pulling new wire in existing buries conduit for PV expansion

[solarken]

I am looking at expanding a PV system that was installed by a certain solar company that went bankrupt. The current system has a single pair of 10AWG THHN and an oversized 6AWG THHN ground in 70ft of buried 3/4 EMT. The installer/designer did this customer no favors by undersizing the array in the first place, then used small conduit and no spare conductors in the DC run. There is plenty of space on the garage roof for more PV. I usually use PVC for underground, and I would have used larger than 3/4 for this and/or pulled in one spare pair to make future expansion easier. I need to decide whether to add another pair of 10AWG conductors in the DC run or just add one string on the garage and utilize the existing capacity of the single pair.
Any thoughts on difficulty of pulling out the existing 2x10AWG + 1x6AWG gnd wiring and pulling in 4x10AWG + 1x10AWG gnd, with this buried 3/4 EMT? I am guessing it is filled with water.

 

[LarryFine]

Five #10s will fit in a 1/2" EMT, so there's plenty of space. It should be an easy pull unless the EMT has rusted out and collapsed. Pulling the existing wires back and forth should give you a good idea.

I would have used PVC.

 

[jaggedben]

Tell the customer you'll give it a try but if you can't do it then there will be a change order to dig a trench and do it properly?

 

[petersonra]

I have never heard of anyone using this type of solution but it seems like it ought to be adaptable to electrical systems.

 

[ggunn]

I have never heard of anyone using this type of solution but it seems like it ought to be adaptable to electrical systems.

It looks vaguely pornographic.

 

[LarryFine]

I have never heard of anyone using this type of solution but it seems like it ought to be adaptable to electrical systems.

 

[solarken]

Tell the customer you'll give it a try but if you can't do it then there will be a change order to dig a trench and do it properly?

Good idea.

 

[solarken]

Five #10s will fit in a 1/2" EMT, so there's plenty of space. It should be an easy pull unless the EMT has rusted out and collapsed. Pulling the existing wires back and forth should give you a good idea.

I would have used PVC.

I use the Southwire excel calculator generally and it sure seems more often than not when I use the minimum conduit size for pulls of any fairly decent length, I regret not up sizing at pull time.

 

[jaggedben]

I use the Southwire excel calculator generally and it sure seems more often than not when I use the minimum conduit size for pulls of any fairly decent length, I regret not up sizing at pull time.

Yup. As they say, the code is not a design manual. Which means it's minimums don't take into account the cost of labor.

 

[LarryFine]

I use the Southwire excel calculator generally and it sure seems more often than not when I use the minimum conduit size for pulls of any fairly decent length, I regret not up sizing at pull time.

I wasn't suggesting using 1/2", just using it to say the 3/4" is plenty.

 

[don_resqcapt19]

I have never heard of anyone using this type of solution but it seems like it ought to be adaptable to electrical systems.

I think it would work on PVC. I know that those types of systems have been used on PVC, clay tile, and cast iron piping. I don't think they would work on rigid and maybe not on EMT as they require that the original pipe be one that will shatter or break with the pressure. Also expect that the smallest version would be for pipes larger than two inch.

 

[pkhosravani]

Buried EMT??? Yikes, sounds like a Powerhome solar project.

 

[petersonra]

I think it would work on PVC. I know that those types of systems have been used on PVC, clay tile, and cast iron piping. I don't think they would work on rigid and maybe not on EMT as they require that the original pipe be one that will shatter or break with the pressure. Also expect that the smallest version would be for pipes larger than two inch.

I think I have seen some youtube videos of pipe bursting of some pretty small pipes, maybe 3/4" inch.

 

[solarken]

Buried EMT??? Yikes, sounds like a Powerhome solar project.

It is. They were terrible. nylon tie wraps holding the PV wires instead of SS clips, oversized ground wire on every array I have ever seen from them, generally undersized arrays and overpromised production.