27
\$\begingroup\$

What are the practical differences between ceramic and glass tube cartridge fuses?

I am trying to find new fuses for a piece of consumer electronics. The original fuses are going out of production.

The fuses the original BOM called for are ceramic cartridge fuses.

It is my understanding that ceramic-tube fuses are significantly more durable, and are able to break a higher-current fault.
However, in this case, both buses have identical markings (CE, UL, etc...) and are sufficiently rated for any fault-situation the device could reasonably be expected to endure.
Also, this is a piece of tabletop-equipment, so durability is not relevant (if you drop the thing, lots more then the fuse will break).

As far as I can tell, the originally specified ceramic fuses are kind of overkill. What should I be concerned about if I switch to glass-tube fuses?

\$\endgroup\$
1
  • 1
    \$\begingroup\$ It would be interesting to know both what fuses specifically you are looking at and what the application is. \$\endgroup\$
    – Peter Green
    Commented Jan 21, 2016 at 23:32

5 Answers 5

Reset to default
19
\$\begingroup\$

Using the wrong type of eg 10 A fuse can result in death - and has done so in some cases.

As well as the aspects mentioned there is an extremely important characteristic of some fuses which Johny's answer was somewhat related to.

The characteristic is termed "high rupture capacity" or HRC. The rupture capacity or breaking current of a fuse is NOT directly rlated to its fusing current. The RC is the current that the fuse can interupt under fault conditions.

A fuse may be rated at say 10A bu an initial fault condition may produce an initial surge current of 100A, or 1000A or even 10,000A. If the fuse is unable to terminate this flowing current then "there will be problems".

Items like multimeters that are intended for mains use may have HRC fuses specified. This is because the mains will happily provide fault currents well in excess of their fusing currents. Currents of hundreds of amps can occur under mains fault conditions. Worst case, people have been killed because a non-HRC fuse was used when an HRC one was specified. An arc develops in the equipment, cannot be extinguished and the resultant arc energy melts and scatters the meter or other equipment essentially explosively.

While many HRC fuses are visibly special See Gargoyle mug shots HERE some appear nearly identical to standard small glass fuses. HRC fuses will almost invariably be ceramic rather than glass.

HRC fuse catalog - these are high voltage by normal standards, but it's interesting to note 3A fuses with 40,000A interruption capability.

Wikipedia - Fuses - breaking capacity

  • The breaking capacity is the maximum current that can safely be interrupted by the fuse. Generally, this should be higher than the prospective short circuit current. Miniature fuses may have an interrupting rating only 10 times their rated current. Some fuses are designated High Rupture Capacity (HRC) and are usually filled with sand or a similar material. Fuses for small, low-voltage, usually residential, wiring systems are commonly rated, in North American practice, to interrupt 10,000 amperes. Fuses for larger power systems must have higher interrupting ratings, with some low-voltage current-limiting high interrupting fuses rated for 300,000 amperes. Fuses for high-voltage equipment, up to 115,000 volts, are rated by the total apparent power (megavolt-amperes, MVA) of the fault level on the circuit.

This Answers answer says

  • The main advantage offered by an HRC fuse is that, when a fault current condition occurs, a tremendous amount of heat is created within the fuse. That heat melts the silica sand filling of the fuse into glass. Glass, being an insulator, suppresses any arc-over and breaks the circuit instantaneously. This behavior minimizes the possibility of a continuing - and dangerous - "high arc current" situation from developing, which is what happens if a normal fuse fails to break a heavy fault current.

    ... choosing to use an HRC fuse instead of a normal fuse makes very good sense if the equipment that needs to be protected - or other equipment nearby - would be very expensive to replace if it all went up in smoke just because of a fuse which was not capable of stopping a high fault current flowing.

    So, if some expensive electrical equipment was supplied with one or more HRC fuses installed to protect it, you would be very foolish indeed to replace them with normal "non-HRC" fuses.

Read more: http://wiki.answers.com/Q/What_is_the_advantage_of_an_HRC_high_rupturing_capacity_fuse#ixzz1uCKdwImw

\$\endgroup\$
4
  • \$\begingroup\$ What would be the practical or safety implications of e.g. wiring a 200mA glass fuse in series with a 500mA or 1A HRC fuse, if one expected that circumstances which would blow the glass fuse might arise often enough that expense of replacing HRC fuses could be an issue? I'd expect the glass fuse should be enclosed so as to contain any debris; would such enclosure plus the series-wired HRC fuse be adequate protection against foreseeable failures? \$\endgroup\$
    – supercat
    Commented May 7, 2012 at 16:34
  • \$\begingroup\$ @Supercat - that sounds like an excellent idea. You'd have to arrange things physically so that the HRC fuse provided good isolation and could not be bypassed by worst case disasters to the lower rated fuse but overall it seems that could give you the best of both worlds. So - there must be a law against it :-). \$\endgroup\$
    – Russell McMahon ♦
    Commented May 7, 2012 at 17:30
  • 2
    \$\begingroup\$ My concern would be that I don't know all of the things that might go wrong when a little fuse tries to interrupt a monstrous amount of power. The fact that it might not actually interrupt it is a given; my concern would be that the small fuse might get into a state which restricts current flow enough to prevent the larger fuse from tripping quickly, but still allows enough current through to produce a lot of heat. Is the construction of fuses and behavior of arcing gases such that one would be unlikely to have a stable equilibrium passing moderate current? \$\endgroup\$
    – supercat
    Commented May 7, 2012 at 18:08
  • 2
    \$\begingroup\$ @supercat - This is something I'd need to think further about BUT it seems that as long as the HRC fuse was mounted in such a way that it would break an arc at whatever design level was required, then placing a smaller current rating separate fuse elsewhere in the circuit should be very safe. The sort of current needed to draw an arc across a fuse would be vastly in excess of any operating current so the HRC fuse would blow within milliseconds in such extreme cases. No stable equilibrium would be produced by placing two fuses in series if they were not "environmentally coupled". \$\endgroup\$
    – Russell McMahon ♦
    Commented May 7, 2012 at 20:16
11
\$\begingroup\$

Just to be sure: We're talking about d = 5 mm and l = 20 mm sized fuses?

My experience is that ceramic fuses, compared to glass fuses, tend to be better when it comes to things like switching off ("tripping", "blowing") during high-current events. A rough estimate is that the best fuses have a ceramic body and contain sand to extinguish any arcs that appear when the fuse blows. The worst fuses I have seen and experienced were indeed glass fuses. There really are very big differences between various fuses, even when they all have the same basic rating (for example: "6.3 A, T, 250 Vac"). Some just trip quite silently, others explode with a massive and loud show including flying pieces of glowing material.

This being said, I am sure you can get really poor ceramic fuses and you probably can get glass fuses that are actually good and were approved to any standards you may require (UL, VDE, ...).

Sometimes, a certain piece of equipment got its UL sign with one particular manufacturer and model of fuse. Strictly speaking, You would violate this UL mark using any other fuse.

\$\endgroup\$
4
  • 2
    \$\begingroup\$ Fuse blowing/breaking characteristic is dependent on the fusible link material and not on the case material. Slow or fast blow type fuses are and can be offered in both glass and ceramic bodies. The bad experience with glass fuses comes from the fact that they're cheaper to build and more ubiquitous - conditions that are highly correlated to the abundance of sub-standard parts (China). wiki.answers.com/Q/… \$\endgroup\$
    – shimofuri
    Commented May 7, 2012 at 14:09
  • 1
    \$\begingroup\$ I agree mostly... However, especially when breaking a DC current where arcing may be present for an extended duration, the material around the fusible link does play a role: How soon will it melt? Will it help extinguishing an arc? (Think: Sand-filled fuses vs. non-sand-filled fuses) \$\endgroup\$
    – zebonaut
    Commented May 7, 2012 at 14:32
  • 1
    \$\begingroup\$ The speed of breaking (how soon will it melt) of the fusible link is specified by its type (slow/fast blow) and is governed by standards. Sand filling is used to absorb the energy released when melting. Heat fuses the sand instead of melting the case and leaking out causing damage. However, that scenario is a concern for high current rating fuses which is not the domain of glass types. Typically, glass cases are not offered from 10A x 250V upwards. If conformant to standards, ceramic and glass fuses of the same rating are functionally equivalent. \$\endgroup\$
    – shimofuri
    Commented May 7, 2012 at 15:08
  • 1
    \$\begingroup\$ "How soon will it melt?" was not about the fusible link - it was about the case. Glass melts sooner than ceramics do, and this is critical when the fuse opens with an arc. Fuses breaking a circuit, especially with a DC current, may do so with an arc burning quite long, and once the fuse's body becomes a mixture of molten glass and molten metal, this is anything but helpful or safe. \$\endgroup\$
    – zebonaut
    Commented Jun 5, 2012 at 7:18
4
\$\begingroup\$

Glass tube fuses are transparent: an advantage over ceramic fuses as you can visually determine if the fuse is busted.

\$\endgroup\$
3
  • 2
    \$\begingroup\$ This probably isn't broad enough to warrant an answer - there are a lot of other things that should be mentioned really. \$\endgroup\$
    – Cybergibbons
    Commented May 7, 2012 at 10:35
  • 2
    \$\begingroup\$ @Cybergibbons The query is asking about practical differences. The querent had already supplied the basic difference between glass and ceramic: the latter being more durable. Everything else held constant (which was also specified/implied: rating, form factor), I don't see any other practical difference between glass and ceramic save for the former being transparent. Unless, of course, visual troubleshooting that takes a second versus a couple minutes of extraction and resistance testing is not practical for you. \$\endgroup\$
    – shimofuri
    Commented May 7, 2012 at 10:44
  • \$\begingroup\$ @shimofuri, but this answer is very short and not detailed. Either of your comments to zebonaut contain more information then this answer does. Why include some of that, explain that glass fuses will only be used a lower currents and that you must use sad for higher currents and voltage, why that is and maybe even why a cheap fuse from china can throw off your product, that is up to you but this answer as it is is not very useful. \$\endgroup\$
    – Kortuk
    Commented Jun 3, 2012 at 14:16
0
\$\begingroup\$

All fuses should have a AIC (Ampere interrupting capacity). Do the proposed replacement glass fuses have a AIC greater than or equal to that of the ceramic fuses originally specified?

\$\endgroup\$
1
  • 5
    \$\begingroup\$ Is that a question or an answer? \$\endgroup\$
    – stevenvh
    Commented May 7, 2012 at 15:39
0
\$\begingroup\$

When I compared spec sheets for fast glass and fast ceramic fuses of one manufacturer, I observed:

Ceramic fuses are faster than glass fuses of the same rating.

Glass fuses have lower cold resistance than ceramic fuses of the same rating.

\$\endgroup\$

Not the answer you're looking for? Browse other questions tagged or ask your own question.