IR test sets off gas hob igniters - WTF?

[NickD]

As per the title really, IR test @250V DC, (L+N)-E, whole-installation test of domestic property, main isolator switch open (obviously), testing caused the piezo igniters on the kitchen gas hob to spark even though no-one was pressing the knob to ignite them, and failure of IR test at about 150kohm. Switching off the appliance FCUs in the kitchen made it stop, IR test then passed at 2.2Mohm. What the hell's going on there?

 

[malcolmsanford]

Not sure about this model but most sparking units have a connection with the hob frame to complete the circuit and produce the spark. This is why if you energise the spark and touch the case you can get a tingle.

 

[telectrix]

yeah. it's because the spark goes to earth.

 

[Knobhead]

So you’ve shoved 250V DC up an AC appliance and wonder why the readings were strange?

It’s a wonder you’re not buying a new cooker.

Was this an EICR or a specific test on the cooker?

 

[davesparks]

Why were you testing with appliances connected?
Why were you testing at 250V?
Why were you testing the whole lot at once?
What results did you get testing between L and N?
How long did you apply the test for?

 

[Marvo]

Not sure exactly why it caused the igniter to operate but you're taking a big chance IR testing with appliances of any kind still connected. You're lucky the control board and the ignition board is still working TBH.

 

[Broken handle]

Not sure exactly why it caused the igniter to operate but you're taking a big chance IR testing with appliances of any kind still connected. You're lucky the control board and the ignition board is still working TBH.

Tested live & neutral connected together and that connection tested to earth. On circuits previously working fine (i.e. no live - earth reversal) that should not cause a problem, esp at 250 volts.

 

[edexlab]

The op says he's linked L-N and tested to earth I was told to do this by lecturers and Nic said its ok to do it as a global IR on an Eicr
Personally I'll do it on individual circuits this way on an Eicr just in case something is still connected as a way of highlighting any items still connected before I do the 500v test if that makes sense.

 

[Plonker 3]

The op says he's linked L-N and tested to earth I was told to do this by lecturers and Nic said its ok to do it as a global IR on an Eicr
Personally I'll do it on individual circuits this way on an Eicr just in case something is still connected as a way of highlighting any items still connected before I do the 500v test if that makes sense.

Well that's it the gospel has spoken.

Have you thought what if you have equipment that leaks to earth (eg PCs etc) is still connected your test results could be flawed?

 

[trev]

Oh well, if NIC says it's ok then who are we to even consider questioning them.

 

[Broken handle]

Well that's it the gospel has spoken.

Have you thought what if you have equipment that leaks to earth (eg PCs etc) is still connected your test results could be flawed?

Yes, he then has to spend time unplugging items that may have caused dodgy readings and then test again.

 

[edexlab]

Yes I know what your saying and you are correct they should say something to that effect when recommending this method.
But in my experience usually any item such as a pc is connected to the ring in a visible place and you'd be pretty daft not to check the obvious things that may be connected, I did say it was "just in case there are items still connected"
And no I don't believe everything the Niceic tell me but I listed them amongst persons more qualified than me who have given this advice out, I reckon the op got this method from a similar source

 

[edexlab]

Also if you read the post I did say "before I do the 500v test" I wouldn't do it as a sole IR test as many do

 

[jimmymac]

Oh well, if NIC says it's ok then who are we to even consider questioning them.

NIC who? Nic Clegg? St. Nic?

 

[davesparks]

I wonder how much better 250v DC is for an AC appliance than 500v DC?

 

[Plonker 3]

Also if you read the post I did say "before I do the 500v test" I wouldn't do it as a sole IR test as many do

So 250 volts DC won't do any damage to any equipment rated for 230 volt AC use?

 

[edexlab]

Lets be honest here hands up who has done an IR test on a circuit and then realised they've just damaged an item
Oops too late now

 

[Marvo]

I'd say linking the L+N together with appliances still plugged in to do an insulation test to earth is bad practice. Many appliances have electronic control boards and often the boards themselves or their associated power supply board will have surge arrestors with one leg on earth. If your test voltage exceeds their clamping voltage they'll conduct and give you false IR readings. Many motors with speed control inverters also have output filtering circuits that use the earth as a functional circuit and these are also increasingly seen in a domestic environment and could be damaged by the high DC voltages used in IR testing. There may be people that disagree but I'd recommend you disconnect rather than relying on a short circuit L-N to prevent damage.

 

[Plonker 3]

I wonder how much better 250v DC is for an AC appliance than 500v DC?

Just half as much damage lol

 

[edexlab]

Marvo what your saying is true but here we're talking about something which is common practice for domestic installs not commercial or Industrial where judging by the majority of test sheets I've come across the IR testing never happened