Rewiring conduit

[martinxxxxxx]

Hi I have been called to an old couples flat and they have metal conduit, they also have storage heating supplied in a radial from a wylex 30A fuse. It looks ike it is only 2.5mm singles, and as they have 3 off 1Kw and want to add a 3Kw to this. It seems to me that the wiring needs to be changed to 4mm. I am a bit worried about using the exsisting singles to pull new wires through. Please can you give me any advice about doing this. I have never rewired conduit before, so pardon me if this comes across a bit green.

Martin

 

[Sintra]

Hi I have been called to an old couples flat and they have metal conduit, they also have storage heating supplied in a radial from a wylex 30A fuse. It looks ike it is only 2.5mm singles, and as they have 3 off 1Kw and want to add a 3Kw to this. It seems to me that the wiring needs to be changed to 4mm. I am a bit worried about using the exsisting singles to pull new wires through. Please can you give me any advice about doing this. I have never rewired conduit before, so pardon me if this comes across a bit green.

Martin

Leave just one of the original singles in the conduit tape new cables on and pull through. Should be ok if you don't have many bends to go round.

 

[jimmyjazz]

I'd strip the ends of the singles & twist them together, then bind with tape before pulling. Make sure you keep the connection small.

 

[martinxxxxxx]

This is where I am worried, we go up, then along then right left then down. Also there are other cables in the conduit and the earth ones seem to be covered in white cloth as a sheath.

The cable has 7 strands of about 0.4mm but I don't know the rating and it was made by Enfield Standard cables.

Martin

 

[jimmyjazz]

Are there any inspection covers on route?

 

[martinxxxxxx]

When pulling new cables with old I normally crimp all three strands (on t+e) at different places then tape the lot up.

But I am worried about the crimps snagging on the internals of the conduit.

Also getting caught up with other wiring in there.

Wish i could be sure of the siz of the existing wiring, it should have always been 4mm it just does not look it.

Martin

Are there any inspection covers on route?

Nope

 

[Des 56]

The first thing to do would be to find out if you have movement by pulling one of the cables ,ideally an earth wire
Strip the earth cable and a new piece of cable for about 3 inches each.
Make an hangmans noose of the one,then thread the other through and twist it firmly,apply tape to stop any snagging
The joint should end up no bigger than the cable you are pulling out
Apply lots of fairy liquid and get someone to feed the one end in, whilst you pull on the other side

When you are confident of good movement pull the other cores out ,then pull some lenhth through on the tied cable, taping new ones on as you puill in, whilst applying lots of liquid
If the cable gets caught on a bend,resist trying to force it past by pulling back and forth until it gets past the probable bend

If they are corded cables ,they will be a lot harder to pull out than the new ones to pull in so,
Be confident whilst trying to avoid snapping the tied on cable joint, and you will be ok I'm sure

 

[Sintra]

This is where I am worried, we go up, then along then right left then down. Also there are other cables in the conduit and the earth ones seem to be covered in white cloth as a sheath.

The cable has 7 strands of about 0.4mm but I don't know the rating and it was made by Enfield Standard cables.

Martin

I wouldn't chance trying to pull 3 x 4mm singles into a conduit with existing cables in, especially with the amount of bends you mention. You have a high chance of damaging the existing cables.

 

[benji]

do we know what size the conduit is ,is it imp. or metric ,how many bends/sets,how many cables in conduit at present and how many cables will there be when you finish?

yours benji

 

[xraytek]

The cable has 7 strands of about 0.4mm but I don't know the rating and it was made by Enfield Standard cables.

Martin

If you have one of these you could measure the diameter of a single strand and calculate CSA.
I calculate using 0.79 x D x D x number of strands as its simpler than pye.

Once you know the CSA you could compare it against the charts in the BRB

 

[Davey101]

Get some 'yellow 77', or similar cable pulling lubricant, basically the same as using washing up liquid. It will make a HUGE difference to how well cables pull.