Heating element PSA - WORTH A LOOK

[RussH]

I just thought I'd post this, as it may prevent others from letting the smoke out of their element connectors / wiring.

When I built my brewery, I tinned (soldered them to keep the strands all together) all of the wire ends. I have had issues in the past on other projects, where when a wire was inserted into a screw down block, one strand separated from the group and shorted with another terminal, and tinning the wire ends eliminates the possibility of this.

I have been brewing on this system for a couple of years, and generally boil at around 50% duty. Last week I brewed an imperial stout, and to get the gravity up, I boiled for a full 2 hours at 100% duty. When I went to unplug the kettle for cleaning I found that the two halves of the connector had melted together! After prying them apart, and disassembling the connector I found this: (see images below)

I talked it over with an electrician at work, and found out that tinning large gauge wire is not recommended, since it prevents the strands from squishing flat in the screw down, and results in a fairly small contact are for the current to travel through.

I have ordered new parts, and will be cutting off all the tinned ends of my large gauge connections. These plugs are 240V 30A rated, running 5500W elements, so they are safely below the rated load. I just wanted to give you all a heads up. I’m just thankful I didn’t burn down the garage.

 

[voltin]

I had a very similar problem, and more or less the same result (although not as bad.) I too was thankful I didn't burn my house down.

It was recommended to me to keep the wire as flat as possible so that the pressure plate can make a good contact with the wire. They also recommended that I cut back the cord until I got to clean shiny copper for each wire.

 

[kal]

This is a great PSA - thanks for posting.

Absolutely right that if the stranded wire is tinned such that it becomes solid, the connection point(s) will become smaller, almost like solid core wire. More current through a smaller connection point means more heat. (This is why higher current requires higher gauge wire).

Devices where solid core wire are used (like the outlets in the walls of North American homes) usually have a screw where the wire needs to be looped around to create enough of a contact point to avoid the creation of heat. Like this:

(I know that lots of standard 15A/120V residential grade outlets like this can also be "backstabbed" where you push the wire into a spring loaded retainer but frankly, that scares the crap out of me. Gimme a screw down connection method any day).

The plugs and receptacle you show above don't really have this: You push the wire in and then screw down.

Kal