Zs on ring main high

[cliffed]

A bit more info as requested by @timhoward would help.

Dropping the OCPD to 25A is a "fix" only in the sense the Zs, and (probably) VD figure allowed, become consistent with the circuit implemented. But it is not really satisfactory as such a long RFC suggests it is something like a whole house on one circuit, and so total load would be high and might make 25A trip-prone.

Is there any point where you could break the RFC and link up two more cables as legs to make two RFCs? Taking great care of course not to have them cross-linked!

There are 3 RM in the house… this RM travels a distance from the DB before looping into the power points….in most cases being RCD protected this would not be flagged up

 

[cliffed]

What is your r2?

soz r2 1.96 R1+R2 0.76

 

[Pretty Mouth]

r2 ever-so slightly high, although not by much really. Otherwise too long for theoretical voltage drop limits then. What is this circuit likely to power?

 

[timhoward]

What are people's thoughts on adding a parallel 4mm separate CPC to the first point in each direction? Mathematically that would probably get the Zs under the bar. Do regs allow that?

 

[Pretty Mouth]

What are people's thoughts on adding a parallel 4mm separate CPC to the first point in each direction? Mathematically that would probably get the Zs under the bar. Do regs allow that?

I think the Zs is well under the permitted 1667 ohms as it is

 

[timhoward]

I think the Zs is well under the permitted 1667 ohms as it is

I know what you mean, but this is NICEIC.....we can't expect them to know that.

 

[cliffed]

r2 ever-so slightly high, although not by much really. Otherwise too long for theoretical voltage drop limits then. What is this circuit likely to power? Table lights, TV, Chargers normal house equipment

 

[cliffed]

I know what you mean, but this is NICEIC.....we can't expect them to know that.

Exactly the inspector actually calculated the length by the resistances…we can all do that…under normal circumstances

 

[Pretty Mouth]

I know what you mean, but this is NICEIC.....we can't expect them to know that.

I'm so glad I'm not registered, I don't have to go through any of this

 

[cliffed]

What are people's thoughts on adding a parallel 4mm separate CPC to the first point in each direction? Mathematically that would probably get the Zs under the bar. Do regs allow that?

Not really possible now… not too sure on the outcome on this one… waiting for Niceic response