Help! Supplying two ovens from a single radial

[andy100]

Hello,

I have a 6mm t&e protected radial circuit running from the CU to the kitchen, this was originally going to feed just a new Neff Oven, rated at 3.68KW total connected load ~ 16Amp. This was fine, but now it turns out that the new Microwave we’re getting is rated at 3.1KW total connected load and the technical specs state it should be protected at 15Amps. The Microwave was originally going to be less powerful and would have been able to connect into a 13Amp FCU off of the mains ring but now I have the problem that I have a single 6mm t&e radial that I need to feed both appliances. I have seen the appendix on the 17th ed and know this is allowed.

I have a 32Amp MCB which will protect the 6mm cable and allow enough current to supply both appliances but I’m concerned about short circuit protection for the appliances themselves as well as protecting the 2.5mm flex tails that will run from the isolator switches to the appliances. Any advice would be much appreciated.

Thanks

Andy

 

[telectrix]

fit a 2.5mm to each oven.fed from 2 16A MCBs in an enclosure in the kitchen.

 

[andy100]

Thanks telectrix for the quick response. Do you think I would still need 2 all-pin isolation switches as well or would the main switch within this new enclosure be sufficient for maintaining an all-pin isolation although it would be for both appliances at the same time.

 

[Guitarist]

Thanks telectrix for the quick response. Do you think I would still need 2 all-pin isolation switches as well or would the main switch within this new enclosure be sufficient for maintaining an all-pin isolation although it would be for both appliances at the same time.

Guessing that you're not a domestic electrician

 

[Engineer54]

If the 6mm cable is supplying a CCU, then just fit a dual connection plate and connect both appliances to that. I take it that the hob is Gas??

 

[i=p/u]

Think he's on about the 2.5 flex e54 .

you could change the flex too 4mm ..

 

[andy100]

thanks engineer54, at the moment, instead of using a dual connection plate, I'm just using a 60amp junction box (as this is big enough to get 3 x 6mm into it)
In = 6mm from CCU
Out = 2 x 6mm to feed each isolator switch then 2.5mm flex to each appliance.

Correct me if i'm wrong, but a dual connection plate still doesn't resolve my issue of short circuit protection for the appliance itself and cable protection (2.5mm flex). Even if I used 4mm flex as i=p/u suggested, the weakest link just moves to the internal wiring of the appliance itself and more importantly the appliance.

thanks for your feedback so far.

Also hob is induction but on a separate circuit.

 

[i=p/u]

Well what does manufactured instructions say, maybe you you to try telectrix idea and add small enclosure if you don't want to remove flex...

 

[Engineer54]

thanks engineer54, at the moment, instead of using a dual connection plate, I'm just using a 60amp junction box (as this is big enough to get 3 x 6mm into it)
In = 6mm from CCU
Out = 2 x 6mm to feed each isolator switch then 2.5mm flex to each appliance.

Correct me if i'm wrong, but a dual connection plate still doesn't resolve my issue of short circuit protection for the appliance itself and cable protection (2.5mm flex). Even if I used 4mm flex as i=p/u suggested, the weakest link just moves to the internal wiring of the appliance itself and more importantly the appliance.

thanks for your feedback so far.

Also hob is induction but on a separate circuit.

Short circuit protection is afforded by the 32A MCB. The appliances are fixed equipment so the flex's/cords cannot overload. So there is absolutely no need to go to the lengths you seem to be going too...


What's more, accessory fuses are there to provide protection for flex/cords, NOT the appliances themselves. If these appliances were portable/moveable then yes you would need a fused plug top or FCU, but not absolutely necessary where fixed appliances are concerned...

 

[telectrix]

433.3.1 (ii). i believe.

 

[i=p/u]

Wish had me book to read that reg . I have change flex to 4mm in past in this scenario

 

[i=p/u]

So you'd be happy connecting 2x 2.5mm cables to 6mm . What's that reg in brief tel.

 

[Amp David]

Fit one of these and job done.

Polar 45A Dual Appliance Outlet Plate - Bright White


The search on the forum works too you know

 

[i=p/u]

Well as I read it , it's fine as todo with fault current and overload on resistive loads...

 

[Engineer54]

So you'd be happy connecting 2x 2.5mm cables to 6mm . What's that reg in brief tel.

If 2.5mm cords not over 3m, i can't see a problem, ...can you??

 

[i=p/u]

That's If there is an internals fuse .

 

[Engineer54]

That's If there is an internals fuse .

Does it?? Where would the internal fuse(s) be located then, on say a hob and oven installation??

 

[telectrix]

So you'd be happy connecting 2x 2.5mm cables to 6mm . What's that reg in brief tel.

briefly, a fixed load is not likely to overload a cable. the only time would be a short circuit, in which case the MCB in the CU provides s/c protection but not overload protection.

 

[i=p/u]

So is overload not a problem in op scenario . 2.5 joined with 6mm on 32A breaker .

And would your answer change if inductive load

 

[Engineer54]

So is overload not a problem in op scenario . 2.5 joined with 6mm on 32A breaker .

And would your answer change if inductive load

You mean like you'd find with an ''Induction Hob'' ...lol!!

Answer to your question then, is NO!!

 

[andy100]

briefly, a fixed load is not likely to overload a cable. the only time would be a short circuit, in which case the MCB in the CU provides s/c protection but not overload protection.

Appreciate all the responses, so telectrix are you of the same opinion as engineer54 in that a local enclosure in the kitchen is overkill and all that's required is a 32A MCB feeding both appliances with local switch isolation. I also spoke to Neff who said there are no internal fuses within the appliance themselves.

 

[Engineer54]

Appreciate all the responses, so telectrix are you of the same opinion as engineer54 in that a local enclosure in the kitchen is overkill and all that's required is a 32A MCB feeding both appliances with local switch isolation. I also spoke to Neff who said there are no internal fuses within the appliance themselves.

Jesus!! ....Did you honestly think that there would be??


Why do you think a made for purpose wall accessory in the form of a ''dual connection outlet'' (see link post # 13) is available on the market??

 

[andy100]

the only reason I thought there might be is because it shows the following details in the Technical data section of the manual:-

Power supply 220 - 240 V, 50 Hz
Maximum total connected load 3100 W
Microwave power setting 1000 W (IEC 60705)
Grill output power 2000 W
Hot air output power 1950 W
Microwave frequency 2450 MHz
Fuse 15 A

 

[telectrix]

think that's specifying the fuse you should fit.

 

[Guitarist]

In this case, manufacturers instructions are specifying 15A fuse or 16A MCB (one would assume). Personally, I wouldn't connect this directly to a 32A cooker supply.
Post #2 sums it up for me.

 

[Engineer54]

I wouldn't need to think twice about connecting these two appliances via a CCU and a dual connection outlet, if that's what was available!!

Why would you be complying with the manufacturers instructions which are based on non UK, European installations , which Neff generally do as a matter of course, with a little bit of fine print about following your own countries electrical codes?? So, how are you going to comply with the 15A fuse?? Say's nothing about 16A fuse or 16A MCB. Or maybe you are going to start changing/reverting things back to UK requirements again?? lol!!

If either of these appliances actually needed it's own OCPD then one would have been fitted.

 

[andy100]

Thanks all for your input, it's been really helpful!! Dual connection plate with 32A MCB it is!

 

[i=p/u]

But are you happy leaving 2.5 mm protected by 32A mcb

 

[telectrix]

i would be. read section 433 in bgb regarding providing short circuit protection only on a fixed load. specifically 433.3.1 (ii).

 

[i=p/u]

Just testing his confidence in deciding...

 

[Engineer54]

Just testing his confidence in deciding...

Think it's more like your confidence that needs testing!! lol!!:wink5:

 

[i=p/u]

Yes I doubt myself sometimes is why I use too waste time changing to 4mm...

 

[andy100]

Well, for the microwave, it has a 2.5mm 1m flex tail pre-cabled so can't change this anyway.

If the concern is that the 32A MCB is not going to protect the 2.5mm cable then surely you would have another problem with the Oven wiring itself e.g I can see that the onward internal wiring from the connection plate of the oven is at most 2.5mm. So if my 2.5mm cable isn't protected, the oven wiring certainly isn't either. Therefore on that basis I can't see any advantage to change my connection tails to 4mm.

 

[i=p/u]

Uh I wasted my time and customers money

 

[i=p/u]

So what fault current can a 1.5mm flex take

 

[Guitarist]

So the manufacturers instructions are just being ignored?

 

[Engineer54]

So the manufacturers instructions are just being ignored?

Only if they are obviously referring to European type regulations, .....and remember European plug tops and wall accessories do not include fuses!! Yet another reason why chopping a moulded fused plug top from an appliances lead/cord can't and won't void any manufacturer's warranty, no matter what the service company say's, if it is then connected to the mains supply in accordance/compliance with BS7671!!

The big problem with multi national manufacturers instructions, is that rarely do they fully relate to countries outside of the appliances country of origin. Look carefully and you will usually see some form of small print, stating that appliance must be connected to a mains supply in accordance with your countries recognised codes/regulations!!!