Design of Ring Final Circuit

[mark the spark]

Read all the books spend 5 years at college and no...
still dont know the full understanding of designing a ring circuit!!!

Whats the total load?
How do apply the diversity?
What will my design current be?
Does this effect my earth loop impedance when calculating R1 + R2 Value???



Dont misunderstand me I do know but I'm just testing!! Reply now if you dare!!

 

[The Jeep]

For a 2.5mm² ring circuit, the Ib (design current) = In (nominal current) = 32Amps.
No diversity is allowed for each individual circuit (so you have to assume 32A load for each final ring circuit). If , however, you have more than one ring, you can apply diversity of 40% for all but the largest circuits when taking into account overall current demand of the installation.
Sound confusing? It is - see p84-87 and App 8 of OSG for more.

 

[The Jeep]

Dont misunderstand me I do know but I'm just testing!! Reply now if you dare!!

???

 

[plugwash]

Whats the total load?

you don't know so you assume its the breaker rating

How do apply the diversity?

none within the circuit

For multiple rings fed from a board there are some diversity guidelines in the regs but they grossly overestimate for typical modern domestic use of rings,largely because they make no allowance for the fact that many rings aren't covering anything like the max allowed floor area. Many typical houses come out way over 100A yet the standard 60-100A services are just fine.

What will my design current be?

see above comment about total load.

Does this effect my earth loop impedance when calculating R1 + R2 Value???

no but the existance of paralell paths from it being a ring does, the values will be worst at the midpoint of the ring so you devide the length of the ring by 4 (devide by 2 for paralell paths and 2 for the fact that the midpoint is half a ring length from the origin) to get actual worst case values.

 

[The Jeep]

no but the existance of paralell paths from it being a ring does, the values will be worst at the midpoint of the ring so you devide the length of the ring by 4 (devide by 2 for paralell paths and 2 for the fact that the midpoint is half a ring length from the origin) to get actual worst case values.

Hmmm...imo the R1+R2 values will be more-or-less the same wherever you measure in the ring. If a socket is near the CU, then it has one leg that is short and one leg that is long...in otherwords, they all equal (r1+r2)/4 wherever they are located. True?
It's the spurs that will have the higher reading, and you take the 'worst-case' of these to put down as your final figure for the circuit.