Maximum permissible ring resistance

[brizospark]

What is the highest permissible ring main resistance of conductors, end to end?

 

[Deleted member 26818]

Depends on the CPD, and the Ze of the installation.

 

[brizospark]

is there a rule of thumb figure?

 

[Sintra]

Also depends on the loading and voltage drop as to how long the ring is.

 

[Deleted member 26818]

is there a rule of thumb figure?

Yes, you determine the Ze and the CPD, which will then give you the maximum allowed R1+R2.
As a rule of thumb, you could use the nominal maximum Ze figures for whatever system you have. i.e. 0.8Ω for TN-S and 0.35Ω for TN-C-S, and then if you were to use a 32A type B MCB/RCBO you'd be looking at 1.44Ω less the value for whichever system you have.

 

[i=p/u]

isnt there pages in the osg already calculated for you???? think pg 45+

 

[brizospark]

what does CPD stand 4?

 

[brizospark]

surely if your Zs is within reason then the ring cables are within length?

 

[Deleted member 26818]

Circuit Protective Device.

 

[truckster]

Rule of thumb? 2.5 T/E ring around hundred metres cable length