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Titivating a Pottery Kiln

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awemawson:
Having the drive dog for the Beaver Powered Tooling lost wax cast in bronze started me thinking that really I should be doing this for myself rather than outsourcing it.

In the past I had a full set up, pottery kiln for wax burn out and mould heating, various furnaces, vacuum pump etc etc but have never re-commissioned it since I moved here 11 years ago  :bang:

So today I decided to dig out the pottery kiln and see if it was viable to connect it up. Originally it was a 3 phase 13.5 kW 415 volt beast that I had reconfigured to run off single phase as I didn't have the luxury of 3 phase on tap. Well now I have  :ddb:

First thing was to extricate it from the junk that has accumulated around it  and refresh my memory of how I'd converted it, (probably about 16 years ago). So junk moved and I  firstly emptied it of what had been piled in just prior to the move in 2007. A HUGE 63 amp single phase plug and socket (this draws 54 amps single phase), and amusingly one of the last lost wax burn outs of a recumbent lion, done in sodium silicate sand, that would still be viable to use today

Then putting it on the pallet truck I pulled it into the welding shop for investigation. Pulling off the cover panels to expose all the wiring, my conversion was discovered as 'dead simple' ! All I'd done was parallel up the three incoming phases, as there are three banks of six heating elements, one end of each going to the (neutral) star point, the other end via the control contactor to a phase.

A quick test with a meter showed that I had an earth leakage problem - about 250k to earth from the neutral star point that will easily trip my workshop RCD. Now this is not really surprising - at my last place it was in an unheated workshop at the bottom of the garden (which didn't have RCD protection) and for the last 11 years it's sat in the fireproof annex I built to house the foundry which again has no heating.

So at the moment it is sat with a 4 kW fan heater blowing inside at the elements and we'll see what happens to the leakage.

awemawson:
. . .cont

Well strangely, although the leakage decreased and resistance initially increased I've just measured it again and it's at 90 - 100 K  Neutral to earth   :scratch:

awemawson:
Having cooked it for a bit, the earth / neutral resistance is up to 1.5 Meg ohm, but noticeably falls off as the warmth decreases. Separating the ends of the three heating elements from the rest of the electrics shows me that a/ it is the elements giving the leakage and that b/ the right hand side is worse than the others.

No doubt the rather porous firebrick inner insulation that has channels cast in it for the heating elements has got a bit damp, as will have whatever insulation is behind it.

I don't fancy leaving a 4 kW heater running over night, so I've put two 100 watt inspection lamps inside with the door closed as far as the cables will allow. There is a roof vent which I've left open so air should circulate.

I'm pretty sure that if it continues improving it'll be fine to connect to mains in the morning, and then of course the drying out will be somewhat faster.

. . . fingers crossed for the morning  :scratch:

seadog:
Do you have an isolating transformer, Andrew? If it was me I'd leave the earth of and fire it up.

awemawson:
Yes but not rated at 13.5 kw - I  think mine is 3 kw  and only single phase :clap:

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