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My question is related to a 300A rated dual fuse holder of the following type which is to attach to the positive terminal of an AGM battery:

enter image description here

If 2 x 100A fuses were to be mounted onto this fuse holder, would both fuses blow when the total load exceeds 100A or theoretically could 99A pass through each fuse (198A total load) without either fuse blowing?

Fuse specifications:

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Fuse holder specifications:

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    \$\begingroup\$ are those fuses in series or parallel, it's not clear from the picture? '100A' fuses don't blow at 100A. They are rated to carry 100A for some 1000s or hours, and will break at some larger current, after some typical time (maybe 200A takes 10s to blow it, depends on the specific fuse, check its specifications). Two parallel fuses will share current depending as much on the variable contact resistance to the holder as to their internal resistance. In the worst case, one fuse will hog all the current if the other has a poor connection. \$\endgroup\$
    – Neil_UK
    Commented Feb 14, 2019 at 9:31
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    \$\begingroup\$ Usually a spec of the fuse helps a lot. You will find a graph time to blow vs. current. \$\endgroup\$
    – Marko Buršič
    Commented Feb 14, 2019 at 9:37
  • \$\begingroup\$ @Neil_UK I’m obviously new to these electrical engineering concepts. I have updated my question and added a diagram from the product’s data sheet that may clarify whether the fuses are in series or parallel. \$\endgroup\$
    – Guru Josh
    Commented Feb 14, 2019 at 9:57
  • \$\begingroup\$ @MarkoBuršič I have updated my question and added the fuse specifications. I see that it would take a current with amperage of 200% of the fuse’s amp rating for 60 seconds to blow it. \$\endgroup\$
    – Guru Josh
    Commented Feb 14, 2019 at 9:59

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From your diagram, it looks like the fuses are totally independent and supplying separate circuits, therefore they will both be capable of continuously supplying 100A each.

If one of the circuits draw enough current to blow its fuse, the other fuse would be unaffected.

As @Neil_UK stated in the comments - "They are rated to carry 100A for some 1000s of hours, and will break at some larger current, after some typical time (maybe 200A takes 10s to blow it, depends on the specific fuse, check its specifications)"

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  • \$\begingroup\$ I have added the fuse specifications to my question. I can see that it would take 60 seconds of current at 200A to blow a 100A fuse. It’s good to understand this concept. I guess my question was more around the concept of whether the amp rating of this terminal with 2 x 100A fuses connected would be the same as for a single fuse holder with 1 x 100A fuse connected or whether it would be doubled. If the 2 fuses are independent then I imagine the rating is effectively doubled. \$\endgroup\$
    – Guru Josh
    Commented Feb 14, 2019 at 10:37
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    \$\begingroup\$ You will be able to continuously draw 2 * 100A from the terminal. As it says on the side of the terminal in the photo, it is capable of a total between the two fuses of 300A maximum. \$\endgroup\$
    – HandyHowie
    Commented Feb 14, 2019 at 11:00
  • \$\begingroup\$ I am trying to understand the amp rating of the fuses and how that relates to the amp rating of the fuse holder itself. What if the combined amp rating of the fuses exceeds that of the fuse holder? Say there are 2 x 200A fuses in the holder. What happens if the current exceeds the holder’s rating of 300A but is less than the current required to blow one or both of the fuses? \$\endgroup\$
    – Guru Josh
    Commented Feb 14, 2019 at 11:56
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    \$\begingroup\$ @GuruJosh Probably nothing. That thing's a big block of metal, it's likely it can handle more than 300A without much damage. \$\endgroup\$
    – Hearth
    Commented Feb 14, 2019 at 13:31

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