4mm T&E for ring circuit

[gselectrical]

Depends on accessory manufacturer bud, the likes of MK isnt a problem.AndyGuinness

Just don't use Volex, u'll struggle to get them in. They're crap.

GS

 

[Sidewinder]

You cold look here for additional info, not much mind!:

http://www.voltimum.co.uk/news/10827/cm/iee-ring-final-circuit-meeting.html

There was a write up on the IET website and abstracts if not the full papers but I can't find them now.

IIRC the RFC was brought into the UK at or around the end of WW2 due to lack of copper & the electric heating requirements, which combined gave us the basic RFC design we have. Again IIRC the 32A rating & 100 sq metres was combined with the impedances etc. due to the power required to heat 100 sq m.

 

[Evans Electric]

4mm ring is OTT , a seperate kitchen ring will do the job , as I always say, don't invent problems.

 

[kme]

Would agree with Deke.

 

[mosschop]

Can the tumble dryer be put in the garage and then you will not have to worry about the load and put in 2.5mm ring main

 

[Chr!s]

Sidewinder

I have the articles your talking about, though there to big to download onto the forum

Their still on the iet website though to download, goto main page and the select iee wiring regs and its on the top left

Regards chris

 

[Sidewinder]

Plumber,

I believe you can design a domestic ring, especially a kitchen ring, as you do know most of the loads, if you are going to plug the fixed appliances into the ring.

Otherwise yes it is more difficult.

+1 to the other sugestions for multiple rings and it does give a more robust install.

Also can't see the need for a 4mm ring unless you are struggling with volt drop or Zs. However you can't correctly calculate volt drop in a ring unless you apply Kirchoff and have known loading. It is a messy process, if anyone has the ESC essential guide there is some info in there on this if you don't know what I am on about.

Perhaps an ideal situation would be a seperate kitchen cu?

Lights & ring, then radials for cooker & other fixed appliances?

You'd have to watch sub main rating though.

Discuss?...

 

[kme]

Ok

To discuss -

There will ALWAYA be a trade-off between the optimum install, and the customers` finacial position.

There was a similar discussion r.e hi-integ boards, loaded with RCBos. In an ideal world, a seperate CU for different areas of a (larger) house would be ideal; the negatives that immediately spring to mind:

1. Cost - if you`re quoting for multi boards, you`re going to be way more expensive than the generic guy who`ll ram the "standard layout" in.

2. Complexity for future - You`re introducing (at least one) sub, thereby creating more circuits for PIATs, and a corresponding increase in said costs.

3. Discrimination - if the distribution cct(s) need RCD protection, are you just going to lump the submain onto one half of a twin RCD board; provide an RCBo, or use an external RCD. In any of these scenarios, an earth fault on a final circuit of the submain DB necessitates rest of the RCD at the main board - how well are generic customers going to understand that you`ve given tham a "kitchen DB", but, if it trips, they`ve got to reset at the origin?

I know where you`re coming from, and agree to a point, but I feel there can be a tendancy to "over-engineer" domestic wiring, especially from those of us who have ind / comm experience & background.

KME

 

[Voltimax]

I have installed a few 4mm rings, but this was only because thermal insulation was an issue.

 

[Sidewinder]

KME,

Good points,

Financial constraints are a very good an valid arguement & even HSE take these into account when deciding on necessary actions in their area (a little different I know, just giving an example).

The just ram in a standard layout guy is what we are all up against when we try to offer added value to the customer.

Unfrotunately there are many out there who don't even do that!

Complexity is again a good point, yes it does add complexity, but it simplifies any fault finding, provides a more robust & fault tolerant install though.

As far as discrimination goes i would stay clear of RCD's where at all possible, and use RCBO's. However we are then back to the cost/compelxity/ram in a std layout again.

Your over engineering suggestion is probably spot on though!

I can remember jobs where by each mcb had an auxilliary contact connected to the PLC which then told you which breaker had tripped!

 

[Sidewinder]

Volti,

Good point, that had not even crossed my mind when I posted my comments earlier about 4mm rings!

So there folks is another reason, and probably more common in domestic, thus probably more worthy of consideration.

 

[kme]

Yup, done the aux contact jobs a couple of times - not in a domestic environment, I hasten to add.........

I find these discussions can be more of a "mental exercise", than an actual, real-world usable solution; for the most part.

KME

 

[Sidewinder]

Yes, that is true, but it does get people to think about things, i.e. mental exercise!

Though there are times when the theory can cross over to the real world.

 

[sanny]

The 27A capacity for a 2.5 mm conductor applies for a radial only this is much higher when its wired in a ring otherwise we wouldnt protect such circuits with a 32a rcbnly time it would be a problem is if there is ever a break in the ring then you would have 2 radials on a 32a breaker not giving the cable the protection it needs.As mentioned before the only time 4mm would be used is where there is thermal insulation not neccesarily the whole ring only where it passes through the thermal insulation

 

[kme]

The 27A capacity for a 2.5 mm conductor applies for a radial only

Would you like to re-read this part of your post?

Yes, you could increase the conductor size through the insulation, but that introduces other issues.

Sorry mate - I can sort of see the logic, but its flawed.

KME

 

[ianmacd]

433.1.5 does not state that a ring has to be wired in the same size cable all the way round, just that its a minimum of 2.5mm and has a current carrying capacity of at least 20A.

Broken rings are the main reason I avoid instlaling them where possible. Seen too many disconnected rings on CU changes. All it takes is a kitchen fitter to swap a socket and not get a wire in properly when putting it back on and its no longer a ring.

 

[a1spark]

Volti,Good point, that had not even crossed my mind when I posted my comments earlier about 4mm rings!

So there folks is another reason, and probably more common in domestic, thus probably more worthy of consideration.

You didnt read my 1st post on the thread then SW ? ?:|

 

[steptoe]

I am not convinced with using 20 amp radials the way I see it ring mains have been used for the last 50 odd years and I can't remember having problems with one being overloaded but I have had customers say they have had 20amp circuit breakers trip when vacuum cleaners are plugged in not commen I admit but a few times I have been told this. I would imagine its because the starting of the vacuum the 20 amp breaker cannot withstand the motor current start up. I cannot see the advantage of 20 amp radials and will carry on using ring mains unless there is a real convincing argument to say they should not be used.

a RFC consists of a cable (2.5) that can only carry 27a at most being protected by a 32a protective device (usually)

The 27A capacity for a 2.5 mm conductor applies for a radial only this is much higher when its wired in a ring otherwise we wouldnt protect such circuits with a 32a rcbo.Only time it would be a problem is if there is ever a break in the ring then you would have 2 radials on a 32a breaker not giving the cable the protection it needs.As mentioned before the only time 4mm would be used is where there is thermal insulation not neccesarily the whole ring only where it passes through the thermal insulation

where does this little nugget of information come from?

 

[batty]

a RFC consists of a cable (2.5) that can only carry 27a at most being protected by a 32a protective device (usually)where does this little nugget of information come from?

Do you not have two cables at each outlet and all around circuit so that is up to 54 amp capacity?

 

[Voltimax]

You didnt read my 1st post on the thread then SW ? ?:|

You didn't mention it specifically.