Thanks

[ovoloknight]

A few points:

You are allowed to spur only once off any socket on a ring main.

If you so wish you could put in as many Junction boxes on a ring main as you liked and spurred off each of those junction boxes once each. (Not adviseable but technically nothing wrong with it.

If you Connect a Switched Fused Spur into the ring you can add as many sockets on the outgoing (load) side of the spur like, as a radial. Though when you do this, the radial can only pull as much as the fuse in the spur will allow (ex. 13A)

 

[JohnW2]

You are allowed to spur only once off any socket on a ring main.

As I observed a few posts back, although this is a frequently-heard assertion, I'm struggling to find a basis for it in the regs or even a guidance to that effect in the OSG.

Whilst I agree that it may be difficult to fit in four cables (unless one uses a very deep back box), and to find a socket with terminals rated for 4 x 2.5mm² conductors, I'd be interested to hear from anyone who can explain the basis for their believing that it is 'not allowed'.

Kind Regards, John

 

[Taylortwocities]

Appendix 15 is the best guide to how to provide spurs. This does not detail having more than one spur off one point - but the regs do not specifically exclude it.

IMO It's not good engineering and could provide a point of high current on a ring. We are supposed to consider how to reduce this.

 

[JohnW2]

Appendix 15 is the best guide to how to provide spurs. This does not detail having more than one spur off one point - but the regs do not specifically exclude it.

Indeed - that is my very point; the common belief that 'it is not allowed' does not actually seem to be true. In fact, to be pedantic, since it is only 'informative', Appendix 15 could not really 'not allow' anything.

IMO It's not good engineering and could provide a point of high current on a ring. We are supposed to consider how to reduce this.

I agree that one should seek to avoid potentially large point loadings of a RFC, particularly towards the ends of the ring (much less of an issue near the middle of a ring); one can even argue that it's not ideal in engineering terms to install a double socket very close to one end of an RFC. However, the same people who say that two spurs from one point on a ring 'is not allowed' will often also say that it's fine to have one spur off each of two sockets which are only inches apart. In other words, such people are talking about a regulation which they wrongly believe exists, whilst at the same time seemingly not understanding the underlying engineering principle which makes it less-than-ideal to have two spurs connected to the same (OR very close) points on an RFC.

I quess I'm just saying that, particularly since most people who come to this forum are not familiar with the regs (and are often seeking to learn about 'what is allowed'), it would be good if there couild be more clarity/correctness in indicating whether something is disallowed by regulations or whether it is a non-ideal engineering practice.

Kind Regards, John.

 

[johnsville]

What you legally "can" do and best practice are very different things.

A line of FCUs on a worktop serving heavy appliances is not ideal, although seen all over.

I would rather have a heavy radial cable (or two parallel 2.5mm cables) serving an appliance distribution box for kitchen appliances. A grid switch setup can do that. MK even have DP 20A switches with appliance names on them. It is a much more sensible approach and saves all that tiling around FCUs.

 

[holmslaw]

..

 

[JohnW2]

What you legally "can" do and best practice are very different things.

Indeed so,although we're actually talking about regulations/standards, not legislation,so it's not literally a question of 'legally'.

A line of FCUs on a worktop serving heavy appliances is not ideal, although seen all over.

Indeed, and I never really understand why people use FCUs - which are usually connected to a socket ito which the appliance's (fused) plug is plugged. Isolating switches (such as grid switches,as you go on to describe) are all that's needed.

One thing that some people seem to forget when talking about these things is that, in terms of the pattern of loading of the RFC, having a line of FCUs (or, indeed, unfused spurs) is essentially no different from having a line of sockets - although because people tend to think of the former as 'spurs', they think that it is in some way 'worse'.

I would rather have a heavy radial cable (or two parallel 2.5mm cables) serving an appliance distribution box for kitchen appliances. A grid switch setup can do that. MK even have DP 20A switches with appliance names on them. It is a much more sensible approach and saves all that tiling around FCUs.

Again I agree; I have essentially that very arrangement in my kitchen. Mind you, it gets pretty crowded inside the grid switch backbox.

Kind Regards, John.

 

[bernardgreen]

Again I agree; I have essentially that very arrangement in my kitchen. Mind you, it gets pretty crowded inside the grid switch backbox.

What about a mini CU with RCD serving the kitchen appliances,one MCB per appliance, and fed by a suitable feed from the main CU non RCD side via a cable protecting MCB

 

[JohnW2]

Again I agree; I have essentially that very arrangement in my kitchen. Mind you, it gets pretty crowded inside the grid switch backbox.

What about a mini CU with RCD serving the kitchen appliances,one MCB per appliance, and fed by a suitable feed from the main CU non RCD side via a cable protecting MCB

That would obviously work, provided one was content with SP isolation of individual appliances. If one wanted to (e.g. because of lack of capacity in the main CU), the mini-CU could also be fed from a fuse-protected sub-main. Aesthetically, one would probably want to hide such a mini-CU away somewhere, whereas visible grid switches are not too displeasing to the eye. In fact, even a line of DP switches (as I said, I really don't see why they need to be FCUs), on a suitable ring or radial circuit, would be visually acceptable to many people.

Kind Regards, John.

 

[Chri5]

Again I agree; I have essentially that very arrangement in my kitchen. Mind you, it gets pretty crowded inside the grid switch backbox.

Tell me about it!


I've got a 6 way grid and it has:-

Untitled

• Chri5
• 21 Jan 2011
• 2

It was a PITA to loom nicely

 

[JohnW2]

Again I agree; I have essentially that very arrangement in my kitchen. Mind you, it gets pretty crowded inside the grid switch backbox.

Tell me about it!
I've got a 6 way grid and it has:-

Untitled

• Chri5
• 21 Jan 2011
• 2

It was a PITA to loom nicely

OK, so per what I recently wrote, can you explain why you've included all those FCUs, rather than just direct cable runs to single sockets for each of the appliances to plug into (with fused plugs, of course)?

Kind Regards, John.

 

[johnsville]

A much easier and cheaper way is have a local isolator for the circuit. eg 32a supply from cu to isolator mounted in kitchen, wire ring final from isolator to sockets behind/beside appliances. When you need to access an appliance, turn off isolator, remove and unplug appliance, turn isolator on.

Do you mean one kitchen isolator for all appliances?

The grid switch setup with a fused module per switch means the appliance can be connected directly behind and the fused appliance plug eliminated. All are in one place, isolators and fuses. Neat.

I can't stand those rinky dinky kitchen grids. Every few years they change the style of these things, so when you replace a switch its likely it won't match and will look even worse than the original install.

It is best to have a few spare switches in case

 

[johnsville]

Again I agree; I have essentially that very arrangement in my kitchen. Mind you, it gets pretty crowded inside the grid switch backbox.

What about a mini CU with RCD serving the kitchen appliances,one MCB per appliance, and fed by a suitable feed from the main CU non RCD side via a cable protecting MCB

That is a good idea which I was considering. However, you need bulky and expensive double pole mcbs.

This and grid switching is far better than ugly FCUs over worktops.

 

[johnsville]

Again I agree; I have essentially that very arrangement in my kitchen. Mind you, it gets pretty crowded inside the grid switch backbox.

Tell me about it!


I've got a 6 way grid and it has:-

Untitled

• Chri5
• 21 Jan 2011
• 2

It was a PITA to loom nicely

There is no need for the FCUs. Have a fuse module after the DP grid switch (located next to it) and remove the fuse plug on the appliance wiring directly. Fuses behind integrated appliances is a dumb idea. All isolation and fusing can be on the grid switch panel.

 

[plugwash]

What really matters on a ring is NOT how close loads are together but

1: how far they are from the electrical center* of the ring (appliances close to the centre will draw current roughly equally from both legs, applicances near the ends won't)
2: how they are balanced between then two sides of the ring.

Pretty much any practical ring can be put into an overloaded condition by plugging in a load of high drain appliances on one side of the ring. All you can really do is try to avoid horriblly big imbalances and keep an eye on the location of any large semi-permanent loads.

If doing a grid to power more than one large load I would strongly suggest putting it on it's own circuit (a ring can actually work quite well since it will be easier to get the thinner cable into the grid modules and all your load will be in the middle so there will be no balance issues)

* If cable sizes are mixed (e.g. larger cable used on some sections because of insulation) then the electrical center may not be in the physical center, whether this is good or bad depends on the specifics of the partituclar ring