Split Concentric as a submain

[frontier219]

Hi All,

Having a little discussion with my old man over a job. The job is a domestic property, the CU is around 7 metres in cable length from the meter. There is a switch fuse around 4m from the meter, in a cellar. However, the tails are run very shoddily in an old bit of water pipe and then hanging across the ceiling. We have suggested ripping the whole lot out and running a new submain in, with an isolator at the mains. We are deciding what cable to use. I have suggested split concentric, as it is smaller and easier to run than SWA. However, my dad seems to think split concentric cable should not be used in this way, as he 'heard something about it a few years back'. We can't find anything definitive on the subject so I wondered if anyone on here could give us a bit more of a clue?

Cheers,

Dan

 

[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.

 

[frontier219]

Having scratched my head for a minute, I'm with you now. I was briefly confused before I had a quick read up! Have to say, discrimination is something that I should've learned more about at college. Not a well-taught subject for me, that.

 

[spark 68]

Having scratched my head for a minute, I'm with you now. I was briefly confused before I had a quick read up! Have to say, discrimination is something that I should've learned more about at college. Not a well-taught subject for me, that.

It is unlikely you would be able to get full discrimination in domestic anyway, partial at best, I have seen a faulty cable on a table lamp fitted with a 5A plug fuse trip out the 32A MCB supplying the RFC.

 

[frontier219]

Not a bad shout, but I personally think concentric looks neater. I'm also looking at using it in a Nursing home I am quoting for. Having done a bit more research, I think my dad may have been getting confused between concentric and split concentric. However, I'm not that familiar with the stuff so I'd like to make sure it can be used. I'm also currently assuming that for current carrying capacity, table 4D2A in the BGB would be used. Can anyone confirm this?

Just as a side-note, before the conversation drifts too far, can anyone confirm this for me? I can't find anything specifically mentioning split concentric.

 

[spark 68]

Just as a side-note, before the conversation drifts too far, can anyone confirm this for me? I can't find anything specifically mentioning split concentric.

You might be better off using the cable manufacturers data for the cable you are planning on using, this often gives more favourable results than the generic tables in 7671.

 

[Engineer54]

If you have never terminated a Split Concentric cable before, then use a SWA cable. I have rarely seen a split Concentric terminated correctly, nine times out of ten they end up looking like a pig ear or as if amateurs been at work. Plus the fact that it is unlikely that you'll get the termination into a typical switch fuse using a gland.

To stand any chance of making off a neat professional end to this cable a heat shrink 3 spout cable breakout and heat shrink tubing is required for the bare earth conductors....

 

[GB.Kayak]

If you have never terminated a Split Concentric cable before, then use a SWA cable. I have rarely seen a split Concentric terminated correctly, nine times out of ten they end up looking like a pig ear or as if amateurs been at work. Plus the fact that it is unlikely that you'll get the termination into a typical switch fuse using a gland.

To stand any chance of making off a neat professional end to this cable a heat shrink 3 spout cable breakout and heat shrink tubing is required for the bare earth conductors....

... in our times ... it probably was 'amateurs been at work'!

 

[frontier219]

If you have never terminated a Split Concentric cable before, then use a SWA cable. I have rarely seen a split Concentric terminated correctly, nine times out of ten they end up looking like a pig ear or as if amateurs been at work. Plus the fact that it is unlikely that you'll get the termination into a typical switch fuse using a gland.

To stand any chance of making off a neat professional end to this cable a heat shrink 3 spout cable breakout and heat shrink tubing is required for the bare earth conductors....

I totally appreciate your comments, but I must respectfully disagree. Thank you for the advice on how to do the termination properly though. I understand your comments are borne out of a respect and passion to do this trade properly. I share that passion - I would rather take twice as long on a job and get it right for the same money than throw things in half-arsed (In fact, I left one of my employers curing my apprenticehip at the risk of losing out because I didn't feel the education they were giving me was up to scratch - I ended up being nominated for Apprentice of the Year). However, I do have to actually have a first go at something in order to know how to do it correctly. As it stands, this job is for a family member. There is not a lot of profit in it, but there is also no time pressure, which gives me a chance of learning how to do it correctly in my own time.

 

[Engineer54]

I totally appreciate your comments, but I must respectfully disagree. Thank you for the advice on how to do the termination properly though. I understand your comments are borne out of a respect and passion to do this trade properly. I share that passion - I would rather take twice as long on a job and get it right for the same money than throw things in half-arsed (In fact, I left one of my employers curing my apprenticehip at the risk of losing out because I didn't feel the education they were giving me was up to scratch - I ended up being nominated for Apprentice of the Year). However, I do have to actually have a first go at something in order to know how to do it correctly. As it stands, this job is for a family member. There is not a lot of profit in it, but there is also no time pressure, which gives me a chance of learning how to do it correctly in my own time.

Then best of luck trying to get that termination into a fuse switch, i know that i wouldn't even attempt it. Oh and remember that once the sheathing has been removed the inner conductors that are insulated, are no longer Insulated and sheathed or Double Insulated.

The correct way to learn how to terminate any cable that you are not familiar with, is to watch and learn from a mentor, not to go in head first with the ''Have a Go'' attitude.

 

[frontier219]

Then best of luck trying to get that termination into a fuse switch, i know that i wouldn't even attempt it. Oh and remember that once the sheathing has been removed the inner conductors that are insulated, are no longer Insulated and sheathed or Double Insulated.

The correct way to learn how to terminate any cable that you are not familiar with, is to watch and learn from a mentor, not to go in head first with the ''Have a Go'' attitude.

Thanks, I appreciate the good luck.

It's easier said than done finding such a mentor, but nevertheless, thanks to your advice I will go in with my 'Have a Go' attitude with a couple of metres of split concentric with which to practice on in my shed before going for the real deal.

I do understand your attitude, but I have to learn somewhere.

 

[davesparks]

Thanks, I appreciate the good luck.

It's easier said than done finding such a mentor, but nevertheless, thanks to your advice I will go in with my 'Have a Go' attitude with a couple of metres of split concentric with which to practice on in my shed before going for the real deal.

I do understand your attitude, but I have to learn somewhere.

And what measure will you use to assess whether you have done it correctly or not?