Mechanical Protection vs RCD Requirements

[rich.250]

I see what your saying, never really thought of the amount of PeFC required for the disconnection time in this circumstance. Thanks spinlondon
In that case, the RCD will have to stay. :/

 

[SW1970]

Great input guys, so, the options are:

1) Leave RCD at origin in place (TN-S arrangement) - undesirable because of the inconvenience factor in room 3, or
2) Replace the RCD at origin with RCD-S and provide suitable mechanical protection along the cable and then RCD protection in room 3. Question here though: is mechanical protection required on the whole length, or just the parts that are hidden?

Cheers!

 

[Rauer]

Can you not change the RCd at the incomer for a main switch , extend the cables elsewhere and provide RCd protection from that point? I know this sounds easy on here and realise its not always that practical , am just throwing another idea in the air!

 

[rich.250]

As spinlondon said, the problem is you will be making the installation less safe due to the higher disconnection time /PeFC to operate device.
If it was a new install it would be possible providing the required disconnection time for the earthing arrangement was met for the submain.

 

[Rauer]

It won't be tho cause your just moving the RCd to another place , say for example the RCd is in the room at the mo , extend the main tails from the meter and extend the mains to the flat into a hallway for instance and add the RCd protection in there, then all existing cables will have RCd protection just make sure that your mains from the supply cables are either surface or buried more than 50mm

 

[rich.250]

I see what your saying, and i do agree, its just the submain is still part of the install. aslong as the installing sparks is confdent it is not deemed less safe. Its fine
Also need to make sure that the tails are fused down so that 3m is not exceeded for the DNO lol

 

[Rauer]

Yeah u will need to fuse them down but all of the submain that is currently in place will still be RCd protected , u will be just extending it and re-feeding from another place

 

[rich.250]

That sounds ok to me

 

[SW1970]

Hi, but as spin was saying I cannot remove RCD protection where it is already provided because it makes the installation less safe. So, the question is whether this solution is ok?

Point of supply --- Meter --- Main isolator with RCD-S --- 30m of T&E (some surface, some hidden) --- Consumer unit with RCD

If the time delay RCD is not acceptable, then is my only option to provide additional mechanical protection on the 30m of cable, and if yes, is the additional mechanical protection required on the surface mounted cable as well as the hidden cable?

Cheers!

 

[Deleted member 26818]

It seems to me, that there are four options:
Remove the RCD, and provide another acceptable method of additional protection. You would have to be able to argue that the other method of additional protection offers the same degree of safety.
Provide all the tennants with access to the unit where the RCD is sited. Something I assume the tennant of the first unit will not be happy with.
Alter the installation so as access can be provided without having to access the first unit. Perhaps build a cupboard round the DB, and make a new doorway into the cupboard from ouside the unit? Or perhaps re-site the DB so as it is outside of the unit?
The final and probablly the cheapest option, is to either add an auto re-set device to the existing RCD, or change it to an auto re-set type. http://www05.abb.com/global/scot/sc...04dfb9b/$file/f2c-ari-bedienungsanleitung.pdf

 

[Knobhead]

The remote reset looks a neat solution to the problem.
But unless I’ve misread something it needs a control transformer as the closing operates at 12 to 30V.

 

[Deleted member 26818]

The remote reset looks a neat solution to the problem.
But unless I’ve misread something it needs a control transformer as the closing operates at 12 to 30V.

There's a few out there Tony, Legrand do one, and I was fairly certain that ABB did an all in one device, rather than an add on module.
Thes add ons, aparently work with MCBs as well as RCDs?
Electrical Distribution - Schneider Electric

 

[Knobhead]

I suppose it makes sense to use LV. It’s OK the supply being knocked off and then having 230V running through the protected area to reset it.

 

[SW1970]

Thanks loads guys - these auto-on and auto-reclosers are a great idea! Solves the problem. Cheers. SW