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Old 12-23-2010, 09:33 PM   #1
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Furnace fuse holder


I've got a furnace that has a burned up fuse holder. One of the fuses wasn't making the best connection and burned up the fuse holder. I need to replace it with something more modern. The furnace is fed by 2 2pole 60 amp breakers. For 120 amp total. Each #6 goes to a fuse and then on the other side splits into parrallel #10s. The whole fuse holder is probably 8 inches across. Not much room to mount breakers. What should i do?


i drew up a sketch of what i have.
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Old 12-23-2010, 10:31 PM   #2
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Furnace fuse holder


Is this part of the furnace? If not, it isn't legal to parallel #10 wire.


what are the fuse sizes (not just rating but the entire letter and number combination)? It will allow me to see how big they are.

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Old 12-23-2010, 11:57 PM   #3
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this is part of the furnace, itself. The lugs on the right side of the picture is where you terminate the feeders. Its a pretty old furnace. Id like to get this working again, safely without having to replace the furnace.
I don't know the numbers on the fuse, theres not really much legible on them
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Old 12-24-2010, 06:30 AM   #4
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Furnace fuse holder


#6 wires is rated for 50A, could be more depending on insulation type, so everything is already overlaoded for 60A fuses. All conductors in a circuit must be the proper size for the max load. In other words, all wire should be at least #6.
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Old 12-24-2010, 11:30 AM   #5
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As far as replacing the fuse box you can get the part that holds the fuses seprately and you could buy a new one to replace the burnt one. You would need to know the size and type of fuses to order the new fuse block. Also if your breaker pannel has room for 4 double pole circuits it might be best to just run 4 seperate 30 amp circuits. So you do not have #10 wire on 60 amp fuses.
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Old 12-24-2010, 11:43 AM   #6
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Furnace fuse holder


The wires inside the fuse block came for the manufactor, and has been tested.
This is not an uncommon setup for a furnace.

If you can remove the block, you should go to a supply house and get one close.
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Old 12-24-2010, 11:48 AM   #7
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Furnace fuse holder


Quote:
Originally Posted by Just Bill View Post
#6 wires is rated for 50A, could be more depending on insulation type, so everything is already overlaoded for 60A fuses. All conductors in a circuit must be the proper size for the max load. In other words, all wire should be at least #6.
2 columns that I see for rating:
#6 wire 60c is rated for 55a....60a fuse OK
#6 wire 75c is rated for 65a
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Old 12-24-2010, 12:08 PM   #8
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Furnace fuse holder


UL listed furnaces are allowed to have internal wiring such as #10 conductors connected to incoming supply fused at 60 Amps, as long as it was part of its original design.

You do not have to apply the amperage tables of the NEC to the internal wiring of such apparatus.

Most air handlers with internal strip heaters are wired similarly with #10 conductors (or even smaller) connected to larger supply conductors. It is not necessary to replace undamaged internal wiring in these furnaces.

The worn-out fuse block(s) in this case are what need replacing here.
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Old 12-24-2010, 01:43 PM   #9
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I thought that might be the case with the internal wiring allowd on the 60 amp fuses but was not sure.
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Old 12-24-2010, 01:48 PM   #10
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Furnace fuse holder


Can we get off the topic of whether the internal wiring of the furnace is up to the NEC? Cuz appliances don't have the same codes to follow.

I tried a couple parts houses and the couldn't get me the same part. Is the only option a similar fuse holder? Theres no breaker setup that would fit in there?
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Old 12-24-2010, 01:59 PM   #11
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Furnace fuse holder


If there are 60 amp breakers protecting the lines are the fuses necessary?
If they are not couldn't you just splice the #10 wires directly to the #6 wires? Or since the fuse blocks are part of the furnace would that be a problem? As for getting replacement fuse blocks you could order them but it might take a while for them to get to you.
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Old 12-24-2010, 04:29 PM   #12
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Furnace fuse holder


measure the actual fuses. Just need to know how much room you are looking at here.
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Old 12-24-2010, 06:51 PM   #13
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Furnace fuse holder


I'm with WDR on this one. Bypass those fuses altogether, leaving the protection duties to the 60 Amp feeder breakers.
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Old 12-24-2010, 08:13 PM   #14
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the only caution I can see is if they are quick blow fuses. They can react quicker than a breaker can and may be a good idea to retain.
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Old 12-25-2010, 08:05 AM   #15
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Furnace fuse holder


Take the Model number of the unit and get a replacement fuse block "like and kind" and replace it and the same size fuses. Keep looking you'll find it.

After it's all been replaced take amp readings of the entire heaters.

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