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!

 

[Octopus]

Getting back to facts, what does the Electrical Installation Certificate, provided to you by the chap who fitted the new fuse board, state about the cable sizes?

2nd try

 

[Octopus]

Getting back to facts, what does the Electrical Installation Certificate, provided to you by the chap who fitted the new fuse board, state about the cable sizes?

2nd try

 

[Sally Mills]

sorry Murdoch.. I was given a certificate but know idea where it is. In touch with electrician and waiting for him to get back to me.

2nd try

rry

 

[Sally Mills]

sorry Murdoch.. I was given a certificate but know idea where it is. In touch with electrician and waiting for him to get back to me.

rry

sorry waiting for the electrician to get back to me. Know idea where the cert is11...do remember he gave me one though.

 

[The Ghost]

I presume you mean certificate?

 

[jamie-spark]

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!

The resistance doesn’t change. If the voltage is reduced so is the current

 

[Andy-1960]

The resistance doesn’t change. If the voltage is reduced so is the current

I am quite aware of that fact, I was reckoning the kiln would be rated for a nominal voltage of 230v (harmonised 400v for Europe). The OP does not state the voltage rating of the kiln only the voltage it is being supplied with. So I was reckoning it’s rated 11kW at 230v

 

[westward10]

I find it difficult to believe the xlpe insulation which I assume it to be of a swa cable has broken down due to external exposure.

 

[jamie-spark]

Ahh right.

Just I thought you said in your post
“ only need the peak demand to pull the volts down a bit on the distributors transformer for the current to rise” which would imply the opposite

 

[Richard Burns]

That makes sense thanks Richard. The cable from kiln RCD/MCB to the house is 15 meters long and cost a blooming fortune to have installed. I assume if the is a problem along this run the whole length has to be replaced?
Your help is much appreciated. x

It is possible (if there is enough slack in the cable) to repair a section of cable with a joint, however you would need to be sure of the location of the fault, which can be difficult to determine without very specialised equipment. I installed a similar cable for a similar application at 50m long so I am aware of the cost and troubles.

If the cable is damaged do you think the non regulation bends (as Vortigern suggested) in the cable might be an area of weakness/earthing?

It is possible that the sharp bends in the cable could have pushed core conductors through the bedding into the steel wire or compressed the insulation enough for cores to be almost touching and causing the fault. However it might just be that where the cable at the house was overheated it managed to cause unseen damage at that point.
Then again there may also be heating damage at the fuse box at the kiln. Investigation and testing should narrow down these possibility.

 

[dmxtothemax]

You say it only happens at the hottest part of the cycle ?
Perhaps you have insulation breakdown at high temp ?
Maybe a failing element.
I think a megger test is in order ?

 

[The Ghost]

failing element

See #1 from OP

 

[Ian Mills]

Have you looked at the kiln I worked on these in UK and it could be that the resistance of the elements is changing or a earth fault starts to show as temp goes up if you can get clamp amp meter on it check amps it is using as it reaches this temp and check earth leakage straight after tripping (within 1 min or so)

 

[Octopus]

So back on track .......... employ spark, isolate kiln building fuse board and properly test the submain from the main house fuseboard.

will take 1 hour

Then you'll know whats going on on the submain

 

[Ian Mills]

Just would add the reason the trip in the house goes and not at kiln room is there maybe a small earth fault on cable to house so when fault happens on kiln house trip goes first because fault current is slightly higher there