Please help, I can't explain to my boss ! RCD protection

[preppar]

Good afternoon gents and ladies.

So I am having an argument, I say if I do any work on nearly any circuit, namely lighting and power, commercial
I have to upgrade protective devices so the circuit would be up to regs and on this case have either RCBO or RCD,
I ask you kindly to help me and tell me am I right or am I not right in saying that ?

Many thanks for your answers.

 

[NDG Elecs]

Whatever happened to Eng54. For some reason he has just sprung to mind!

 

[Hawk]

Provided a suitably low value of Zs is permanently and reliably assured. As I can't assure the condition of the ground I think it is best practice to use an rcd in a tt system. After all it is the preferred method.