Cooker trips the RCD

[Vinny]

Fitted a new consumer unit in my flat for additional safety and installed a 10way split board with two 30mA RCD’s protecting 5ways each.
The RCD protecting the cooker circuit trips when the cooker is switched on, so checked the cooker elements with a 500v insulation tester and found that some have a low resistance to earth and are “leaking” sufficient current to trip the RCD.
Ive been out of the trade for a while now and only have a copy of the 16th edition which seems to stipulate that the downstairs sockets must be protected by a 30mA RCD so Im considering replacing one RCD with a 100mA and connecting the cooker and lights to that side, with all other ccts left on the other 30mA RCD.

Anyone see any problems with this

 

[WarrenG]

Fitted a new consumer unit in my flat for additional safety and installed a 10way split board with two 30mA RCD’s protecting 5ways each.
The RCD protecting the cooker circuit trips when the cooker is switched on, so checked the cooker elements with a 500v insulation tester and found that some have a low resistance to earth and are “leaking” sufficient current to trip the RCD.
Ive been out of the trade for a while now and only have a copy of the 16th edition which seems to stipulate that the downstairs sockets must be protected by a 30mA RCD so Im considering replacing one RCD with a 100mA and connecting the cooker and lights to that side, with all other ccts left on the other 30mA RCD.

Anyone see any problems with this

Umm this is a good one.

New Regs state that cables buried less than 50mm should be protected by a 30mA RCD including lighting........

When did you change the CU before the 17th Edition came into force? i.e. 1st July 2008?

Cookers do tend to have leakage current.

Is the leakage enough from the cooker to trip the RCD on its own?

If not and just a suggestion that you might be able to try and comply with the regs is change the arrangement and put the cooker on its own 30mA RCBO?

Probably find its cheaper to put new elements in the oven.

 

[Vinny]

Hi WarrenG thanks for your reply.
I should clarify something first. The flat I mentioned is one of three I rent out. In another of the flats each element on the cooker caused the rcd to trip (little tinker) I ended up buying a new cooker for the tenant which cured the problem (for now). The other flat had a newer cooker installed and it works fine (also for now)
I put the CU in all flats after the 17th edition came into force and had them verified by an authorised testing company. Yep I agree cooker elements do leak and more so as they get older and yep even one ring trips the rcd. It seems a bit hairy though to have to renew a cooker or its elements in order to get over this problem. I have an old 16th edition “On Site Guide” which has a diagram showing a TN-C-S system connection (p12) of a CU installation and the 30mA rcd is only protecting circuits supplying portable equipment outdoors and socket outlets. The rest of the circuits including the cooker and lights are shown on the none protected side of the board. I therefore assumed that a 100mA rcd is better than none at all.
Regarding the RCBO, won’t this trip equally as well as the 30mA rcd?
Suppose I could leave the lights on the 30mA side though?

 

[WarrenG]

Vinny,

My thinking is that if the leakage total for (all the circuits protected) is the cause of the 30mA RCD to trip then it may be possible to put the cooker onto its own RCBO seperated from other circuits so that you have less leakage coming from the cooker only and sufficient enough for a single 30mA RCBO? Hence still having protection for the cooker @ 30mA

Other equipment can have leakage as well i.e. fridges, washing machines, IT equipment and could be adding the total leakage current?

If as you say one ring is tripping the 30mA RCD on its own with out any of the other circuits then its time for an element change.

After all the RCD is doing its job and providing the protection. If its above the rating then its a potential hazard.

I changed a cooker element for someone recently, it was a piece of cake and the element didn't cost an arm & a leg.

Here's a good link for elements supplies should you find this as your best solution.

The Element Man: Supplier of cooker oven spare parts and elements for all manufacturers of cookers, ovens and grills" />

Better to be safe than sorry.

Warren

 

[Vinny]

Cheers for your input Warren and I take your points. However what are your thoughts on a 100mA protecting the other ccts where a 30mA protection isn’t specified, typically cooker, alarm, bell transformers and the like. Do you think this would be compliant with current reg’s?
As you quite rightly say other white ware items are also leaky considering the number of transient suppression capacitors that are fitted these days.
I have no idea how long it takes for an element to become sufficiently leaky to cause rcd problems, but if the rcd is already on hairy edge of tripping because of other equipment then it probably wouldn’t take long for the problems to start again. Are we then limited to changing elements the rest of your days?
I’m to old for all this hassle. I’m already a paid up member of the Grumpy old mens club, so this aggravation could see me challenging for the chairman’s job
Vinny

Latest update, Spoke to my tenant this afternoon and said I would first change the faulty cooker ring, she then said oh! I had thiought it was just one but in fact three of the four rings are now tripping the rcd.
So sod it Im going to put the cooker onto a 100mA and be done with it.
I think I'll contact the IEE for their view on the matter and will report back in case anyone else as Im sure there must be loads who are suffering the same problems.

 

[WarrenG]

Vinny,

As far as I understand the new 17th Edition personal protection should be by way of a 30mA RCD and the cooker requiring personal protection.

Here's a list of some of the 17th requirements for RCD's:

RCD 30mA

• All socket outlets rated at not more than 20 A and for unsupervised
  general use
  
• Mobile equipment rated at not more than 32 A for use
  outdoors
  
• All circuits in a bath/shower room
  
• Preferred for all circuits in a TT system
• All cables installed less than 50 mm from the surface of a
  wall or partition (in the safe zones) if the installation is
  unsupervised, and also at any depth if the construction
  of the wall or partition includes metallic parts
  In zones 0, 1 and 2 of swimming pool locations
  
• All circuits in a location containing saunas, etc
  
• Socket outlet final circuits not exceeding 32 A in agricultural
  locations
  
• Circuits supplying Class II equipment in restrictive
  conductive locations
• A circuit supplying Class II heating equipment for floor and
  ceiling heating systems.
  

RCD 100mA

• Socket outlets of rating exceeding 32 A in agricultural
  locations.
  

If the leakage is high enough to trip the 30mA RCD then I personally wouldn't recommend by passing this problem with the use of a higher 100mA RCD.

There are other causes that could be adding to your total leakage such as loose connections, wet plaster, condensation, moisture ingress etc?

Quite a common Rcd problem that you can find on new installs is a crossed neutral on a split load board? - may be worth checking?

Warren

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[Vinny]

Thanks lads for your input. You’re probably right as the root cause seems to be the cooker rings aging but what a faf having to replace elements each time I'll probably just get them changed and the grill or oven will crap out next. Hope they last a while before causing probs again. No crossed neutral Warren as Im now wise to that very problem at one of my other rentals (semi) when the feed to the stairs 2way had been taken from the downstairs rcd while the neutral had been taken from the upstairs rcd. I'll also take some measurements to try to determine what leakage current ther is when the cooker is off.
Once again thanks for all your efforts and input.
Only wish I'd been a plumber now