Kitchen Appliance circuit

[Snapester]

Designing a kitchen appliance circuit, i plan to feed a bank of grid switches with a 6mm T&E fed via a 32A MCB, then each switch will have a 2.5mm cable to a fcu supplying an under counter appliance.
My main question is, is it ok to change down to 2.5mm and then feeding the FCU? As the cable cannot be overloaded as the main load is connected to the FCU at position?

Regards

 

[i=p/u]

move the mcb to the exit:. ive seen this in older installations but not in new ones....

 

[Des 56]

There was an article in NICEIC mag about putting grid switches on ring and how it needs to be balanced at the middle of the ring, i will see if i can dig it out! Also the grid switch is one point so i wouldn't want to run a ring to one point?

Why not ?

If the grid assembly is the only outlet on that circuit,the ring will be almost perfectly balanced

I would say keep it simple 2,5mm ring to the grid assembly on its own 32A mcb,
If you want ,you can fit grid fuses as well for the loads and outlet plates for the appliances

I would also suggest the 20 amp rating refers to the switch contacts not the supply terminals

 

[telectrix]

i'm with des and murdoch here. 2.5mm RFC to grid. as in K.I.S.S.

 

[Snapester]

run a ring to a grid switch?

 

[Des 56]

run a ring to a grid switch?

--- assembly,yes

 

[Snapester]

It seems a little strange running two ring legs from the CU straight to the grid plate? Surely 1x 6mm will be exactly the same? I fail to see the difference apart from conductor size?

 

[J&M Electrical]

run a ring to a grid switch?

Yes, its 1 switch but the switch is effectively 6/9/12 points or however many Appliances your switching.

 

[Snapester]

I gather the whole idea that the switch supplies x amount of points but why run 2x 2.5mm 20m to the grid whereas 1x 6mm will be more than adequate?

 

[Des 56]

It seems a little strange running two ring legs from the CU straight to the grid plate? Surely 1x 6mm will be exactly the same? I fail to see the difference apart from conductor size?

Do 2 installations,one with a 6,0mm radial supply and another with 2,5mm ring.fit the grids then decide which was the easiest and better quality arrangement

 

[Snapester]

Yes i may do this.

 

[DaveyD]

It seems a little strange running two ring legs from the CU straight to the grid plate? Surely 1x 6mm will be exactly the same? I fail to see the difference apart from conductor size?

Would you even get two 6mm conductors in? If its MK, crabtree or GET I could'nt do it.

 

[Snapester]

Well according to Mk Data sheet 2x6mm is possible! Although i think looping with 4mm will be a better option and just having main feed as 6mm.

 

[Des 56]

You have had many opinions, so all I can now say is, everyone to their own ways, hope it works out for you

I will think of this thread the next time I'm putting those little loops across the grid switches

 

[Snapester]

Could always use a 6mm wago connector in the backbox and loop off with 2.5 to each switch!

 

[DaveyD]

What about in the event of a short circuit at the FCU?

Edit: Or a fault at the FCU that somehow results in 32A and no more being drawn through the 2.5mm cable?

Fire hazard me thinks

OK - I'm not tring to be contentious here - I'm sure you are more experienced than me; but are you saying that my reply is incorrect? I was thinking say for example on a 32a radial in 4mm T&E. You are permitted to spur off to one double socket in just 2.5mm T&E. We are not suggesting that 2.5mm will be ok at 32a.
Happy to be corrected so long as it's constructive.

 

[Snapester]

Ha thanks Des56 i do take onboard everyones opinions and am also very grateful for everyones input.

 

[DaveyD]

Well according to Mk Data sheet 2x6mm is possible! Although i think looping with 4mm will be a better option and just having main feed as 6mm.

Wow, if I had a hat I would doff it to you now Im in near tears working on a 4 way grid in a 2.5mm RFC. What a spoon I am.

 

[Snapester]

Looking at Fig 15B Page.426 in BGB, on a 4mm radial protected by 30/32A OPD you can have an unfused spur run in 2.5mm.

 

[DaveyD]

Looking at Fig 15B Page.426 in BGB, on a 4mm radial protected by 30/32A OPD you can have an unfused spur run in 2.5mm.

Yes, thats what I refering to.

 

[Snapester]

DaveyD just read your other post to which i have just also stated the same opinion as yourself!

 

[DaveyD]

DaveyD just read your other post to which i have just also stated the same opinion as yourself!

... ah, so now do YOU have a hat on ?

 

[Snapester]

So in essence the radial basically has many 2.5mm spurs! And i wouldn't need FCU i could just use unswitched socket outlets.
Wow learn something everyday on here!

 

[D Skelton]

OK - I'm not tring to be contentious here - I'm sure you are more experienced than me; but are you saying that my reply is incorrect? I was thinking say for example on a 32a radial in 4mm T&E. You are permitted to spur off to one double socket in just 2.5mm T&E. We are not suggesting that 2.5mm will be ok at 32a.
Happy to be corrected so long as it's constructive.

I read what you wrote in post #19 to mean that if an appliance is only pulling 13A then it's ok to use a 2.5mm radial and protect it using a 32A breaker. If that is indeed what you meant then yes, your reply is incorrect, however I'm not so sure now that is what you meant.

Could you eleaborate for me so that I understand fully the solution you propose?

 

[DaveyD]

I read what you wrote in post #19 to mean that if an appliance is only pulling 13A then it's ok to use a 2.5mm radial and protect it using a 32A breaker. If that is indeed what you meant then yes, your reply is incorrect, however I'm not so sure now that is what you meant.

Could you eleaborate for me so that I understand fully the solution you propose?

OK, cool. I was just repying to IPU post #15 asking what would be protecting the 2.5 from the switch to the FCU. I think he was asking what was stopping the full 32a from going down that spur. The OP was designing a radial circuit with a 32a CB in 6mm and then suggesting drops from each switch to FCU in 2.5. I was telling IPU in my opinion this was ok as each drop was a single spur off the radial via a DP switch. The radial itself would need to be =>4mm on 32a but a single spur to a FCU would not.

 

[D Skelton]

Ah, ok, well, yes, unfortunately, in my opinion, you are incorrect as there is no such thing as a spur on a radial circuit. The breaker has to be selected so that it protects all cables within the circuit.

If you have a 32A breaker and 4mm feeding the grid switch, you would need 4mm feeding each 13A SFCU also. Only from the SFCU to the appliance could you then use 2.5mm cable.

Lets say for example you wanted to take a feed off a 40A cooker circuit to feed a single socket outlet (not that anyone would do it this way) then you wouldn't be able to take a 2.5mm feed from the cooker outlet plate to a SFCU, then on to the socket. The feed to the SFCU would have to be 6mm, the same as the cooker circuit. If you took a 2.5mm feed from the cooker outlet plate to a SFCU, even if it was only a few inches, then that length of cable between the cooker outlet plate and the SFCU would not be adequately protected.

My solution to the OP's problem seems the simplest:

Use two seperate A3 radial circuits, each supplying half of the 20A DP switches within the grid, then use 2.5mm cable straight from each individual grid switch to each individual socket outlet designed to supply an appliance. There is also no need for SFCU's whatsoever.

I myself have done this a couple of times but only using one A3 radial to supply the grid switches as there was only 4/5 appliances in each scenario.