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Topic Title: Practical solutions to 10mm2 cooker flex connection
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Created On: 04 March 2019 10:48 am
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 04 March 2019 10:48 am
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TimJWatts

Posts: 467
Joined: 07 August 2013

Hi, I'm looking at a cooker, 90cm induction.

After discussion with a sparky he recommended dropping in a 40A circuit which he did.

So roll on... Nearly ready to procure said cooker. One candidate comes with what looks like 10mm2 rubber flex with an approx OD of getting on for 20mm.

There's no way I can see that will fit comfortably in the 40A flex connection plate that is fitted as standard.

So I see 2 possible options:

1) As suggested by cooker shop (who do fit them): 60A surface junction box like: https://www.toolstation.com/60a-junction-box/p98775

2) (also suggested by them) - replace rubber flex and run 10mm2 T+E into cooker as per the old days...

1 is OK as an idea, but the extra thickness of the JB may push the cooker forward an necessitate bump stops to prevent the cooker clonking the JB. I think those JBs are about 35mm deep compared to the 15-20 for the flex plate.

Flex plate is close to floor (30cm) so probably need to bend the T+E link the hard way...

Anyone know the bend radius for T+E bent the hard way (rather than the other easy way)?

2 overall seems less trouble. Don't know if it's frowned upon these days - used to be the defacto method when there weren't any others.


The plus is the cable will sit down low, so I don't see any over heating problems with 70C T+E.


Any other practical solutions would be welcome

Cheers - Tim
 04 March 2019 11:08 am
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daveparry1

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What is the kW rating of the cooker? It probably doesn't need anything like 10mm flex from the connection unit to the cooker (unless it's a very long way away!) 4mm or 6mm sounds nearer the mark if it's just a couple of feet away which is more usual.
 04 March 2019 11:21 am
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mapj1

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this claims to take 2 10mm2 cables

But if not will the 10mm T/E (or the flex) strip to singles for the last leg, and then oversheath in heatshrink while bent to shape, so that you have a bit more curvature and retain the required insultion ? easier than chisseling bits out of the walls.

3 core 10mmsq H05RN-F is nominal 19.5mm diameter from Eland

the HO7 stuff has much thicker rubber.

-------------------------
regards Mike
 04 March 2019 11:21 am
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AJJewsbury

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Perhaps the manufacturer is expected a high ambient temperature around the flex (hence both rubber sheath & large c.s.a.)

I'd check very carefully the amount of space behind the proposed cooker (and where it's available - the backs are rarely flat). I've fitted some where even a fairly flat cooker outlet would have stopped the cooker/oven being pushed all the way back in some positions. Some cookers have 'hollows' in their back panels that would easily allow enough space for say an adaptable box and stuffing gland - but you'd need to position it in the right place relative to the cooker's position. There seems to be absolutely no standardization about this kind of thing between manufacturers - I can see why kitchen fitters have basically given up and just make connections in (or under) an adjacent cupboard.

- Andy.
 04 March 2019 01:57 pm
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TimJWatts

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Hi Dave,

The background: The sparky who did this circuit for me recommended going up to 40A for "range" style induction just based on his experience - I was initially going to propose 32A.

Looking specifically at the Smeg CPF9IPWH, it's difficult to do a diversity calc: It only quotes a "nominal load" of 11.4kW - not sure what that means. I have the plate powers but not the ovens.

Total plate power, a 5 rings on max would be 9.5kw so that plus 3 ovens which sounds like it might be a tad more than 11.4kW.

However, back to the flex - this gets weird.

The manufacturer supplies it with with hefty flex. I couldn't get close enough in the shop to measure but it looked like 20mm OD which would put it at 10mm2 H07 style cable.

That is backed up by the instructions which actually specify, for single phase supply (it can do 3 phase too), 3x10mm2 conductors.

Presumably they reckon it could be wired to a 50A circuit potentially?

So back to 40A - 6mm2 H07 or 6mm2 T+E should be sufficient.

Manufacturer does imply replacing the cable is permitted as they describe how to do so in the manual.

Any idea if a 15mm OD 6mm2 H07 or H05 fits in a standard cooker flex connector plate?

Cheers,

Tim

Edited: 04 March 2019 at 02:59 pm by TimJWatts
 04 March 2019 03:34 pm
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potential

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"nominal load" of 11.4kW

I think you will find with induction cookers that the load is controlled electronically.
If the ovens call for more power the power to the hobs is reduced automatically.
 04 March 2019 04:11 pm
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mikejumper

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Originally posted by: TimJWatts
It only quotes a "nominal load" of 11.4kW - not sure what that means.

That's getting near to 50 Amps @ 240V.
My guess is it's the load before diversity is allowed for.
 04 March 2019 04:34 pm
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chrispearson

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Well, I reckon that the above Smeg cooker cannot be installed.

Its instructions specify a 50 A (SP) supply and they specify that diversity has been taken into consideration.

For that load, Table 4D5 states that 10 sqmm T&E is required IF reference method C applies, otherwise 16 sqmm will be required. As for the flex, it must be capable of surviving 90 deg C at the cooker end, but cannot be rated above 70 deg C at the supply end. Table 4D2A allows only 48 A for 6 sqmm PVC flex, so once again 10 sqmm flex is required.
 04 March 2019 05:27 pm
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geoffsd

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It could, of course, be that the manufacturers don't know what they are talking about.
 04 March 2019 06:02 pm
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mikejumper

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Originally posted by: geoffsd
It could, of course, be that the manufacturers don't know what they are talking about.


 04 March 2019 06:09 pm
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mikejumper

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Originally posted by: daveparry1
....4mm or 6mm sounds nearer the mark if it's just a couple of feet away which is more usual...


I agree.
In fact 4.0mm max probably fine.

If it needs more then the cooker is an environmental disaster.
 04 March 2019 06:11 pm
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TimJWatts

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Originally posted by: chrispearson

Well, I reckon that the above Smeg cooker cannot be installed.

Its instructions specify a 50 A (SP) supply and they specify that diversity has been taken into consideration.

For that load, Table 4D5 states that 10 sqmm T&E is required IF reference method C applies, otherwise 16 sqmm will be required. As for the flex, it must be capable of surviving 90 deg C at the cooker end, but cannot be rated above 70 deg C at the supply end. Table 4D2A allows only 48 A for 6 sqmm PVC flex, so once again 10 sqmm flex is required.


Hi - thanks for the reply

Just out of interested, where does it say 50A? Or are you deriving that from the nominal power? Are we looking at the same manual?

I did a search in the user manual (which covers installation) here:
SMEG Website

Nothing about diversity that a search is picking up.

But it also says on that webpage:

"Nominal power: 11.40 kW
Supply can vary depending on usage, please consult a qualified electrician for ampere requirement"

---

Assuming, just for the following, we conclude it will function on 40A, we should be back to 6mm2 for Ref Method C for either cable type (I haven't got my book to hand, relying on online resources).

But you make a good point about the cooker end needing to support higher temperatures. We don't expect it to be baking the wall but the area inside the terminal bay could run hot.

I prefer suitable rubber flex, if the means to connect it are available...

I must admit, I slightly regret not building a 60cm slot and going for a regular cheaper cooker with simpler requirements... But we had space and it seemed like a good idea :-0

And I'm not committed to that make or model... They just happened to have one in the shop so I've seen it.
 04 March 2019 06:47 pm
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geoffsd

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Originally posted by: TimJWatts

Just out of interested, where does it say 50A? Or are you deriving that from the nominal power? Are we looking at the same manual?

11.4kW @ 240 V is 47.5A

Nothing about diversity that a search is picking up.

Manufacturers never mention diversity.

"Nominal power: 11.40 kW

We're not quite sure what that means. Perhaps a mistake?
Nominal means 'in name only'; perhaps it can't even use that all at once.

11.4kW isn't very big; old fashioned cookers were that and perfectly happy on the standard 32A circuit - which, incidentally had to have 6sq.mm. cable because of the rewireable fuse. 4sq.mm. (method C of course) is adequate with MCBs.

Supply can vary depending on usage,

How can the supply vary? Another mistake?

please consult a qualified electrician for ampere requirement"

Exactly.

Assuming, just for the following, we conclude it will function on 40A, we should be back to 6mm2 for Ref Method C for either cable type (I haven't got my book to hand, relying on online resources).

Correct.

Using diversity, a 50A supply would be good for 34kW.
 04 March 2019 06:57 pm
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TimJWatts

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Thanks Geoff.

So the answer here is probably to change the flex down to 6mm2, sticking to a 90C rated flex and at 15mm OD, we *might* even stand a chance getting that in a cooker flex outlet - or go via a 60A surface JB with a short bit of surface clipped T+E is needed.

Earlier I did tot up all 5 rings on max and arrived at 9.5kW assuming powerboost robs others without affecting total load.

No cooker needs all rings on max for long and there's still 2kW ish for the ovens, which shouldn't take that much when up to temperature.

So 40A feels reasonable.
 04 March 2019 07:01 pm
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geoffsd

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Yes to all.
 04 March 2019 07:14 pm
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TimJWatts

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I have to admit - I assumed this would be a common practical problem faced by many... It's not the first range cooker I've seen with an unwieldy flex on the back...

Talking of lumpy flexes, Big Clive did a good one the other day on PowerSafe connectors (400A and bigger).

https://youtu.be/tTakz9rYIqY
 04 March 2019 08:06 pm
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chrispearson

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Originally posted by: TimJWatts

Nothing about diversity that a search is picking up.


The manual says: "The aforementioned power cables are sized taking into account the coincidence factor (in compliance with standard EN 60335-2-6)."

Let's not start going by rule of thumb - it doesn't work. The manufacturer has specified the supply, and as I see it, you have to comply with it. Of course if you want to find some justification for going smaller, be my guest, but don't complain if your kitchen catches fire.
 04 March 2019 08:25 pm
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TimJWatts

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Originally posted by: chrispearson

Originally posted by: TimJWatts



Nothing about diversity that a search is picking up.




The manual says: "The aforementioned power cables are sized taking into account the coincidence factor (in compliance with standard EN 60335-2-6)."



Let's not start going by rule of thumb - it doesn't work. The manufacturer has specified the supply, and as I see it, you have to comply with it. Of course if you want to find some justification for going smaller, be my guest, but don't complain if your kitchen catches fire.


Nothing should be catching fire - the 40A RCBO would protect a cable, provided the cable was designed for a 40A Type B protective device.

It might lead to spurious tripping if the cooker generated sufficient load for sufficient time.

I find the manual rather unclear. If we had the oven ratings, we could at least apply 10A+30% to it and have a general answer.

I was rather more interested in the practicalities of terminating such a beast of a cable - though if this cooker really demands a 50A supply, it may be off the list.

Perhaps I should ring Smeg and get some clarification on the load and diversity factors they think are appropriate. I've never seen a 50A cooker circuit in a domestic setting (though I have seen perhaps half a dozen such circuits in detail).
 04 March 2019 09:14 pm
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potential

Posts: 1774
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Originally posted by: TimJWatts

Originally posted by: chrispearson



Originally posted by: TimJWatts







Nothing about diversity that a search is picking up.








The manual says: "The aforementioned power cables are sized taking into account the coincidence factor (in compliance with standard EN 60335-2-6)."







Let's not start going by rule of thumb - it doesn't work. The manufacturer has specified the supply, and as I see it, you have to comply with it. Of course if you want to find some justification for going smaller, be my guest, but don't complain if your kitchen catches fire.




Nothing should be catching fire - the 40A RCBO would protect a cable, provided the cable was designed for a 40A Type B protective device.



It might lead to spurious tripping if the cooker generated sufficient load for sufficient time.



I find the manual rather unclear. If we had the oven ratings, we could at least apply 10A+30% to it and have a general answer.



I was rather more interested in the practicalities of terminating such a beast of a cable - though if this cooker really demands a 50A supply, it may be off the list.



Perhaps I should ring Smeg and get some clarification on the load and diversity factors they think are appropriate. I've never seen a 50A cooker circuit in a domestic setting (though I have seen perhaps half a dozen such circuits in detail).

I think the word "nominal" is probably a mistranslation.

This cooker can be wired to operate on 1, 2 or 3 phases.

There is no getting away from the fact that the manufacturer states that for a single phase supply a 10mm cable is required.
 04 March 2019 09:41 pm
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TimJWatts

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Originally posted by: potential

There is no getting away from the fact that the manufacturer states that for a single phase supply a 10mm cable is required.


I shall ring them and ask a simple question: will it work on a 40A fused supply? And see...

It's not the first 90cm range I've come across that has a 3 phase option - I wonder if they are just covering all their bases regarding countries they can sell to. Not everyone has generously sized 100A services.

Other makes I have seen are a little clearer about recommended supply sizes though. Some induction hobs are even programmable to limit the max power draw to suit the available supply.
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