oven one the unprotected side of CU?

[tpt]

Evening everyone.

Just fitting a kitchen and have finished first fit. As i'm supplying most things and the oven is changing from a single to a double i was looking at the consumer unit today to order a new breaker to suit the uprated load. it currently has a dedicated 6mm cable on a 32amp breaker.

anyway, i'm used to seeing the split load style CUs and no surprise this looks to be one. RCD on left with shower, plugs, etc all labelled. on the right hand next to the main switch are lights, smoke alarms and OVEN! on the far right. oven would have been original fit when the house was built 20 yrs ago.

i haven't opened the CU, i was only looking for model etc, but is it likely that this is right? seems to me that the oven isn't on the RCD unless i'm missing something with the CU design. looks to be a hager unit.

a shower has been retro fitted at some point (its in an extension) and thats on the left side, so unless im missing something this would mean that the original spark and the one who fitted the shower has ignored or done this wrong???

p.s. spark is out on friday but is on holiday - hence the post.

 

[tpt]

image may help. oven is far right. with the dodgy attempt to highlight it!

Untitled

• tpt
• 29 Aug 2011
• 1

 

[Luckyphil]

Ovens were often put on the Non RCD side of the Board , the only time it was frowned upon was when The Cooker Isolation Switch had an integral Socket on the Faceplate/

Lucky

 

[echoes]

There's no requirement for an oven per se to have an RCD.
Even under the 17th, if the cable installation does not call for an RCD, and the cooker switch does not incorporate a socket, and TN- earth, no RCD required.

So as long as your oven circuit was compliant when it was installed under the 16th, there is no obligation for it to be brought up to date subsequently.

 

[tpt]

thanks for the reply.

Should they be?

so as long as its not spur'd off to anything else its perhaps not an issue?

 

[tpt]

sorry for all the questions - compliant as in depth (50mm?) of cable and direction (straight lines etc).

 

[echoes]

The 16th ed. on-site guide (now I've blown the dust off it) says that RCDs were required (abridged):
a) on TT systems where Zs was too high to operate a fuse/MCB
b) socket outlets on TT systems
c) socket outlets reasonably expected to supply outdoor equipment
d) circuits supplying outdoor equipment by means of flex.

So not as onerous as the 17th as regards cable depth and sockets - but the safe zones still applied and must be adhered to irrespective of RCD protection.

And there is a nice example of an installation with lights, cooker, water heater all on the non-RCD side.

 

[tpt]

Thanks everyone. stops me worrying!

Cable is being extended by 10m (total run 18m) and is a dedicated cable for the 4.4kw double oven. new cable is installed in compliant manner, can only guess\hope that old cable is!

like i say, the spark is actually connecting it all on friday but i dont want to have to take units off to mess around after.

thanks again.

 

[echoes]

Sadly, the new cable should be installed to the 17th, which means that if it's buried unprotected <50mm then it should be RCD protected, according to the 17th.

Now assuming that your spark keeps the oven on the non-RCD side (?) and does not bury the cable deep or use earthed steel conduit, then he will not complied.

In that situation, I would take a view that the installation has not suddenly be made dangerous and would still sleep soundly at night. But that's just me.

 

[JohnW2]

Sadly, the new cable should be installed to the 17th, which means that if it's buried unprotected <50mm then it should be RCD protected, according to the 17th.
Now assuming that your spark keeps the oven on the non-RCD side (?) and does not bury the cable deep or use earthed steel conduit, then he will not complied.

Indeed. If it would fit (and it looks from the pic that it probably wouldn't) upgrading the MCB (which has to be changed, anyway) to an RCBO would be one solution - or, as you imply, the electrician might decide to try to wire the cooker circuit to the RCD side of the CU. As a final option (if an RCBO wouldn't fit), the electrician might leave the cooker circuit where it is in the CU and give it an external RCD (in an enclosure) of its own.

In that situation, I would take a view that the installation has not suddenly be made dangerous and would still sleep soundly at night. But that's just me.

I would be inclined to agree - but that obviously would not make it complaiant!

Kind Regards, John.

 

[JohnW2]

Sadly, the new cable should be installed to the 17th, which means that if it's buried unprotected <50mm then it should be RCD protected, according to the 17th. Now assuming that your spark keeps the oven on the non-RCD side (?) and does not bury the cable deep or use earthed steel conduit, then he will not complied.

It's just occurred to me that thsi begas a question relating to how silly the regs actually are....

...if one undertakes, today, work which involves extending a circuit, is it intended that the whole of the circuit concerned has to be made compliant with the current edition of BS7671, or is it acceptable for only the new work to be so compliant? In other words, if the OP's present cooker circuit were extended with cable in steel conduit, or with SWA, but leaving the existing cable as T&E buried <50mm, would it be acceptable to leave the circuit unprotected by an RCD, on the basis that none of the new wiring requires RCD protection?

Kind Regards, John.

 

[echoes]

Yes, as I understand it, only the new work needs to be 17th compliant, so even if the old wiring was <50mm, only the new would have to be protected by steel conduit. And if one chose not to use steel conduit, invoking the RCD requirement, that RCD could be at the old/new interface.

Suppose just the MCB at the CU was changed (e.g. to 40A for some reason), rather than the cable being extended. That would be classed a new circuit requiring RCD protection?

Wherever there are rules with boundaries, there will always be examples of nonsense and inconsistency. The tax system being another case in point...

I gather this was the reasoning in the proposed 17th ed amendment that never was, which permitted omission of RCD if the modified socket circuit was no less safe than before. Never mind.

 

[JohnW2]

Yes, as I understand it, only the new work needs to be 17th compliant, so even if the old wiring was <50mm, only the new would have to be protected by steel conduit. And if one chose not to use steel conduit, invoking the RCD requirement, that RCD could be at the old/new interface.

That's what I expected you would say

Suppose just the MCB at the CU was changed (e.g. to 40A for some reason), rather than the cable being extended. That would be classed a new circuit requiring RCD protection?

Goodness knows! Indeed, I suppose you could even ask the same question about changing the accessory connected to the other end of the cable! As you go on to say ....

Wherever there are rules with boundaries, there will always be examples of nonsense and inconsistency.

Very much so. However, to be 'fair', I can't really see that there are any particularly workable alternatives, given that it's obviously impossible and unreasonable to insist that all installations are updated every time a new edition of the Wriring Regs is published!

Kind Regards, John.

 

[ericmark]

Before BSI got involved with the regulations it did say common sense should prevail and although not longer stated it still is needed. Clearly the rules on buried 50mm can't apply to SELV supplies but there is no exception listed in the regulations.

The problem with any device using mineral insulated heating elements is moisture can cause leakage problems so it was normal not to install that type of fixed equipment through a 30ma RCD.

However the new rules on 50mm buried cable means either one should use Ali-tube cable or use a 30ma RCD. Where the cable is already installed clearly using of Ali-tube is not an option and the installer has to do a risk assessment as to if a RCD or non RCD supply is used.

Personally I have not had a problem with modern ovens mainly as the element tends to be out of the way hidden at the back around the fan. The older type hobs however have in the past been a problem. With ceramic hobs again the element if it exists is protected with induction of course there is no element so there is no leakage problem so they don't have a problem with 30ma protection.

However this is all down to the guy signing the certificates and it does not really matter what we all think it is up to him and him alone to decide if a 30ma RCD is used or not.

Personally every circuit in my house has been RCD protected since 1991 and although they do trip from time to time especially with electric storms I consider they are well worth while and likely have saved my son when younger from injury as he started with his hobby of being a radio ham.

As my father-in-law pointed out to me in 1990 I would never forgive myself should my family get injured when it was so easy to fit RCD's. However he has never fitted them to his house! Personally I did not wait to be forced by regulations to fit RCD's and I question why anyone would want to be forced to protect their family.