Ring main.

[JKMRK1]

Question I have is, is it ok to have x2 ring main circuits on one 32amp type B MCB??

If so does this meet the current regs.

TIA.

 

[nicebutdim]

Pete and dave are clearly scrupulous in their application of regs etc. End of. However, regs must always be seen as a minimum standard. If possible, it's best to be ahead of the curve rather than behind it..We decided to downgrade to a 16 amp mcb for a number reasons. One, as you mentioned appliances are becoming increasingly more efficient. Seven or 8 years ago we either ran a 6mm to the utility to allow washing machine and drier etc to run simultaneously or 2 x 2.5 t& e, depending on the rating of appliances. In the most recent kitchen we did, the entire load of W. M. and Drier was 3.3 KW. That trend will almost certainly continue. General sockets circuits are no longer used for electric heating like they used to be. Down rating the supply does, nt save us any money but it dies "future proof" the installation regarding the installation of more insulation (which is the norm here).
Your point about the increase of appliances, is a valid one. The solution is also simple.As standard we always run in an extra 2.5. to utility/kitchen. Future proofing.

I get your thinking, but remain unconvinced that derating from 20A to 16A in this way is a great means of future proofing. If I was building a new home I'd much rather have more current available at outlets than less - while it may not ever be required, it would surely be advantageous to have it readily available.

On the subject of running in additional circuits; I'm not generally in favour of the idea, unless they are intended for a specific requirement that is to be commissioned in the near future. In my parent's house, the only non-bodged electrical work since the initial introduction of electricity also included the installation of two additional rings and one lighting radial. That was 30 years ago and I wouldn't want to use any of it after three decades of being coiled up in a floor space, with intermittent rodent activity. I mention these additional circuits as I happened upon them a couple of years back - two were cut out and one was left in situ as it could be useful for pulling new cables in the future. In short, those additional circuits weren't a particularly great use of money or cable.

 

[LastManOnline]

But what do you actually do with it? Do you leave it unteeminated somewhere or what?

Yes. Unterminated and taped off in a JB, but obviously accessible. The utility is the location of choice.

 

[nicebutdim]

I remember many years ago there was some discussion about the goal of an common EU-wide electrical socket. Which as you can see got nowhere. What was the most promising choice was the IEC "kettle" style of connector as it is polarised, in widespread use already, and available at 10A (but often only 5A!) so probably enough for the majority of applications.

I wonder if they planned on naming it "The Esperanto"?

 

[LastManOnline]

I get your thinking, but remain unconvinced that dropping derating from 20A to 16A in this way is a great means of future proofing. If I was building a new home I'd much rather have more current available at outlets than less - while it may not ever be required, it would surely be advantageous to have it readily available.

On the subject of running in additional circuits; I'm not generally in favour of the idea, unless they are intended for a specific requirement that is to be commissioned in the near future. In my parent's house, the only non-bodged electrical work since the initial introduction of electricity also included the installation of two additional rings and one lighting radial. That was 30 years ago and I wouldn't want to use any of it after three decades of being coiled up in a floor space, with intermittent rodent activity. I mention these additional circuits as I happened upon them a couple of years back - two were cut out and one was left in situ as it could be useful for pulling new cables in the future. In short, those additional circuits weren't a particularly great use of money or cable.

Planning for the future is not an exact science. You may for instance never put in garden lights but running an SWA to the garden while the house is been built is much cheaper, more convenient and ascetically far more pleasing than doing it at a later stage. But these are all personal decisions where the homeowner is given the option. If they like gfine, if not, fine. We provide a, service at the end of the day.

Regarding the 2 5 t&e, its continuous current rating when covered in insulation drops to 19.5 amps. If installed in wavin it drops to 18.5 amps

I get your thinking, but remain unconvinced that derating from 20A to 16A in this way is a great means of future proofing. If I was building a new home I'd much rather have more current available at outlets than less - while it may not ever be required, it would surely be advantageous to have it readily available.

On the subject of running in additional circuits; I'm not generally in favour of the idea, unless they are intended for a specific requirement that is to be commissioned in the near future. In my parent's house, the only non-bodged electrical work since the initial introduction of electricity also included the installation of two additional rings and one lighting radial. That was 30 years ago and I wouldn't want to use any of it after three decades of being coiled up in a floor space, with intermittent rodent activity. I mention these additional circuits as I happened upon them a couple of years back - two were cut out and one was left in situ as it could be useful for pulling new cables in the future. In short, those additional circuits weren't a particularly great use of money or cable.

Planning for future needs is not an exact science of course. Sometimes it running in an extra, cable can be good insurance but as you state it can also be wasted. It's a choice at the end of the day.

Regarding from 20 to 16amp circuits. You will see from the table that their is a significant difference in current carrying capacity between a surface clipped 2.5 and one embedded in insulation. Approx 8 amps. In fact the rating of a 2.5 t&e in insulation is 19.5 amps, thus under 20amps.Though marginal, this figure may still require other derating factors (like wavin pipe, 18.5 amps) and bunching (derating factor is 0.80), which is often inevitable in an attic.You can see why we feel much more comfortable with a 16amp mcb in installations likely to be insulated
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Planning for the future is not an exact science. You may for instance never put in garden lights but running an SWA to the garden while the house is been built is much cheaper, more convenient and ascetically far more pleasing than doing it at a later stage. But these are all personal decisions where the homeowner is given the option. If they like gfine, if not, fine. We provide a, service at the end of the day.

Regarding the 2 5 t&e, its continuous current rating when covered in insulation drops to 19.5 amps. If installed in wavin it drops to 18.5 amps

Planning for future needs is not an exact science of course. Sometimes it running in an extra, cable can be good insurance but as you state it can also be wasted. It's a choice at the end of the day.

Regarding from 20 to 16amp circuits. You will see from the table that their is a significant difference in current carrying capacity between a surface clipped 2.5 and one embedded in insulation. Approx 8 amps. In fact the rating of a 2.5 t&e in insulation is 19.5 amps, thus under 20amps.Though marginal, this figure may still require other derating factors (like wavin pipe, 18.5 amps) and bunching (derating factor is 0.80), which is often inevitable in an attic.You can see why we feel much more comfortable with a 16amp mcb in installations likely to be insulated

Sorry for confusion. Thought I lost my first post, then it reappeared
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@Edmond Noonan The UK's post-WW2 situation was unusual as so much reconstruction was needed and not that many places actually had electricity outside of major conurbations, and so changing systems in use was practical and advantageous at that point. No one now is going to change the plug/socket type in use due to the massive headache it would cause! (I remember it was still common to see the round-pin outlets in to the 70s)

So really the ring/radial debate is limited to the UK and countries with a shared electrical background where both types are possible.

I remember many years ago there was some discussion about the goal of an common EU-wide electrical socket. Which as you can see got nowhere. What was the most promising choice was the IEC "kettle" style of connector as it is polarised, in widespread use already, and available at 10A (but often only 5A!) so probably enough for the majority of applications.

But then you get in to the details of local fuse/switch or not, and even the issue of shutters. The IEE was not willing to have open sockets and other standard bodies were not bothered as they never had shutters to keep kids from poking stuff in, etc.

Yes. Its often just history, is, nt it. Anyway if debating pro, s and con, s of rings /radials is our biggest problem, we must be in a good place.
Onwards and upwards

 

[nicebutdim]

Sorry, I'd taken your earlier post to mean you ran in additional circuits as standard and not at the customer's request.

I'm in a 3 year old house with all socket circuits wired as rings. I'd have been happy enough with 20A radials upstairs and also downstairs, with the exception of kitchen and utility, but that discussion never took place. If the option had been put to me and those radials were to have been 16A, I'd have requested 32A rings or 20A radials run in 4mm at a relatively small additional cost. Chances are that 16A would be sufficient for our needs (outside of kitchen and utility), but I'd rather know that additional capacity was available.

A few years ago our eldest bought himself a 2kW fan heater for his bedroom, because he's special and needs to look after himself better than the rest of us I've no idea how long he had that heater, but can tell you that he didn't have it for long after I discovered it. Now I've no idea of the power factor of such heaters, nor that of most domestic appliances, but even in the best scenario that heater and a vacuum cleaner running on the same circuit must get close to tripping a 16A breaker.

 

[Risteard]

That's fine Risteard. Do you also still "support and endorse" the installation of a 4ft earth rod (as we are both required to install under Irish regs) but as has been demonstrated here on this forum by multiple sparks in multiple posts is actually less than useless?

Yes I do, and as you rightly state essentially I have no choice. I myself have pointed out how a very low impedance would be required in many circumstances (depending on the load) to limit the touch voltage to a safe level. However I still believe that an Earth electrode is better than no Earth electrode. I honestly feel that the IEE Wiring Regulations are at odds with the rest of the world on this, and there is a reasonable probability that they will change in due course.

But yes - we should ideally be striving for a much lower impedance connection, although this could mean substantially more work to achieve this.

 

[pc1966]

Yes. Its often just history, isnt it. Anyway if debating pro, s and con, s of rings /radials is our biggest problem, we must be in a good place.
Onwards and upwards

As they say "First world problem"

 

[LastManOnline]

Yes I do, and as you rightly state essentially I have no choice. I myself have pointed out how a very low impedance would be required in many circumstances (depending on the load) to limit the touch voltage to a safe level. However I still believe that an Earth electrode is better than no Earth electrode. I honestly feel that the IEE Wiring Regulations are at odds with the rest of the world on this, and there is a reasonable probability that they will change in due course.

But yes - we should ideally be striving for a much lower impedance connection, although this could mean substantially more work to achieve this.

Yes. You made the valid point about the need for a very low impedence in a previous point. Agreed. That's, essential. But before we would recommend to other countries (UK for example) that they should install a 4ft rod can we explain clearly to them why? Its, been clearly established mathematically (here on this forum) that a 4ft rod is of no use as a, return path in the event of a broken neutral. Secondly, its been argued (mathematically) that the rod does, nt bring down the touch voltage during fault conditions. I would go one step further and argue (mathematically) that a 4ft rod will actually be a potential safety hazard under fault conditions. I would be happy (even reassured) to be proved wrong in that assumption

 

[Mike Johnson]

Hmm my French house has a TT supply and a 3M rod, resistance value is 56Ω should I panic now?

 

[LastManOnline]

Hmm my French house has a TT supply and a 3M rod, resistance value is 56Ω should I panic now?

No absolutely not. The issue is actually with TNC-S and the widespread (but erroneous belief) that the rod plays the same role in this supply system as it dies in a TT system. By the way a res of 56 ohms?? That's a dream come true over here
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No absolutely not. The issue is actually with TNC-S and the widespread (but erroneous belief) that the rod plays the same role in this supply system as it dies in a TT system. By the way a res of 56 ohms?? That's a dream come true over here☺

Did you test that rod isolated from other earth's?

 

[davesparks]

Yes. Unterminated and taped off in a JB, but obviously accessible. The utility is the location of choice.

So in the future, if it is needed as the customer has bought a new appliance and overloaded the 16A circuit you installed, they have to call you back to connect this other cable and make more current available?

That sounds like a terrible installation design to me, and I'm sure the customers will agree

 

[Mike Johnson]

Did you test that rod isolated from other earth's?

This is on the outside of most rural properties in France for exactly that purpose.

 

[LastManOnline]

So in the future, if it is needed as the customer has bought a new appliance and overloaded the 16A circuit you installed, they have to call you back to connect this other cable and make more current available?

That sounds like a terrible installation design to me, and I'm sure the customers will agree

How is that the wisest course of action? Limiting socket circuits to 16A does not seem like a sensible plan.
If you had said you calculate cable size as if there was more insulation than there actually is I could understand it. But to make an arbitrary decision to put all socket circuits on 16A OCPDs seems daft to me.

What size cable do you use for the 16A socket circuits usually?

Do you make the circuits smaller and run more of them to compensate for the reduction in available current?

Yes. Simple run in more circuits. Not complicated. You will find most continental countries have their socket Circuits at 16 amps. Appliances generally have their own curcuits.

DAVE SPARKS "if you had said you calculate cable size as if there is more insulation..". That's exactly what I said. The decision was, spe ifically made in relation increasing insulation. Reread my post.
I use 2.5 t&e for socket circuits.

Now, an exercise. Check the tables for current carrying capacity of a 2.5 t&e in insulation. Use the appropriate derating factors and see if you are still comfortable using a 20amp mcb?

By the way how many appliances, in your home will trip a 16 amp mcb.

Lastly, no decisions are set in stone. We play what's in front of, but always erring on the side of caution.

 

[davesparks]

Now, an exercise. Check the tables for current carrying capacity of a 2.5 t&e in insulation. Use the appropriate derating factors and see if you are still comfortable using a 20amp mcb?

By the way how many appliances, in your home will trip a 16 amp mcb.

That is a ridiculous exercise as it does not follow the rules for calculating cable size.
You apply rating factors to the nominal current and then select a cable size based on that calculation.

Your 'exercise' suggests starting with a cable size and working backwards to a nominal current, this is incorrect.

I am well aware that a 20A circuit wired in T&E through insulation will require a minimum of 4.0mm, but that is irrelevant to the point.

On their own i don't think any appliance with a plug will trip a 16A MCB unless faulty. However a combination of 2 or more on the same circuit will trip a 16A MCB quite easily.

 

[Mike Johnson]

Yes. Simple run in more circuits. Not complicated. You will find most continental countries have their socket Circuits at 16 amps. Appliances generally have their own circuits.

Ah ha Edmond you have been listening.