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I'm thinking:

If I have two fuses of same type and rating in parallel, the current would split approx 50/50.

If one fuse have a lower resistance, then more current will flow in that, it will get hotter than the other. Then the resistance will rise, to the point where both fuses will carry the same current.

So two fuses in parallel will blow at (almost) the double current.

Am I wrong?

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  • \$\begingroup\$ And also see electronics.stackexchange.com/q/169413/152903 \$\endgroup\$
    – Solar Mike
    Jul 8, 2020 at 11:40
  • \$\begingroup\$ Your logic (and the physics) is not wrong, but remember a 10A fuse does not really blow instantly at exactly 10A. It takes some time dependent on the actual fault current and in that time some damage may occur. By using two fuses you will affect that time differently than selecting the correct fuse at the outset. \$\endgroup\$
    – Jay M
    Jul 8, 2020 at 11:41

2 Answers 2

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If you need a 100A fuse then use a 100A fuse.

Do not try to use two 50A fuses in parallel.

So, a fair comment says I should explain this, well it has been explained on here several times so have a look at these Q&A where there are several good reasons given:

Is it possible to combine two fuses together (with different current rating) to make a bigger fuse?

Using thermal fuses in parallel?

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  • \$\begingroup\$ Stack Exchange has a "mark as duplicate" feature. \$\endgroup\$ Jul 8, 2020 at 13:43
  • \$\begingroup\$ @user253751 will you collect all the duplicate questions together? there are several for consideration... \$\endgroup\$
    – Solar Mike
    Jul 8, 2020 at 14:11
  • \$\begingroup\$ @SolarMike Stack Exchange practice is to just pick the best one \$\endgroup\$ Jul 8, 2020 at 14:18
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    \$\begingroup\$ Page 14 of this guide from Cooper suggests paralleling fuses is not an uncommon practice and requires care. \$\endgroup\$ Jul 8, 2020 at 14:24
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    \$\begingroup\$ It is not a duplicate of any answered question. The first reference is to a relatively dumb question about 40 A + 5 A to make 45 A that obviously won't work, but it's not what the question asks! The second referenced question has not been answered because people have shut it down in the same dismissive way. Nobody has explained it rationally. \$\endgroup\$ Jul 8, 2020 at 15:27
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If you can *guarantee two identical fuses, equal cooling (convection, cooling and radiation), equal resistance wiring, equal contact resistance THEN it may work as long as there is not some other "absolutely equal" factor I've missed.
Murphy loves overlooked factors.

In practice it is unlikely that the fuses will blow absolutely together.
I'd guess, and may be wrong, that one fuse will be noticeably faster to fuse than the other, and that the second one would then follow relatively quickly thereafter as it has a higher current (but probably less than double).

So - the result may well not be too bad. But, no guarantees.

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