Problem with 11KW Kiln

[Sally Mills]

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!

 

[Andy-1960]

Is there any other equipment connected to the board in your studio?

 

[The Ghost]

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.

 

[ruston]

Is your studio outside and if so what type of cable is it ( eg Armoured or PVC)? And as above , how is it run ?

 

[LeeH]

Posting twice only confuses matters....

 

[Sally Mills]

There is a double plug coming off board in studio where I plug in heater but this is always turned off when firing kiln.

 

[Sally Mills]

sorreee!! wasnt sure I put post in right place

 

[Spoon]

Posting twice only confuses matters....

I've put a post in the other one asking all future replies go in this post.

 

[Sally Mills]

Here are some photos of fuse and cabling. Assume its PVC and it runs underground for 2meters.

 

[Sally Mills]

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.

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!!

 

[The Ghost]

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.

 

[DPG]

I think Vortigern is right - needs some IR testing/leakage testing maybe.

 

[The Ghost]

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.

 

[Sally Mills]

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.

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.

 

[Octopus]

Personally I am not sure I would have used an RCBO there with the RCD protection.

?????

Definitely a good idea NOT to put it on a shared RCD IMHO

 

[Octopus]

OP - can you post a picture of the fuse board where the kiln is?

 

[telectrix]

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).

 

[davesparks]

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).

No testing or fault finding? Just straight to removing the RCBO and up-rating the ocpd?

 

[telectrix]

sorry, dave. skimmed through the posts. never saw RCBO. of course i would test the curcuit before energising.

 

[Andy-1960]

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!