Cooker flex/cable again!

A few weeks back I asked "cable or flex to connect an oven". Thumbing through the oven instructions I now find "Connection must be made using an H05RR-F 3 G 1.5 mains connection cable". Whilst I accept the consensus view that T&E is safe to use where does the scope of "wiring regs" end - cooker connection unit? and if it stretches to the cable/flex does a manufacturer's statement as above override regulations?

Of more interest is the recommended cable. At

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the applications for a H05RR-F cable are "Light portable tools, temporary or portable lighting, extension leads indoors or outside where there is minimal physical damage expected." and the "3 G 1.5 " is 3 core 1.5mm with a green yellow earth. Could someone with access to the IEE Regs Table 4H2A&B give me the current rating of the cable? The appliance a Neff U1644 built in double oven has a total connected load of 7.2KW. I feel an email to Neff may be in the offing.

Peter K

Reply to
PeterK
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Why are you getting so wound up over it. Who are you going to report yourself to! Who is going to see or be remotely interested in your cooker wiring? If in doubt, follow the instructions if it makes you feel better or question the manufacturer at length. I am sure they will be more than happy to speak to you all day.

Reply to
Mark

These tables start at 4mm².

That doesn't sound at all compatible with 1.5mm² cable.

Reply to
Andrew Gabriel

I think you are missing the point here, the OP is concerned that, the instructions are specifying a cable that appears to be far too small for the appliance.

For 7.2KW @ 230v I would be using 6mm² cable to connect from the wall plate to the oven, you could probably get away with 4mm², but as it can get warm behind there, I personally would be using 6mm² (And defiantly 6mm² form the consumer unit to the wall plate, unless the run was extremely short.)

1.5mm² is far too small, and is liable to melt, posing a very high fire risk!

If the oven was drawing around the 3-3.5KW mark, then 1.5mm cable would be fine.

Sparks... (Not an electrician)

Reply to
Sparks

1.5 mm flex is rated at 18 amps - ie 4.3 kW at 240v or 14.1 at 230v
Reply to
Dave Plowman (News)

Note that many cooker connection instructions seem to assume you are connecting three phase - with a correspondingly lower current demand per phase. Generally I find it usually makes more sense to ignore the suggestion in the "one size fits all of europe" handbook and select an appropriate cable based on the actual load.

The table you cite starts at 4mm^2 with a rating of 41A, which might do nicely for the 7.2kW load.

Reply to
John Rumm

Mark Thanks for your concern about my mental health. Very simple reasons for the post:

  1. Self education - like understanding the difference between "should" and "must" in building regs.
  2. Self Protection. Professional tradesman carry third party liability insurance. If I do something for myself I don't - this is a litigious world and insurance companies will look for the slightest excuse to reduce/refuse a claim.
  3. To email Neff. I still believe that manufacturers are concerned about the accuracy of their guidance. Even if it doesn't stop someone walking into B&Q with these Neff instructions and walking out with 2m of 1.5 3 core I'm prepared to waste 5 mins of my life to make an effort to prevent it.

PeterK

Reply to
PeterK

I think you've identified the reason for the "translators error". Thanks

Peter K

Reply to
PeterK

Sorry I've only just seen this thread.

This is not a 'cooker' but a double oven built in unit.

7.2kW @ 230V is 31.3A [1] but as this is a cooking appliance in a domestic setting then the expected loading is: 10A + (31.3A- 10A) x30% = 16.4A (diversity applied)

So a 20A breaker should be right for this circuit. I haven't got data for flexibles below 4mm² This would probably [2] need 2.5mm² flex which is readily available in short lengths for immersion heaters. There is a likelihood that you wish to run the oven from an existing 32A supply. This would require at least 4mm² but the oven may not have suitable terminals to receive such a cable. So really you need to put the right MCB on the circuit.

[2] The high ambient temperature does not help but the installation method of hanging free should help. My guess is that 25A would reasonable to expect for this flex. [1] If the power rating is at 240Vac then the max current is 30A and the expected domestic load 16A (DA). So a 16A MCB and 1.5mm² heat resisting flex should be OK.
Reply to
Ed Sirett

But then the specified cable would need to be at least 4-core and more probably 5-core, with a neutral required for controls. So that would be H05RR-F 4G1.5 or '5G1.5. The 3G spec (which just means 3-core, one of which is ground) suggests that the writer had a single-phase supply in mind.

I wouldn't be surprised if the 1.5 mm^2 spec is just a mistake. They've copied across from instructions for a single oven and have forgotten to change it. I would suggest a minimum of 4 mm^2 cable on a 32 A circuit here, as the "first 10 A + 30% of remainder" diversity rule doesn't really seem appropriate for a double oven alone. (Although it could be applied to the combination of oven and an electric hob fed from a single final circuit.)

Also if the OP is going to use a flexible cable in a normal cooker connection unit then some form of crimp ferrules (bootlace ferrules) will be needed to dress the ends of the flexible conductors to make satisfactory connections to the 6 or 10 mm^2 7-strand circuit cable. The appliance end probably needs crimp terminals too - rings at a guess.

Reply to
Andy Wade

Unless they were thinking of using multiple flexes...

I saw exactly this recomendation recently on a halogen hob (6 and a bit kW IIRC). It was not a Neff, but I can't remember what it was (might have been Beumatic).

The instructions were a bit dire really, I have a feeling the diagram showed 3x 1.5mm^2 three core flexes, and then a footnote to the effect of if you are wiring to a single phase supply, then don't remove links L1 and L2 (which were copper strips that commoned L1, 2, & 3).

I could not make much sense of the cable recommendation either at the time, so just carried on in 6mm^2 T&E which I had just used to wire the circuit with.

Reply to
John Rumm

In many cases though you would run a circuit to power both oven and hob, so sizing the OPD for 2.5mm (or thinner) cable may not be acceptable anyway.

I think I would be wary of putting this type of load on a 16A MCB, since it will trip in about 200 secs on 30A according to the graphs. That is unlikely to get both ovens past preheat to the point where they are cycling on their stats. The is a fair chance that if both ovens are required, they would both be turned on at the same time. You could then be running 10 mins or so at full load while they preheat.

The 1.5mm^2 flex if rubber insulated (i.e. 90 C rather than 70), might just hack it (although instict says use something bigger and don't push it to the limit). If you take the voltage drop at about 30 mV/m/A, and the length at say 1.5m that would mean a drop of 1.35V, and so a cable resistance of 0.045 ohm. Dissipation would hence be 40w in the cable.

Reply to
John Rumm

Just to say TLC appear to have added 4mm Butyl (35 amps) to their range for cooker tails and sell it in cut lengths. 3.36 gbp a metre plus the VAT.

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Reply to
Dave Plowman (News)

I never thought of that.

Bizarre.

Sensible.

Reply to
Andy Wade

I'll soon also be fitting a Neff oven, though a single oven in my case=20 rated at 3.6KW, it too recommends 3x1.5mm^2 H05RR-F cable, which I see=20 is available from "proper" wholesalers over here, but I've opted to go=20 with heat resistant 3 core 2.5mm^2 flex which is available in 5m lengths =

from the sheds, it's maximum rating is 25A

Are you sure the diversity rule is appropriate? If you use both ovens=20 you'll take 31A which would certainly exceed the cable rating of the=20

2.5mm^2 cable I've seen, even before thinking about any temperature=20 de-ratings ...
Reply to
Andy Burns

But the MCB will be 20A so the flex would be protected.

Reply to
Ed Sirett

Why recommend a 20A MCB where the oven can draw 31A when both halves are used concurrently?

Reply to
Andy Burns

replying to Dave Plowman (News), mrmike wrote: According to BS7671 1.5mm current carrying capacity is 26A when the cable is in free air (ref method F)

Reply to
mrmike

I wonder if Peter K's oven is still going after TEN YEARS.

Reply to
Graham.

Might also be nice if the information posted was even correct!

Reply to
John Rumm

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