Inserting pulling metal wires in existing empty conduit

[Cobul]

Inserting wires in existing empty conduit

There is an empty PVC conduit size 1.5748" (40mm) in the main entrance panel. It was built around 8 years ago. There is metal wire (see picture above) inside the conduit to pull the main electrical wires from the inside or outside. Is there any technique the electrician can successfuly use to insert the metal wire?

And usually what maximum electrical wire size can fit the empty PVC conduit size 1.5748" (40mm). 2 Live plus one ground wire. Will apply full permit. Don't worry. Just want to know if the conduit can still be used. Thanks.

 

[Tom.G]

"Pulling" is usually done with a "fish tape." This is a ribbon of tempered, springy, Steel that can be pushed thru the conduit. For heavier (or many) wires, as you have, the fish tape is then used to pull a rope thru. The rope is then used to pull the wires.

The photo you show seems to be Aluminium wire. That may work if the conduit is a straight run, but trying to push it around elbows or thru couplings can be a problem, it isn't stiff enough and when it hits an obstacle it stops. Then you try pushing harder and it bends somewhere in the middle and piles up there.

My handy pocket reference says 5 #2 conductors will fit in that conduit, however I have learned not to rely on that reference, it has too many errors. Still, it seems like there is plenty of room. I'm expect the permit folks will flag anything they don't like.

Cheers,
Tom

 

[Baluncore]

Inserting wires in existing empty conduit

Make a small soft ball of cotton wool, that will be just less than the size of the conduit. Gently wind a thread around the ball without tension, make sure the cotton ball stays shaped like a sphere. When a sufficient length of thread has been wound onto the ball, cut the thread and tie off the tail at one end of the conduit. Place the ball in the conduit.

Go to the other end and connect a vacuum cleaner to the conduit. The ball will be pulled through, laying the thread in the conduit as the cotton ball rolls along. Use the first thread to pull a string, then a wire, until you can pull the cables.
You might need to pull another wire in the future, so remember to pull a string into the conduit with the cables.

Use the vacuum cleaner when no one is watching, when they ask, tell them you have a pet mouse called Benjy, that you taught to run cables.

 

[Cobul]

"Pulling" is usually done with a "fish tape." This is a ribbon of tempered, springy, Steel that can be pushed thru the conduit. For heavier (or many) wires, as you have, the fish tape is then used to pull a rope thru. The rope is then used to pull the wires.

The photo you show seems to be Aluminium wire. That may work if the conduit is a straight run, but trying to push it around elbows or thru couplings can be a problem, it isn't stiff enough and when it hits an obstacle it stops. Then you try pushing harder and it bends somewhere in the middle and piles up there.

My handy pocket reference says 5 #2 conductors will fit in that conduit, however I have learned not to rely on that reference, it has too many errors. Still, it seems like there is plenty of room. I'm expect the permit folks will flag anything they don't like.

Cheers,
Tom

I read that "To calculate conduit fill:

1. Get the 40% area value from the table corresponding to the type of conduit you're using (Table 4).
2. Get the approximate area value for the size conductors you're using (Table 5).
3. Divide the 40% conduit area by the conductor area, to determine the number of conductors allowed.
NOTE: When calculating conduit fill, if the calculation results in a decimal of 0.8 or larger, you can round to the next whole number.

EXAMPLE:
- 1/2" Schedule 40 PVC 40% fill = 0.114 in².
- 12 AWG THHN conductor = 0.0133 in².
0.114 in² / 0.0133 in² = 8"

1. No problem with that. But let's take the case of AWG 4. In this calculator. AWG 4 corresponds to 21.15 mm^2 cross sectional area. AWG to mm/mm2 | Gauge to mm conversion (rapidtables.com)

But in Table 5. AWG 4 corresponds to 53.16mm^2. There are 2 kinds of area? One cross section of the whole cable. The latter in table 5 is area of what?

2. How long can a 1 1/2 (40mm) PVC conduit still work on fish tape? The conduit length from outside to inside is about 100 feet or 30 meters.

3. If the conduit underground has water inside, how do you think it would affect existing system? Recall many buildings have underground pvc conduits and who knows if many are cracked already.

4. Lastly, AWG 4 can carry 75 A for THHN 75C. If you put 2 AWG 4 pairs from main breaker to inside, the Ampere capacity would become twice, or 150A? Or still 75A? Not that I'd do this. But just thinking how the electrons can traffic themselves and move down 50% each path.

Thank you!

 

[Tom.G]

1. No problem with that. But let's take the case of AWG 4. In this calculator. AWG 4 corresponds to 21.15 mm^2 cross sectional area. AWG to mm/mm2 | Gauge to mm conversion (rapidtables.com)

But in Table 5. AWG 4 corresponds to 53.16mm^2. There are 2 kinds of area? One cross section of the whole cable. The latter in table 5 is area of what?

That calculator has a problem. It always shows the same area regaardless of the wire size I enter.

2. How long can a 1 1/2 (40mm) PVC conduit still work on fish tape? The conduit length from outside to inside is about 100 feet or 30 meters.

Don't know, ask the guy that will be installing it.

3. If the conduit underground has water inside, how do you think it would affect existing system? Recall many buildings have underground pvc conduits and who knows if many are cracked already.

If you expect it to get wet, consider insulation for underground (direct) burial, if I recall correctly it wil be UG style rather than THHN.

4. Lastly, AWG 4 can carry 75 A for THHN 75C. If you put 2 AWG 4 pairs from main breaker to inside, the Ampere capacity would become twice, or 150A? Or still 75A? Not that I'd do this. But just thinking how the electrons can traffic themselves and move down 50% each path.

I've seen it done when there is not a wire size made for the current, but a single conductor is cheaper if available.

 

[Cobul]

That calculator has a problem. It always shows the same area regaardless of the wire size I enter.

Maybe you are using incompatible browser? It always works for me. Let's just use existing table then.

Let's take the case of AWG 4. In the first table or standard you can find anywhere. AWG 4 corresponds to 21.1mm^2 cross sectional area. But in Table 5. AWG 4 corresponds to 53.16mm^2. There are 2 kinds of area? One cross section of the whole cable. The latter in table 5 is area of what?