Problem with 11KW Kiln

S

Sally Mills

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Can you clever people advise as to why I might be having an issue with my ceramic kiln. I am a potter not an electrician so I will endeavour to give you what technical information I have.

11kw kiln running off a domestic board with its own 50A fuse on board in the house, 15m lenght of 10mm cable runs from house into my studio where it has its own board with a 62A breaker and 50A fuse.

The fuse in house is tripping when firing cycle reaches about 1060 degrees (kiln should reach 1250 degrees). It used to reach 1180 degrees before tripping but over a few years it has been tripping earlier and early.

The firing cycle of the kiln goes up slowly, automatically over 5 hrs automatically turning on and off until the end when its on full load. Kiln fired fine with no tripping day before yesterday (post element change) when taken fast at full load to temperature, but when I did a slower firing last night it tripped.

Kiln engineer took a reading of 45Amp and there is a drop in voltage from 240 to 232 when under load.

I have had kiln serviced and elements replaced this week and tripping still happening so pretty certain its not the kiln.

Questions: Can anyone see an issue with the electric maths? Is the cable thick enough? Can a domestic fuse be upped to next level? Can cables get tired and old?

Any advise as to what to try next would be greatly appreciated as I'm soooo frustrated with this ongoing issue.

Cheers lovelies!
 
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The cable is fine in theory. It depends on how it is installed i.e. clipped direct onto a wall or in thermal insulation. Photos of the route of the cable and the "fuse"(s) you speak of will also help identify the type of MCB in use. It may be that the MCB is defective and not operating withing required parameters. The maths otherwise is fine on the design of the circuit.
 
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Here are some photos of fuse and cabling. Assume its PVC and it runs underground for 2meters.

IMG_0104.JPG


IMG_0105.JPG


IMG_0106.JPG


IMG_0107.JPG
 
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Vortigern said:
The cable is fine in theory. It depends on how it is installed i.e. clipped direct onto a wall or in thermal insulation. Photos of the route of the cable and the "fuse"(s) you speak of will also help identify the type of MCB in use. It may be that the MCB is defective and not operating withing required parameters. The maths otherwise is fine on the design of the circuit.
Click to expand...

Cable is clipped onto wall, thinks its PVC. I have added photos previously.

MCB in the house is also new as I had whole new board fitted. Sorting this problem so far has cost me a fortune!!
 
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Ok so thats an RCBO, (the switch in photo) so it is very likely an earth fault not a thermal aspect of the other function of that switch. So someone is going to have to test/trace where the earth fault lies.
Personally I am not sure I would have used an RCBO there with the RCD protection. Unless it is not on the circuit the RCD is governing. Sorry to get techy but someone needs to check it out for earth leakage.
 
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Actually looking at the bend in that cable (SWA cable) outside the door it does not meet the required bend radius where it comes out of the wall and that may be your problem if I am seeing right! It may have caused the earth fault.
 
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Vortigern said:
Actually looking at the bend in that cable (SWA cable) outside the door it does not meet the required bend radius where it comes out of the wall and that may be your problem if I am seeing right! It may have caused the earth fault.
Click to expand...
Ah ok..... it also bends like that in 3 other places too...at the other end of wall and where it enters and comes out of the ground.
 
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i would replace the MCB in the house with a fuse.this can be done by an electrician by removing the armoured cable from the consumer unit and feeding from a separate switch/fuse. maybe can go up to 63A, (cable calculations allowing).
 
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telectrix said:
i would replace the MCB in the house with a fuse.this can be done by an electrician by removing the armoured cable from the consumer unit and feeding from a separate switch/fuse. maybe can go up to 63A, (cable calculations allowing).
Click to expand...

No testing or fault finding? Just straight to removing the RCBO and up-rating the ocpd?
 
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sorry, dave. skimmed through the posts. never saw RCBO. of course i would test the curcuit before energising.
 
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I think the 50A breaker is a bit tight for an 11kw heating load. At 232v that works out to 47.5A.
Only need a peak demand to pull the volts down a bit on the distributors transformer for the current to rise.
May also be the tolerance on the rating of the breaker is in the minus!
 
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What does the certificate for the fuse board change state?

Looks like the small CU has a RCD too ........... which one is tripping?

Wonder why the installer fitted an upfront RCBO ?
 
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As Murdoch says, the upfront RCBO doesn't seem necessary. Tel's idea of changing it for a fuse may be wise. After the necessary testing obviously.
 
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I
Murdoch said:
What does the certificate for the fuse board change state?

Looks like the small CU has a RCD too ........... which one is tripping?

Wonder why the installer fitted an upfront RCBO ?
Click to expand...
I asked electrician to replace board as the kiln cable had almost caused a fire inside the old plastic board (melted the casing a little)!! Scary!. He decided to put the RCBO in.

It is the CU (on the left in picture) on house board that trips. The RCD on the right is for the lighting circuit of house.

IMG_0104.JPG
 
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Murdoch said:
Did the spark not fit the SWA cable?
Click to expand...
Cable fitted 10 years ago by newly qualified friend!! Always wondered if he did the right thing.

Really appreciate all your advice. Without finding the cause I have no business. Just though many heads better than one as I am desperate and I was right..you're all great. I'll make you all a cyber cuppa :)
l
 
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Ok , that happens too .
If the wall that the cable is on is south facing and gets lots of sun , and judging as it is business use and is on for long periods - that cable is going to have a good start at getting preheated.
It could be as has been said before the insulation resistance has been compromised. , or the cable has been damaged by the first overheat incident.
If I were you I would get a reputable electrician to inspect and test this circuit .
Maybe someone on here is nearby.
 
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Sally Mills

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Problem with 11KW Kiln
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