# main fuse, will AC work for DC? no!



## Joel (Jul 29, 2008)

i found a fuse with holder on ebay that seems affordable.
the seller says it is rated for 130VDC and gave me the part number
it is an A3T400

http://www.circuitprotection.ca/pdf/ClassT_A3T_A6T.pdf

according to the manufacturer's spec, it can break 160VDC.


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## Mjolinor (Sep 15, 2008)

This is not related to knowledge of EVs (I have no knowledge of EVs) but is related to a knowledge of fuses.

When a fuse is specified the figures quoted are normally just the maximum (or designed) working voltage and the current at which the fuse will blow. Along with that is the breaking capacity, you normally have to dig into the specification to find it.

The breaking capacity is a maximum current that will result in the fuse going open circuit, if you are above that then the fuse may burn and the spark across the contacts will continue to carry electricity. Both over current and over voltage will result in a fuse not blowing the difference being that an over-voltage will create a spark where the molecules are riped apart (ions and such things) but an over-current will result in a flow of electricity in burnt material like a welding spark.

It is significantly more difficult to break a DC spark than an AC as the AC inherently drops to zero on it's own, this is why the DC breaking capacity is always less than the AC.

The data sheet here shows the breaking capacity to be 200,000 (AC) amps which is pretty normal for HRC fuses.

Fuse design is like radio antenna design, there is magic involved somewhere.


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