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!

 

[davesparks]

True, but what the betting it’s rated at 230v

Pretty unlikely considering the age of it and most heating elements are still built and rated for 240V with the 230V rating being a secondary rating to appease the mythical 230V rules.

 

[Sally Mills]

All your knowledge and advice is so very welcome, thanks all.

So have a sparky coming during this week. He is trusted and been at it 20 years.

So from the most likely and cheapest to test, where would you guys start to find fault, replace parts etc.? It worries me that someone might come in and say you need £600 of cabling when actually changing an RCBO for a fuse might be all that’s needed.

Many thanks

 

[Pete999]

Take a lok at your Conversations Sally

 

[The Ghost]

Keep us informed Sally if you have any doubt about what is suggested or price.

 

[David M]

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

How do you conclude that? The load is 11kw so at 240v the current would be around 45.8A , @ 230v around 47.8A

There are a number of factors to consider why the rcbo is tripping. It is either going to be thermal overload or earth leakage. My initial suspicion was thermal overload since the kiln is what's commonly known as an intermittent kiln. These types of kiln get up to around 900 degrees quite quickly but then demand a lot of energy to get them up to 1200. This means that at around 1000 degrees + they are pulling full power (max current) for a long period of time. It could also be, as mentioned already, that as the temperature in the supply cable increases the insulation resistance decreases and you get the earth leakage. This would mean replacing the damaged cable where required.
Hopefully your electrician will be able to determine the cause of the problem and advise you on best practice to rectify it.

On a personal note: Based on my experience with these kiln types ( the control gear and supply cables get a lot of hammer) I would have uprated the supply cable and associated protection devises and would not have - in series RCDs.

 

[DPG]

He's saying that if a resistance remains constant, and the voltage applied across it reduces then so does the current. Ohm's law.

 

[Octopus]

So from the most likely and cheapest to test, where would you guys start to find fault, replace parts etc.? It worries me that someone might come in and say you need £600 of cabling when actually changing an RCBO for a fuse might be all that’s needed.

That's precisely why you need to pay somebody to test the cable, and the RCBO at the house end before ANYTHING else.

If they ask you for money, make sure they state the results of the tests on a certificate, or the invoice.

Once you have this information, then post the details on here

It could simply be that the RCBO is BER

 

[davesparks]

How do you conclude that? The load is 11kw so at 240v the current would be around 45.8A , @ 230v around 47.8A

That’s is nonsense, by that same logic if you reduced the voltage to 120V then the current would be 91.6A and if you reduced the voltage to 24V the current would be 458A.

 

[davesparks]

So from the most likely and cheapest to test, where would you guys start to find fault, replace parts etc.? [/ATTACH]

I would start with having a good look at all parts concerned and discussing the full background of this fault with you.

Then I would decide what to test first, usually in such a situation I would be looking at the appliance first.

I wouldn’t normally replace parts until they have either been proved to be at fault by testing or process of elimination.

 

[jamie-spark]

How do you conclude that? The load is 11kw so at 240v the current would be around 45.8A , @ 230v around 47.8A

fundamental physics I=V/R

 

[David M]

That’s is nonsense, by that same logic if you reduced the voltage to 120V then the current would be 91.6A and if you reduced the voltage to 24V the current would be 458A.

Yes you are correct, I was focusing on achieving the load - 11 kw. My apologies for the confusion.

 

[DPG]

Farmer, I'd be interested to know why you've disliked my comment. Or is it just one of these random dislikes?

 

[Pete999]

Farmer, I'd be interested to know why you've disliked my comment. Or is it just one of these random dislikes?

Yes I was wondering why the dislike, could be a case of sausage finger strikes again

 

[Octopus]

^^

Joking.

It's so easy to do on a mobile

 

[Pete999]

^^

Joking.

It's so easy to do on a mobile

Crikey you had ne wondering there Murdoch, agree about the phone I have one of those soft penjobbies for texting etc, picked it up last year at ELEX, foc of course, and no I don't polish it, also got a KLEIN TOOLS bottle opener.