Split Concentric as a submain

[frontier219]

Ahhh, I see, I was trained under the 17th. So presumably he has either been misinformed or has got the wrong end of the stick. I have always assumed it would be treated similarly to T+E, but from what you say it could have been used in the same way as a SWA pre 17th ed?

 

[frontier219]

Why are you limiting your available supply to 63A ?

Your SF needs to be within 3m of the incomer/meter, this is to satisfy the DNO by not relying on their service fuse, you can use an 80A SF to fulfil this requirement, a 63A SF won't discriminate with the DNOs 80A fuse anyway.

I have to admit I wasn't aware of this, I may as well use an 80A fuse. I had assumed that discrimination would still be an issue. Thanks!

 

[Leesparkykent]

I have to admit I wasn't aware of this, I may as well use an 80A fuse. I had assumed that discrimination would still be an issue. Thanks!

The Rule of Thumb is "An upstream fuse will discriminate with downstream fuse of half it's rating."

 

[frontier219]

Hmm. This isn't something I was ever taught. So if I have a 40A Submain DB, does this mean that I can only have 20A circuits fed from it?

 

[spark 68]

The Rule of Thumb is "An upstream fuse will discriminate with downstream fuse of half it's rating."

True, but we are not trying to discriminate here, it is only to satisfy the DNO, they don't like you relying on their service fuse past about 3m, I believe it is also so they can guarantee their Ze figure, they have to draw the line somewhere as to what they will accept, the 3m rule seems to be about being reasonably practical in this regard, after your SF is your problem so to speak .

 

[Leesparkykent]

Hmm. This isn't something I was ever taught. So if I have a 40A Submain DB, does this mean that I can only have 20A circuits fed from it?

No lol

 

[Leesparkykent]

True, but we are not trying to discriminate here, it is only to satisfy the DNO, they don't like you relying on their service fuse past about 3m, I believe it is also so they can guarantee their Ze figure, they have to draw the line somewhere as to what they will accept, the 3m rule seems to be about being reasonably practical in this regard, after your SF is your problem so to speak .

Totally agree, I was just pointing it out lol

 

[frontier219]

No lol

Good! Don't scare me like that! Haha

 

[Leesparkykent]

Good! Don't scare me like that! Haha

Sorry haha

 

[davesparks]

Hmm. This isn't something I was ever taught. So if I have a 40A Submain DB, does this mean that I can only have 20A circuits fed from it?

No, it means that a fuse greater than 20A will not discriminate with the submain fuse, so you would need to select an alternative OCPD for the final circuit which does discriminate.