Grounding of kettle heating elements

[Meddo]

G'day all, prefacing this by stating that all work is going to be done by a licensed leccy. Prior to that happening I'm after a bit of advice please if anyone can help.

I've got two Romar elements in junction boxes that are going into my 1V brew kettle, mounted on opposite sides. Previously it housed a single KK element with 3-pin power cord.

My question is around the grounding of these elements. From the photos and hacked-up diagram below, will the contact between the base of the element, the wall of the kettle, and the mounting screws on the element base be sufficient to be able to use one of those mounting screws to ground the system? There appears to be some sort of fibre washer supplied with the elements but I assume I don't need to use this?

I'm asking here, rather than waiting to speak to the leccy, because if this method is not appropriate and I need to mount a grounding screw/lug somewhere I'd prefer to have that done prior (hourly rate and all...).

Also I would welcome any feedback on whether my mounting method is appropriate or can be improved. For context, these will be driven by a matho's controller, using the same waterproof connectors that the controller uses for power into of the junction boxes. It just occurred to me that perhaps the silicon washer should be on the outside of the kettle for a better seal, and if that were the case then the ground circuit contacts would be mounting screw to element base to backing nut to kettle wall.

Thanks anyone for your help.

 

[TheWiggman]

By the looks of it your element base actually has a gasket (green thing in pic 2). This would mean continuity is insufficient. If you removed the gasket and had metal-on-metal contact then the element would be sufficiently 'connected' to the kettle.
However...
The kettle isn't necessarily grounded/earthed. You'll need to run an earth (from the power cable or your house wiring) to the element. It's important to earth the element, not the pot, as that is the source of the electricity. By the looks of it your screws fixing the element to the junction box would be adequate, but too hard to tell from this pic. Also of [nitpicky] note in the first pic is '+ve' and '-ve' - it's an AC element, should be active and neutral.

Your sparky will make the final call on it anyway if a separate ground needs to be run elsewhere. He/she will likely utilise the screws on the element.

Regarding washers I would put the flat silicone washer on the outside of the pot and the round one on the inside where it should line up with a recess on the nut. Edit: that's going to be a challenge with your insulation. I'd cut out a square of it for the J-box, else good luck to you.

 

[Hpal]

I would ground to the mounting screw, but an electrician might like to confirm as I am just a boxhead fitter. I sealed my element the same as here http://www.theelectricbrewery.com/heating-elements?page=7 and it works a treat. I tried putting another o-ring under the backing nut but there wasn't enough thread on the element.

 

[malt junkie]

Cool, so The mounting screw goes through to the base; the base should be in contact with the pot, as stated above the green washer would only serve to isolate the pot(which we'd rather not do). The silicone washer is all that's required to create a seal.

1.Ditch the green washer.
2. drill a hole in the lowest point of the enclosure box so if the worst happens and you have a leak, the liquid can escape before things go tits up.
3. test, obviously at first un powered, but then at full rolling boil and watch closely for leaks (things expand when heated so you may need to adjust tension)
4. Have your work checked by a sparky, electricity kills.

Ed : forgot the most important bit DBS'd slap me!

 

[Meddo]

Excellent, thanks for the help everyone. And nit-picking is welcome, Wiggman - that's what I came here for. It's a long time since I slept through the electrical engineering course at uni... The insulation on the kettle should be fine though as the base of the element isn't flush with the junction box - it extends about the same distance as the insulation thickness.

So the verdict is that the silicon washer should be on the outside of the kettle for best seal, and ground continuity runs through: the wiring into the junction box, to the mounting screw, to the element base, to the backing nut, to the kettle/liquid. As per below? Without the green washer that was supplied with the element being used.

Thanks malt junkie - the sparky will be doing it all, just checking here that I have the right plan of attack and don't need to do any hardware mods first.

 

[timmi9191]

My $0.02

The silicon washer should be on the inside. By sealing it on the outside you will be allowing wort to sit in area between the element and the washer. Unless you are going to be removing and cleaning after every use, thats going to be a muck hole growing god knows what list of nasties. Sealing it on the inside should keep this area clean.

Caveat - Im not a sparky.
While Im sure the contact of the earthed element to the pot will provide earthing of the pot, would it hurt to earth the pot with a specific earth wire leading back into the junction box?

 

[TheWiggman]

Agree Timmi, I mentioned a round washer but meant silicone O-ring. Normally elements come with one which fits on the nut. If only one silicone washer then yes on inside + copious thread tape.
Earthing the kettle won't hurt but it's not necessary. If the element does melt down, say, it will make the element itself live. If the body of the element is earthed, it'll trip the circuit. There's no way I can see that the element could make the pot live before the element body.
I have same caveat.

 

[Camo6]

I'd keep the seal on the inside. You'll likely need thread tape to seal the thread and this will reduce the contact between the element/nut/pot wall reducing earth continuity. With the element base directly against the pot wall you'll achieve a better earth. Confirm this with an ohmeter. Ensure you have a well earthed pot. You're applying voltage to a device with exposed metal parts, they must be earthed. An RCD is a secondary safety measure and should not be relied upon. An earth fault loop is imperative.

 

[rude]

I would be welding a 6mm or 4 mm bolt to the kettle inside the j- box for an earth stud
I would then use a proper earth lug on the earth wire something that won't break
Also I would double nut it for a secure connection

 

[SCR29]

For mine whether needed or not, used an aluminium box to house in so when screwed in to seal element etc. had direct contact to kettle and attached earth to Ali box.

 

[hairydog]

Hey meddo,

Sounds like your on track with your element installation the sparky will ensure that the resistance from the earth pin on the supply plug and all metal
parts of the appliance does not exceed 1 ohm ensuring good continuity,this is done with an insulation resistance tester,good luck.

 

[rude]

Its done with an ohm meter

 

[Camo6]

Its done with an ohm meter

Haha. A fellow pedant I see. Luckily, an ohmmeter is incorporated into an insulation resistance tester (or Megger if you still call a chillybun an Esky).

 

[sp0rk]

Its done with an ohm meter

By a sparky yes, but when it's done by a basic test and tag bloke, they use an insulation tester or portable appliance tester (at least they always have when I've been in charge of organising to have offices tested)

 

[wynnum1]

Earth stake on the house not all wiring in houses are up to standard best to get checked.

 

[Lyrebird_Cycles]

Element diagram 2.png

If you put the washer on the inside it will probably leak. The probability will increase with time.

To see why, have a look at your diagram above. If the washer is as shown, the leakage paths are between the washer and the wall and between the washer and the element base. The washer is compressed against these by the screw thread, all is good (except you have screw threads exposed to process fluid, never good).

If you move the washer to the inside, you have a third leakage path between the threaded section and the inside diameter of the washer. For this to seal you are relying on the axial expansion of the washer when compressed. Not good, unless it was designed as a compression gland (it wasn't).

While I'm on my hobby horse, don't teflon the threads. Teflon tape works on tapered thread fittings because it forms a compressible seal. If the threads are parallel there's no compression, you are hoping the teflon will work as a packed gland. It won't, you need to redo the joint.