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Julian Duerksen
05-14-2012, 04:57 AM
Molly #300 about 5 years old
One of the three main cables to the elements melted not at the connection but 1.5" behind the crimped copper connection. This does not seem to be due to a lose connection. The furnace was idling at working temp when it happened. Any idea what might have caused the cable to melt? Age? crimped lug?
Cut the cable back and replaced it with an aluminum lug that I luckily had. Got the furnace going again at 1335 F and ramped it back up slowly.

Pete VanderLaan
05-14-2012, 05:06 AM
If you looked at the material inside the crimped section, I am willing to wager that the copper has turned almost to a blackened dust. Heat is generated where there is resistance which is why these things work. Somewhere, right at the end of that cable was a totally oxidized section of copper and it got hotter and hotter until it arced. Crimps are tricky to use. I think they have to be installed with the proper tools and even then they have a life span. I cut my cables back as part of regular maintenance once a year but I inspect them once a month. The buss blocks are replaced once a year as part of that maintenance. The cable contracted at idle and that invited the arc.

Moly's are funny. They are the safest furnaces and the most dangerous furnaces out there all at the same time. If you don't monitor them, they will fail on you. Check your other two cables now.

Barb Sanderson
05-14-2012, 08:01 AM
Also what size cables are you using? I had several partial melts before replacing all cables with ones designed to carry the load. The stadlemans came with cables not quite up to par according to my electrician. Be very careful once you start cutting back those cables - the arcing may have gone further than you saw and you may be at risk for more in the near future. Listen to Pete and do the maintenance one a month like clockwork. He's not kidding!
Barb

Pete VanderLaan
05-14-2012, 08:21 AM
I use 350MCM cable on everything I build or repair unless it's one of those 600lb things in which case it needs 600MCM. My experience tells me that OOOO welding cable is undersized.

Cut the cable back until you hit bright metal.

Use a laser heat gun. The ryobi is $30 bucks at home depot. It will tell you way in advance where trouble is getting started.

Rollin Karg
05-14-2012, 08:26 AM
Work a little harder at cooling the connections and specifically the place that arced and the the immediate area around the arc.

Jeff Thompson
05-14-2012, 11:19 AM
I'll bet you've got an element near failure.

Josh Bernbaum
05-14-2012, 04:55 PM
Moly's are funny. They are the safest furnaces and the most dangerous furnaces out there all at the same time.

Most dangerous, or most prone to potential problems?

Pete VanderLaan
05-14-2012, 05:09 PM
prone to problems that can cause catastrophic failures, all preventable with maintenance. I checked my connectors today and there was one that needed tightening. It ran about 200F hotter than the rest.

Steve Stadelman
05-14-2012, 10:15 PM
I'll bet you've got an element near failure.

No, probably not.

Pete VanderLaan
05-15-2012, 05:46 AM
No, probably not.
******
With which I agree.

Jeff Thompson
05-15-2012, 10:38 AM
Well it looks like we've got an ol' fashioned wager going on!

Julian, let us know if the element fails in the next 12 months. thx!

Pete VanderLaan
05-15-2012, 11:44 AM
12 months is a long time. Lots of stuff can happen in 12 months. Why not say five years?

I see a lot of these furnaces these days and I can't correlate element failure to arcing conditions at all. I can almost always correlate it to minimal maintenance.

Steve Stadelman
05-15-2012, 03:02 PM
Julian's furnace was one of the very first I built. I am curious how many heaters he has gone through that were not lost through blunt force trauma. I am pretty sure the furnace has been moved.

Mark Rosenbaum
05-15-2012, 05:27 PM
Julian's furnace was one of the very first I built. I am curious how many heaters he has gone through that were not lost through blunt force trauma. I am pretty sure the furnace has been moved.

I got mine in early '06 IIRC, so how can a 5 year old furnace be one of your first??? :confused:

Steve Stadelman
05-15-2012, 07:31 PM
I got mine in early '06 IIRC, so how can a 5 year old furnace be one of your first??? :confused:

Julian approached me at the 2003 gas conference in Seattle. His was the first I took a contract for. Maybe living in British Columbia is so blissful that he doesn't notice time passing.

Pete VanderLaan
05-15-2012, 09:48 PM
It seems to me that my moly was a 2002 project but time plays tricks on us. I remember flying to Portland and seeing the furnace at both Jon and Steve's, ordering the transformer from Brazil electric. We bolted the SCR to the wall. I remember silver soldering the clamps to the 0000 cable and later all the solder just flowed out.

All the early furnaces were 450/450 6/12 elements running on 60V. Those elements are fragile. The original furnace photos are in antiques and classics as the portland furnaces.

George Tessman
05-15-2012, 10:45 PM
I will say again.
Adding temp check of connections into a maint. schedule will help not only in prevention of, but in diagnosing, problems. Guns cost are less then a couple of hundred bucks and the time to check connections is minimal.

Pete VanderLaan
05-16-2012, 05:54 AM
Home Depot- Ryobi for about 30 bucks. Good to 600F which is all you need.

Julian Duerksen
05-17-2012, 04:52 AM
Thank you all for your advice and suggestions. I will invest in a laser heat gun.
I probably have lost track of time in Beautiful British Columbia. I was guesstimating operational time. I checked my furnace log it is six years running time. The furnace was moved. The furnace was shoved into a metal shipping container along with the rest of my shop. Hoisted onto a truck, Stacked and stored for a few months in a container yard in a neighboring municipality and then moved again to a new location. I expected the worst and fortunately it survived vary well. I have broken a few elements with my own clumsiness in the stress of moving my shop but I have never had an element fail on its own. This is the furnaces first connection melt down and involuntary shut down. I do check my connections but because the lugs were crimped I have not checked behind the crimped lugs. All my connections are up off the top of the furnace. This is one of those 450/450 6/12 60v furnaces. I donít think itís as juiced up as the newer ones but its worked great and served me well. What are some of the signs of a possible resistance failure in the end of a cable for the element banks? Are copper lugs better than aluminum in minimizing resistance?

Pete VanderLaan
05-17-2012, 04:57 AM
Cracking insulation is the primary sign. Check your transformer connections too. If you have a failure there, it can really cost you if anything gets down in the windings.

6/12's are simply more fragile. They don't necessarily have less power. They cost a lot less too.

Steve Stadelman
05-17-2012, 09:59 AM
Just use the aluminum bolt-on lugs labeled AL-CU and for your furnace 250 mcm.