Circuit breaker vs UK plug fuse / testing mains circuits - Page 1
Forum section: electronics / beginners

author: GoJuice
author_rank: Contributor
timestamp: June 25, 2021, 08:26:01 pm
content: I built a simplemains AC > bridge rectifier > small 400v capcircuit and blew some fuses not realising how much inrush current that circuit must pull at switch on.I’ve found a littlepanel mount 1A circuit breakernearby on eBay, I was thinking of getting it to essentially be a resettable fuse replacement, to avoid blowing fuses because of accidental shorts or to use when testing mains circuits like the one above. Does that seem like a good idea?It needs to trip before a 13A fuse can blow at least (if I don’t bypass the UK plug fuse). I’m not sure if it’ll trip fast enough or if 1A circuit breaker would be a bit too sensitive.

author: Benta
author_rank: Super Contributor
timestamp: June 25, 2021, 08:56:57 pm
content: Based on your question, I'd say keep your hands off before you kill yourself.You don't seem to know what you're doing. Start with lower voltages, eg, 12 V and play around to get a feel.

author: Gyro
author_rank: Super Contributor
timestamp: June 25, 2021, 10:00:53 pm
content: Ah yes, I remember your SMPS 'experiments' from last year.Pleasestop now. A non mains-isolated and raw 400V supply is no use to man nor beast You have so many opportunities to kill yourself!

author: themadhippy
author_rank: Super Contributor
timestamp: June 25, 2021, 10:02:49 pm
content: What sort of fault current can your circuit breaker handle? is it rated for mains use?Quoteyou'll find that information on the IT graph

author: james_s
author_rank: Super Contributor
timestamp: June 25, 2021, 10:08:58 pm
content: What you need to do is limit the inrush current so that it is not tripping the protection. Circuit breakers are much slower than fuses though and much less likely to blow.I agree with others though, if you don't know what you're doing you should not be messing with this stuff. It only takes one mistake and you are done, there is no second chance.

author: themadhippy
author_rank: Super Contributor
timestamp: June 25, 2021, 10:40:30 pm
content: QuoteBit of a sweeping statement,for example the starting current of a decent size motor will trip a type B mcb whilst the same rated BS88 fuse will happily let the starting current pass.

author: Manul
author_rank: Super Contributor
timestamp: June 25, 2021, 11:01:19 pm
content: Quote from: GoJuice on June 25, 2021, 08:26:01 pmWhat I will say is that blowing fuses is not something what should happen often. I work a lot with various stuff, blow a fuse maybe once a year or less.My point is that maybe it is good that you blow fuses, need to buy them and replace. This must be annoying. And it is good, that it is annoying. It creates at least some negative feedback for being careless and clueless. It will push you to learn stuff, think twice, be more focused and develop other good traits. I'm serious, this is not humor.

author: james_s
author_rank: Super Contributor
timestamp: June 26, 2021, 07:58:53 am
content: Quote from: themadhippy on June 25, 2021, 10:40:30 pmTrue. I should have said that in general, fuses can act much faster than most circuit breakers. You can of course get deliberately slow acting fuses, but there's a limit to how fast a circuit breaker can act.

author: GoJuice
author_rank: Contributor
timestamp: June 30, 2021, 06:21:18 pm
content: Quote from: Gyro on June 25, 2021, 10:00:53 pmLol, yeaheekI think I give wrong impression with my basic questions. I know you can use an isolation transformer or variac for testing mains circuits, but I can’t really go down that route at the moment.I didn’t find a datasheet for the 1A panel mount breaker. I got a sort of rough idea about trip times with MCBs type C, type D, type A, etc vs fuse trip times. I was basically just spit balling an idea that seemed not completely unreasonable at the time I posted, especially since other countries don’t even have a fuse in their plugs.

author: GoJuice
author_rank: Contributor
timestamp: June 30, 2021, 06:30:23 pm
content: Quote from: Manul on June 25, 2021, 11:01:19 pmYeah, this. I blew some fuses but now I’ve learned about needing inrush limiting from it. I suppose I got my answer right there.

author: themadhippy
author_rank: Super Contributor
timestamp: June 30, 2021, 06:33:32 pm
content: QuoteOther country's don't have a 32A device protecting there socket circuits either,you could do away with your plug fuse if you was to use 4mm2or larger flex.

author: Terry Bites
author_rank: Super Contributor
timestamp: July 02, 2021, 05:20:36 pm
content: You're scaring me man!

author: james_s
author_rank: Super Contributor
timestamp: July 02, 2021, 06:08:18 pm
content: Quote from: GoJuice on June 30, 2021, 06:21:18 pmFrankly if you can't go down the route of doing this stuff safely then you can't (or shouldn't) go down the route of playing with it at all. 240V mains is seriously dangerous stuff, people get killed by it, sometimes even people who know what they're doing.