Steel LB Surrounded By PVC Conduit

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Fred B said:
Also, other than killing the bus full, the threads on each pictured above while almost will fit is not exactly the same and will not seal properly. A rigid conduit thread is a tapered thread (npt) and used on the LB above, and is not the same as that used with a nut which is a straight thread used on the box adapter fitting above.
The use of the 2 pictured together as above would be a technical violation even though many might use them together. In dry area might not be as much of an issue other than the fitting might break as a result of the taper of the lb during installation, but in a wet area not using matching tapered fittings will allow water intrusion and if in a area of the country that freezes it can break the parts. (Seen it)
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I don't buy that argument Fred. There are "approved" thread combinations where one is tapered and one is not, i.e. the factory couplings on a stick of RGS, so I refuse to accept that tapered thread with non tapered thread has anything to do with it or is an issue.
 
Fred B said:
Also, other than killing the bus full, the threads on each pictured above while almost will fit is not exactly the same and will not seal properly. A rigid conduit thread is a tapered thread (npt) and used on the LB above, and is not the same as that used with a nut which is a straight thread used on the box adapter fitting above.
The use of the 2 pictured together as above would be a technical violation even though many might use them together. In dry area might not be as much of an issue other than the fitting might break as a result of the taper of the lb during installation, but in a wet area not using matching tapered fittings will allow water intrusion and if in a area of the country that freezes it can break the parts. (Seen it)
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Conduit outdoors is considered a wet location, no matter what fittings are used. I've never understood the hand wringing over water getting into outdoor conduit; condensation will eventually fill the pipe with water no matter what we do, unless it is arranged to drain.

If water is freezing and bursting the conduit, then it isn't installed correctly; it' supposed to be installed to drain any accumulated water. Not saying it was you who installed it, but it sounds like someone screwed up if something's full of water/ice.

I for one don't loose any sleep with male PVC threads screwed into things like LB's and Bell boxes. If you feel so inclined, use a bit of Teflon tape on the PVC threads; it also makes it much easier to screw in.


SceneryDriver
 
SceneryDriver said:
Conduit outdoors is considered a wet location, no matter what fittings are used. I've never understood the hand wringing over water getting into outdoor conduit; condensation will eventually fill the pipe with water no matter what we do, unless it is arranged to drain.

If water is freezing and bursting the conduit, then it isn't installed correctly; it' supposed to be installed to drain any accumulated water. Not saying it was you who installed it, but it sounds like someone screwed up if something's full of water/ice.

I for one don't loose any sleep with male PVC threads screwed into things like LB's and Bell boxes. If you feel so inclined, use a bit of Teflon tape on the PVC threads; it also makes it much easier to screw in.


SceneryDriver
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It is pretty much impossible to get rid of the water in an underground conduit that rises up out of the ground at each end. The only way to avoid ice damage on that type of run, is to have the conduit below the frost line, but even then, the conductors in the riser are subject to ice damage.
 
don_resqcapt19 said:
It is pretty much impossible to get rid of the water in an underground conduit that rises up out of the ground at each end. The only way to avoid ice damage on that type of run, is to have the conduit below the frost line, but even then, the conductors in the riser are subject to ice damage.
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If you slope the line then there are any number of ways to get rid of the water, assuming you are above the local water table. You could drill the bottom of the conduit at the low point to allow the water to drain, maybe place it over a short gravel bed to reduce the chance of dirt entering through the holes. Heck, wrap that section with geotextile if you like. At one end, use a tee instead of an elbow and leave the run open into some gravel, etc.
 
gadfly56 said:
If you slope the line then there are any number of ways to get rid of the water, assuming you are above the local water table. You could drill the bottom of the conduit at the low point to allow the water to drain, maybe place it over a short gravel bed to reduce the chance of dirt entering through the holes. Heck, wrap that section with geotextile if you like. At one end, use a tee instead of an elbow and leave the run open into some gravel, etc.
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I am not aware of any AHJ that will let you drill the conduit, or let you install a tee fitting below grade.
 
don_resqcapt19 said:
I am not aware of any AHJ that will let you drill the conduit, or let you install a tee fitting below grade.
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The hell with code, when it comes to this I would do whatever I needed, even if it meant making changes after the inspector left.

I was just talking to a friend today who does O&M for PV sites and we got talking about water issues. I guess he had some DC combiners in a low area that had a foot of water in them. I guess they had weep holes but the weep holes froze shut. I like my homemade expansion couplings made out of two different sizes of PVC as they let water out. He said one thing they have been doing is removing the o-rings from the factory expansion couplings so they're not sealed. I think weep holes in the conduit, for underground entry into say a basement, is a great idea and actually that's what I did at my house.
 
don_resqcapt19 said:
What you put in the raceway does not change the rules for the raceway.
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Sorry, if I install some metal that could be a raceway, but make a choice that means it doesn't meet the raceway rules, but I don't need to use any of the permissions granted to a raceway (such as being able to run individual conductors in it), why is that a problem?

Cheers, Wayne
 
electrofelon said:
I don't buy that argument Fred. There are "approved" thread combinations where one is tapered and one is not, i.e. the factory couplings on a stick of RGS, so I refuse to accept that tapered thread with non tapered thread has anything to do with it or is an issue.
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Let the record show that PVC gendered adapters have tapered threads, and not straight threads. Maybe at one point, they had straight threads, but every datasheet and product I've seen in person has the tapered threads. Look for the designation of NPT, as the T stands for taper. NPSM is its straight thread designation.

The way I understand it, is that in the electrical application, it is OK to have tapered male threads in straight female threads, because you don't need any pressure-rating for the connection, like you do with plumbing. Just a general resistance to unfastening, and a degree of watertightness with typical rain and snow in mind. Even drain plumbing needs a nominal amount of pressure rating more than an electrical conduit connection would require, so you would need tapered threads on both genders for drain plumbing. In electrical, the mix of straight female and tapered male is enough to get raintightness, mechanical continuity, and electrical continuity for metal conduit. Tapered-in-tapered would also be an acceptable combination, as it is for a Myers hub, or an integrated hub in an enclosure.

The issue is when you mix straight male threads with anything other than a locknut as its female partner. Such as running threads, EMT connectors, and LFMC connectors. It's done all the time, and it is a lot harder to source the proper products for the alternative, but it is a technicality that is an issue with the product listing. I don't see any real life consequence of this, since the male fitting has a shoulder to bottom-out the connection. The alternative is to use transition couplings, which are analogous to female adapters in these raceway types, and locally transition to RMC nipples for connecting to equipment requiring it. But these transition couplings are a lot harder to get, and not available in all sizes.
 
Carultch said:
Let the record show that PVC gendered adapters have tapered threads, and not straight threads. Maybe at one point, they had straight threads, but every datasheet and product I've seen in person has the tapered threads. Look for the designation of NPT, as the T stands for taper. NPSM is its straight thread designation.
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Interesting, strange I never noticed the taper. I didn't believe you so I grabbed a few specimens and my dial calipers and some parallels and took some measurements. I have a 3/4 TA - scepter, a 1.5" TA- scepter, a 2" TA - carlon, and a 2" FA - scepter. The 3/4 and 2" TA's have a taper but a bit less than the standard .75"/foot, about .65". Strangely, the 1.5 TA has no taper at all. The FA has excessive taper at 1.125"/foot. The inconsistencies are strange.

The way I understand it, is that in the electrical application, it is OK to have tapered male threads in straight female threads, because you don't need any pressure-rating for the connection, like you do with plumbing. Just a general resistance to unfastening, and a degree of watertightness with typical rain and snow in mind. Even drain plumbing needs a nominal amount of pressure rating more than an electrical conduit connection would require, so you would need tapered threads on both genders for drain plumbing. In electrical, the mix of straight female and tapered male is enough to get raintightness, mechanical continuity, and electrical continuity for metal conduit. Tapered-in-tapered would also be an acceptable combination, as it is for a Myers hub, or an integrated hub in an enclosure.

The issue is when you mix straight male threads with anything other than a locknut as its female partner. Such as running threads, EMT connectors, and LFMC connectors. It's done all the time, and it is a lot harder to source the proper products for the alternative, but it is a technicality that is an issue with the product listing. I don't see any real life consequence of this, since the male fitting has a shoulder to bottom-out the connection. The alternative is to use transition couplings, which are analogous to female adapters in these raceway types, and locally transition to RMC nipples for connecting to equipment requiring it. But these transition couplings are a lot harder to get, and not available in all sizes.
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I'm not saying those aren't reasonable arguments, but have you seen anything in any product standard or from a testing agency that says such things or are those just your opinions?
 
electrofelon said:
Interesting, strange I never noticed the taper. I didn't believe you so I grabbed a few specimens and my dial calipers and some parallels and took some measurements. I have a 3/4 TA - scepter, a 1.5" TA- scepter, a 2" TA - carlon, and a 2" FA - scepter. The 3/4 and 2" TA's have a taper but a bit less than the standard .75"/foot, about .65". Strangely, the 1.5 TA has no taper at all. The FA has excessive taper at 1.125"/foot. The inconsistencies are strange.
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Indeed, the inconsistences are strange. Maybe some manufactures have an intent on making the terminal adapters inter-compatible with all female threads made for RMC...eventually...so that it will eventually be proper to connect PVC directly to integrated hubs.

A 0.65"/ft taper instead of the standard 0.75"/ft, could be explained with manufacturing tolerance and imprecision in your measurement methods, given the low sample size of the fitting length. But a 1.125"/ft taper seems like there is an intentional reason why it is that different than the standard taper.

electrofelon said:
I'm not saying those aren't reasonable arguments, but have you seen anything in any product standard or from a testing agency that says such things or are those just your opinions?
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This is my reasoned judgement from the patterns I see, when certain products indicate "for use with RMC and IMC conduit". And from the rules on running thread, that disallow it from being used with RMC couplings (344.42). There's also the UL whitebook from 2012 that states that "
All male threaded fittings and nipples have only been investigated for use with locknuts", and "fittings with internal female threads (e.g., hubs, conduit bodies, couplings) have only been investigated for use with threaded rigid conduit." So this could be just a lack of UL ever investigating the combination, rather than any prediction that the assembly will have any physical consequences.

I'd prefer to see improved inter-compatibility of the conduit fittings, so that we don't have to speculate on what is supposed to connect to what.
 
electrofelon said:
How is that different than punching holes in a cabinet or a box? Do I need to show instructions that permit me to do that?
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The difference is, that you have conduit fittings that are listed for maintaining a given NEMA rating of the enclosure, when connecting the conduit to the box by that assembly of fittings. Depending on the product, you may see instructions that specify where conduit connections can happen.

petersonra said:
What code allows you to drill weep holes in fittings?
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There in lies a case of "damned if you do, damned if you don't". Drill a weep hole, and you technically lose your product listing for its environment. Don't drill a hole, and you end up with water intrusion and no way to remove it.
 
Carultch said:
There in lies a case of "damned if you do, damned if you don't". Drill a weep hole, and you technically lose your product listing for its environment. Don't drill a hole, and you end up with water intrusion and no way to remove it.
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In my opinion, it is our responsibility to adapt our installations to the environment. I'll routinely drill two 1/8" holes in the bottom surface of boxes, upward-pointing LBs, etc., and other items not designed to drain.

As I like to say "We professionals know how to break the rules correctly!"
 
petersonra said:
What code allows you to drill weep holes in fittings?
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314.15 Damp or Wet Locations.

In damp or wet locations, boxes, conduit bodies, outlet box hoods, and fittings shall be placed or equipped so as to prevent moisture from entering or accumulating within the box, conduit body, or fitting. Boxes, conduit bodies, outlet box hoods, and fittings installed in wet locations shall be listed for use in wet locations. Approved drainage openings not smaller than 3 mm (1⁄8 in.) and not larger than 6 mm (1⁄4 in.) in diameter shall be permitted to be installed in the field in boxes or conduit bodies listed for use in damp or wet locations. For installation of listed drain fittings, larger openings are permitted to be installed in the field in accordance with manufacturer’s instructions.
 
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