Buried conduit: To swab or not to swab?

[Jon456]

In my previous post about wire pull problems, I was surprised to learn that several members replied that they would not swab buried conduits as a matter of practice, unless it was specifically stipulated in their contract. The reason I was surprised is because, at ~$100, a swab is not that expensive for a contractor bidding on large commercial jobs, and it doesn't really add any time to the job: the swab can be pulled through the conduit as the mule tape is pulling in the pull rope.

Whether or not it was stipulated in the contract, if I were the electrical contractor on our particular installation, I would have wanted to swab for no other reason than to make the pull easier, let alone minimize the risk of damage to the insulation and future warranty service. I think these images will show why...

The following illustration shows the relation between the distribution panel, the Christy box, and the conduits. The relative elevations in the diagram are correct, but the slope of the conduits is exaggerated because the actual distance between panel and box is 185 feet. It's important to note, however, that the conduits do slope downhill from the box to a low-point below the panel.

The Christy box was buried in the base of an earthen levee; outside the levee is a saltwater creek. Because our property is below sea level at high tide, we have a high ground-water table and intrusion of salt water into our soil. After fifteen years, ground water ingress had washed 12 inches of soil into the Christy box, depositing it in the bottom of the box and completely covering the conduit openings.

Christy box uncovered (some inside soil already dug away to expose top of conduit):

Detail inside Christy box:

After soil was removed:

Common sense dictates that at least some soil would have been washed into the downward sloping conduits. In the next photo, you can still see soil inside the openings of the conduits, even after cleaning out by hand.

Detail of conduit openings and feeders to distribution panel:

If you were the contractor on this job and you saw this, would you swab the conduits even if your contract didn't require it?

 

[Jon456]

I should have mentioned the following:

There are five conduits: four of the conduits each contained four 500 mcm aluminum XHHW feeders and one 1/0 aluminum EGC; the fifth conduit was a spare. We wanted to extract the existing feeders and EGCs out of the four conduits, and pull them back into two of the conduits. That would give us three open conduits to pull in additional new feeders for a different circuit.

 

[chris kennedy]

I should have mentioned the following:

There are five conduits: four of the conduits each contained four 500 mcm aluminum XHHW feeders and one 1/0 aluminum EGC; the fifth conduit was a spare. We wanted to extract the existing feeders and EGCs out of the four conduits, and pull them back into two of the conduits.

Did anyone do the math on this? Besides now having derating issues, if those are 4" sched 40 your over by .9in?.

 

[iwire]

I was surprised to learn that several members replied that they would not swab buried conduits as a matter of practice, unless it was specifically stipulated in their contract.

I will not answer your poll because of the way you set it up, basically you set it up so either you 'swab' the conduit or you are a hack.

I have no set rules, if we installed the conduits and they are still sealed up then no, I would not bother.

On the other hand if they looked like the ones in your pictures of course we would clean them up.

 

[Hv&Lv]

I will not answer your poll because of the way you set it up, basically you set it up so either you 'swab' the conduit or you are a hack.

I have no set rules, if we installed the conduits and they are still sealed up then no, I would not bother.

On the other hand if they looked like the ones in your pictures of course we would clean them up.

I would clean the conduits in this picture, as a matter of cost savings. I agree with you about cleaning depending on circumstance and conditions.
Go ahead and answer, the question is: Would you swab these conduits

 

[jwelectric]

I will not answer your poll because of the way you set it up, basically you set it up so either you 'swab' the conduit or you are a hack.

I didn?t answer because he seems to be trying to get people to agree that the way the contractor made the installation in his other thread was a non-compliant installation. In my opinion this is the first steps in not paying a bill and is trying to use this site as a foundation for doing so.

Removing the old conductors would set the precedence of whether or not to swab.

 

[plumb bob]

In this case I probably would swab the conduits. Like has been said above every situation is different. I would also carefully watch what comes out of the pipe as the wire was removed. Lots of water- well I would expect that and maybe i would run with it. Lots of dirt and mud would give me more incentive to swab. Also remember running a swab through the conduit may help clean it out but in no way guarantees the integrity of the conduit.

 

[jusme123]

I will not answer your poll because of the way you set it up, basically you set it up so either you 'swab' the conduit or you are a hack.

I have no set rules, if we installed the conduits and they are still sealed up then no, I would not bother.

On the other hand if they looked like the ones in your pictures of course we would clean them up.

I agree with iwire on this one, circumstances do play a part in the decision, especially if its your own work.

 

[cmreschke]

Did anyone do the math on this? Besides now having derating issues, if those are 4" sched 40 your over by .9in?.

This. It is 47.7 percent of conduit fill. Needs a 5 inch to comply. The op might not be concerned with that issue though, as ripping up the ground and just installing new conduits might have cost his boss even more. Also the same reason to pull out the old and reinstall it like it was new.

 

[don_resqcapt19]

...
If you were the contractor on this job and you saw this, would you swab the conduits even if your contract didn't require it?

If the pull box had not been opened at bid time, I would be asking for a change order to swab based on "unknown conditions". Cleaning those conduits to make sure there will be no damage to the new conductors as they are installed will take more than just swabbing out the raceway.

 

[Jon456]

Did anyone do the math on this? Besides now having derating issues, if those are 4" sched 40 your over by .9in?.

Yes, I did the math. The electrical contractor should have done the math, but he did not. He simply whipped out his Ugly's Electrical Reference** and stated it couldn't be done (this, after promising the owner during the bidding process that he could get the new feeders -- along with our existing feeders -- into these conduits). I had to assure him repeatedly that it could be done. Even the day before the pull, he was still questioning whether the fill ratio was correct, and asked me several times to double check my numbers. Since he is the electrical contractor hired to do the job (and he is also an electrical engineer), one would think he'd want to calculate the fill himself. But he never did.

I did not just look at the NEC tables. I did the math by hand, just to be sure:

500 mcm Alcan aluminum XHHW-2 phase conductors: 0.870" OD = 0.5945 sq in.
1/0 Alcan aluminum XHHW-2 EGC: 0.450" OD = 0.1590 sq in.

4" Sched 40 PVC: 3.998" Nominal ID = 12.554 sq in.

(8) 500 mcm aluminum phase conductors + (1) 1/0 aluminum EGC = 4.9150 sq in.

Fill ratio: 4.9150/12.554 = 39.15%

I derated our service from 1,200A to 1,000A by changing out the rating plug in the upstream OCPD.

Unfortunately, there's the nagging problem of the EGC: it's undersized, and thus a NEC violation. I stated emphatically that the 1/0 aluminum EGC was incorrect and a code violation. I wanted to replace it with 2/0 copper. But against my protestations, the electrical contractor convinced the owner that it was OK to re-use the existing 1/0 aluminum wire. That will be the subject of another thread.

Had we replaced the 1/0 aluminum EGC with the correctly-sized 2/0 copper as I recommended, the fill still would have worked:

500 mcm Alcan aluminum XHHW-2 phase conductors: 0.870" OD = 0.5945 sq in.
2/0 Southwire copper XHHW-2 EGC: 0.521" OD = 0.2132 sq in.

4" Sched 40 PVC: 3.998" Nominal ID = 12.554 sq in.

(8) 500 mcm aluminum phase conductors + (1) 2/0 copper EGC = 4.9692 sq in.

Fill ratio: 4.9692/12.554 = 39.58%


**Note: I didn't just assume the contractor "whipped out his Ugly's Electrical Reference" to check the fill; I saw him do it.

 

[cmreschke]

Unless I'm mistaken your one grounding conductor short. Your installing parrallel runs do you not also parrallel your grounds as well? Also I believe your group.d was not undersized for the original install as there were for of them and they were sized per the feeder size that they were pulled with.

 

[Jon456]

I will not answer your poll because of the way you set it up, basically you set it up so either you 'swab' the conduit or you are a hack.

I had two ways to go with this poll:

A) To ask if all existing buried conduits should be swabbed

B) To ask if these particular conduits (the ones pictured in this thread) should have been swabbed.

Upon re-reading my first paragraph in this thread, perhaps I should have chosen (A). But because I went with (B), I wrote the poll questions to reflect what actually occurred on our job.

On a Friday afternoon, we met with the contractor to discuss the wire pulling procedure that would occur the following day (Saturday). We had already uncovered the box and excavated the soil. The contractor had seen the interior of the box both before and after the soil was excavated, so he knew exactly what the conditions were. He assured the owner that he would pull a mandrel through each of the conduits to clear and test them for damage. After the meeting, the contractor asked me if I knew anyone who had a mandrel he could borrow. I called a couple of sources with no luck. I then called several local suppliers and found only one that had a 4" mandrel; I don't recall the price but it was in the $100 to $200 price range. Because it was already late in the afternoon, it was impossible to source the mandrel from any other supplier. I informed the contractor about the supplier, but he told me that his foreman was going to borrow one from somewhere.

Saturday morning, the contractor and foreman showed up on site with no mandrel, swab, or anything else. Remember, that we were going to pull eight existing 500 mcm feeders (plus EGC) out of two 4" PVC conduits and re-feed them into one. The fill ratio was 39.15%. There was clear evidence that soil had been washed into the conduits. And the contractor had told the owner that he would clean and check the conduits.

After pulling out eight of the sixteen wires, the contractor wanted to pull them back in without doing anything to clear the conduits. I insisted that they at least pull a rag through to wipe out any soil in the line. The contractor relented and we pulled the rag through. A lot of water and mud came out into the Christy box. I was at the other end of the pull (at the distribution panel), so I didn't see if any rocks came out.

The second pull of eight was done about a week later. Again, no mandrel or swab. The contractor was away on vacation, and the foreman decided pulling a rag through was unnecessary because the first pull went well the week before. They started the pull and eventually the wires got stuck. The foreman wanted to just keep pulling harder, but I managed to convince the other senior crew member on site (the carpenter, who was running the wire puller) to stop and pull the wires back out. After that, we swabbed the conduit with a rag and then successfully pulled the wire in.

That's why the second poll option is: "Take your chances"

 

[Jon456]

Unless I'm mistaken your one grounding conductor short. Your installing parrallel runs do you not also parrallel your grounds as well? Also I believe your group.d was not undersized for the original install as there were for of them and they were sized per the feeder size that they were pulled with.

I had some questions about this as well, partly because our contractor was giving us incorrect information and confusing us with improper terminology (e.g., he was calling our feeders "service entrance" conductors). So I posted a thread asking the same questions you're asking now.

In summary, only one EGC is required per conduit for the parallel conductors. However, per NEC 250.122(F), the EGC must be fully sized to the capacity of the upstream OCPD.

 

[Jon456]

I didn’t answer because he seems to be trying to get people to agree that the way the contractor made the installation in his other thread was a non-compliant installation. In my opinion this is the first steps in not paying a bill and is trying to use this site as a foundation for doing so.

Please read my reply in the other thread regarding your assertion that we're trying to avoid paying the bill. The contractor is getting regularly scheduled payments for his work. (I don't know if he's being paid weekly or biweekly or whatever... I'm not involved in the money side of this project. But I have seen the owner hand him some very big checks.)

The issues regarding these feeders are simple: we only want to know that the wires -- particularly their insulation -- were not damaged. I asked for industry standards and best practices because we may need to justify calling in a third-party to test the wires. While opinions are useful, they are just that: opinions (even if coming from the very experienced and informed members in this forum). The opinions have been enlightening, and at least one was even reassuring, but in the end they are of little practical use to us. I was hoping for actual references. Like this publication from Southwire: Installation and Application Guide for 600V Conductors (which, by the way, happens to support my position that the wire was pulled improperly).

If there is a problem with our feeders, then obviously the contractor will be liable for the labor and materials to replace the damaged conductors. There will not be any withholding of payment -- on this, or any other aspect of the job -- unless the contractor fails to meet his contractual obligations. Certainly no financial decisions would ever be made based on posted opinions made in this forum or any other Internet forums. To suggest we would try to do so is both absurd and illogical.