Testing garage CU for assesment!!!

[Octopus]

Sorry Murdoch, you've mentioned using a switch fuse (#36) and Davesparks said 'why feeding a submain from an mcb is rarely the best practice' (#33). I understand the use of a switch fuse feeding a distribution circuit for a domestic property CU, but for a log cabin CU?

Why not.

If you read the OP, he thinks that making the cabin TT, any tripping will be internal to the cabin and not the house despite the submain being on a "shared" RCD.....

Its very difficult to get proper discrimination between MCB's so when a switch fuse can be used, its better all round.

Most people avoid this option because its far more expensive.

 

[Pete999]

Can I ask why the OP is being recommended to not use a not RCD protected way in the house CU, with RCD CU in log cabin, presuming he uses the PME?

You can ask.

 

[davesparks]

Sorry Murdoch, you've mentioned using a switch fuse (#36) and Davesparks said 'why feeding a submain from an mcb is rarely the best practice' (#33). I understand the use of a switch fuse feeding a distribution circuit for a domestic property CU, but for a small CU for a log cabin or garage etc?

For a small CU in a log cabin discrimination is less of an issue I agree, and the implications of a lack of discrimination are unlikely to be much.
However it is better, in my opinion, to design and install to the highest possible standard.

Also this particular installation appears to be being done especially to please an NIC assessor so following the book to the letter may be sensible.

 

[Midwest]

Why not.

Its very difficult to get proper discrimination between MCB's so when a switch fuse can be used, its better all round.

Most people avoid this option because its far more expensive.

Thanks for that. I get the discrimination thing. But in most cases, I've seen garage CU's supplied from an mcb in main CU. Its recommended by various members on here as a default way of supply, when someone seeks advice on supplying garage, shed, office CU's etc. In reality, I can't see a customer being happy, with a switch fuse put along side their CU in the hallway, not withstanding it would be easier to achieve that sort after discrimination.

 

[Midwest]

For a small CU in a log cabin discrimination is less of an issue I agree, and the implications of a lack of discrimination are unlikely to be much.
However it is better, in my opinion, to design and install to the highest possible standard.

Also this particular installation appears to be being done especially to please an NIC assessor so following the book to the letter may be sensible.

Just that most domestic designs would follow the MCB approach, I don't think the assessor would be too critical of such a design?

 

[Octopus]

Just that most domestic designs would follow the MCB approach, I don't think the assessor would be too critical of such a design?

Critical no, but they should be asking about the different ways to do such an installation.

As I previously commented, cost is almost certainly the "driver" - metal clad switch fuses don't come cheap!

 

[Midwest]

Critical no, but they should be asking about the different ways to do such an installation.

As I previously commented, cost is almost certainly the "driver" - metal clad switch fuses don't come cheap!

I'm thinking something like this in the hallway;


Then adding this;

 

[Richard Burns]

I'm thinking something like this in the hallway;
View attachment 41732

Then adding this;

View attachment 41733

If there are already five CUs in the hallway one more switch fuse wont make a difference.

A fuse carrier in the CU (if they are available) would be a neater solution, but there are not many makes readily available. You may also then come up against different manufacturers in one CU!.