Fuse to Breaker Conversion

Basically, technically speaking in nearly all cases low voltage fuses can be replaced by breakers but there are notable exceptions:

1) In some cases local regulations don't allow it (doesn't make sense from a technical POV but you've to accept it). Where continental European rules apply you don't have that issue.

2) Power seminconductors can often only be protected by special fuses because breakers can't meet the requirements due to technical limitations.

3) Excepted at some very low voltages, DC currents may require specific breakers, especially if voltage and current are high. With DC always check carefully the specs and how to wire the contacts of the breaker.

4) For very low currents (a few hundred mA or less) there are not always suitable breakers but there are other, mostly electronic, options.

There are no hard and fast rules, it depends on the case and it would be too long to explain it here. There are too many fuse types and it's also about what you protect, depending on the case you can optimize the protection using a breaker so there's no basic recipe which gives you one breaker type + setting set to replace one given fuse.

Personally I design nearly always fuseless (excepted in the cases 2 to 4 above) so I don't really care about replacing fuses if I upgrade to breakers in most cases it's not complicated to do.

IMO fuses a just major PITA so I try to avoid them whenever possible (some will disagree but there could be endless discussions about pros and cons of fuseless designs).

You don't state what the application is but: if it residential or a comparable current range commercial installation, yes go right ahead. Replace the fuses with circuit breakers of the same current as each fuse is. Do a swap of components and enclosures that meets local electrical codes. Some times you can accommodate this easily by taking out the guts of the fuse box, use it as a junction box for the old wires to newly installed wires which are connected to each breaker in a circuit breaker panel mounted adjacent to or close by to the old box. Run extensions of the supply wires in the same way to the main breaker of the c/b panel. Use a solid cover on the old fuse box. Make sure you have your power supplier pull the meter at the pan so you are not working "hot". Some times, although seldom, the guts of the fuse panel can be removed and the guts of the circuit breaker panel installed directly in it. This is very rare with newer panels and old fuse boxes.

If it is a low voltage dc system, such as on a boat, RV or camper, or other unit treat it the same way. There are breaker panels made for this application. Install dc low voltage breakers of the same capacity as the old fuses.

If it is an industrial situation with high currents, high voltages, induction motors and that sort, get an appropriately trained Electrical Engineer or other person trained and very knowledgeable in that task for correct calculations and specifications. Don't ask the neighbor who designs integrated circuits or computer chips for help. He will try to miniaturize it, add all sorts of trips, oscillators, amplifiers, LDO's, FET's, etc. and you will never get it done before the modifications are needed.

Before doing any of these or other methods, make sure the one you choose meets local codes.

Good Luck, Old Salt

Of course there are. Your local electrical standards are immediately applicable. Don't leave home without them!

One uses British Standard 7671.

Standards aren't a religion. There are even cases where you can't abide to standards because it won't work, but if so as long as you can prove that you cannot follow existing standards while the basic principles of all safety requirements are met you can still request derogations. Standards aren't a set of hard and fast rules even if they cover most cases.

Of course I'm referring to very specific cases, like for example some industrial high power HF systems or research equipments.

Just to revive the never-ending discussion, there is one pro and con here in India. Pro: When you see an MCCB, you have no clue as to what is its stae. Has it broken two Ics faults and is about to explode ? Or has it never operated on load and is as good as new? On the other hand, a fuse is always new. WHen it blows, you replace it with a new one. No doubts,

Cn: Fuses have silver in them usually. Asking to be stolen.

i have got outstanding results in Type 2 Coordination tests per IEC 60947-4 when i used fuses as SCPD. Never great results with MCCBs unless i used really good current limiting ones from good companies - ABB, Schneider, GE, Eaton, Siemens etc.

As I live in a very modern small European country known worldwide for its very high industrial quality standards it's not that much an issue to use devices from good known manufacturers. So the situation is slightly different to the one you mention.

With fuses you also never know how it has been stressed during before being submitted to an overload or short-circuit which is supposed to blow it. Fuses age and can also show some odd behavior in some cases (fault arcing).

Fuses are also only unipolar as such while breakers are omnipolar (referring to main poles).

Last but but not least, fuses are way more dangerous than handling a breaker and there's also a risk that fuses are not replaced by the right type or that they're manipulated. Of course errors with breakers are possible too but I prefer by far handling a breaker than replacing fuses.

Breakers are also more reliable to check remotely (using auxiliary and/or signalling contacts) because fuse indicators are not that reliable. Electronic or mechanical fuse control I don't like much either.

Usually the fuse in question is replaced with the closest size circuit breaker.

Try that with a 4000 A semiconductor protection fuse in a DC circuit. :)

As said, there's no hard an fast rules, it depends on the case. You can't simply respectively match A's and kA's.

I never said a direct replacement for all fuses. Just that usually the fuse can be replaced

I know but the question is if those who ask will understand the nuance of "usually".

The problem is that there are so many different IEC fuses (I don't know US fuses excepted in some special cases for semiconductor protection). Indeed fuses are not that rarely replaced by a wrong type of the same ampère rating, typically if there's no other fuse available on-site.