Retrofitting an existing wall oven and hob with a replacement range that has gas hob (no electric elements) and combined electric oven.
Existing setup uses a 6mm from board and splits into two 4mm for the original hob and oven.
Referring to 4.18.1.3(b) I intend placing a 15A socket behind the range (hence its inaccessible), and putting a switch (functional) within 2metres of the range. Switch will obviously be outside of the zones in figure 4.17.
Question1: I cannot find any reference to separation of the socket outlet to the range gas connection, other than a mention in 3.9.8.4(b) that states a 25mm separation. Additionally Figure 4.20 really doesn't apply. Is this distance defined anywhere? obviously common sense would separate the two where possible behind range.
Question2: As I'm upgrading the existing range connection from a hardwired connection to a 15A socket, do I need to upgrade the existing 4mm (from range to switch) up to 6mm or can I just drop the entire series 6mm/4mm run down to 20A at the board?
Gas Range Conversion
Re: Gas Range Conversion
First point is that the 2018 edition of "3000" has not yet been cited by ESRs.
However in this case following the later edition WRT overcurrent protection and separation of services isn't likely to cause a non-compliance with the cited edition (2007 +A1+A2).
Q1
3.9.8.4 (b) covers separation between electrical wiring and the gas pipe. There is no required separation between the socket and the gas outlet.
The wiring rules deal do prohibit placing general electrical fittings in Zones where it is likely that a "hazardous area" may exist under normal operating conditions; but there are no such Zones for gas appliances. Basically there can't be a build-up of gas leading to a potentially explosive atmosphere when appliance is operating normally, as all the gas discharged is consumed.
Q2
For the existing 6mm2 reducing to 4 mm2, with both appliance connected by direct connection; Exception 3 to 2.5.1.3 may well have applied.
The equipment could not apply an overload to the smaller cable, so 2.5.3.4 (b)(ii) allowed the overload device that is required by default for any reduction of CCC to be omitted.
Changing from direct connection (fixed wiring) to detachable connection (socket outlet) means that pathway to compliance is no longer valid.
Can't be sure that was the existing pathway, as you didn't mention the rating of the circuit protection nor the installation conditions for the wiring.
May actually have been 2.5.3.4(b)(i); since 4 mm2 has a CCC of 31 A partially surrounded, and 39 A touching. The 6 mm2 may have been primarily to avoid voltage drop. This pathway would still be available for the new configuration.
If not quite fitting that (eg if circuit protection greater than CCC for the existing 4 mm2 in the conditions; probably easier to de-rate the circuit than replace the section of cable - the new appliance isn't likely to need a 32 A circuit.
The other factor with this change is that the new socket requires RCD protection [2.6.3.3.4 of 2018 edition, 2.6.3.4 of current edition].
Under 2018; this requirement is changed so that we only have to provide the RCD for new sockets on existing circuits if RCD protection would be required in same circumstances for a new final subcircuit.
So, assuming this is residential, apply 2.6.3.3.1 - and Exception 2 allows no RCD provided the socket is (a) not readily accessible and (b) labelled .
BUT while we are allowed to follow 3000: 2018, we can only do so provided that doesn't lead to non-compliance with currently cited edition.
And the requirement in current clause 2.6.3.4 for every socket added to an existing subcircuit to be protected by an RCD doesn't have any escape clause at all.
So RCD protection must be provided regardless of rating & purpose of socket, and regardless of whether domestic or non-domestic.
However in this case following the later edition WRT overcurrent protection and separation of services isn't likely to cause a non-compliance with the cited edition (2007 +A1+A2).
Q1
3.9.8.4 (b) covers separation between electrical wiring and the gas pipe. There is no required separation between the socket and the gas outlet.
The wiring rules deal do prohibit placing general electrical fittings in Zones where it is likely that a "hazardous area" may exist under normal operating conditions; but there are no such Zones for gas appliances. Basically there can't be a build-up of gas leading to a potentially explosive atmosphere when appliance is operating normally, as all the gas discharged is consumed.
Q2
For the existing 6mm2 reducing to 4 mm2, with both appliance connected by direct connection; Exception 3 to 2.5.1.3 may well have applied.
The equipment could not apply an overload to the smaller cable, so 2.5.3.4 (b)(ii) allowed the overload device that is required by default for any reduction of CCC to be omitted.
Changing from direct connection (fixed wiring) to detachable connection (socket outlet) means that pathway to compliance is no longer valid.
Can't be sure that was the existing pathway, as you didn't mention the rating of the circuit protection nor the installation conditions for the wiring.
May actually have been 2.5.3.4(b)(i); since 4 mm2 has a CCC of 31 A partially surrounded, and 39 A touching. The 6 mm2 may have been primarily to avoid voltage drop. This pathway would still be available for the new configuration.
If not quite fitting that (eg if circuit protection greater than CCC for the existing 4 mm2 in the conditions; probably easier to de-rate the circuit than replace the section of cable - the new appliance isn't likely to need a 32 A circuit.
The other factor with this change is that the new socket requires RCD protection [2.6.3.3.4 of 2018 edition, 2.6.3.4 of current edition].
Under 2018; this requirement is changed so that we only have to provide the RCD for new sockets on existing circuits if RCD protection would be required in same circumstances for a new final subcircuit.
So, assuming this is residential, apply 2.6.3.3.1 - and Exception 2 allows no RCD provided the socket is (a) not readily accessible and (b) labelled .
BUT while we are allowed to follow 3000: 2018, we can only do so provided that doesn't lead to non-compliance with currently cited edition.
And the requirement in current clause 2.6.3.4 for every socket added to an existing subcircuit to be protected by an RCD doesn't have any escape clause at all.
So RCD protection must be provided regardless of rating & purpose of socket, and regardless of whether domestic or non-domestic.
Re: Gas Range Conversion
Thank you for the in-depth answer Alec.
Things have got a little messy now as I've pulled the cabinets out and the 4mm has been eaten by rats, hence I'm replacing from switch to oven socket anyway.
So my approach forward will be;
1/ Leave existing 6mm from board to switch in place.
2/ Replace tail from functional switch to oven socket with 2.5mm (only a 3metre run unenclosed touching).
3/ Fit 15A socket behind oven (inaccessible)
4/ Downgrade mcb in board to 20A
From board to oven is 16metres so VD ok (especially since 2/3rds of run is still in 6mm). CCC for 2.5mm unenclosed touching from 3008 Table 10 is 30A so dropping MCB to 20A meets my CCC.
Re adding RCD, sorry I missed the ESR not citing 3000-2018 yet. However even in 2007-A2, they allow the exception for a non-RCD socket on an oven, or am I mis-reading 2.6.3.4 exception (3) ? The wording sounds like a double-negative.
All that said, if I'm changing the oven feed from 32A down to 20A I may as well use an RCBO (boards a little full), and improve safety all around. Just hoping leakage current on a modern Smeg oven is low enough not to nuisance trip!
Things have got a little messy now as I've pulled the cabinets out and the 4mm has been eaten by rats, hence I'm replacing from switch to oven socket anyway.
So my approach forward will be;
1/ Leave existing 6mm from board to switch in place.
2/ Replace tail from functional switch to oven socket with 2.5mm (only a 3metre run unenclosed touching).
3/ Fit 15A socket behind oven (inaccessible)
4/ Downgrade mcb in board to 20A
From board to oven is 16metres so VD ok (especially since 2/3rds of run is still in 6mm). CCC for 2.5mm unenclosed touching from 3008 Table 10 is 30A so dropping MCB to 20A meets my CCC.
Re adding RCD, sorry I missed the ESR not citing 3000-2018 yet. However even in 2007-A2, they allow the exception for a non-RCD socket on an oven, or am I mis-reading 2.6.3.4 exception (3) ? The wording sounds like a double-negative.
All that said, if I'm changing the oven feed from 32A down to 20A I may as well use an RCBO (boards a little full), and improve safety all around. Just hoping leakage current on a modern Smeg oven is low enough not to nuisance trip!
Re: Gas Range Conversion
A 30 mA leakage would equate to IR only 7667 ohms, well under the 10 k ohm limit.
Even with most RCDs actually operating around 23 mA; basically if it trips, then it would fail an IR test.
For your new bit of cable; even if there's no BTI present we stil have to assume that it will be, making "partially surrounded" the best installation condition we can use. For 2.5 mm2, that's 23 A, so all good.
Yes the current edition has an Exception in 2.6.3.1 for new circuits supplying socket for fixed cooking appliance.
But that Exception doesn't apply to a socket added to an existing subcircuit, under 2.6.3.4.
The reasons behind this situation are long & complicated, and since they don't change the fact of what the letter of the rules says not really worth explaining.
The newer edition fixes the problem; by allowing us to apply the same Exceptions to "adds-&-alts" as are available for new final subcircuits
But until ESRs cite the 2018 edition; ALL sockets added, anywhere for any function, must have RCD protection. NO exceptions.
Even with most RCDs actually operating around 23 mA; basically if it trips, then it would fail an IR test.
For your new bit of cable; even if there's no BTI present we stil have to assume that it will be, making "partially surrounded" the best installation condition we can use. For 2.5 mm2, that's 23 A, so all good.
Yes the current edition has an Exception in 2.6.3.1 for new circuits supplying socket for fixed cooking appliance.
But that Exception doesn't apply to a socket added to an existing subcircuit, under 2.6.3.4.
The reasons behind this situation are long & complicated, and since they don't change the fact of what the letter of the rules says not really worth explaining.
The newer edition fixes the problem; by allowing us to apply the same Exceptions to "adds-&-alts" as are available for new final subcircuits
But until ESRs cite the 2018 edition; ALL sockets added, anywhere for any function, must have RCD protection. NO exceptions.
- Rating: 16.67%
Re: Gas Range Conversion
The existing cable is run under floor below already existing Expol BTI, so unless they blow insulation into an internal wall I'm ok (but as you state I'm ok either way).
Re RCD requirement, for the minimal cost the safety improvement makes me feel happier anyway so all good.
Really appreciated your advice
Re RCD requirement, for the minimal cost the safety improvement makes me feel happier anyway so all good.
Really appreciated your advice
Re: Gas Range Conversion
No problem.
The effect of 2.6.3.4 applying to all sockets in all installations is not widely understood; and was probably never intended
- partly a result of how the RCD clause has been constantly changed over the years.
I believe the Exceptions that follow it were originally Exceptions to the entire clause, but over time were increasing read as applying only to that sub-clause. The 2018 edition provides clarity
The effect of 2.6.3.4 applying to all sockets in all installations is not widely understood; and was probably never intended
- partly a result of how the RCD clause has been constantly changed over the years.
I believe the Exceptions that follow it were originally Exceptions to the entire clause, but over time were increasing read as applying only to that sub-clause. The 2018 edition provides clarity