Ring or Radials

[Mad_Doctor_X]

Hello!

Just after a bit of advice with circuit design if possible.
The circuit(s) are for our lounge and dining-room/office (odd combination I know!) in a terrace house and I'm wondering whether I should go for a ring main for the lot or have two radials, one for each room.

If I do the whole lot as a ring the total length of the circuit would be 50 m (including 10%) and would connect fifteen 2 gang 13 A sockets (I'm trying to eliminate extension leads!).

I calculated a worst case scenario for the load (everything was turned on at once, including hoover and three 100 W table lamps) then the current would come to 15 A. Is this how you're supposed do these calculations? I ask because this would limit the circuit length to 35.5 m on 2.5 mm² 2&E and I understand that the on-site guide puts the maximum length for 2.5 mm² 2&E at around 80 m on a 32 A MCB?

I'm also having problems calculating the earth fault loop impedance for this circuit. I have my part P certificate for the shower we had installed and this states the external earth fault loop impedance as 165 Ω. I've been following the tlc guide to these calculations and the examples they use have Ze of around 1 or less. Putting a Ze of 165 Ω into these equations would put the maximum circuit conductor length less than 0. I assume I've made an error here...!?

I was wondering if it would better to go for two separate radial circuits. This has some advantages as I can complete one circuit, get it tested and then move on to the next one. I've seen a comment about ring circuits having complications with respect to electromagnetic interference. While the floorboards are up I was thinking of getting some data cabling in and was wondering whether interference is something that should seriously influence the choice of circuit.

Last question if I may, if I go for radials then how fiddly is getting 4 mm² cable into 13 A sockets?!

Thanks in advance

 

[ban-all-sheds]

The circuit(s) are for our lounge and dining-room/office (odd combination I know!) in a terrace house and I'm wondering whether I should go for a ring main for the lot or have two radials, one for each room.

My vote would be for radials over rings, and more circuits rather than fewer.

What does your electrician advise?

I calculated a worst case scenario for the load (everything was turned on at once, including hoover and three 100 W table lamps) then the current would come to 15 A. Is this how you're supposed do these calculations?

No - the next occupant could arrive with a boot full of 3-bar electric fires. You have to make a socket circuit capable of carrying the maximum load the breaker will permit.

I ask because this would limit the circuit length to 35.5 m on 2.5 mm² 2&E and I understand that the on-site guide puts the maximum length for 2.5 mm² 2&E at around 80 m on a 32 A MCB?

I think you're mixing up the limits for rings and radials there.

I'm also having problems calculating the earth fault loop impedance for this circuit. I have my part P certificate for the shower we had installed and this states the external earth fault loop impedance as 165 Ω.

Hopefully because you have a TT supply.

I've been following the tlc guide to these calculations and the examples they use have Ze of around 1 or less.

For TN supplies.

Putting a Ze of 165 Ω into these equations would put the maximum circuit conductor length less than 0. I assume I've made an error here...!?

The calculations are different when you are relying on an RCD to clear an earth fault.

I was wondering if it would better to go for two separate radial circuits. This has some advantages as I can complete one circuit, get it tested and then move on to the next one.

What do you mean by "get it tested"? By whom, and most importantly, for what reason?

I've seen a comment about ring circuits having complications with respect to electromagnetic interference.

Rubbish.

While the floorboards are up I was thinking of getting some data cabling in and was wondering whether interference is something that should seriously influence the choice of circuit.

No.

Last question if I may, if I go for radials then how fiddly is getting 4 mm² cable into 13 A sockets?!

Fiddlier than 2.5mm².

Do you not think you might be better off getting an electrician?

Do you live in England/Wales?

 

[Mad_Doctor_X]

I do live in England and Wales. I haven't contacted an electrican yet as I'm trying to work out whether it would be practical to notify the council myself, do the work myself and then get it tested and so signed off under part P.

 

[ban-all-sheds]

What arrangements does your council make, or insist you make, regarding DIY electrical work?

 

[Mad_Doctor_X]

No - the next occupant could arrive with a boot full of 3-bar electric fires. You have to make a socket circuit capable of carrying the maximum load the breaker will permit.

Now I am confused. So if I have 15 2 gang sockets I have to design a ring main circuit that could conceivably take 30 3-bar electric fires? i.e. 90,000 W drawing a current of 375 A at 240 V?

Thanks for the help.

 

[Mad_Doctor_X]

What arrangements does your council make, or insist you make, regarding DIY electrical work?

I have been installing a lighting circuit and a ring main upstairs. I've been doing them a room at a time and building control have been round to inspect the first fix. Once I have completed the circuits my understanding is that i will notify them and then have to pay to get the circuits tested.

 

[Risteard]

I do live in England and Wales.

You live in both countries simultaneously?

 

[ban-all-sheds]

Now I am confused. So if I have 15 2 gang sockets I have to design a ring main circuit that could conceivably take 30 3-bar electric fires? i.e. 90,000 W drawing a current of 375 A at 240 V?

No, you design it so that it could carry the maximum load of the breaker, e.g. 32A, evenly distributed.

 

[Mad_Doctor_X]

You live in both countries simultaneously?

 

[ban-all-sheds]

I do live in England and Wales.

You live in both countries simultaneously?

Maybe he's bought the Lion pub in Llanymynech and converted it to a house....

 

[Mad_Doctor_X]

Maybe he's bought the Lion pub in Llanymynech and converted it to a house....

It looks like it used to have a copper mine, so I suppose it would have a vague link to electrical work...

 

[industryspark]

I would go for a ring circuit myself covering both the office/dining room and the lounge. A 32A ring would be more than adequate for the load you describe. Im a fan of rings myself as they can be advantageous over radials a lot of the time. The problem with rings is they can have faults on them that you can be unaware of but designed and installed correctly they are fine.

Are you doing a seperate ring or radial for the kitchen may i ask?

Regards.

 

[1john]

I would opt for the radials, easier to add to in the future too.

 

[martinxxxxxx]

I do live in England and Wales.

You live in both countries simultaneously?

Do you live half way up the High Street in Knighton?

 

[Mad_Doctor_X]

Are you doing a seperate ring or radial for the kitchen may i ask?Regards.

I will get the kitchen done professionally when we get round to it and therefore I hope it will be on a separate ring/radial!

The original installation was one "ring" for the whole house, however this ring consisted of a small ring with a number of spurs. One of the spurs had the immersion heater, a socket on the landing and the kitchen work top points on it. The other spur appears to include the fridge and freezer.

Once the downstairs circuits I have been asking about are in then the old "ring" will be just supply the kitchen stuff and it can be binned when we get the kitchen done.

Thanks for the advice