Kiln Rewire - 3 Phase to Single Phase

Thread Starter

leeforresterglass

Joined Jun 17, 2020
1
Hi All, Any advice or knowledge welcome!

I am looking to convert my Electric Kiln from a 3-Phase wiring configuration to a Single-Phase config.
I am assured by the manufacturer that this is an easy job for any electrician, though I can't source either a 3 or single-phase wiring diagram.
I know that really they're relatively simple pieces of kit but seem to be shrouded in mystery.
I'm not really open to the suggestion of a phase-convertor, as I believe this is more for 3 phase motors rather than the kiln application.
I'm not intending on doing this myself, I would just like to be as informed as possible, as I love building my technical knowledge being a routine kiln user.

The kiln: Stanton T35 circa 1995

Originally single-phase, it was rewired to 3-phase by the school that I bought it from.
7kW should draw approx 30.5Amps when reaching absolute max temp, or getting to temp as fast as possible, currently should draw 10Amps in 3-phase config.
Kiln rating plate indicates 400/230V
Has a digital programmable controller, with no infinity switch or manual control.
6 heating elements, currently powered in pairs, 2 to each line/phase.
Relay appears to be rated at max 20 Amp Continuous Current?
I'm in the UK on domestic supply, from a garage-style Consumer Unit in an outbuilding away from the main property, with enough capacity to run the kiln. My query is purely around the conversion of the kiln.
Marked up images of current wiring attached

Key Questions

  1. Is the relay likely to need upgrading for higher amperage? I would like it swapped to SSR in future (probably at the same time as installing a more up to date controller) but for now, I just want the kiln useable.
  2. Is it likely that the wiring will need changing to a thickness rated for higher amps if it was originally designed as a single-phase unit? Would it have been likely that the wiring had to be changed at the previous conversion?
  3. Would the single-phase wiring setup run the elements in series, in pairs parallel (currently in pairs per line/phase) or each element in parallel individually?
  4. Any guestimations of cost for a job like this or recommendations of someone able to do this kind or work from the Wirral/Liverpool area North West, UK?
  5. Anything else I'm glaringly missing and should be thinking about?

Thanks so much folks!
IMG_0372.jpg IMG_0373.jpg IMG_0374.jpg IMG_0377.jpg

IMG_0375.jpg 61384304579__87A6892E-36AB-41BE-8BE2-D845F9C007EE.jpg

IMG_0380.jpg IMG_0381.jpg
 

dendad

Joined Feb 20, 2016
3,591
If you connect all the 3 phases together, then it will run on 240V.
It must be wired in by a qualified electrician, with a dedicated feed from the power fuse box I expect. At least, it would be here in Oz.
 

Reloadron

Joined Jan 15, 2015
5,604
  1. Is the relay likely to need upgrading for higher amperage? I would like it swapped to SSR in future (probably at the same time as installing a more up to date controller) but for now, I just want the kiln useable.
  2. Is it likely that the wiring will need changing to a thickness rated for higher amps if it was originally designed as a single-phase unit? Would it have been likely that the wiring had to be changed at the previous conversion?
  3. Would the single-phase wiring setup run the elements in series, in pairs parallel (currently in pairs per line/phase) or each element in parallel individually?
  4. Any guestimations of cost for a job like this or recommendations of someone able to do this kind or work from the Wirral/Liverpool area North West, UK?
1. I am going to say no because going to single phase your elements will be placed in a parallel configuration so what you see as L1, L2 and L3 can be tied together on the line in side of the relay. Each contact will handle the same current as it previously did. In time if you want to use an SSR you certainly can. Your T-35 kiln has a current draw of 10 Amps three phase and 30.5 Amps single phase.

2. The existing wiring is fine but where I mentioned above how L1, L2 and L3 would be tied (bonded) on the line entry side? There out you need a wire gauge capable of handling 30.5 Amps and allowing overhead here in the US I would call out AWG 8 wire gauge so you want the metric equivalent. The inside wiring is just fine and when the conversion was done they likely added a three phase relay (contactor) and there was originally a larger feeder line.

3. I am winging it on this but it looks like there is a total of 6 heating elements. Possibly each element is 120 volts so they place two elements in series for 240 volts. I don't know what the three phase voltage was. Here in the US using 3 phase 480 volt Delta is common so we take 240 volts elements and place two in series phase to phase. I did find this general purpose manual on your kiln but no actual schematics or voltages mentioned? If it does have six heating elements and they are 240 volt elements then if your mains is 230/240 volts all six would be placed in parallel. Either way not difficult for a good electrician who understands heater elements. In this case parallel pairs would go to the relay and all three contacts tied or bonded.

4. Cost in the UK I haven't a clue. The way it works on my side of the pond is a good competent electrician looks at the job, estimates material cost and his labor cost based on his estimate of time for the job. Your materials cost should not be high as all that is needed is wire but there is also a matter of connecting to a suitable source or creating one. You are looking at 240 volt (or 230 volt) 40 amp service. Then time for all of whatever needs done. Here it is just called time & parts. No clue what a UK electrician labor rate is. We do have a large number of UK members including the Liverpool area so hopefully one of them can get you going.

Like Oz, here it would be a dedicated service line from supply panel. So materials needs to include that run.

Ron
 

ronsimpson

Joined Oct 7, 2019
807
Is the relay likely to need upgrading for higher amperage?
The relay is rated for 20A per section. Each section powers one of the three heating elements. If you connected all three phases outside the box then each section will operate like normal.

I would connect all 3 red wires to "hot" and the black to "N". Green = ground. Give it a try.
 

Dodgydave

Joined Jun 22, 2012
9,305
The 3 Phases that come in on the Black mains cable, just connect All 3 Reds together externally in the fuse box to Live, Black to Neutral , Green to Earth, and fuse it with a 20 to 32Amp breaker.

If in doubt get an Electrician !!
 
Last edited:

Delta prime

Joined Nov 15, 2019
425
Hello gentleman.I kind of feel as if I'm intruding,Sooo...An option perhaps would be obtaining a single phase output from a 3 phase supply is to place a single phase transformer across two phases of a 3 phase supply. The effect of this system is to pull the full rated current in two of the supply lines and zero current in the third line. This is probably acceptable up to a rating of about 5kVA on a 400V system (13Amps / 13Amps / 0Amps). Above this level an alternative method may be required to achieve a better balance of currents flowing in each of the three phases.
I wish you all the best! Be safe!
:)
 
Top