Metal Fuseboard on TT

[somersetsparks]

On one of my 'other jobs' which I mentioned the other day,
One building which is TT and fed by an SWA, although the earths are isolated and this building is protected by a rod, has single insulated cores feeding the incomer (100ma rcd).
However the whole installation is protected by a 300ma Time delay at source, so would the double insulation of the incoming cores still be necessary?

cheers

 

[Rockingit]

Erm, if I'm understanding you correctly, you've got a submain running to a building on two core and the earth to that board is by TT.

To turn your question around, if you wanted to change the incoming feed for singles then those cables would need additional protection - either by trunking/conduit/whatever or double insulation if being surface clipped.

 

[sparks1973]

Erm, if I'm understanding you correctly, you've got a submain running to a building on two core and the earth to that board is by TT.

To turn your question around, if you wanted to change the incoming feed for singles then those cables would need additional protection - either by trunking/conduit/whatever or double insulation if being surface clipped.

double insulation or insulation and sheething?..

 

[Rockingit]

double insulation or insulation and sheething?..

which is what I was meaning by 'whatever'. Basically, one layer between you and the copper is a bad idea.

 

[somersetsparks]

Sorry original question a bit cr*p!

Basically, The origin of the installation is PME, The workshop and office are submains and connected PME, and I have upgraded the bonding.
This sub board feeds another building using 2 core SWA (16mm). This building is TT'ed as it could contain livestock, however the building has a metallic consumer unit being fed from the 2 core SWA.
As I understand a TT installation should have an insulated consumer unit or double insulation to the incoming cables,
BUT... as the whole installation is protected by a 300ma time delay at origin is this necessary?

 

[Rockingit]

Has the SWA been divorced?

 

[somersetsparks]

Has the SWA been divorced?

Aye, it is terminated into a placcy dappy box.

 

[StuSpiers]

Has the SWA been divorced?

Nope happily married with 2 kids.

Sorry.......


Somebody had to do it.

 

[Rockingit]

Well, by the sounds of it you've got a correctly installed system, so why the question?

 

[somersetsparks]

Just wasn't sure whether the Main RCD had to be at the origin of the TT installation or back at the origin of the whole installation, every time I have done a TT we have used an insulated board and have had a time delayed RCD mains switch,
Just thought this was a bit funny having a metalclad unit with the Time delayed being back at the origin.
However I can see nothing 'wrong' with it, just not something I have seen before.

The TT sub-board has a 100ma non-delayed RCD which is faulty, I may just replace this with a 100a dp main switch then as it is already RCD protected further back in the system.

 

[JD6400]

Hi Somersetsparks , i can not make my mind up as to whether you need the shielding installed in the cu or not as you have the upfront 300ma !
I suppose it should be covered by it , but it just don't sit right with me for some reason ?

 

[JD6400]

Just wasn't sure whether the Main RCD had to be at the origin of the TT installation or back at the origin of the whole installation, every time I have done a TT we have used an insulated board and have had a time delayed RCD mains switch,
Just thought this was a bit funny having a metalclad unit with the Time delayed being back at the origin.
However I can see nothing 'wrong' with it, just not something I have seen before.

The TT sub-board has a 100ma non-delayed RCD which is faulty, I may just replace this with a 100a dp main switch then as it is already RCD protected further back in the system.

No way !
If i have read the post right , the shed would not be protected correctly .

 

[somersetsparks]

Hi Somersetsparks , i can not make my mind up as to whether you need the shielding installed in the cu or not as you have the upfront 300ma !
I suppose it should be covered by it , but it just don't sit right with me for some reason ?

Same with me, hence the question. Theres not really anything wrong but It just doesn't seem right!
I am in the rare situation of working for a farmer (a mate) who likes to have things done properly, although he still insists on running cables, digging trenches etc. Which is fine with me!

I may double insulate the incoming SWA cores for good measure, has anyone done this before and have a good method of achieving it?

 

[somersetsparks]

No way !
If i have read the post right , the shed would not be protected correctly .

But why not? the shed (well pretty big barn) would still have 300ma time delayed protection from the RCD upstream (at origin).

Difficult one I know

 

[JD6400]

As for the knacked 100ma one , I know this will get a bit of flack but I would replace it with a 30ma .
I know it will take the whole board out , but even if you replace it with a 100ma and use rcbo's you have lost any discrimination as the 100ma will not be a s type .