Will a downstream 30A fuse will always blow before an upstream 100A fuse?

[brandonbreon]

A downstream 30A fuse will always blow before an upstream 100A fuse.

False was the answer. Why is this? The article included essentially stated that the 30A fuse will always blow first.

http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/solution-center/technical_library/BUS_Ele_Tech_Lib_Time_Current_Curves_How_to_Read.p df

[evanfus]

A downstream 30A fuse will always blow before an upstream 100A fuse.

False was the answer. Why is this? The article included essentially stated that the 30A fuse will always blow first.

http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/solution-center/technical_library/BUS_Ele_Tech_Lib_Time_Current_Curves_How_to_Read.p df

The 30A will always blow first when there is between more than 30 amps and less than 100 amps. However, when there is more than 100 amps going downstream (Let's say 150 amps), then the 100A fuse would blow first before it gets to the downstream 30A fuse. Hope this answers your question.

[gchoquette]

A downstream 30A fuse will always blow before an upstream 100A fuse.

False was the answer. Why is this?

If the 30 amp fuse is a slow blow type and the 100 amp is fast blow, then when the current exceeds 100 amp, it is possible that the 100 amp will blow first.

[darinlamos]

A downstream 30A fuse will always blow before an upstream 100A fuse.

False was the answer. Why is this? The article included essentially stated that the 30A fuse will always blow first.

http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/solution-center/technical_library/BUS_Ele_Tech_Lib_Time_Current_Curves_How_to_Read.p df

I'd say this is a tricky question. They may be coming at this with the idea that at high fault current levels the fuse melt curves are on top of each other. In that situation the mis-coordination may cause the 100A to blow first.