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Topic Title: 1 Phase -v- 3 Phase
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Created On: 14 January 2017 11:25 AM
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 14 January 2017 11:41 AM
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Sandtree

Posts: 6
Joined: 14 January 2017

Don't seem to be able to ask Q in the Wiring forum yet so will ask it here.

The studio is a sub unit of a former factory, the landlord stated that there is a 3 phase power supply to the building but all electrical work must be done by their preferred electrician. We need to install a kiln into the studio which can be done off of a 1 phase 220v or 3 phase 400v supply but is also expandable by adding an additional element to it that increases the output by 3kW.

I finally manage to get hold of the contractor, simply by bumping into them when they were on site, and they advised the board could support up to a 40 amp supply and does have 3 phase but for reasons not specified he said that 1 phase was a better idea. The retailer of the kiln however said that if you can do 3 phase it's much better for the life of the kiln.

On 1 phase the unexpanded kiln is 26 amp and comes with a 32 amp cee form plug. From what I make out when expanded this goes up to 31amp. On 3 phase its initially 13 amp with a 16amp plug and 15 amp if expanded. The expansion doesnt involve changing the wiring of the kiln itself so I am guessing these numbers must be right as the expanded form still fits within the capacity of the plug on the unexpanded form.

So to the Qs.....

1) Is there really that much benefit of a 3 phase supply?
2) Am I correct in thinking that the new socket can be put in and wired & fused/breakered for the 32amp (1phase) or 16amp (3phase) and then used correctly/safely wether the kiln is expanded or not? ie when using a lower current it shouldnt have a lower rated breaker or such

Many thanks

Edited: 16 January 2017 at 02:36 PM by Sandtree
 16 January 2017 02:36 PM
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Sandtree

Posts: 6
Joined: 14 January 2017

Thanks for moving topic
 16 January 2017 02:53 PM
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OMS

Posts: 22359
Joined: 23 March 2004

It's better on 3 phase rather than 1 phase if only to balance phase loadings on the system supply

Other than that, it's a simple engineering decision - what does the client want and what will the "landlord" allow

If the expanded form doesn't exceed 31A on single phase and 15A on 3 phase then a 32A single phase or 16A three phase socket is fine

(noting that personally, I would use a degree of conservatism in the cable selection and CPD rating and socket selection - where I come from we don't like to run things "hot")

OMS

-------------------------
Let the wind blow you, across a big floor.
 16 January 2017 03:04 PM
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deejackson

Posts: 358
Joined: 13 May 2005

Much of the answer is in the hands of the kiln manufacturer...

You can have either variant of the supply installed: 32A single phase or 16A three phase.... and in all probability the MCB/breaker could be the full socket rating regardless of the expanded/unexpanded nature of the kiln. But it is really the duty of the manufacturer to confirm this. Equally, for a correctly designed heating load, single or three phase should be equally good. If the kiln supplier can justify their preference then you can make an informed judgement. Your contractor may have site/loading reasons why a particular choice is preferred, but if both variants are practical then go with the manufacturers recommendation.

Hope that helps more than it confuses.
 16 January 2017 03:16 PM
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AJJewsbury

Posts: 15823
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On 1 phase the unexpanded kiln is 26 amp and comes with a 32 amp cee form plug. From what I make out when expanded this goes up to 31amp. On 3 phase its initially 13 amp with a 16amp plug and 15 amp if expanded.

There's something odd with those numbers - single phase 26A equates 5.98kW, but 13A 3-phase comes to 8.97kW (presuming all three phases are used). If the kiln were really intended for either single or 3-phase operation I'd expect three banks of 230V elements with a common N, with each bank connected to a different phase for a 3-phase supply, but connected together for a single phase supply. Either way the overall power output should be the same.

It sounds like either the kiln is equipped with just two banks of heaters (in which case it's really setup for 2-phase operation and won't properly balance on the 3rd phase - not a disaster but maybe worth bearing in mind) or it's got three banks but only two are used for single-phase supplies (maybe to keep within the limit for a 32A plug) - in which case it'll run at a lot lower power (so either at a lower temperature or take a lot longer to heat up) - which might be significant to you as the user. Or perhaps just the numbers are wrong of course.

- Andy.
 18 January 2017 09:25 AM
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Sandtree

Posts: 6
Joined: 14 January 2017

Many thanks all for your help.

Originally posted by: AJJewsbury

It sounds like either the kiln is equipped with just two banks of heaters (in which case it's really setup for 2-phase operation and won't properly balance on the 3rd phase - not a disaster but maybe worth bearing in mind) or it's got three banks but only two are used for single-phase supplies (maybe to keep within the limit for a 32A plug) - in which case it'll run at a lot lower power (so either at a lower temperature or take a lot longer to heat up) - which might be significant to you as the user. Or perhaps just the numbers are wrong of course.


Andy, the kiln is rated at 6 kW (9 kW when expanded) on both options. It would appear that I miss understood the power requirements on expansion though as the 1 phase goes up to 39 amps, if I am now reading the table correctly the 3 phase doesn't change.

That said, what you say possibly makes, the expansion rings increase the power by 50%, in 1 phase it increases the amps by 50% too but in 3 phase it possibly just draws on the previously unused phase?

Actually, just found the circuit diagram which whilst blurred seems to say exactly that
https://www.dropbox.com/s/0noa7phbw3x7cy7/KilnDrawing.png

Originally posted by: deejackson
Much of the answer is in the hands of the kiln manufacturer

The manufacturer is in Germany and given my lack of German (being limited to being able to say I'm 15 years old isnt as useful as it once was) I was a little reluctant to force them to speak English and so had been speaking to the retailers here.

I did email them though the other day and they redirected the query to their UK representative who's also their service agent. His view was that 3 phase will have a slightly longer life but its not a massive difference but he'd recommend a 1 phase kiln due to the resell issues of 3 phase ones if not a giant sized capacity

Thanks again all
 18 January 2017 11:00 AM
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mapj1

Posts: 9356
Joined: 22 July 2004

If you only have german language documentation and would like it interpreting, I may be able to help.

Fundamentally, there will be some resistances that are heater elements, that may be wired to connect from phase to neutral or from phase to phase, and some sort of timer/thermostat controller that turns them on and off.

The real choice is I suspect between 400V or 220V elements - after all 220 v elements can still be used on 3 phase, so long as a neutral is available, or strapped in parallel to make a big single phase load. (400v elements cant play this trick.)



If the building has a 3 phase supply, then it makes it easier in terms of load balance to use all 3 phases.

Is the thing really likely to ever be moved ? normally big kilns are pretty much installed for life.

Get a 32A 3 phase and neutral socket fitted to the wall

-------------------------
regards Mike
 02 February 2017 09:59 AM
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Sandtree

Posts: 6
Joined: 14 January 2017

I dont know what rating the elements are but I do know that all the kilns are "3 phase" when built and the 1 phase version has an extra "box" added to it. That box can also be added aftermarket to convert an existing kiln but its "free" if bought at the time of purchasing the kiln and obviously charged for if bought later and fitted.

We have ultimately decided to go for a 1 phase, the electrician we must use still doesnt like the idea of doing a 3 phase supply for reasons he wont explain and the UK importer unlike the retailer very much recommends 1 phase if there is any chance you'll ever be reselling it. The kiln is a relatively modest 80L capacity and so its not outside the realms of possibility that it may need to be replaced at a later date if she decides to focus more on ceramics than she currently believes she will.

If I could ask one more favour, the electrician has quoted for the work they say's needed:

Supply & Installation of 32 amps Single phase Isolator, Cabling , Plugs and Connection Etc

They've not been in our studio or asked where we'd want the plug to be located which makes me a little concerned that theres enough fat being built in that it'd cover putting it anywhere. That said we are on the 2nd floor, on the first floor directly below us is what looks like an oversized Consumer Unit in the hallway and so if that is it then the cabling would simply be going up that stud wall and come out the otherside of it on our floor.

With no choice of electrician we are going to have to pay his fees but I was wondering what a fair "all in" price (inc VAT if relevant) would be for such a job in London?
 02 February 2017 03:49 PM
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mapj1

Posts: 9356
Joined: 22 July 2004

I reckon it has 220v elements, and the add-on box is simply a junction where they can be put in parallel .
Anyhow, while your question is perfectly understandable, to answer it without seeing it, is I'm afraid not really possible.
IF we know that the existing supply is adequate or not, if there is a spare 'way' in that fuseboard or not, what else needs turning off to connect to it, if the cable route crosses any firebreaks in the building or not conspire to make the variation in difficulty enormous. Equally I cant see how your sparks can quote it accurately without that sort of info either.

There will be folk here who have a good idea of the day rate for your area, but I'd hazard that the job duration could be anywhere from half a day to about two, depending on what else is needed to be done to get power to it.
Unless the cable run is tens of metres, the cost of labour will almost certainly exceed the cost of materials, so performing some 'enabling works' like clearing stuff out the way and clearing away after can save time and bring the cost down if you have the right sort of relationship.

-------------------------
regards Mike
 02 February 2017 03:58 PM
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Delbot321

Posts: 180
Joined: 06 November 2012

Not sure I'd want to advise on price given that London can be very varied depending on exactly where the job is and when it can be carried out etc, but you can always get a.n.other electrician to quote, you don't need to tell them they won't get the job, and it will also give you a comparison price to work against. If the landlords electrician is over-charging significantly then you can take it up with him.

There may be technical reasons on site for choosing a single phase supply such as:
- the distribution board you are connection from is only single phase,
- there may not be a spare 3 phase way (which is basically 3 single phase ways together), or
- the existing board already has significant loads on 2 of the 3 phases.
All of these are perfectly valid reasons for choosing single phase but the fact that they won't give you a good reason would lead me to ask further questions such as is their electrician competent to work on a 3 phase distribution board.
 02 February 2017 04:04 PM
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Sandtree

Posts: 6
Joined: 14 January 2017

Many thanks Mapj1

The chap is the landlords preferred electrician and has "done a lot of work in the building" according to the landlord so I suspect the basics he already knows and he can access the fuse boxes without accessing our unit. The only thing he definitely hasnt done/asked is where within our unit we intend to install the socket.

Anyway, speaking to the landlord he's actually said it was a recommendation not requirement to use his electrician so waiting nearly 3 months for a quote was unnecessary. Will get a couple of comparison quotes and see.
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