Very low IR results on oven?

[HappyHippyDad]

I have just been carrying out an EICR and I have got some results that I am unsure about.

The property has 2 ovens on the same circuit, the circuit has a line-earth IR of 0.004Mohms when the cooker isolation switch of one of the ovens (oven 1) is closed, and 0.4Mohms when the other cooker isolation switch is closed and oven 1 switch is open Is there any reason that the electronics within an oven would cause this?

In the same area of the kitchen there are equally as bad IR results on the ring. The house has a very bad damp problem particularly in this area which I know is affecting the sockets but I was unsure with regards the electronics in an oven?

I realise this is an EICR but I will be carrying out the remedials over the next few days.

There is no RCD for the property.

Cheers all.

 

[davesparks]

You should be disconnecting appliances before IR testing. You are not testing the appliances, just the installation

 

[Lucien Nunes]

Davesparks has a point, however the accidental discovery of an appliance with a strikingly low IR would make me want to know why and whether it's safe to re-energise.

As I stated repeatedly in the recent thread about low IR with connected appliances, there is no reason for normal electronic devices to cause low IR (i.e. less than a few MΩ) to earth at 250V. However as I also mentioned in that thread, sheathed heating elements, especially ones that have not been used for a while, are one of the few examples of loads that sometimes go low by themselves without being terminally faulty.

0.004 MΩ is not a very precise reading. If your MFT allows +/- a few counts it could be almost anywhere from a hard short to 10kΩ - in either case it's low even for an element and quite likely to trip an RCD. Personally I would be reluctant to re-energise without either baking the elements or finding the cause.

Of course, if that was a 500V test you might be looking at surge suppression in the control module, unlikely but I would check again even with a DMM. If it's low on a DMM, there's a genuine problem, hopefully not one caused by the 500V test.

 

[davesparks]

As Lucien had suggested, that value is low enough to be read properly on a Kohms scale on a dmm, or possibly the continuity range on some mfts (I know my megger will but my kewtech won't)

Ignoring the 1M thing for a moment another (very old) method of establishing a minimum IR is that the leakage current should be no more than 1/10,000th of the FLC (leakage current being calculated from the IR)

There is a slim chance that of its one of the ridiculously over-complicated modern ovens then the problem may have been caused by you shoving 500V up its arse

 

[bigspark17]

On an EICR test should be carried out to isolators/outlets with loads disconnected, you are testing the wiring not appliance, that would come under IITEE.