Part P + Upgrading Oven

[enly1]

Hi all,

Please be gentle. I'm trying to work out where I stand and if I am allowed to replace my oven myself (part P and if my logic is correct.

I have an oven connected to the consumer unit on a dedicated 6mm run (through cooker switch ( big red on/off and 13A socket ).
The consumer unit currently has a 16A circuit breaker for the cooker.

I have yet to buy a new oven, but wanted to have the option of a 4.8KW+ rated oven.

My question is simple - can I just wire in a new oven on the existing cable, but change the fuse to something more appropriate ?

PS - i've checked the RCD capacity, and I have room to increase the MCB without exceeding the 100A capacity ( assuming no magic is required when totalling the MCB figures )

Guidance Welcomed.

PS - I've been spending most of the day looking for answers, so sorry if I missed a similar question.

Thanks in advance.

 

[riveralt]

A 4.8kw oven with a cooker switch/socket after diversity is 18.2 Amps so you need to increase the MCB.

Your 6mm cable is okay for what you propose.

Straight replacement of an oven isn't an issue for part p.

 

[Adam_151]

Simple swap of the oven is not notifiable however exchanging the circuit breaker foe one with different charateristics is (and the logic is sound on this one - someone thought to be verifying the zs is in spec for the new breaker, and that the cable, as installed is suitable*)


*In your case unless theres something excpetional, I can't see the later being an issue, and the former isn't likely to be an issue unless theres something wrong (but until you take the Zs you don't know)

 

[riveralt]

Simple swap of the oven is not notifiable however exchanging the circuit breaker foe one with different charateristics is (and the logic is sound on this one - someone thought to be verifying the zs is in spec for the new breaker, and that the cable, as installed is suitable*)


*In your case unless theres something excpetional, I can't see the later being an issue, and the former isn't likely to be an issue unless theres something wrong (but until you take the Zs you don't know)

Understand the logic, but can you show me where it says that?

 

[enly1]

The logic of changing the circuit breaker was why i was asking about the part P stuff.

As I wasn't changing the cabling, I thought I would be okay, but with the MCB changing, I'm effectively changing the configuration of the circuit, so was wondering.

Really happy if I don't need to get someone in to eyeball it for me, but want to be sure before I go and wire something up.

Thanks for the info so far !

 

[Adam_151]

the text below is from the SI and lists work which is exempt from notification, theres nothing which refers to MCBs directly, but it clearly dictates that consumer units not covered by these exception, and I'd take that to mean the devices contained within as well, as without the MCBs its just a din rail and box, especially as the next exception allows you to replace enclsoures as long as you don't affect the protective measures of the circuit

1. Work consisting of -

(a) replacing any fixed electrical equipment which does
not include the provision of—

(i) any new fixed cabling; or

(ii) a consumer unit;

(b) replacing a damaged cable for a single circuit only;

(c) re-fixing or replacing enclosures of existing
installation components, where the circuit
protective measures are unaffected;

(d) providing mechanical protection to an existing
fixed installation, where the circuit protective
measures and current carrying capacity of
conductors are unaffected by the increased thermal
insulation.

(e) installing or upgrading main or supplementary
equipotential bonding;

........ (snipped off some stuff about heating systems, doors and lighting)

 

[Stoday]

The Approved Document part P explains how to meet part P of the requirements of the Building Regulations. It says that you do not have to notify work consisting of replacing any fixed electrical equipment. I believe that a MCB is fixed electrical equipment and so you don't have to notify its change.

There are no words constraining the replacement such as "like for like" or "providing the circuit's protective measures are unaffected". The latter applies to the replacement of enclosures and cables, but not to electrical equipment itself.

Like you, I cannot fathom the logic behind this, but I'm not a lawyer. That's why the law is explained to us in the Approved Documents. You can only go by what they say, no matter how illogical.

 

[riveralt]

I know, I haven't found any reference to the MCB myself...

Reason for raising this issue is that I have been advised by my scheme that I do not need to complete a part P notification if I replace, for example a shower (same power characteristics) and upgrade the mcb - because the old one failed to comply with manufacturers instructions.

Now I know the circs are slightly different here inso much as I would and did check the Zs and was comfortable with the outcome and reported same on minor works sheet - but it does seem crazingly expensive for someone changing an MCB to have to spend upward of £200 in my area to contact BC.

I could advise the OP, but I wouldn't of course, to buy a £10 multimeter, make sure the circuit is dead and check the R1+R2 reading themselves, especially if they were going to change the MCB themselves from say a 16Amp to 20Amp. i.e. connect the cables line (red/brown) with the cables earth at the consumer unit and test test between same at the end where they intend to connect the cooker to. Using the tables, assuming no insulation issues and a length of 20meters you should expect a figure of around 0.15ohm.

Then ask the electricity supplier what type of earthing system they had
in their property - since the max allowed of the supplier for PME (TN-C-S) is 0.35ohms and TNS 0.8ohms). If the supplier does not supply an earth I would stop here and get an electrician in.

You could then add the R1+R2 reading to the TN-C-S or TNS reading and if the figure is less than say 1.84ohms for a type B 60898 MCB you would satisfied that the Zs meets the criteria for that MCB.

Alternatively, get an electrician in to do the job.

 

[Stoday]

theres nothing which refers to MCBs directly, but it clearly dictates that consumer units not covered by these exception, and I'd take that to mean the devices contained within as well,

But would you advocate such if it were going to cost you ~£150 BC fee?

 

[Adam_151]

But would you advocate such if it were going to cost you ~£150 BC fee?

Thats for the OP to decide, the other way could cost him a lot of hassle if he ever moves house, I know what I'd do, but its the OPs decision....

 

[enly1]

All,

Thanks for the heads up on this one - as I originally said, I've not purchased my new oven yet and this was an exploration into the complexities if I chose to go for a more powerful unit.

Given the potential cost / complications, I may just stay within the 16Amp circuit and just go for a like for like swapout.

Assuming I keep under 3Kw, I assume I'm okay with the existing breaker...

Cheers.

 

[riveralt]

All,

Thanks for the heads up on this one - as I originally said, I've not purchased my new oven yet and this was an exploration into the complexities if I chose to go for a more powerful unit.

Given the potential cost / complications, I may just stay within the 16Amp circuit and just go for a like for like swapout.

Assuming I keep under 3Kw, I assume I'm okay with the existing breaker...

Cheers.

If you are concerned a local spark should not cost a lot of money - for supplying and replacing an MCB, checking your circuit and issuing a minor work certificate - £40.

Alternatively swop you 45amp cooker switch for one that does not have a socket included then you could have your proposed oven on a 16Amp MCB.

Figures are for 5kw oven (you could have up to 6.5) -
5000/230 = 21.74Amps.
Diversity = 10Amps + (11.74*.3) = 13.52Amps.

Hope this helps

 

[enly1]

Can I ask one more question.

Given that Diversity is supposed to be applied to allow for a potential maximum load with several load sources on a single feed, how does that apply to an oven ?

I know showers are not allowed to have diversity applied - why would an oven be any different.

I can understand cookers with ring elements and the oven, but when the oven is the only thing on the circuit, surely it would reach its maximum and blow the MCB ?

Sorry if I'm being thick, but it doesn't make much sense to me at the moment.

PS - Please ignore the socket for any discussion.

Cheers

 

[ban-all-sheds]

Simple swap of the oven is not notifiable however exchanging the circuit breaker foe one with different charateristics is (and the logic is sound on this one - someone thought to be verifying the zs is in spec for the new breaker, and that the cable, as installed is suitable*)


*In your case unless theres something excpetional, I can't see the later being an issue, and the former isn't likely to be an issue unless theres something wrong (but until you take the Zs you don't know)

Understand the logic, but can you show me where it says that?

Unless you'd like to argue that it is not reasonable to check that a cable won't melt or that an MCB won't fail to operate properly before just sticking a higher rated one into a circuit.

 

[riveralt]

Can I ask one more question.

Given that Diversity is supposed to be applied to allow for a potential maximum load with several load sources on a single feed, how does that apply to an oven ?

I know showers are not allowed to have diversity applied - why would an oven be any different.

I can understand cookers with ring elements and the oven, but when the oven is the only thing on the circuit, surely it would reach its maximum and blow the MCB ?

Sorry if I'm being thick, but it doesn't make much sense to me at the moment.

PS - Please ignore the socket for any discussion.

Cheers

Firstly, diversity is applied because it is recognised that for the majority of the time the cooker will not be on full power all of the time. You may think an oven is being fed x amps but in reality the oven warms up to temperature and then a thermostat will take over to keep the temperature at the set mark - turning the oven on and off when appropriate. While most electric showers in our cool climate are on full belt for the duration of the shower - so no diversity here. Although quite a few showers will cut out automatically after 15 minutes of use.

Secondly, the purpose of the MCB is to protect the cable from overload. A 6mm T&E cable is rated at around 45Amps depending on insulation etc although it can take higher loads for a short period - So the idea is that the MCB will blow before the cable does.

Thirdly, the MCB type B, although rated for 16Amps can in actual fact handle a prospective current of several times for a short while.

Not sure I can add any more - read up about diversity on the web if you want to know more.

If you are concerned about part p then swap your cooker switch for one without a socket.
If you are concerned about overcooking the MCB - fit a larger one - up to 32Amps for this cable size -then have a debate whether you want to inform BC.
If you are still concerned about both of the above - leave oven as it is........