Radials Circuit Designing

[Snapester]

Hi guys, doing a rewire in which i plan to do the circuits in 4mm as radials, one down one up and kitchen. When designing how can i work out the loading along the circuit? Also how can you work out the loading on a lighting circuit radial as the load will be split along the length so the furthest point may only be loaded at 100w?

Hope this makes sense.
Cheers

 

[highspark]

Is there any reason why you are using 4mm cable oin a radial circuit in a domestic premise? Over 50m2 is a massive area and sometimes I think sparks tend to go for overkill with this trying to be smart. I tend to stay away from 4mm, its a nightmare to first and second fix and very expensive. If your loading is too big for a radial, why not just throw a ring in, in 2.5mm.

 

[Des 56]

Hi guys, doing a rewire in which i plan to do the circuits in 4mm as radials, one down one up and kitchen. When designing how can i work out the loading along the circuit? Also how can you work out the loading on a lighting circuit radial as the load will be split along the length so the furthest point may only be loaded at 100w?

Hope this makes sense.
Cheers

Maybe calculations for volt drop and the overall length of the lighting circuit can be considered where the limits are getting too close for comfort
The usual calculation for the circuit volt drop is, per ampere per meter taking the whole circuit current as uniform,but in a near the limit lighting circuit,the volt drop could be calculated in sections to get a lower figure, because the level of current is dropping after each lamp

Is this along the lines of what you were thinking on ?

 

[ackbarthestar]

Its not too difficult to add up the volt drops for each section. The length increases as the current drops. Put it into a spreadsheet and it will do all the calculations for you.

Consider 4 lamps spread out equally across the circuit

For a normal radial then the Vd = mV/A/m * L * Ia) / 1000

So for a radial with separated loads as would be the case with a lighting circuit
Total length L = L1 + L2 + L3 + L4

Ia = total current demand but will diminish by one fitting for every new length
n = Total number of light fittings on the circuit (Assuming that the light fittings are the same wattage) will increase at each fitting

Section 1: (mV/A/m * L1 * (Ia / (n-(n-1))) /1000
Section 2: (mV/A/m * L2 * (Ia / (n-(n-2))) / 1000
Section 3: (mV/A/m * L3 * (Ia / (n-(n-3))) / 1000
Section 4: (mV/A/m * L4 * (Ia / (n-(n-4))) / 1000

So total Vd = Sections ( 1 + 2 + 3+ 4)

 

[Snapester]

Its not too difficult to add up the volt drops for each section. The length increases as the current drops. Put it into a spreadsheet and it will do all the calculations for you.

Consider 4 lamps spread out equally across the circuit

For a normal radial then the Vd = mV/A/m * L * Ia) / 1000

So for a radial with separated loads as would be the case with a lighting circuit
Total length L = L1 + L2 + L3 + L4

Ia = total current demand but will diminish by one fitting for every new length
n = Total number of light fittings on the circuit (Assuming that the light fittings are the same wattage) will increase at each fitting

Section 1: (mV/A/m * L1 * (Ia / (n-(n-1))) /1000
Section 2: (mV/A/m * L2 * (Ia / (n-(n-2))) / 1000
Section 3: (mV/A/m * L3 * (Ia / (n-(n-3))) / 1000
Section 4: (mV/A/m * L4 * (Ia / (n-(n-4))) / 1000

So total Vd = Sections ( 1 + 2 + 3+ 4)

Yes this how I worked it out to be fair, I saw somewhere someone has seen and equation in the IEE electrical installation design guide but I can't seem to find it?

 

[ajelec10]

4mm Radials are great the stranded cable make it slightly more flexible than 2.5, but beware i have installed a few in the past and with a 1.5 cpc in the 4.0 T+E the max earth fault loop impedance creeps up on you with any length. make sure you use B type or you will have problems, I have tried to Buy 4.0 T+E with a 2.5 CPC but no luck.
I would however look at a ring circuit for the Kitchen as the complexity of the circuit with spurs for appliances etc, can get a bit tight with 3 x 4.0 T+E's at a switched spur??

 

[telectrix]

bring back 7/029, i say.

 

[Engineer54]

This opening post just beggars believe!! I'm thinking someone that doesn't know how to test RFC's!! Why else would anyone arbitrarily plan to use 4mm radials for every power circuit, which will virtually nullify any chance of future spurred outlets without the use of a JB!!

Whatever happened to providing/designing suitable circuits to installations, to meet the situation and required loads etc??

 

[robsparky1975]

Ill tell u what what happenned eng54,all these Electrical Trainee centres opened their doors,tin hat on lol,goodnight from me:sleep1:

 

[ackbarthestar]

Ill tell u what what happenned eng54,all these Electrical Trainee centres opened their doors,tin hat on lol,goodnight from me:sleep1:

If the Government pull the plug on all these money making training providers and make it only available to legitimate electrical companies then some sort of apprenticeships make take on.

 

[Snapester]

So i don't know how to test because i want to install radials! haha you guys are are funny on here. Why would i want to run an unbalanced ring when i can run a radial that will cope with the load perfectly?
Maybe you only install ring finals as thats all you know how to do.

 

[T&Earth]

Hi Ackbarthestart
are the figures you put in the spreadsheet at the bottom of your post as not too sure about spreadsheets.

Cheers T&E

Its not too difficult to add up the volt drops for each section. The length increases as the current drops. Put it into a spreadsheet and it will do all the calculations for you.

Consider 4 lamps spread out equally across the circuit

For a normal radial then the Vd = mV/A/m * L * Ia) / 1000

So for a radial with separated loads as would be the case with a lighting circuit
Total length L = L1 + L2 + L3 + L4

Ia = total current demand but will diminish by one fitting for every new length
n = Total number of light fittings on the circuit (Assuming that the light fittings are the same wattage) will increase at each fitting

Section 1: (mV/A/m * L1 * (Ia / (n-(n-1))) /1000
Section 2: (mV/A/m * L2 * (Ia / (n-(n-2))) / 1000
Section 3: (mV/A/m * L3 * (Ia / (n-(n-3))) / 1000
Section 4: (mV/A/m * L4 * (Ia / (n-(n-4))) / 1000

So total Vd = Sections ( 1 + 2 + 3+ 4)

 

[Engineer54]

So i don't know how to test because i want to install radials! haha you guys are are funny on here. Why would i want to run an unbalanced ring when i can run a radial that will cope with the load perfectly?
Maybe you only install ring finals as thats all you know how to do.

No, Quite to opposite, I design/install circuit arrangements that are suitable to meet the requirements and situation for what they are being installed for. I certainly wouldn't run a 4mm radial to supply All the socket outlets in a kitchen, that's for sure!!

Are you saying now, that you don't know how to install a balanced/staggered Ring circuit?? ...lol!!!

 

[ackbarthestar]

Hi Ackbarthestart
are the figures you put in the spreadsheet at the bottom of your post as not too sure about spreadsheets.

Cheers T&E

There are various ways of writing it, I've chosen one possible method.

The key is to recognize that at the first fitting the maximum current will be drawn but at the shortest distance.
At the last fitting the minimum current will be drawn but at the longest length.

1/ Draw the circuit for the number outlets to be calculated
2/ At each outlet the current diminishes. so calculate the current in that section of the cable leading up to each outlet.
3/ Now for each section of cable calculate the volt drop
4/ add the different volt drops for each section

 

[Snapester]

Even if there are only two sockets in the kitchen, or even if the calculated circuit would allow 4mm radial you wouldn't use it in a kitchen??
Creating a balanced ring is not always possible and in most cases they are not close to being balanced?
Clearly you like to create arguments on forums designed to help people, good for you.