they too have 7a fuses rated at 10a per channel. Before MCB and the like became affordable, it was a way of ensuring more delicate parts of the circuit were not overloaded. I've never melted a fuseholder yet and have run 4 x 500W lamps from a single circuit with no issues. I've never needed to see if I can get the full 10amps per channel. Link to comment Share on other sites More sharing options...
Brian Posted June 20, 2013 Share Posted June 20, 2013 I have three old UK build Berkey Colortran "6 Pack"s .... Built like a tank, I got rid of the last of mine last year. They were very second-hand when I bought them from Samuelsons; I collected them directly from their last job which was the film set for 'Aliens'. Link to comment Share on other sites More sharing options...
jonball Posted June 20, 2013 Author Share Posted June 20, 2013 Thanks very much for the comments. I've now tried an old ex-HTV Castor on it and the best part of 9 amps was happily flowing through the 7a fuss without a problem so the 1979 conversation still holds good! The fuse was a little warm to the touch afterwards as you would expect, but the fuseholders are certainly not going to melt. Link to comment Share on other sites More sharing options...
dbuckley Posted June 21, 2013 Share Posted June 21, 2013 And I'm sure I'm not alone in having a small pile of 7A fuses, from back when these dimmers were what White Light rented... Link to comment Share on other sites More sharing options...
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