Switch on surge.

Graham. wrote:

yup
not sure it makes much difference what you call it :)

Its rare that they dont have sufficient insulation for that. Microwave tranformers dont, and probably some very old bobbinless ones.
NT
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Dave Plowman (News) wrote:

http://www.tlc-direct.co.uk/Products/WYNSC30.html
HRC fuses are fine and can have advantages from time to time. Re-wireable are allowed, but there is no sane reason for fitting one.
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Cheers,

John.

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I only really looked for Hager - that's the CU fitted.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Oddly Hager was always my first choice for HRC carriers - however when I looked this time I could not see them.
I have one here feeding my garage/workshop. The existing cable was a bit smaller than I would have liked (but a relatively major pain to upgrade), so to get best usage on it, I put a 32A HRC at the head and use a 32A MCB on the power circuit for the workshop - which should hopefully discriminate on a fault.
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wrote:

They still show on Hagers web site
http://www.hager.com.sg/menu/product/protection-connection/fuse-carrier/800-2343.htm
Adam
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ARWadsworth coughed up some electrons that declared:

http://www.hager.com.sg/menu/product/protection-connection/fuse-carrier/800-2343.htm
Might be special order time down at TLC, who do have an account with Hager directly (almost obviously) and can, if asked nicely, actually get *anything* from Hager's catalogue (I got them to get me some double pole RCBOs - try B&Q for that!)
Personally, I would try a type C breaker first - they're easy enough to get for Hager boards (I have a Hager, specifically because the massive choice of MCBs and RCBOs is excellent).
Cheers
Tim
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Tim S wrote:

http://www.hager.com.sg/menu/product/protection-connection/fuse-carrier/800-2343.htm
At 10x rated current a type C can trip in as little as 0.0015 seconds. I doubt it would do. A wire fuse is closer to a D type, which is orders of magnitude slower at 10x rated current.
NT
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snipped-for-privacy@care2.com coughed up some electrons that declared:

I don't have my books to hand, so I'll not argue. But if that is correct, then the conditions for putting in a Type D breaker or something with a similar trip curve are considerably more onerous in terms of having a low loop impedance on the local circuit *and* on the supply (ie in the event of a dead short L-E fault, would the breaker or fuse clear before the cable damages itself through overheating?).
It would be quite possible to have a perfectly ordinary and good installation where adding a type D to a random circuit would make it both non compliant and dangerous (particularly from risk of fire, but also shock if the breaker/fuse cannot reliably clear a fault.
However, this does change if there is RCD protection (don't think that was mentioned) - but even so, personally, I would want to then ensure that a L-N fault would clear in the expected times, which is an easier target to meet, but not necessarily a forgon conclusion.
I'd be cautious about jumping straight to something with that sort of characteristic without risking a few quid on the middle option first (there's always ebay if a Type C doesn't work out).
IIRC (memory poor, open to correction) a Type C is several times less sensitive on the instantaneous trip part of the curve compared to a Type B, so there's a good chance it would buy enough margin.
I'm happy to come back tomorrow and reel off some numbers, or I think if one digs into Hager's literature, the trip curves for most of their devices are in there somewhere. Might have a rummage later...
Cheers
Tim
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Tim S wrote:

10x rated i is a reasonable ballpark for a toroidal startup surge. That's 12.5A in this case, which is only just over 2x the MCB's rated i - I was thinking 10x MCB rated i, so you may well be right with a type C.
NT
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snipped-for-privacy@care2.com coughed up some electrons that declared:

Aye - I was more concerned about randoming banging Type D's - or something equally thick skinned - in without a more detailed test of the installation (loop impedances mainly), which is why I was discouraging it.
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wrote:

Have you thought of wiring a soft start dimmer in the supply? Just leave it on max and hide it somewhere. Make sure it can handle inductive loads though.
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[snip]
Nice info Andrew - but doesn't help with the problem. ;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Change to an electronic transformer. Better regulation, dimmable, etc.
I have a 100W toroid to which I fitted a NTC thermistor, but this isn't the sort of modification I would suggest someone does unless they are fully familiar with designing safe mains appliances. e.g. a thermister in series with a toroidal transformer could in theory burn out and sustain an arc for long enough to ignite nearby materials with the transformer acting as a ballast and preventing any fuse blowing, and you need to design a solution which removes the fire risk from that failure mode.
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Andrew Gabriel
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Just looking at TLC, the largest they do is 150 watts. And with 15 20 watt lights that doesn't compute for two of them. And as I said it might be difficult to rewire it to split the load.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Andrew Gabriel wrote:

I cant quite get my head riound it, but I am sure there is something comprising a big triac, and a diode capacitor and a few components that acts as a 'startup dimmer'
Also a zero crossing switch is possible, but again memory fails me...
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Dave Plowman (News) wrote:

And the connection between cause and effect is plain wrong.
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I've added this link to a soft start circuit for toroidal PSUs on power amps - so should do what is needed technically. However, it may be over complicated for what you want, and especially in terms of getting new circuitry into the enclosure of the lamp.
http://sound.westhost.com/project39.htm
Charles F
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Thanks for that - very interesting. I'm wondering in this app whether the relay connected directly across the supply would provide a long enough delay to prevent the MCB tripping? After all, they don't operate immediately. I do have some 10 amp 240v coil relays lying around and there would be room for one plus resistors inside the 'base'. Making up the timer section would be too costly, time wise.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

There may be an easier way..
Use a relay in series with a diode and a resistor, and with a fat electrolytic across the coil.
In fact, I suspect something like a triac would work in that mode, too.
But I still like the thermistor the best.
Less components, and possible to use a really big fat one!
The CL-80 from here looks about right
http://www.farnell.com/datasheets/85914.pdf
peak current would be limited to about 5A, and at 2A resistance has dropped from a cold value of 47ohms to less than an ohm. The only issue is that these things will get very hot, and may be running at mains potential, so you need something like an earthed mesh box to pop it into.
I think I would be tempted to put it in the actual backing box of the switch itself.
One end into the switched live terminal, and the other crimped to the switche live wire. Then glue some insulation to any nearby part of the backing box in case it touches that.
Or, if it was not appropiate to use the backing box, use another backing box with a 4 terminal block in it, and mount that where it can get hot in peace!
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wrote:

I have something similar made up to delay the switch-off of a heating pump, with an older boiler that doesn't sensibly control it - but I had enough space for small transformer. I wonder if you could use a high voltage DC relay, with directly rectified mains, a resistor and C - to just slow the relay closure down enough. Would all be rather nasty high voltage stuff though....
Charles F
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