Ring Too Long.

[Octopus]

I do have a self certified friendly spark, I can get his verdict on my work, I did get him to look at the job before I started... I wasn't impressed by his approach... Quick & easy & I wasn't going to start drilling structural joists just for a shorter route..

If I chock the whole place out should be a two minute job to drop a meter across them though.

Many thanks to everyone who's taken an interest in my posts..

He was probably looking at the job and looking at the most cost effective way to do it and hence his ideas - not many customers are happy to spend more than necessary.

 

[Engineer54]

Originally Posted by Jack of all
I do have a self certified friendly spark, I can get his verdict on my work, I did get him to look at the job before I started... I wasn't impressed by his approach... Quick & easy & I wasn't going to start drilling structural joists just for a shorter route..

If I chock the whole place out should be a two minute job to drop a meter across them though.

Many thanks to everyone who's taken an interest in my posts..

Doesn't say much for the size of your structural joists if you're worried about drilling a hole for cables are going to weaken them!! lol!!

 

[Jack of all]

I have spend a long time researching this project, before deciding to do it all myself.
I downloaded a PDF on drilling structural timbers & it lists limits to hole sizes & notches as well as their permitted positions. But first of all it say if drilling them can be avoided in any way then it should be.

Still no feedback on feeding a ring at it's central point with an extra cable from the same mcb ???

 

[Pete999]

I have spend a long time researching this project, before deciding to do it all myself.
I downloaded a PDF on drilling structural timbers & it lists limits to hole sizes & notches as well as their permitted positions. But first of all it say if drilling them can be avoided in any way then it should be.

Still no feedback on feeding a ring at it's central point with an extra cable from the same mcb ???

Well it wont be a ring then will it?

 

[telectrix]

Still no feedback on feeding a ring at it's central point with an extra cable from the same mcb ???


​that is a complete NO NO. how's that for feedback?

 

[Leesparkykent]

I have spend a long time researching this project, before deciding to do it all myself.
I downloaded a PDF on drilling structural timbers & it lists limits to hole sizes & notches as well as their permitted positions. But first of all it say if drilling them can be avoided in any way then it should be.

Still no feedback on feeding a ring at it's central point with an extra cable from the same mcb ???

if you are willing to put in a extra cable, you may as well put in two cables and split it in to two rings.

 

[Octopus]

I have spend a long time researching this project, before deciding to do it all myself.
I downloaded a PDF on drilling structural timbers & it lists limits to hole sizes & notches as well as their permitted positions. But first of all it say if drilling them can be avoided in any way then it should be.

Still no feedback on feeding a ring at it's central point with an extra cable from the same mcb ???

Consult your BYB?

 

[Engineer54]

Originally Posted by Jack of all
Still no feedback on feeding a ring at it's central point with an extra cable from the same mcb ???



​

Right, with thoughts/intentions like this, it's time to bring in your qualified electrician friend and leave the lot to him. As far as i'm concerned you're nowhere near competent to be carrying out this installation no matter how much you ''think'' that you are!!

 

[gutterball]

You downloaded a PDF? Do you have the correct current reg's books or have you just been googling how to do the job.

 

[Jack of all]

The whole point in me asking the question, is that I'm competent enough to know when somethings going to be at it's limits.
I do know it would work absolutely fine, but in the interests of being 100% I'll be pulling off some capping, adding 2 new long cable runs & ending up with 4 rings on a 2 bedroom place....

I was trained properly & time served, all a long time ago now, even have a city & guilds silver medal among-st other awards. I have no illusions over my capabilities but have been glad to run ideas by people with more recent "by the book" experience.

Many thanks again...

 

[Welchyboy1]

Options are really

like suggested, run 2x extra Legs and split into 2x 32a ring final, split existing to 2x 16a or even 20a radial circuits if needed
or may well be fine, the loading shouldnt be a problem with 2x 16a rads

You need to do a few tests to acertain your options but offthe top of my head 150m of ring circuit will give you an r1+r2 of approx .6 to .8 ohms(without having the bible to hand) so with ze you should be ok for max zs on a 32a mcb, just volt drop to check, and with what your suggesting you loading shouldnt be anywhere near 32a

i would unofficially say, dont sweat it!

 

[Jack of all]

You downloaded a PDF? Do you have the correct current reg's books or have you just been googling how to do the job.

You're right I don't have the book..... And understanding the flow of electrons won't tell me how many capping nails are required for a 2M length.....

 

[TJ Anderson]

Agree with Welchyboy. You will get sub 1.00 ohm Zs. If it was a kitchen on that ring then maybe, but with the loadings you are talking about (couple of TV's, lamps and the hairdryer now and again), it will be fine.

 

[Jack of all]

i would unofficially say, dont sweat it!

Thanks...... I really do care a bit too much what building control will say...... I've no idea who will be checking my work, or how critical they may be..... All my cable clips are nails down & 200mm apart.... it all looks good ... not as good as a well ordered control panel but still neat..
This isn't my usual work, but my own place one day, so got to be right...

 

[Engineer54]

I have spend a long time researching this project, before deciding to do it all myself.
I downloaded a PDF on drilling structural timbers & it lists limits to hole sizes & notches as well as their permitted positions. But first of all it say if drilling them can be avoided in any way then it should be.

Still no feedback on feeding a ring at it's central point with an extra cable from the same mcb ???

If this is an old barn, the joist sizes will far exceed anything like the sizes now being used in modern house /flat construction....

Well accordingly, it very much sounds the reason why and how you have ended up with a 150m ring circuit. Maybe if you had listened to your electrician friend, you wouldn't be in your present situation...

 

[Jack of all]

If this is an old barn, the joist sizes will far exceed anything like the sizes now being used in modern house /flat construction....

Well accordingly, it very much sounds the reason why and how you have ended up with a 150m ring circuit. Maybe if you had listened to your electrician friend, you wouldn't be in your present situation...

The barn had 'A' frame & purlin roof, this left poor headroom & my son is 6'8", so I reroofed it with new raised tie trusses, all new 47mm X 200mm .... The only downside is it's left me with no usable loft space, so altering wiring after the ceilings are up is impossible..
Hence the reasons for being so cautious over getting it right now..

Many thanks again.

 

[SJD]

If the RFC has 150m of 2.5mm2 T&E, this has a resistivity [L+N] of 18 mOhm/m (green OSG table F6).

So for 150m, r1 should work out at 1.35 Ohm, and r2 at 2.25 Ohm.
So (r1+r2)/4 works out at 0.90 Ohm.
Max permissible Zs for B32 MCB is 1.16 Ohm (from green OSG table B6).
So if Ze is under 0.26 Ohm, you'll be just OK with a B32 MCB.
Really you need to know Ze to decide if OK, as said near the start of this thread.

Don't know about where you are, but round here, building control will be more interested in the foundations and drainage than any electrics!

 

[HandySparks]

If the RFC has 150m of 2.5mm2 T&E, this has a resistivity [L+N] of 18 mOhm/m (green OSG table F6).

So for 150m, r1 should work out at 1.35 Ohm, and r2 at 2.25 Ohm.
So (r1+r2)/4 works out at 0.90 Ohm.
Max permissible Zs for B32 MCB is 1.16 Ohm (from green OSG table B6).
So if Ze is under 0.26 Ohm, you'll be just OK with a B32 MCB.
Really you need to know Ze to decide if OK, as said near the start of this thread.

Don't know about where you are, but round here, building control will be more interested in the foundations and drainage than any electrics!

I think you've included the correction for working temperature of conductors twice.

Table F6 shows mV/A/m at 70C, but table B6 is for conductor temperatures of 'ambient'. If you're going to use the table B6 temperature-corrected values for max permitted Zs, I think conductor resistances should be taken from table I1 (at 20C).

 

[SJD]

I think you've included the correction for working temperature of conductors twice.

Table F6 shows mV/A/m at 70C, but table B6 is for conductor temperatures of 'ambient'. If you're going to use the table B6 temperature-corrected values for max permitted Zs, I think conductor resistances should be taken from table I1 (at 20C).

Yes, you are right, I have corrected twice, sorry.
The resistance at ambient is about 15 mOhm/m (table I), so r1=1.13, and r2=1.87 at ambient.
Which gives (r1+r2)/4 as more like 0.75 Ohm at ambient.

 

[Jack of all]

Don't know about where you are, but round here, building control will be more interested in the foundations and drainage than any electrics!

I've known most of the building control team for years.... They're happy with me doing this whole project on a building notice. Underpining.. Sewage system.. Insulation.. New roof.. all no problem.. But Electrics I don't think that they even have an in house inspector, so quite an unknown alltogether.

I was told that there'd be a sort of interview to ascertain my competence in order to determine the level of inspection.... I'll have to wait & see..

My friend has offered a third party certificate on my works, but if I miss the building regs first fix inspection out & he's not available by the time I get past decorating & second fix then that'll leave me stumped.