split load consumer units and part P regs?

[Stueeee]

In a situation where there is a built in hob/oven in a domestic kitchen which is fed from a split load CU. The cooker is currently connected to a 32A MCB on the RCD protected side. The hob (which has previously been replaced with the same fault) is tripping the RCD from time to time when the rings are turned up high -haven't had any test gear on the circuit but this seems to me to be the kind of nuisance tripping you would expect to get from heating elements.

Two questions occur to me-

Is it OK to have the cooker hob connected to the non-RCD protected side of the CU

Would this be Part P work? i.e. do I need to get a qualified spark to do what would be a simple changeover in the CU.

Thanks in anticipation for any replies.

 

[WorkshopChris]

No as it is very unlikely that the cables are either mechanically protected and buried deeper than 50mm from any surface and or surrounded by a metallic conduit.

Need to measure the elements with a megga. But could also be a build up of combined leakage and the elements just push it over the 30ma.
You can get sensitive earth leakage clamp meters.

Brightspark may be able to confirm about the cables i don't get involved with domestic but that's the reg from memory.

Edit, just a thought you could have the oven circuit put on a RCBO that way if it trips its only going to take the oven out not your other circuits. But it might be an idea to get the combined leakage on the main RCD looked at.

 

[Dee J]

Heating elements in regular use should not trip an rcd on their own (sometimes new or unused elements can accumulate moisture and trip on first use). So its likely that it's combined leakage from several circuits on the rcd half of the split panel. Ideally the various leakage sources should be fixed, but the symptom can be alleviated (as has been suggested) by putting the cooker on its own rcbo.

 

[dobbslc]

A new circuit? Pretty sure it's notifiable work.
If the hob has already been replaced once with "the same fault" it will be dangerous to then wire it to a non RCD protected circuit as if the fault gets worse (they always do) it will just sit there live until someone touches it!
30ma's is considered to be the maximum survivable current flow though the body, that's why they use them.
Get a new hob.
Also try turning off everything on that RCD then turn on the hob, if it runs ok then turn back turn on everything else. See if it trips when you turn on the toaster or something else like an electric shower, if it trips then it's probably a build up of fault current.
You can put the hob on its own RCBO and that will help. But still get it checked over by somebody that knows what they are doing, that's probably not the service "engineer" they send out.....

 

[Stueeee]

Thanks for the useful replies.

Heating elements in regular use should not trip an rcd on their own (sometimes new or unused elements can accumulate moisture and trip on first use).

Interesting, my experience (long time ago) with industrial stuff has been that there occasionally has been some leakage from enclosed heating elements.

No as it is very unlikely that the cables are either mechanically protected and buried deeper than 50mm from any surface and or surrounded by a metallic conduit.

Need to measure the elements with a megga. But could also be a build up of combined leakage and the elements just push it over the 30ma.
You can get sensitive earth leakage clamp meters.

I do have a megger, but will just change the hob after putting the megger on the cable, just in case someone has put a nail through the cable somewhere

Brightspark may be able to confirm about the cables i don't get involved with domestic but that's the reg from memory.

Is this reg for schedule 17? or has it been in place for a while. The installation isn't new.

Edit, just a thought you could have the oven circuit put on a RCBO that way if it trips its only going to take the oven out not your other circuits. But it might be an idea to get the combined leakage on the main RCD looked at.

the symptom can be alleviated (as has been suggested) by putting the cooker on its own rcbo.

I will put the new cooker/hob on an RCBO as even if the fault recurs, the tenant won't lose the ring mains if/when when there's a trip.

A new circuit? Pretty sure it's notifiable work.

Not a new circuit, will be a change of hob, and will be a change from MCB on the RCD side to RCBO on the other side of the CU -is that going to be Part P notifiable?

You can put the hob on its own RCBO and that will help. But still get it checked over by somebody that knows what they are doing, that's probably not the service "engineer" they send out.....

Have just bought this house from an absentee landlord, so a lot of the work has probably been done by an "engineer" as you say. The house is rented, so basic electrical certification is already in place, the very reason for this post is so that I can get the issue properly fixed.

Whether I'm someone who knows what they're doing is for others to judge, but all the three phase installation work in my workshops was done by myself and was also properly certified on completion.

 

[piman]

Hello Dobbsic,

"it will be dangerous to then wire it to a non RCD protected circuit as if the fault gets worse (they always do) it will just sit there live until someone touches it!"

Not if the earth circuit is sound.

Alec

 

[dobbslc]

With earth leakage you will still get a fault current. 30, 500, 2000 ma's won't blow a 32amp fuse, do you want to risk a shock off of it?

 

[rtbcomp]

Hello Dobbsic,

"it will be dangerous to then wire it to a non RCD protected circuit as if the fault gets worse (they always do) it will just sit there live until someone touches it!"

Not if the earth circuit is sound.

Alec

If.

Someone was killed in a bath because of a faulty heater in a bedroom and a faulty earth circuit.

Personally I think a cooker must be connected via an RCD given the environment it's used in, water and steam &c.

 

[brightspark]

With earth leakage you will still get a fault current. 30, 500, 2000 ma's won't blow a 32amp fuse, do you want to risk a shock off of it?

the rcd will not trip if its a line to neutral short circuit fault it will only trip if theres a line or neutral fault to earth. current imbalance

 

[dobbslc]

I know ^
What I'm saying in a round about way is don't risk hiding a fault on an appliance by taking it off an RCD protected circuit.
It might just be a duff element that needs changing, so to Stueee see if you can isolate each element and test with your meter on the highest ohms setting between the terminals and the metal ring / casing, it should read clear, if you've meggered it with a proper insulation resistance tester you might see it start a bit iffy then slowly go clear on the meter.
A 2 kilowatt element should read between about 20-30 ohms across the two terminals, if it's starting to play up the reading will possible jump around a bit.
Worth checking the wiring in the hob itself as it can chaff on the sharp edges on the steel work. I had an new oven that had a tiny cut in one of the silicone wires rubbing on something metal that the appliance engineer didn't see or when I spotted it think was a problem..... hence the comment in my post above.
Good luck.

 

[Stueeee]

Thanks for the further replies. I have just ordered an RCBO to go in the non-RCD side of the CU.

I have also ordered a new inset hob unit, although the tenant has said that it has previously been changed out, the existing inset hob looks scabby, I think that the managing agent's "engineer" may have swapped it out for a secondhand unit. Before doing any connecting up of the new stuff, I will megger the cable just to be sure, probably wouldn't be the first time that there was a woodscrew or such going through the hidden cable somewhere in the run.