L6-30 receptacle overheating on brew kettle

[Punx Clever]

I have a 10-gallon 3-vessel HERMS setup using one heating element in the HLT and one in the boil kettle. The elements are 5500w tri-clamp style with integrated L6-30 plugs like the one below:

I power them using a single-channel PID controller built with an Auber SYL-2362, 50-amp ssr, and 30-amp mechanical shut-off relay powered by a 30-amp 240v circuit. The controller has an output cord (approximately 5 feet of 10/3 cable) with a l6-30 receptacle at the end. I shut off the element at the controller then swap the cable from the HLT to the boil kettle during the sparge in preparation for boiling.

I typically run a 60-70% duty cycle during the boil.

I typically brew once or twice a month, so maybe 20 brew days a year.

Now, my problem:

In the past 3 years, I have overheated three receptacles on my output cord, scorching the plastic. This only occurs on the boil kettle... the HLT has never caused this. The first time I replaced the receptacle and got a couple of brew days in before it happened again. The second time, I decided the kettle element must have gone bad, so I replaced both the element and the receptacle. This was fine for several more brew days, but has happened again.

Of note, it seems to happen on hot days out in my brew-shed. The brew shed is fully finished inside, but does not have climate control (A/C or heat). Summer days get pretty warm and muggy inside the shed even with a couple box fans moving air in and out.

Is it possible that the heat from the kettle (nominally 212*, sea-level boiling and all that) combined with the environment (likely at or near 100* in the shed during a hot summer brew day) isn't allowing enough heat to be pulled from the plug, or should I be looking at some other cause?

 

[golfindia]

What brand plug?

Some cheap ones are designed poorly, and the metal is just too close to the outer plastic. I burnt up a few and it stopped when I got some good name brand ones.

Make sure they stay tight as well.

 

[Bobby_M]

One thing to double check is if there is any epoxy on the blades of the element. The epoxy potting used sometimes gets messy and a very thin layer of is left on the blades. That provides excess resistance and that will cause overheating. Scrape them with a utility blade.

 

[Punx Clever]

What brand plug?

Some cheap ones are designed poorly, and the metal is just too close to the outer plastic. I burnt up a few and it stopped when I got some good name brand ones.

Make sure they stay tight as well.

Three different brands... I remember the second plug was damn expensive at lowes because I needed it that day... which ones have actually worked well for you?

One thing to double check is if there is any epoxy on the blades of the element. The epoxy potting used sometimes gets messy and a very thin layer of is left on the blades. That provides excess resistance and that will cause overheating. Scrape them with a utility blade.

I'll check that. Out of curiosity, do you happen to have a standard resistance value for the 5500w elements? Back of the envelope math says somewhere around 10.5 ohms. I figure I can hook up a multimeter to them to determine if I've cleaned up the blades enough.

 

[Dland]

Hubble and Pass & Seymore Legrand are well made plugs. I had Cooper that came with my Auber controller self destruct.

 

[golfindia]

Leviton plugs I have are still working great. I don't remember what brand melted, but they were $9.95. Leviton brand were 2x that.

 

[Punx Clever]

Finally getting around to replacing the plug and checking resistances... It does look like the culprit could be something causing poor connection between the plug and the element.

Both of the elements that had problems meter out at around 11 ohms, which should be right... but had trouble getting a solid reading until I took some steel wool to the blades. The HLT element, despite never burning up a plug, also had issues getting a solid reading. So I cleaned it up too.

Anywho, I'm running a test to heat up some water and clean with it now. Figure I'll find out if I fixed it or not.

 

[augiedoggy]

I use the same plug pictured in you pic above... only 8 of them in my 3bbl setup and no issues.. try swapping the heaters from kettle to kettle next and see if the issue moves with the element? this would be one of the those cases where a built in amp meter would help narrow things down also.

 

[golfindia]

Take the black cap off of the heating element and make sure that the plug tines are securely spot welded on.

I've had 2 break over the years, due to crappy Chinese spot welds. Quick fix with the tig torch. I won't say where I bought these elements from to prevent the flood of angst and consternation.....

 

[Punx Clever]

I use the same plug pictured in you pic above... only 8 of them in my 3bbl setup and no issues.. try swapping the heaters from kettle to kettle next and see if the issue moves with the element? this would be one of the those cases where a built in amp meter would help narrow things down also.

An ammeter would be handy, for sure... but my little control panel has just enough room for the necessary components as it. The relay is below the pump and element switches, the PID controller extends nearly to the bottom of the box, and the SSR takes up the other wall.

I should have went ahead and measured the impedance of the elements the first time... but it seemed like an obvious problem with the plug.

 

[augiedoggy]

It very well could be a poor weld like mentioned above I havent seen it yet myself but I have seen the small spot welds and I remember for a time there was reports of them breaking from a popular supplier and the design was changed I believe.

 

[Punx Clever]

Two brews in after scuffing up the contacts on my element before each brew and no more issues with the plug getting too hot.

Sucks that they needed to be cleaned up from new, but at least I've got the solution to my problem.

 

[augiedoggy]

Two brews in after scuffing up the contacts on my element before each brew and no more issues with the plug getting too hot.

Sucks that they needed to be cleaned up from new, but at least I've got the solution to my problem.

sounds like you may want to replace the female plug again..

 

[Punx Clever]

sounds like you may want to replace the female plug again..

Why's that? Was replaced two brews and a solid test run ago, same time I started cleaning the contacts.

Finally getting around to replacing the plug and checking resistances... It does look like the culprit could be something causing poor connection between the plug and the element.

Both of the elements that had problems meter out at around 11 ohms, which should be right... but had trouble getting a solid reading until I took some steel wool to the blades. The HLT element, despite never burning up a plug, also had issues getting a solid reading. So I cleaned it up too.

Anywho, I'm running a test to heat up some water and clean with it now. Figure I'll find out if I fixed it or not.

 

[augiedoggy]

Why's that? Was replaced two brews and a solid test run ago, same time I started cleaning the contacts.

something is wrong if you have to keep cleaning the contacts. That means there is too much resistance or too much current passing through causing excessive heat- causing corrosion and oxidation of the metal

 

[Tartan1]

Why's that? Was replaced two brews and a solid test run ago, same time I started cleaning the contacts.

A couple of thoughts come to mind here.

(1) if the blades (male) on your elements are oxidizing due to resistance issues then more than likely the (female) blades on the plug end will also be oxidized. I agree with @augiedoggy with regards to changing out the female plug end. In addition this could be an issue whereby the blade tension within the female end is not making a solid enough connection if you have proven the element is not the problem.

something is wrong if you have to keep cleaning the contacts. That means there is too much resistance or too much current passing through causing excessive heat- causing corrosion and oxidation of the metal

(2) ^^^ Agree, you shouldn't have to clean electrical connections after each use. If cleaning occasionally you should clean your element blades with a qtip and an approved contact cleaner. By sanding or etching off oxidization with steel wool or sandpaper you are effectively scoring (micro abrasions) the blade making more of a resistance problem in the future. Not to mention you are reducing the thickness of the blade on a micro level each time you clean it.

 

[Punx Clever]

something is wrong if you have to keep cleaning the contacts. That means there is too much resistance or too much current passing through causing excessive heat- causing corrosion and oxidation of the metal

I don't have to keep cleaning them, just seemed prudent since that was the root cause of the problem. I checked resistance with my multimeter at the contacts themselves and through the new plug. The resistance is in spec and consistent now.

If you are suggesting that I stop cleaning contacts between brews, that's one thing... if you are telling me to replace a brand new plug when resistances check out sat and no indications of further problems exist...

A couple of thoughts come to mind here.

(1) if the blades (male) on your elements are oxidizing due to resistance issues then more than likely the (female) blades on the plug end will also be oxidized. I agree with augiedoggy with regards to changing out the female plug end. In addition this could be an issue whereby the blade tension within the female end is not making a solid enough connection if you have proven the element is not the problem.

I did prove the elements were the problem. See post #7 above. They were metering inconstantly until cleaning the contacts. Now they meter consistently around 11 ohms.

BobbyM mentioned that the epoxy used in potting these type of elements can be left in a thin film. That tracks with what I mentioned back up in post #7

(2) ^^^ Agree, you shouldn't have to clean electrical connections after each use. If cleaning occasionally you should clean your element blades with a qtip and an approved contact cleaner. By sanding or etching off oxidization with steel wool or sandpaper you are effectively scoring (micro abrasions) the blade making more of a resistance problem in the future. Not to mention you are reducing the thickness of the blade on a micro level each time you clean it.

The thickness of the blades per NEMA spec is 0.070" =/- 0.005". 0000 steel wool is used for final stages of polishing. There is no possible way that a quick rub with steel wool before each brew day is ever going to cause the steel blades to thin out below spec within the usable lifetime of the element. The fact that the surface is being polished (reducing abrasions) from where it was in the first place is providing better contact anyways.

 

[golfindia]

I'm not sure you can even get a meaningful measurement of contact resistance by just putting a regular joe multimeter across the two plugs.....

 

[Tartan1]

B

The thickness of the blades per NEMA spec is 0.070" =/- 0.005". 0000 steel wool is used for final stages of polishing. There is no possible way that a quick rub with steel wool before each brew day is ever going to cause the steel blades to thin out below spec within the usable lifetime of the element. The fact that the surface is being polished (reducing abrasions) from where it was in the first place is providing better contact anyways.

Sorry should have been more specific. I was referring to the thin protective electroplate found on the terminal blades when I mentioned "reducing the thickness of the blade on a micro level". Polishing,buffing whatever you want to call it, you are still in essence removing material.
You seem to have remedied the problem, looks like its working for you, that's all that matters. Brew on