"just bang it on an RCBO!"......... TABLE 41.3

[cashnotakite]

this slightly confuses me;

whenever a Zs reading comes up too high, e.g on a particularly long run, to get around the problem if you cant change the MCB rating, I get told to change it for an RCBO.

Table 41.3 of the regs gives max Zs values for both MCB and RCBO protection. If our Zs value exceeds the recommendation why can we just use an RCBO?

Is this to do with the 30mA trip and if so is there anywhere in the regs that this is written down in?

thanks in advance

 

[Ponty Massive]

Provided your Zs is below 1667 ohms, by using a RCBO you will meet the disconnection time required; however unless it's a TT system, most people will use the Zs requirements for the MCB rating to ensure disconnection times and not have to rely on the RCD.

 

[Adam W]

Is this a high Zs due to a high Ze or a high R1+R2?

 

[cashnotakite]

Is this a high Zs due to a high Ze or a high R1+R2?

high R1/R2 readings

thanks for your feedback guys