Low insulation readings on kiln - at what point is acceptable?

[cornburn]

Hi guys

I was asked by a customer to have a look at a kiln which had failed its PAT test. There's low L-E and N-E insulation readings on the element itself (several coils inside daisy chained together). Readings were about 0.25MOhm so way too high to actually be in contact with the chassis anywhere. I also traced each coil and you can see it's not touching the case anywhere.

As I don't do PAT testing I wondered if anyone knew the acceptable level of leakage allowed to pass and whether there was a way around this so the customer can continue to use the machine?

It seems to me as if this leakage is probably by design (old machine), and the heat insulation inside the kiln is probably ever so slightly conductive.

Any thoughts? I don't to tell them to chuck it as it seems fine, just obviously was designed before some genius came up with PAT testing ............................

 

[IQ Electrical]

Hi guys

I was asked by a customer to have a look at a kiln which had failed its PAT test. There's low L-E and N-E insulation readings on the element itself (several coils inside daisy chained together). Readings were about 0.25MOhm so way too high to actually be in contact with the chassis anywhere. I also traced each coil and you can see it's not touching the case anywhere.

As I don't do PAT testing I wondered if anyone knew the acceptable level of leakage allowed to pass and whether there was a way around this so the customer can continue to use the machine?

It seems to me as if this leakage is probably by design (old machine), and the heat insulation inside the kiln is probably ever so slightly conductive.

Any thoughts? I don't to tell them to chuck it as it seems fine, just obviously was designed before some genius came up with PAT testing ............................

I'm no PAT expert but I do recall a minimum IR figure of 0.3MΩ for some heating equipment.

Also remember that mineral insulated elements absorb moisture and if the appliance has not been used for some time, IR readings can suffer.

 

[cornburn]

Cheers for that. The element itself is just bare wire coil that sits on the fire proof blocks. I had wondered whether the blocks themselves would absorb moisture as you say and give a reading. Each individual coil gave a reading of about 4MOhm, when all connected in series this obviously drops down to the 0.25.

I wonder if I can tell them to get their PAT tester to do a visual inspection or something as I've checked everything? After testing at temperature first I think to dry it out. As it's a school they're stuck with needing the pointless sticker on the side of it to be able to use it!

 

[IQ Electrical]

Cheers for that. The element itself is just bare wire coil that sits on the fire proof blocks. I had wondered whether the blocks themselves would absorb moisture as you say and give a reading. Each individual coil gave a reading of about 4MOhm, when all connected in series this obviously drops down to the 0.25.

I wonder if I can tell them to get their PAT tester to do a visual inspection or something as I've checked everything? After testing at temperature first I think to dry it out. As it's a school they're stuck with needing the pointless sticker on the side of it to be able to use it!

You can recomment that they ask their PAT guy to do a 'touch current measurement'.

This test can be used where you suspect that IR readings are being influenced by something other than a fault.

I'm hoping a PAT expert pops along soon to double check my advice as it's not my particular area of expertise!

 

[malcolmsanford]

the 0.3 Mohm is for class 1 heating and cooking equipment not exceeding 3kw all other class 1 should be 1Mohm as normal.

The touch test or "soft test' is highlighted in section 15.6 of the IET code of Practice page 76.

I amaze myself with this PAT lark ...............

 

[cornburn]

Do you think that using a "soft test" is likely to give a different result? I see after looking on the net that it can be used on non-IT equipment now but don't have a copy of the code of practice I'm afraid

PS The kiln is only small and on a plug top so should be 3KW or less

 

[IQ Electrical]

the 0.3 Mohm is for class 1 heating and cooking equipment not exceeding 3kw all other class 1 should be 1Mohm as normal.

The touch test or "soft test' is highlighted in section 15.6 of the IET code of Practice page 76.

I amaze myself with this PAT lark ...............

Lol!

Are you sure it was 'not exceeding 3Kw' I thought it was for appliances 'exceeding' 3Kw?

So if we class a kiln as a heating/cooking appliance which in effect it is, what is the rating of this particular item?

 

[cornburn]

The kiln is only small and on a plug top so should be 3KW or less - couldn't find a sticker but similar on the web are all 2.9Kw

 

[UNG]

I would allow it to warm up a bit then do the test had similar problems with PAT tests. A mate of mine supplies fruit ripening equipment and was getting a lot of equipment returned having failed a PAT test I was asked to look at it and identified humid conditions the equipment is operated in as the problem and damp in the temperature probe as the issue to resolve, when the equipment was put through a short cycle and retested no fault showed up as the probe had dried out.

 

[malcolmsanford]

Lol!

Are you sure it was 'not exceeding 3Kw' I thought it was for appliances 'exceeding' 3Kw?

So if we class a kiln as a heating/cooking appliance which in effect it is, what is the rating of this particular item?

Lol so I haven't got this PAT testing lark right lol and that is with the book in front of me ..................

As the learned man says it is for Class I equipment EXCEEDING 3kw

I shall now go back to my comfort zone and sulk

 

[Adam W]

Ordinarily you'd do a type 2 IR rather than testing L-E, N-E.
A soft test should only be carried out if there is a risk of damaging internal electronics such as in IT or telecoms equipment.

 

[i=p/u]

ive heard/i should know turn them on full for 15 mins then retest , otherwise do touch current test

 

[Knobhead]

As suggested turn it on to dry it out. But do tests every 15 minutes for a couple of hours if you can spare the time. Just watch the readings come up!

I used to swap a laboratory kiln every 6 months for the lining to be repaired. It was a 20KW unit with ceramic elements. To get the repaired unit to work I’ve had to resort to using a gas torch (oxy-propane) to get some heat in to it to stop it tripping the supply. Another advantage I found was I wasn’t swapping the elements every hour while the temperature came up. The elements could be swapped from the out side with the kiln still working, it was bloody hot work though.