interspark

Hello All,

As part of a small project I am looking the effect of fuse wire in the event of a fault, whilst my question is only partly related to this I wonder if anyone can confirm my findings;

I have a piece of 20A fuse wire and lets say the breaking capacity is 40A and say the csa is 1mm

If I used two pieces of 20A fuse wire would you agree that the breaking capacity would still stay the same the only thing that would change would be the csa it is now 2mm.

It may seem a strange question but I can assure my interest is genuine.

regards

MDShunk

If you're paralleling two fues elements, the current carrying capacity is effectively doubled. If you arrange them in series, the current carrying capacity, before the fuse wire melts off, is still the same as one fuse wire. Kirchoff's law.

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interspark

Many thanks for your quick reply, I did consider Kirchoff's but what if the current exceeds the breaking capacity of one fuse wires at the node.

regards

MDShunk

If they're both identical, and properly connected at both ends, how could more current ever flow in one more than the other?

This is the basis of how "cable protectors" are employed in parallel wired industrial installations. If something fails by some means in a parallel conductor, the cable protector will open. This may take out several others, due to the increased load on them, and perhaps the main fuses protecting the whole bunch of paralleled conductors.

I realize you're in the UK, and I'm replying with US terminology, but maybe you get the idea.

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interspark

Many thanks for your understanding of my problem, it does confirm my second thought on the matter, what confused me was looking at the breaking capacity of one wire against two. Its okay I do understand your terminology.

Regards

MDShunk

RIght. If, for instance, you have a 30 amp load at the node, you'll only have 15 amps flowing in each paralleled fuse element.

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interspark

Many thanks for your help

regards

frank

Don't forget that there are also temperature coefficients to take into account. These will be variable if you have two //ll fuse wire circuits and therefore will also impact on the current carrying capacity of the fuse wire.So for example two 10amp fuse wire links will not equate to one 20 amp fuse wire link. Although Kirchoffs Law relates to currents at a junction it does not fully help you when determining the rupturing time of a //ll fuse link circuit.

Frank