Table 53.1

[studentspark]

Maximum I delta n 20A for a 2.5 ohm (RA)

A 20 A trip current for an RCD, or have I misunderstood.

Thanks

 

[flameport]

Yes, that's what it says.
The entire table is just 50 volts / resistance = maximum current.
Or 50 volts / current = maximum resistance.

 

[studentspark]

But do you get RCD's with such a high trip current. In 7671, 300mA seems the highest.
Im sure in the industrial / specialist world all manor and scale of things happen.

 

[333rocky333]

Thats a question in the 18th exam, as EFL says you have to bear 50V in mind for the answer

 

[flameport]

They exist, typically they have an adjustable trip current which is set at the time of installation.

 

[333rocky333]

We use ones that fit on the bottom of main switches usually in commercial premises
https://www.tradesparky.com/circuit...-rccb/schneider-lv429211-vigi-rcd-4p-100-160a

This one you can wind up to 10amp
Im no expert but i think the point is too protect the tails etc on TT systems from the main switch to the dist boards etc more so where the cables are in metal trunking

I think the regs say the rcd can be omitted if the cables, prior to a board fitted with 30ma rcds, are reinforced or Double insulated
531.3.5.2.201