A few questions on cartridge fuses - Page 1
Forum section: electronics / beginners

author: lpc32
author_rank: Frequent Contributor
timestamp: July 01, 2015, 01:31:23 pm
content: Is HRC the same as "high breaking capacity"?Is there any well-defined meaning to either term? Like, say, "HBC will withstand properly at least 10 times the rated current".Does HBC imply ceramic, or at least not glass?Does "low breaking capacity" imply glass?Are the speed/characteristic grades well-defined?

author: Tandy
author_rank: Frequent Contributor
timestamp: July 01, 2015, 02:24:11 pm
content: Fast-acting fuses simply have no intentional time-delay. Typical opening times at 500% of the fuse rating range from 0.05 second to approximately 2 seconds. Where as slow blow have deliberate features to delay the breaking.HRC = High Rupturing Capacity, same thing as HBC.Essentially means the fuse can handle extremely high fault currents. A glass fuse will typically explode under huge current fault conditions, a HBC fuse is ceramic and filled with sand to quench the arc.

author: shanky887614
author_rank: Contributor
timestamp: July 01, 2015, 03:43:42 pm
content: hrc are useful because of the high rupture current to blow them.hrc fuses can be rated at over 100KA fault current and gfci or your equivilent of circuit breakers (or glass/fast blow fuses) can be as low as 2-3ka. domestic mcbs are usually 6ka in the uk but you can get upto 20ka for industrial needsthe ka rating is bassically the inrush trip current needed to blow it ( its different on an mcb/gfci because if they hit that rating they will be knackered and will need replacing)hrc is high rupture current btw (im an electrician and use them regually)

author: ConKbot
author_rank: Super Contributor
timestamp: July 01, 2015, 03:58:06 pm
content: The rated interrupting current is usually right on the fuse for larger ones or at least in the datasheet. For example, type RK-5 fuses used for switch disconnects in motors and the like generally can have anywhere from a 50kA AC to a 200kA AC interrupt rating, even the 0.1A fuses.As far as well defined, in general? No, you just need something rated for higher than your fault current. For meters, the CAT rating also implies what fault current is available, and the meter should be able to handle. And a ceramic body is no guarantee of interrupting rating. Buss AGC and MDA fuses are both rated for 10kA @ 120VAC, one is glass, the other is ceramic (and slow-blow) But if a meter is fitted with one and you go mucking around in a panel, leave it in current mode and short something out, you better hope the main breaker for the building kicks in quick because there could potentially be more than 10kA available. According to wiki, CAT III is upto 11kA fault current, so it could be marginal, couldn't find any references for CAT IV.

author: dom0
author_rank: Super Contributor
timestamp: July 01, 2015, 08:26:06 pm
content: CAT III means the nominal current is <11 kA and the fault current is <25 kA. CAT IV is for fault currents >25 kA, <100 kA.iirc. Not an electrician.

author: lpc32
author_rank: Frequent Contributor
timestamp: July 03, 2015, 11:29:07 am
content: Thanks.I've found some more info as well. In summary:HRC and HBC seem to be synonyms. Not sure where HRC originates from, though."High/enhanced/low breaking capacity" is well-defined, for example inIEC 60127-2. Low is the greater of 35A or 10 times rated current. Enhanced is 150A, High is 1500A. There are other specs, like maximum power dissipation, max voltage drop, pre-arcing times per a few given multiples of the rated current. (Oddly: for slow/time-lag fuses, while "High" has generally longer pre-arcing times than "Low", at 10 times the rated current it's shorter.) UL and the likes may have additional stipulations.I wouldn't say that's definitive, butthis random 1 page documentfrom Littlefuse, titled "5x20mm fuse marking according to IEC 127", supports the notion that HBC = ceramic, LBC = glass:QuoteSpeed grades (FF, F, M, T, TT) are defined as well, somewhere inIEC 60127. At least Fast (F) and Time-delay/slow (T) are mentioned in IEC 60127-2. At least FF/F/T/TT are probably mentioned in 60127-4 (page 12 hereimplies this).BTW, I hate this practice of standards bodies/organizations to hide the specs and require payment to access them.