Doubling up 2.5 T&E for workshop electrics

[Evans Electric]

Well Avo, according to the BRB Table 4A2 you can indeed run unarmoured cables in a conduit underground.

I suppose running a parallel pair is an option but I'd say use the 2.5 as a drag and pull in a 4mm .

Still have to say that I've never considered anything other than armoured cable buried direct in the ground .

 

[Avo]

Besides, if PVC is prone to moisture ingress than surely swa PVC type and t&e both fall foul regarding that. A metal sheath around the cable protects the cable from spade attack, certainly doesn't from mini digger attack. T&E down this conduit would bounce a spade attack somewhat, probably leaving a big dent in need or repair, but you wouldn't go all the way into the wire with one strike at least.

I know health and safety is a bit mental these days but seems like many folk are only too keen to agree with their questionable regs.

---------- Post Auto-Merged at 20:21 ---------- Previous post was made at 20:20 ----------

Well Avo, according to the BRB Table 4A2 you can indeed run unarmoured cables in a conduit underground. I suppose running a parallel pair is an option but I'd say use the 2.5 as a drag and pull in a 4mm .

Still have to say that I've never considered anything other than armoured cable buried direct in the ground .

I agree, I though about that, problem is if I try pulling saw through and it gets stuck, I then have no electric cable and I'm flamuxed. Suppose I could rope up the t&e in case I need to pull it back, all a bit too tight though.

 

[ProDave]

I think we have to be practical here. If the bends are too tight to pull another cable through, then go with what you have, the two cables in parallel.

I take it you are fitting a consumer unit in the workshop?

All I would say is due to the lack of armour, feed the house end via an RCD or rcbo, which means you won't need another RCD in the workshop. Because of that, consider an emergency light fitting if being plunged into darkness when it trips is a hazard.

 

[philbas]

And now onto the question of the earthing system

 

[Evans Electric]

I see where you are coming from now, so if you can't withdraw the original cable with a new one attached you may as well scrap the run and lay an armoured in it's place .

 

[Avo]

I think we have to be practical here. If the bends are too tight to pull another cable through, then go with what you have, the two cables in parallel. I take it you are fitting a consumer unit in the workshop?

All I would say is due to the lack of armour, feed the house end via an RCD or rcbo, which means you won't need another RCD in the workshop. Because of that, consider an emergency light fitting if being plunged into darkness when it trips is a hazard.

Practical, yes.

Well I was going for a CU in the workshop with a 30ma RCD but placing a time delay rcd on the house end. Need various protections on the workshop end.

Nothing in workshop could do me harm in the event of lights out, well maybe my soldering iron if I happen to sneeze.

---------- Post Auto-Merged at 20:45 ---------- Previous post was made at 20:44 ----------

And now onto the question of the earthing system

Joking aside the loop impedance is fine, I've checked it. First thing I did

---------- Post Auto-Merged at 20:46 ---------- Previous post was made at 20:45 ----------

I see where you are coming from now, so if you can't withdraw the original cable with a new one attached you may as well scrap the run and lay an armoured in it's place .

Cant, it's partially under the hallway of the building :/

 

[Badger]

@ badger T-n-c-s is PME , just saying lol

maybe this will help explain things sb

PME (truePME) = earthing staked at the edge of the properties connection in the road.

TNCS = earthing utilising the neutral supply conductor back to the substation, or main supply generator/transformer which the neutral is connected to star point of transformer and earth staked using either rods, earth mat or earthing tape.

TNS = earthing is seperate through the cable sheath back to the substation and coinnected to the star point of the transformer which is staked to earth/using either rods or mats or earth tape

tt = earthing is provided on site within the properties boundary and not connected in way direct to the transformer/substaion supply, only through the earths mass. this uses either rods (normally) or earthing mat, or earth tape. laid in the ground.

hope this helps to everyone.

View attachment 2260

 

[SLIPSHOD & SLAPDASH]

How about connecting them as 2 seperate circuits, both with 16 or 20A Rcbo's (haven't worked out volt drop etc) Fit a FCU in the shed with a 3A fuse off one of the circuits for the lights

 

[PC Electrics]

Reading table 4A2, it does say conduit or cable ducting. It does not say "any old bit of scabby plastic pipe from down the builders yard"

I'd be digging up the ends to remove the bends and then pulling armoured through whats left. Or else digging it all up to put armoured in properly.

The tine of a garden fork could quite easily pierce plastic pipe IMO. I wouldn't trust my life to it.

 

[SLIPSHOD & SLAPDASH]

Reading table 4A2, it does say conduit or cable ducting. It does not say "any old bit of scabby plastic pipe from down the builders yard"I'd be digging up the ends to remove the bends and then pulling armoured through whats left. Or else digging it all up to put armoured in properly.

The tine of a garden fork could quite easily pierce plastic pipe IMO. I wouldn't trust my life to it.

It could be the correct pipe as installed for supplies. That has 'Danger electricity' printed on it and is quite robust

 

[ProDave]

Reading table 4A2, it does say conduit or cable ducting. It does not say "any old bit of scabby plastic pipe from down the builders yard"

He did say it was black which is the correct colour for a duct containing an electric cable.

When I built this house, I bought some 2" duct pipe from the builders merchant. It was black, with loose fitting joints (i.e not dead tight like water pipe) and for bends you bought a "hockey stick" which was a bend and about a metre of pipe.

The DNO were happy to feed their concentric cable through it, so that's good enough endorsement for me to believe it's okay for electric cables.

EDIT

Don't you just love the professionalism of the utilities. The first to lay in the supply to our site was the electric. So they dug up the road and laid the same sort of 2" black duct under the road for the supply cable.

Then along comes the water. To save digging up the road again, they thread the water pipe through the same duct.

Then along comes BT, and guess where their cable goes?

So all 3 services under the road in one bit of 2" ducting. And we have to segregate them. : headbang

 

[SLIPSHOD & SLAPDASH]

That sounds the stuff i am talking about. Its made from some sort of nylon, really difficult to damage bt impact but you can cut it with a hacksaw

 

[Avo]

That sounds the stuff i am talking about. Its made from some sort of nylon, really difficult to damage bt impact but you can cut it with a hacksaw

That's the stuff by the sound, not easy to damage at all.

I did think about running the two cables as separate circuits from house, but then I thought that its likely that one of the circuits won't be doing much most of the time, so it's probably better to have the load distributed over the parallel t&e, even though they won't be entirely balanced.

 

[steptoe]

I'd stick them as a parallel radial on a 32A depending on voltdrop.

we still dont know your earthing system(or did I miss that bit?),

you simply telling us your Z is OK really isnt what we need to know.

---------- Post Auto-Merged at 22:43 ---------- Previous post was made at 22:41 ----------

Do elaborate

Very good explanation herehttp://www.talk.electricianforum.co....angements.html

at least when the link works

The first sticky in the student and learning forum.

try this http://www.talk.electricianforum.co.uk/student-learning-zone-c-g-2330-levels-2-3-c-g-2381-c-g-2391-other-co/15480-simplified-earthing-arrangements.html

 

[Apache]

I suppose running a parallel pair is an option but I'd say use the 2.5 as a drag and pull in a 4mm .

But 2X2.5mm is bigger CSA than 4mm! If you double up at both ends you have 5mm2 of copper.

 

[Evans Electric]

He says he can't pull them in though , Patche . Or have I read it wrong !!

 

[Apache]

He says he can't pull them in though , Patche . Or have I read it wrong !!

He already has two by 2.5mm T&E. You suggested using them to pull a 4mm T&E through. What I can't see is why you'd do that as two 2.5mm T&E has a greater cross sectional area and current carrying capacity than a single 4mm T&E.

To my untrained brain that doesn't make any sense. Is it just more 'conventional'?

 

[Evans Electric]

Avo, what is your design current for the garage , what do you expect to plugging in ? I'm missing something here.

'Cos when you say you thought of running two parallel feeds from the house ,where whould you be running them ? And why would they be unbalanced ?

If you're looking at a 20A load ,which is a lot for a garage , you'll be dropping 5.7V .

---------- Post Auto-Merged at 23:14 ---------- Previous post was made at 23:09 ----------

Where did he say 2 X twin /earths I thought he meant 2 - 2.5mms as in a Brown and a Blue in other words a radial.

If there are two 2.5 T/Es in the conduit then yes, where is the problem , are they not already connected in parallel ?

Edit .

Right I misread the OP , what a part, he already has two cables , sorry Patche , wrong end of stick . So wheres the problem??

 

[Apache]

So wheres the problem??

I've been asking that since #5

 

[philbas]

Facts as I see,

2 * twin and earth 2.5mm

In a conduit/pipe buried 2ft under the surface, to provide power to a shed, I assune from this it is not likely to be subject to a plough anytime soon.

Whats the problem?

Lets move onto the earthing type