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Goldenvoice 01-03-2011 05:45 PM

Intertherm elec furnace slowly burns 60A fuses.
History: acquired a used mobile 12 years ago when our house needed to be torn down due to creek bank erosion. The mobile home's furnace is an
Intertherm model FEB-015HA-03
rated BTU (KW) 53,000 (15.5KW)

12 years ago, when we occupied the mobile, the furnace occasionally blew one of the (main) 60A fuses, and probably had the issue previously, as there were several extra fuses in the bottom of the fuse area.

So, we called a local HVAC repair, and the tech shrugged his shoulders, and set down the fan speed. For years, the problem seldom reared its head.

Now, I should tell you we heat mostly with wood, and the electric furnace serves most of the time only as auxiliary heat: I bump it on in the morning to take the chill off the house, while the wood stove heats up. However, last February, we went to Mexico for a few weeks, and didn't want the house-sitter building fires, and instructed her to simply heat with the furnace.

One week into our vacation, the fuse blew, and she had to resort to heating with wood. We returned home, I called a local repair, and on their recommendation, removed the fan, and took in for testing. They said the motor was throwing sparks, and so we had the fan motor replaced to the tune of $460.

Jump ahead to yesterday - gone for 3 days, returned home last evening to a very frigid house, and kicked on the furnace. It ran for somewhere in the neigborhood of 45 (?) minutes before blowing a fuse...

So here we are, still without answers. The fan motor I believe is correctly wired - RED to control, YELLOW to common, although I must say she moves much more air than the old motor did. My current thinking is the motor is not the problem at all.

I'm a logical DIY'er, but have never made a study of an electric furnace - where do we start?

Thanks - cold in Oregon

Marty S. 01-03-2011 06:23 PM

How many circuits does it have? The heat elements alone are drawing 65 amps for 15.5 KW at 240 volts.

Grampa Bud 01-03-2011 07:22 PM

Sounds like Marty hit the problem square on. If the elements themselves are pulling 65 amps to start with and you throw even a 5 amp fan on top of that your cartridges should be at least 80 -NOT 60- amps.

semore 102 01-03-2011 08:18 PM

Usually on 15 kw, 2 circuits are used, A 60amp 240v, and a 30amp 240v. If you only have a 60 amp circuit, drop one of the 5kw off the circuit,only run 10kw. Did you check the wiring to make sure all connections at fuses and main panel. Sometimes the buse bar in the main panel is damaged due to excessive heat due to resistence in the circuit.Circuit breakers also can bake , become brittle, and heat up.

beenthere 01-03-2011 08:55 PM

60 amp fuses are really only good for 11 KWs of electric resistance heat(ok, 11.5).

What size wire is ran to the unit?

Goldenvoice 01-03-2011 08:55 PM

There is a 60A circuit, which drives the 10KW element bank, and the fan motor, and a 30A circuit which drives the 5KW element. It's the 60A I keep loosing.

Now, when the contractor who did the general work-about when we moved the mobile in, saw the furnace leads and breaker in the main (house) panel, thought it was the last installers feed into the panel, and cut the wires! :(

I stopped into the local electric shop, picked up a couple junction blocks and some deoxit, and spliced the wire back together. It IS aluminum wire from the breaker to the furnace. If there were issues in that area, could it affect the fuses in the furnace?

*** before he'd cut the wires, however, the previous owner had the same issue, I believe, indicated by 3 or 4 extra fuses stashed in the furnace...

beenthere 01-03-2011 09:09 PM

What size aluminum wire? Need larger wire for aluminum then for copper.

semore 102 01-03-2011 09:58 PM

Any coductor over 30 amps has to be lugged mechacally. Use fittings rated for aluminium. The metal is softer than copper, . Don't twist, lug it. You have to tighten it in several stages. Intervals of a minute untill it compresses.

Goldenvoice 01-03-2011 10:07 PM

The wire is a non marked cable, with a braided exterior, which measures almost 3/4" x 1 1/8" on the outside. Where the braid is removed as it goes near the fuse blocks, the individual wire, with insulation, is aprox 1/2" diameter...

Does this help? Certainly looks bigger than the #6 as I recall the last time I used it (which was 15 years ago)...

And as far as the splice I made, it was Al rated blocks with set screws.

Goldenvoice 01-05-2011 10:29 AM

So, give me a lesson in theory. If there is a poor connection at any point in the "loop", from the main panel and back, that poor connection acts to increase the load on the circuit? Thus heating the fuse?

Could a tired old breaker do the same? seems it would simply kick off...

What else may we not be thinking of? Should any modules in the unit be cycling, but not? (giving the coils a break)(new to furnace theory;)

I'm temped to call a local repair, but the several times they were out in the past, they called it good... and yet it will burn a fuse in under an hour of non-stop running...

I'm feeling I need more ammo.

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