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Author Topic: Fuses or circuit breakers?  (Read 21344 times)
KC2UGV
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Posts: 441




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« Reply #15 on: August 20, 2013, 04:24:02 PM »

Worst case scenario, in the cases of fuses running out?

Just short the damned fuse.

If you burn out more than 2 fuses during any sort of remote operation, something is seriously wrong with your system.
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W6EM
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Posts: 800




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« Reply #16 on: August 20, 2013, 06:12:34 PM »

Worst case scenario, in the cases of fuses running out?

Just short the damned fuse.

If you burn out more than 2 fuses during any sort of remote operation, something is seriously wrong with your system.

Do that and you might toast more than a fuse link if it faults again......
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KC2UGV
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Posts: 441




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« Reply #17 on: August 21, 2013, 04:45:30 AM »

Worst case scenario, in the cases of fuses running out?

Just short the damned fuse.

If you burn out more than 2 fuses during any sort of remote operation, something is seriously wrong with your system.

Do that and you might toast more than a fuse link if it faults again......

Please see second point.  If you have shorted more than two fuses already, you should stop operating immediately, and figure out what the feck is wrong with your setup in the first place.

Take a HMMV.  I drove the same one for 4 years (On and off) in some of the roughest conditions ever.  I never once burned out a fuse.

My van.  I've owned it for 6 years now.  Only fuse I ever tripped was my front power outlet.

If you burn out fuses at a fast rate you need to fix your system. If you can't be bothered to actually fix your system, then you are useless as an emcomm operator for anything other than filling sandbags and getting coffee.
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W6EM
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Posts: 800




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« Reply #18 on: August 25, 2013, 10:49:12 AM »

There might not always be a second fuse.....that is designed to be a fuse.  It may be some 14 gauge wire that fuses and does a lot of damage in the process.

If the right size and type of fuse was selected by design in the first place, it should be as your experience points out.

73,


Lee
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W9FIB
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Posts: 739




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« Reply #19 on: August 26, 2013, 06:09:30 AM »

Something not touched on very much yet is what size wire you should use. You can't use 14 GA wire from a battery with a 100 A protection device. You must ALWAYS have wiring that can handle the amount of current you are protected at. If not, long before the protection trips, your wire could be on fire. Unfortunately there is no easy pie in the sky chart for this. There are things like wire type, temperature, material the wire is made of, insulation type, length, and more to take into account.

Also not stated is the total current rating of a block that you distribute the power through. I have seen some cheap 10 position ATO fuse blocks that are rated for a MAX current of 30 A. That means the internal busbar that feeds all 10 positions will not handle more then 30 A. I see these marketed more for marine use where you want to hook up a stereo, a fish locater and maybe a few other not so power hungry devices.

You see it is not just what size and type of protection to use, but rather the proper power distribution SYSTEM with each piece properly wired and protected that should be built. Otherwise the individual ratings on the parts are meaningless if they do not meet the needs of the system they are installed in.

A system needs to be designed to handle the load. Any other set up is a potential fire waiting to happen.
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KC2UGV
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Posts: 441




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« Reply #20 on: August 28, 2013, 08:50:47 AM »

Something not touched on very much yet is what size wire you should use. You can't use 14 GA wire from a battery with a 100 A protection device. You must ALWAYS have wiring that can handle the amount of current you are protected at. If not, long before the protection trips, your wire could be on fire. Unfortunately there is no easy pie in the sky chart for this. There are things like wire type, temperature, material the wire is made of, insulation type, length, and more to take into account.

Also not stated is the total current rating of a block that you distribute the power through. I have seen some cheap 10 position ATO fuse blocks that are rated for a MAX current of 30 A. That means the internal busbar that feeds all 10 positions will not handle more then 30 A. I see these marketed more for marine use where you want to hook up a stereo, a fish locater and maybe a few other not so power hungry devices.

You see it is not just what size and type of protection to use, but rather the proper power distribution SYSTEM with each piece properly wired and protected that should be built. Otherwise the individual ratings on the parts are meaningless if they do not meet the needs of the system they are installed in.

A system needs to be designed to handle the load. Any other set up is a potential fire waiting to happen.

Exactly!
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W6EM
Member

Posts: 800




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« Reply #21 on: August 29, 2013, 08:26:17 AM »

Something not touched on very much yet is what size wire you should use. You can't use 14 GA wire from a battery with a 100 A protection device. You must ALWAYS have wiring that can handle the amount of current you are protected at. If not, long before the protection trips, your wire could be on fire. Unfortunately there is no easy pie in the sky chart for this. There are things like wire type, temperature, material the wire is made of, insulation type, length, and more to take into account.
Quote

True.  Insulations have varying operating temperatures.  Teflon and, hold your breath, asbestos (mineral insulation) allow very high conductor operating temperatures.  Well over 100C.  And, yes, ambient temperature does matter for ampacity of conductors just as it does for fuses and breakers of the thermal variety.

There are values of melt energy for copper conductors and are given in I squared t.  Those are the values above which the copper will melt and 'fuse'.  Yes, that, in and of itself will definitely ignite other combustible materials.  Copper melts at 1083C, so that's pretty hot.
Quote
Also not stated is the total current rating of a block that you distribute the power through. I have seen some cheap 10 position ATO fuse blocks that are rated for a MAX current of 30 A. That means the internal busbar that feeds all 10 positions will not handle more then 30 A. I see these marketed more for marine use where you want to hook up a stereo, a fish locater and maybe a few other not so power hungry devices.
  Yes, the bus is rated at whatever the manufacturere says, and needs to be protected from the source side.
 
Quote
You see it is not just what size and type of protection to use, but rather the proper power distribution SYSTEM with each piece properly wired and protected that should be built. Otherwise the individual ratings on the parts are meaningless if they do not meet the needs of the system they are installed in.

A system needs to be designed to handle the load. Any other set up is a potential fire waiting to happen.
Total load does matter.  This usually not a problem for most of us, but could be if we add a large load to an automotive fuse block that already has lots of other loads connected that might be turned on in addition to amateur radio loads.  Best approach is to purchase an off the shelf bus, run it to the battery with suitable cables and protection for it, then attach fuse protected branch circuits to it.  Common PVC insulations are usually rated for 60C operation, so use of NEC values for PVC conductor in air is a good approximation for this type of insulation and wire sizes.  But, don't expect a fuse rated for a 25C ambient to open at as high a value as is the case for 25C ambients.  And, I'd use an AWG 8 conductor size where an AWG 10 is called for under the hood.....
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