Metal clad distribution boards and TT

[Sidewinder]

If you take the tails through separate holes with stuffing glands in a ferious metal enclosure then our friend Mr. Current, first name eddy comes into play!

Thanks Phoenix for messing this up for me!

 

[batty]

The origin of an installation is the position at which electrical energy is delivered. So how can it be upsteam? In my mind I am imagining the main fuse is the origin. Therefore by introducing an RCD in the meter tails (after the meter) the tails entering the metal enclosure are protected fromearth faults by the RCD.

You have to be very careful with having RCD's before the consumer unit even if they are time delayed if using single pole RCBO's in your main consumer unit. If you have a neutral to earth fault on a circuit it can take out the main RCD so you won't comply with discrimination reg. I say this through experience. To me it easier to just use an insulated enclosure on TT systems.

 

[unphased]

Thanks Batty. You have the most distracting avatar on the forum, btw. Does my head in.

Anyway. I feel electricians try to take too many variables in to consideration when putting in installations. As I have recently said the underlying need for all electrical installations is safety. If you try to take every which what and wherefore in to account it gets over complictaed. This thread has demonstrated that not using a metal enclosure on a TT system makes sense. So that keeps it simple, and safe. If you put in a time delayed 100mA RCD downstream and use 30mA RCBOs in the board that is good circuit design. If the 100mA time delay trips before the 30mA does or both trip that is hardly your fault. You have designed the circuit properly, taken precautions to install the correct technology and it doesn't do it the right way round. Okay. It is safe. Insulated and sheathed tails can still be damaged after they are installed so it would make sense to have a time delayed RCD in the tails even with an insulated board on a TT install.

With regard to your comment that you won't comply with discrimination, that is incorrect. If in reality the system doesn't behave as intended you have installed it correctly and it complies with the discrimination. You don't compromise a reg if in practice the component doesn't actually behave in the way it is designed. That is not your fault. You canot possibly allow for every thing that might happen.

How far do you go with ifs, buts and may be's? Not having a dig btw.

 

[Phoenix]

Thanks Phoenix for messing this up for me!

oops!