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Old 10-29-2018, 02:20 PM
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David Patchen David Patchen is offline
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Connecting Kiln Elements

When we have elements in an annealer fail, it's often at the pigtail connection. Invariably a hot spot develops where the element pigtail and the high-temp wire that supplies the power are joined. While I'm not responsible for installing elements and maintaining the kilns, I occasionally need to make emergency fixes because I need a specific kiln and I'm about to blow glass. This is how I see (and fix) these failures.

We often use copper split nuts for these connections. In addition to being really hard to tighten in tights spots and binding once they're used, I get the feeling that they are prone to oxidation and thus create increased resistance which leads to hot spots. I've been preferring to use butt splice connectors like the attached. They are way easier to tighten and I can't say I've seen these fail but I don't fix all the kilns, so I only see the failures that affect me.

If you never have failures at the pigtail/power connection, what do you use? Has anyone tried soldering these connections before using some mechanical connector like a split nut to make the connection more permanent and low-resistance? I think the hot part of the element is far enough from the pigtail termination that the solder would hold.

Thanks glassies....
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Last edited by David Patchen; 10-29-2018 at 05:55 PM.
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Old 10-29-2018, 02:31 PM
Rick Kellner Rick Kellner is offline
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Random thoughts:

I believe that the split bolt connectors are also produced in a tin plated version, which might be better than the plain copper for this application.

Perhaps some NOALOX anti oxidation compound applied to the connection would be a worthy cause.

If you need to beef up the cross sectional thickness inside the connector (and presumably lessen the resistance accordingly) consider wedging a short section of nickel hinge wire in there to double things up a bit.

After the stranded wires have had a chance to settle and spread out after initially tightening the connection, go back and re-torque them down another time or two.
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Old 10-29-2018, 04:22 PM
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Pete VanderLaan Pete VanderLaan is offline
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Noalox indeed does help but tightening them several times after they are fired off helps at least as much. An SCR would also help since it softens up the sine wave of on/off power and cuts down arcing. Lastly, don't let your fingers contact the elements unless you can clean it with acetone at the end. I have element ends in split bolts that have run successfully for ten years but I check snugness.
Don't put Noalox on a moly element.
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Old 10-29-2018, 07:44 PM
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I fail to understand why you think a different type of connection will help if in fact it is failing as you said where the pigtail ends and the heating wire starts. The common problem I see is when the pigtail isn't exposed completely in the kiln. The heat builds up in the refractory and causes failure. Heavy gauge elements are commonly tig welded to to solid stainless rod. The rod end is drilled the wire is inserted and the tig is used on the side of the stainless until it is melted into the wire. This makes a brittle end but rarely fails at that point once installed. My opinion would be a new split bolt has more clamping power then a but splice connector. I have used but splices before and didn't feel it was as secure so it's not just a guess. I do like the allen set screw as it is easier to tighten initially but like I said suspect it will not be a secure of connection.
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Old 10-29-2018, 11:15 PM
Charles Friedman Charles Friedman is offline
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I believe the element wires and wire that make up the pig tail are a little small for split bolts. So I add a few bits of extra wire to fill out the extra room in the split bolt and that mass takes the abuse of the connection.
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Old 10-30-2018, 06:19 AM
John Riepma John Riepma is offline
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I posted about this earlier, here's the link to that thread:

http://talk.craftweb.com/showthread....ad+wire&page=3

The element lead wire that I referenced is made specifically for this type of application and is available from McMaster Carr in short lengths. I used split bolts to connect the panel leads to the element lead wire and then again to connect the other end of about a 6" piece of lead wire to the pigtails. After doing this I have had no more problems with the ends of the panel leads discoloring and burning off. The link to the catalog page with the lead wire is on my last post on page 3.

Check out the temperature ratings on the element lead wire in the McMaster Carr catalog for a better understanding of why this stuff is so effective compared to copper wire.
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Old 10-31-2018, 02:32 PM
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Quote:
Originally Posted by John Riepma View Post
I posted about this earlier, here's the link to that thread:

http://talk.craftweb.com/showthread....ad+wire&page=3

Check out the temperature ratings on the element lead wire in the McMaster Carr catalog for a better understanding of why this stuff is so effective compared to copper wire.
Thanks John--we already use that exact wire to connect elements to. I still find failures periodically. My fixes seem to work fine so I want to standardize our way of connecting and train the others who repair kilns. I'm hoping someone has tried solder and can provide feedback.
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Old 10-31-2018, 02:33 PM
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Quote:
Originally Posted by Sky Campbell View Post
I fail to understand why you think a different type of connection will help if in fact it is failing as you said where the pigtail ends and the heating wire starts.
Because you're not following--the failure isn't where the pigtail ends and the heating coil starts. The failures are at the juncture of the pigtail connects to the wire carrying the power.
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Old 10-31-2018, 03:26 PM
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Pete VanderLaan Pete VanderLaan is offline
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We used silver solder on the wire clamps on our moly and it all just melted right out of there.
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Old 10-31-2018, 04:14 PM
John Riepma John Riepma is offline
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I did use the element lead wire in a much heavier gauge than what the amp rating would seem to indicate would be needed. Smaller gauge wire = more heat, so just being safe. I agree that the split bolts never seem to be in a convenient location to be tightened.
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Old 10-31-2018, 05:25 PM
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Quote:
Originally Posted by David Patchen View Post
Because you're not following--the failure isn't where the pigtail ends and the heating coil starts. The failures are at the juncture of the pigtail connects to the wire carrying the power.
You are correct I did not understand where the failure was. I understand your looking for input so for whatever itís worth Iíll offer mine. It stands to reason you are not getting a good connection or heat is radiating from the kiln causing oxidation. Iím sure you know split bolts used in heating applications are one time use. Locking the wire directly to the pigtail is going to yield a better connection then a but splice. Clean copper wire free of oxidation is also critical. The wire should be directly on the pigtail not one on one side of the spacer and one on the other. Sizing the split bolt is also critical. I see no reason why silver solder wouldnít work for this application but canít see it as needed. In all my years of building equipment and many kilns on line daily I have not run into this problem. I think the first question would be is this a common problem or isolated to the shop your working in? I donít think it is a common problem. I really do think a simple ir thermometer is a must in all shops and connections should be checked for heat on a regular basis. Maintenance or I should say neglect seems to be the common failure of equipment and the leading cause of fire.

One more observation or possibility if the wire going to the kiln is undersized heat will build up at the connection. In return oxidation and then arcing will cause failure. The 80% percent rule is a must for heating or continuous use machines. As elements age they deteriorate inside the natural oxidation layer this over time will increase resistance and will alllow the kiln to pull more power. All these things should all be taken into consideration and looked at as possible source of failure.

I know sometimes the internet can cause some to come off like they are an expert or a know it all but Iím here to say Iím not and just hope to be helpful.
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Old 10-31-2018, 05:30 PM
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I've been using the same pile of split bolt connectors for over thirty years. I'll say it one more time: They need to be tightened more than once. They need to be clean. They get loose. Once they're loose, they arc. I haven't had any sort of an element issue at the pigtail in at least ten years now. Silver solder melted when Steve Stadelman and I tried to use it on 0000 braided wire.
A small SCR will help with the power surge. I don't use them though
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Old 11-05-2018, 09:30 AM
Rollin Karg Rollin Karg is offline
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We've been using Elements from Duralite for over 35 years. On the first one in a fit of tidiness I trimmed off the pigtails close to where they exited the Lehr. That didn't last long. Finally I think in one of his trips out here Elliott came up with the solution we're using now.

The pigtails are now 14" long, he added a second 14"wire which is twisted onto the first one. That gives us 7" outside the Lehr and it's bent down and away from the pass through, away from the heat.
That was the end of our problems and like Pete we use split bolts and reuse them.
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Old 11-05-2018, 10:04 AM
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"Away from the heat". And there's yet another way to describe the heat involved.
If too light a gauge wire is used coming from your 240V source and it is connected to a short pigtail just barely jutting out from the lehr itself, you have two sources of heat instead of just one.

I use 10 gauge hi temperature wire that has that stranded fiber material wrapping it. It's a bit harder to find but it can be sourced. When I used regular THNN wire, it inevitably over heated both due to gauge and wire makeup.

I don't cut my pigtail wire as soon as it's through the split bolt. I like it to run 3-4 inch past and I like the hi temp wire to do the same. That in my opinion helps dissipate the heat.

An SCR or an SSR controls the sine wave nicely and that helps a lot. I just haven't broken elements at the split bolt in years.
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