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Geoff Lee
02-23-2012, 03:09 PM
I've got a 400# Stadelman furnace running on 208 3-phase. Every once in awhile, one of the power cables over-heats and melts the lug that connects to the element straps.

Mayhem usually ensues after.

I can kind of predict when this will happen by looking at the amount of corrosion on the copper ends. If it's black, I know it will probably over-heat soon.

Last week I went and cut down one cable to the fresh copper and attached it with a new lug. I just checked it today and it's already black and corroded. Other cables look fine.

What causes this to happen so quickly? Why the same cable burning out?

Thanks in advance for any help

Geoff

Jordan Kube
02-23-2012, 03:38 PM
You might try stepping up to bigger cables.

Geoff Lee
02-23-2012, 03:46 PM
Yeah I thought about that, but this is a relatively new occurrence. And this is the first time one cable has corroded so quickly

Pete VanderLaan
02-23-2012, 03:55 PM
Did you replace the lug and the straps for that cable when you cut it back. Straps do have a lifespan.

Geoff Lee
02-23-2012, 04:28 PM
I replaced the lug, I'll try the straps next time although they look good too.

Jeff Thompson
02-23-2012, 04:46 PM
Have you checked the connection of the cables into the transformer? I have had hot connections there before.

Jeff Thompson
02-23-2012, 04:49 PM
Also could be that an element is near failure.

Geoff Lee
02-23-2012, 05:07 PM
Jeff,
That's interesting. Every shut-down I check straps, lugs and connections at transformer. At least give them a good tightening.

Never occurred to me that an element might be going. Anyway to know if this is the case without pulling all the elements out?

Pete VanderLaan
02-23-2012, 05:15 PM
I don't think it to be likely. The hot spot occurs because there is resistance to the flow of power. The connection is certainly a point where there is a joint and a less than perfect joint is going to get hot. Use a new lug, I'd recommend checking the cabling if it has turned a dull gray. I don't know what size main cable you have. I do not use anything smaller than a 350MCM stranded annealed welding cable, which has gotten really pricey. Some of Steve's furnaces used a 0000 or ( Four ought) cable. I find it to be troublesome.

While checking the connections in the transformer is a good idea as is cooling the transformer with a small blower, I don't see any reason why the cable would fail at the opposite end. As I said, resistance at the connection is causing the heat.

Dane Gamble
02-23-2012, 07:30 PM
We have had the same problem in the past with our 400# Stadelman. We ended up installing an aluminum bar that the straps attach to and the lug attaches to the end of the bar. We have not had a problem since. It gets the lug off the top of the furnace. We also made sure the cable to lug connection was as tight as we could possibly get it. We put an adjustable wrench on the sides of the lug and then used a t-style allen wrench to tighten the lug set screw. I believe the tightening of the lug set screw had more to do with the elimination of melted lugs than anything else. Make sure after you install a new lug to go back a day or two later and retighten and then check again in a couple of days and retighten again.

Geoff Lee
02-23-2012, 08:05 PM
Dane - thanks for all the help. I also have the aluminum bars but will re-tighten in a couple days.

Pete - not sure what size cables I use, but the lug size is a TA500

Dennis Hetland
02-24-2012, 03:02 AM
We have had the same problem in the past with our 400# Stadelman. We ended up installing an aluminum bar that the straps attach to and the lug attaches to the end of the bar. We have not had a problem since.


{ ""It gets the lug off the top of the furnace.""}

If the lug and a section of the cable are on the top of the furnace this would be an elevated temp situation that the cables would need to be derated for. Adding the aluminum bar set up effectively does this.
If the lug and a portion of the cable are on the top of the furnace then they're in a hot zone. Heat causes more resistance in a wire. If you run a conductor through an area that is hotter than 86 F you need to compensate by increasing the size of the conductor. The cables to your elements should not lay on the top of the furnace. The last time I looked at the top of a moly furnace I'm pretty sure that's what I saw. It didn't occur to me until I saw this post.

Rollin Karg
02-24-2012, 04:51 AM
Dane - thanks for all the help. I also have the aluminum bars but will re-tighten in a couple days.

Pete - not sure what size cables I use, but the lug size is a TA500

The bars are most effective if the connections are at the edge of the furnace. As Dennis says moving them out of the heat is the goal. Add enough airflow and you will not be burning off cable ends. You won't have to be tightening cables and straps either.

Rick Sherbert
02-24-2012, 06:58 AM
You said it didn't occur until recently. What changed? Have you looked for chimneys around the passage bricks? That would allow more heat up there.

Pete VanderLaan
02-24-2012, 07:26 AM
I use a 600MCM lug. I can't get the 350MCM cable into a smaller lug without it looking like butchered surgery and even at 600, it doesn't always go in well. As Rollin says, if you keep the ends cool, there is no problem. I just use tiny blowers. Are you using an antioxidant compound? My experience has been that the 3 phase systems have more problems than the single phase. Steve takes exception to that observation.

If the lug is actually melting, I don't think it to be tight enough and obviously it needs cooling. When you cut the cable back, do you always go to bright metal?

Dennis Hetland
02-24-2012, 09:46 AM
You said it didn't occur until recently. What changed? Have you looked for chimneys around the passage bricks? That would allow more heat up there.

I don't own a moly. I don't think about them that much. I do think about them enough to be curious about the connectors frying. Derating for ambient temperature is basic electrician stuff. I should have thought about it the first time I helped rebuild one.

Dennis Hetland
02-24-2012, 10:25 AM
I use a 600MCM lug. I can't get the 350MCM cable into a smaller lug without it looking like butchered surgery and even at 600, it doesn't always go in well. As Rollin says, if you keep the ends cool, there is no problem. I just use tiny blowers. Are you using an antioxidant compound? My experience has been that the 3 phase systems have more problems than the single phase. Steve takes exception to that observation.

If the lug is actually melting, I don't think it to be tight enough and obviously it needs cooling. When you cut the cable back, do you always go to bright metal?

Those lugs actually have torque specs. My 4th year apprenticeship instructor harped about this a lot. He said that over torquing is bad because of the way it compresses the wire. Testing laboratories like UL test these things to see how they're going to fail and issues guidelines.
Over tightening is not a reasonable fix.

If you nick the wire when you're cutting the insulation back this could be a problem as well. Electricity wants to run on the outside of the wire. If you nick the wire it creates a gap that the electricity has to "jump". This creates a tiny bit of arcing. Everytime the power turns off you get a little more arcing. After a while you have a problem.

John Riepma
02-24-2012, 10:31 AM
When I built our moly furnace I bought the lengths of welding cable from the local welding supply house and had them crimp terminals on the ends. We have never had any problems melting or burning the ends and the IR gun that I use has never shown any abnormal hot spots on either end. Something to think about if that service is available at your local supplier.

Jeff Thompson
02-24-2012, 10:34 AM
While checking the connections in the transformer is a good idea as is cooling the transformer with a small blower, I don't see any reason why the cable would fail at the opposite end. As I said, resistance at the connection is causing the heat.

Yes, I see what you're saying here. I think that a hot connection in the transformer could be part of a chain of events that leads to too-hot of connections at the lug/strap.

Geoff- have you checked the soundness of the connections of the straps to the elements? A simple way to check that part of the system is to turn off all the lights and looks at the strap/element connection for tiny glowing hot spots. How old are your elements? Is it possible that one leg of your three phase is a slightly higher voltage?(I'm not familiar w/ three phase).

Geoff Lee
02-24-2012, 12:34 PM
I'll take some pictures later today and post them to see what you guys think.

Pete VanderLaan
02-24-2012, 01:30 PM
Do you have a vernier caliper you can throw on the insulation on your cable? I want to know the size.

If you were seeing glowing spots on your element clamps you would be at the imminent failure stage. That would not be making your cable clamp/wire connection fail. Dennis is correct about the torque setting but the reality is those things get loose after about one week in service and need to be retightened. They should be checked bi monthly at the least.

Elements don't have a known life span at the temperatures we work at. They break because they are either in tension or compression or have just been generally throttled by someone. They don't go by themselves.

Doug Sheridan
02-24-2012, 03:42 PM
I agree with John, my cables have the crimped terminals and they will never come loose. It has to be done by a pro, not a blower.
FYI, since I started leaving my furnace temp constantly at 2050 melting cullet, all my connections stay tight. Not having to ramp up and down seems to make a big difference in stopping this problem. When I batched, I tightened every week.

Charles Friedman
02-25-2012, 12:02 AM
If your electrical cables are too small, in size, they will have a habit of heating themselves up. Get bigger size cable. Also try insulating them while in a hot environment.
Take a look at this: http://cableorganizer.com/high-temperature-insulation/

Geoff Lee
02-25-2012, 12:06 AM
Was too busy today to get pics of the set-up. Will do it tomorrow.

Thanks for all the help!

Geoff Lee
02-25-2012, 12:06 AM
Was too busy today to get pics of the set-up. Will do it tomorrow.

Thanks for all the help!

Checked for chimney's last time I shut down, didn't see any.

Jeff Thompson
02-25-2012, 12:51 PM
If you check for chimneys when the furnace is hot, they will show themselves much easier.

Pete-I've had glowing spots at the element/strap connection before that, after cleaning up the connection area of the element and replacing the strap, I got 2 more years on the element. Yes, I suppose that 2 years is eminent failure zone for these elements.

Pete VanderLaan
02-25-2012, 02:48 PM
I don't think that glowing on the strap connectors implies anything about the element at all. It just says that the connection at the strap is no good, and is arcing or getting ready to. As I said, to the best of my knowledge, the elements have no known life span at the temperatures we work at. If they are installed under tension or compression, they will eventually break. It may take weeks, it may take years.

The connection issue at the clamp is what is in question here. The clamp isn't going to overheat because there is a poor connection somewhere else. The resistance is right there for you to see. It glows. If you have a point and shoot thermometer, it will tell you that the joint is bad well before it glows. It will be hotter than any other part of the circuit.

Cold creep is insidious stuff. You can torque the connection all you want to. It's actually quite hard to do while on top of the furnace and it is likely you will break an element if you try to use a torque wrench while balancing on the furnace crown. With cold creep, you can tighten it and come back three days later and add another quarter turn. They need to be monitored. After a few adjustments they pretty much settle down.

It may well be true that using compression lugs is better. Steve and I tried it once and it didn't really work out but then again, we didn't have the proper tools. I find that keeping the joint cool with air is what keeps my clamps happy.

Geoff Lee
02-26-2012, 03:39 PM
Ok, here are some images I finally got around to taking. Looked for chimneys and didn't see any. Didn't take any pics of the other cables, just the one that has given me issues. I took a wrench to it today and it wouldn't budge.

Tom Clifton
02-26-2012, 05:02 PM
Are the lugs rated CU/AL and are you using anti-oxidant paste between the copper and aluminum?

----
EDIT
----

Here is a link explaining the difference between a CU/AL (http://lugsdirect.com/WhyAluminumOverCopperFAQ.htm) and a plain aluminum lug.. The important bit is at the very bottom - read it all. This why houses with aluminum wiring used to burn down. I think the Firemen here all know this but it is worth bringing up considering the mysterious nature of the problem.

Pete VanderLaan
02-26-2012, 05:43 PM
If you throw an ammeter on the three cables, does this one read any different than the other two

Dennis Hetland
02-27-2012, 09:50 AM
Ok, here are some images I finally got around to taking. Looked for chimneys and didn't see any. Didn't take any pics of the other cables, just the one that has given me issues. I took a wrench to it today and it wouldn't budge.


What I see in these pictures is not the way to connect anything. You need to loose all the aluminum and get copper bus bars. there are a lot of things in that pic that go against "industry standard". Where do I start the list?

Aluminum expands and contracts too much for this application. You don't put stranded under a screw and there's stranded aluminum around a heating element. You guys should be using some kind of four blot main clamp type connector attached to the element with a tab to attach the webbing stap which then attaches to a buss bar that carries the current to the edge of the furnace where it's not so hot. Then attach you crimped on connected cable to the buss bar. And do it all in copper.
Here's a place that does copper bus bar and custom copper connectors.
http://www.stormcopper.com/

I just called them. I'm going to send them a drawing of what I'm talking about and they're going to send me a quote.

You can't have that cable connection hanging in mid air like that. It needs to be attached to some thing. The vibration and possible movement will loosen the connections too easily the way it is. (Replace it with a buss bar system)

Those lugs aren't listed to be used like that. You need crimp on T/A s.

Geoff Lee
02-27-2012, 10:08 AM
Dennis,
Thanks for all the info and I am not going to disagree with anything you've just said.

But if I understand you correctly, you're saying that everything Steve designed is wrong? The only changes I have made was adding the aluminum bar.

Dennis Hetland
02-27-2012, 10:18 AM
Dennis,
Thanks for all the info and I am not going to disagree with anything you've just said.

But if I understand you correctly, you're saying that everything Steve designed is wrong? The only changes I have made was adding the aluminum bar.

I don't want to say it like that. Steve's design is good, I'm offering criticism. I do think it needs to be improved. What I see in that photo goes against what I was taught as an electrician.

That little piece of aluminum is the bar? I thought there was a buss bar system?

Geoff Lee
02-27-2012, 10:26 AM
No offense taken on my part. Furnace is not my design. :) Bar, buss... not sure of the exact terms.

Some friends of mine have a 600# on island and they were told to use the bars. I went over to their studio, took a look at their set-up and used their remaining to modify my furnace. I guess they were told what to do by Steve.

I can say that I have been having the same problem both before and after I attached the bars.

I have NOT been using the anti-oxidant paste between the copper and aluminum, only between the aluminum and aluminum. When Steve's assistant Cheyenne came out, there was no mention of that.

Dennis Hetland
02-27-2012, 10:36 AM
No offense taken on my part. Furnace is not my design. :) Bar, buss... not sure of the exact terms.

Some friends of mine have a 600# on island and they were told to use the bars. I went over to their studio, took a look at their set-up and used their remaining to modify my furnace. I guess they were told what to do by Steve.

I can say that I have been having the same problem both before and after I attached the bars.

I have NOT been using the anti-oxidant paste between the copper and aluminum, only between the aluminum and aluminum. When Steve's assistant Cheyenne came out, there was no mention of that.

I've always been told not to put Nolox on copper. I've read online that some electricians do.

I don't know exactly what your problem is,but from what I see in those pics I'm not surprised you're having one. I've always questioned the way these elements were connected. It goes against so many things I was taught.

Tom Clifton
02-27-2012, 10:47 AM
I'm not going to take any sides here as I don't have any hands on experience with silicon carbide heating elements. My own experience is with installation and maintenence of -48v telecom power plants. In those I dealt with currents up to 2000 amps at 52 volts, and everything (except the battery connections) was hydraulically crimped tin over copper. Really big copper... (or someimes lead). The big difference here is that nothing really ever got hot (unless there was a problem).

In the case of a furnace with silicon carbide (http://isquaredrelement.com/pdf/RR_brochure.pdf) elements at some point in time you need to connect to the "cold end" of a very hot heating element. The cold end is aluminized which is why aluminum braid is used. At some point in the power chain you will probably need to join aluminum to copper - somewhere between the element and the connection to the SCR and transformer (unless the transformer has aluminum windings, then that is a diffeent problem)

As pointed out, keeping everything supported, tight and cool is very important - You just can't get away from the aluminum though. Tens of thousands of SiC elements are in service in the world using aluminum braid as a conductor contacting the cold end and it if it didn't work it wouldn't be done that way.

It is my understanding that (at least in Moly furnaces) it is common to have 'octopusses' blowing cooling air over the junctions. In addition to going to hydraulic crimps a cooling fan would be of value.

Again - I don't design furnaces - can only leave that to the manufacureres that have a lot more practical experience on a daily basis than I do.

Dennis Hetland
02-27-2012, 11:02 AM
Even if you do attach to the element with webbing it should go straight to something stationary (buss bar) and the cable should be attached to that.
Everyone needs crimped on terminal adapters on the ends of their cables.

Cooling fans on your connections is not a reasonable fix. The size of the conductor in the hot zone(the area above the furnace) probably needs to be increased and a more reliable connection needs to be made.

I'm sure they make copper webbing. Why would aluminum be used instead?

Pete VanderLaan
02-27-2012, 11:17 AM
The installation is straight out of the Super Kanthal Handbook.

Tom Clifton
02-27-2012, 12:17 PM
I'm sure they make copper webbing. Why would aluminum be used instead?

Because the "cold" end of the SiC (http://isquaredrelement.com/pdf/RR_brochure.pdf) element is aluminum per the referenced link on StarBars from the manufacture
The extremities of the elements are metallized with aluminum to provide a low resistance contact surface to which the electrical connections are made using braided aluminum straps.

Rollin Karg
02-28-2012, 04:25 AM
Cooling fans on your connections is not a reasonable fix. The size of the conductor in the hot zone(the area above the furnace) probably needs to be increased and a more reliable connection needs to be made.


Actually I think cooling fans are a reasonable fix. When someone says industry does it this way or that, I think you have to determine which industry they’re talking about. Airplane builders, Tractor makers and Bathtub producers probably do some things the same, but there will be a lot of differences too. In our industry(the glassmakers) we are dealing with a lot heat of 24/7. That’s different from most of industry. Our electrical panels may look the same but I never saw anything that looked like a Stadelman in an airplane plant.

When we added the Bar system and a short while later the Plenums, the issues on top of the furnace ceased. No burnt or melted cables and no loose connections. We only had the crusty cable a couple of times and none since we upgraded. We meant to cool the straps, but all the connections were cooled and I think that was a good thing.

As Pete said checking the Electrical part is a good idea. I would also check the temperature on the connections, on high fire and at idle. I would also add a small squirrel cage fan and direct it at the connection and see if that doesn’t help. If that connection was in a panel away from any heat it might be fine. On top of furnace is a different story.

Pete VanderLaan
02-28-2012, 06:19 AM
three phase systems can and do get out of balance. Check the amps. Also use antioxidant on the connectors, all the connectors except the direct connection to the lements.

Pete VanderLaan
02-28-2012, 06:21 AM
I don't see any thing wrong with that connection setup. I do like cooling the connectors. Three phase systems can and do get out of balance. Check the amps. Also use antioxidant on the connectors, all the connectors except the direct connection to the elements.