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Question on HPWC install

StealthP3D

Well-Known Member
Dec 12, 2018
9,395
73,269
Maple Falls, WA
I'm building a charging station next to the driveway of my ski cabin. It's in the middle of a mature PNW rainforest so I'm putting a little roof over the Wall Connector to keep rain and forest debris off it. I'll be bringing the #6 THWN wire underground through 1" PVC conduit that will run up the backside of the mounting post where a conduit body will turn 90 degrees so I can run a short length of conduit through the center of the 6x6 mounting post the HPWC will be mounted to.

I have a 1" PVC male threaded adapter that will screw into the back of the HPWC (and allow me to glue a short length of conduit to it) but this would require cutting the conduit to unscrew the male threaded adapter (once it's all glued together) if I ever needed to remove the WC for service or replacement. Even though I don't expect this area to get wet due to the roof, what kind of fitting am I looking for that will seal against water but could be unscrewed from inside the WC for removal?

Also, is a wire strain relief clamp required here? I wouldn't think so since the wire is in conduit all the way to the electrical panel but any input appreciated.
 

Bill25cycle

Member
Mar 31, 2011
103
69
I'm building a charging station next to the driveway of my ski cabin. It's in the middle of a mature PNW rainforest so I'm putting a little roof over the Wall Connector to keep rain and forest debris off it. I'll be bringing the #6 THWN wire underground through 1" PVC conduit that will run up the backside of the mounting post where a conduit body will turn 90 degrees so I can run a short length of conduit through the center of the 6x6 mounting post the HPWC will be mounted to.

I have a 1" PVC male threaded adapter that will screw into the back of the HPWC (and allow me to glue a short length of conduit to it) but this would require cutting the conduit to unscrew the male threaded adapter (once it's all glued together) if I ever needed to remove the WC for service or replacement. Even though I don't expect this area to get wet due to the roof, what kind of fitting am I looking for that will seal against water but could be unscrewed from inside the WC for removal?

Also, is a wire strain relief clamp required here? I wouldn't think so since the wire is in conduit all the way to the electrical panel but any input appreciated.

If you use a 1" pvc BOX connector (NPT threads) you can just unscrew the retaining nut INSIDE the HPWC without having to cut the conduit. I wouldn't think that you would need it, but you could use a gasketed coupling and gasketed locknuts to keep all the water out, but a tightly connected box fitting along with a 'roof' overhead I would think would keep all the water out, provided the whole thing isn't submerged in a flood.

If you are going up the backside of a 4x4 pole to hold the HPWC, and you are not using a pvc expansion joint pipe, make sure you bury the pipe in dirt, not in concrete, and pre-stress it on the long side if you install it when it is warm.. That way when it gets cold the pipe won't shrink and pull out of the "LB" 90 degree fitting you have at the top. If you are starting from a concrete base and the pipe is immobilized you'll have no choice but to use an expansion fitting,or transition to metal conduit in the exposed area..

You need one or 2 half moon clamps to hold the pvc to the post, but please explain where the strain is on the wire in your installation?
 

StealthP3D

Well-Known Member
Dec 12, 2018
9,395
73,269
Maple Falls, WA
If you use a 1" pvc BOX connector (NPT threads) you can just unscrew the retaining nut INSIDE the HPWC without having to cut the conduit. I wouldn't think that you would need it, but you could use a gasketed coupling and gasketed locknuts to keep all the water out, but a tightly connected box fitting along with a 'roof' overhead I would think would keep all the water out, provided the whole thing isn't submerged in a flood.

I agree water entry probably won't be a problem but the installation instructions do say this:

Note: There should not be any visible openings to the inside of the Wall Connector, and the Wall Connector should be completely sealed from the environment.

The high local humidity and cold dampness most of the year makes me think I might avoid corrosion better if it were mostly sealed. But I can't find the gasketed products you mention or envision how it might be assembled from the final PVC glue joint. Would I still use the 1" PVC BOX connector?

Tesla does include a rubber seal that looks like it would seal with the 1" PVC male threaded adapter I have but I'm not sure if it would be the right size for the 1" NPT threaded box connector.

If you are going up the backside of a 4x4 pole to hold the HPWC, and you are not using a pvc expansion joint pipe, make sure you bury the pipe in dirt, not in concrete, and pre-stress it on the long side if you install it when it is warm.. That way when it gets cold the pipe won't shrink and pull out of the "LB" 90 degree fitting you have at the top. If you are starting from a concrete base and the pipe is immobilized you'll have no choice but to use an expansion fitting,or transition to metal conduit in the exposed area.

Thanks, I hadn't thought of thermal expansion issues!

You need one or 2 half moon clamps to hold the pvc to the post, but please explain where the strain is on the wire in your installation?

I don't think there would ever be any strain on the power feed wires where they terminate in the Wall Connector but I've seen code require plenty of things that didn't seem necessary in every required instance. I just wanted to check if the NEC required the power wires to be clamped where they enter the Wall Connector.
 

smatthew

Active Member
Jun 9, 2018
1,272
2,066
CA Bay Area
Understand that buried conduit will fill with water, and that's OK. Conduit isn't there to keep water out, it's there to prevent physical intrusion from ruining your day - like someone with a shovel who doesn't know the conduit is there.
 

Bill25cycle

Member
Mar 31, 2011
103
69
Understand that buried conduit will fill with water, and that's OK. Conduit isn't there to keep water out, it's there to prevent physical intrusion from ruining your day - like someone with a shovel who doesn't know the conduit is there.

Oh Boy! I sure hope not - my conduit installations stay bone dry since I use a high-quality solvent weld on plastic installations and make up threaded rigid conduit installations wrench tight, and I'll even pipe dope them if the area seems excessively wet.

'Building wire' (THW,THWN,XHHW,etc) is designed to get TEMPORARILY wet but is expected to remain dry most of the time. Most homes in my area, if fed with URD (Underground Residential Distribution), only have a conduit stub at the house and at the feed end (if above ground) and use DIRECT-BURIAL USE (Underground service entrance) 'triplex' conductors. - the stuff with the yellow stripe on the neutral wire. But that wire is very, very tough and can survive through a freeze. The solar installers around here use #10 copper USE for all the wiring on the roof since the sun won't ruin it.

Of course, I have seen plenty of rickety service entrance installations where the pipe joints were haphazardly made, and/or they didn't properly prepare the trench with a sand bed for the pipes to comfortably lie on. THOSE installations tend to have conduit filled all the time with water, especially the ones with Sweep Ells at the pole made with cheap PVC instead of Galvanized Rigid Conduit, which cannot withstand the slightest bump from a car, and instantly shatter. They last a while on residential feeds, (voltage to ground only 120 volts) but commercial installations of such nonsense with 277 to ground carbon track reasonably quickly - of course these un-fused wires being fed by a nice BIG transformer cluster with plenty of fault-current available make the thing go out with a super BIG BANG when the problem finally avalanches. It is usually traumatic enough that it destroys the other 2 or 3 pipes co-located in the same trench.
 
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smatthew

Active Member
Jun 9, 2018
1,272
2,066
CA Bay Area
Oh Boy! I sure hope not - my conduit installations stay bone dry since I use a high-quality solvent weld on plastic installations and make up threaded rigid conduit installations wrench tight, and I'll even pipe dope them if the area seems excessively wet.

'Building wire' (THW,THWN,XHHW,etc) is designed to get TEMPORARILY wet but is expected to remain dry most of the time. Most homes in my area, if fed with URD (Underground Residential Distribution), only have a conduit stub at the house and at the feed end (if above ground) and use DIRECT-BURIAL USE (Underground service entrance) 'triplex' conductors. - the stuff with the yellow stripe on the neutral wire. But that wire is very, very tough and can survive through a freeze. The solar installers around here use #10 copper USE for all the wiring on the roof since the sun won't ruin it.

Of course, I have seen plenty of rickety service entrance installations where the pipe joints were haphazardly made, and/or they didn't properly prepare the trench with a sand bed for the pipes to comfortably lie on. THOSE installations tend to have conduit filled all the time with water, especially the ones with Sweep Ells at the pole made with cheap PVC instead of Galvanized Rigid Conduit, which cannot withstand the slightest bump from a car, and instantly shatter. They last a while on residential feeds, (voltage to ground only 120 volts) but commercial installations of such nonsense with 277 to ground carbon track reasonably quickly - of course these un-fused wires being fed by a nice BIG transformer cluster with plenty of fault-current available make the thing go out with a super BIG BANG when the problem finally avalanches. It is usually traumatic enough that it destroys the other 2 or 3 pipes co-located in the same trench.

Even if your joints are completely waterproof, you will end up with water in the conduit. That's why you don't put building wire in buried conduit. The reason you will almost always get water is the moisture in the air and condensation.
 
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Bill25cycle

Member
Mar 31, 2011
103
69
Even if your joints are completely waterproof, you will end up with water in the conduit. That's why you don't put building wire in buried conduit. The reason you will almost always get water is the moisture in the air and condensation.
'
Not in the runs I make.... In areas of EXTREME temperature changes (which NEVER happens below ground, incidentally), there might be a few drops forming occasionally, but since the runs that I make are water and air tight (not possible you say? You must never have lived anywhere with plastic plumbing), there is simply no water AVAILABLE even to form a drop since the stagnant air in the pipe is above the dew point..

OF COURSE you can put building wire in conduit. If you have ever been to a shopping plaza the big green box alongside the building (pad transformer) is connected through continuous piping to the building in cable and conduit - the cable in this case is the building wire I mentioned, either xhhw,thwn, or thw. Since this wire can survive an Occasional few drops, in extreme weather in EXPOSED locations (on an unprotected wall, etc) the system survives. Circuits with any load on them at all immediately vaporize this water as the dew point is quickly surpassed.

Just because you have seen how a few houses are wired does not mean this is the general case for all types of electrical work.

Why do people who have no experience with anything more than house wiring automatically assume they are the self-appointed big expert? Now if I had no experience with something, humility would cause me to choose my words more carefully.
 

smatthew

Active Member
Jun 9, 2018
1,272
2,066
CA Bay Area
'
Not in the runs I make.... In areas of EXTREME temperature changes (which NEVER happens below ground, incidentally), there might be a few drops forming occasionally, but since the runs that I make are water and air tight (not possible you say? You must never have lived anywhere with plastic plumbing), there is simply no water AVAILABLE even to form a drop since the stagnant air in the pipe is above the dew point..

OF COURSE you can put building wire in conduit. If you have ever been to a shopping plaza the big green box alongside the building (pad transformer) is connected through continuous piping to the building in cable and conduit - the cable in this case is the building wire I mentioned, either xhhw,thwn, or thw. Since this wire can survive an Occasional few drops, in extreme weather in EXPOSED locations (on an unprotected wall, etc) the system survives. Circuits with any load on them at all immediately vaporize this water as the dew point is quickly surpassed.

Just because you have seen how a few houses are wired does not mean this is the general case for all types of electrical work.

Why do people who have no experience with anything more than house wiring automatically assume they are the self-appointed big expert? Now if I had no experience with something, humility would cause me to choose my words more carefully.
Ok, so you're better than most. But we can't all ensure such levels of quality. That's why code says that underground conduit must have wet rated wire. For instance, THWN, instead of THHN. Unless your conduit is pressurized, you cannot guarantee water will not intrude.
 

StealthP3D

Well-Known Member
Dec 12, 2018
9,395
73,269
Maple Falls, WA
Ok, so you're better than most. But we can't all ensure such levels of quality. That's why code says that underground conduit must have wet rated wire. For instance, THWN, instead of THHN. Unless your conduit is pressurized, you cannot guarantee water will not intrude.

I plan on using duct seal on both ends of the conduit to reduce the chances of condensation (not that I think it would cause a problem, but...). Interestingly enough, even though this installation is in a rain forest, the water table is at least 100 feet below the surface. 8,000 years ago a nearby 8,000-foot mountain (monolithic bedrock upthrust) fractured and collapsed. The fractured rock moved with so much momentum it flowed like a fluid, which formed "rapids" with standing waves of fractured rock boulders that remained when the slide came to a halt. Over the years earthquakes have settled the slide debris such that it is stable. Roads and building sites are prepared by topping with smaller rock and gravel. My site happens to be on top of one of the standing waves and water passes right through.

But what is with all this talk about water in the conduit? I was under the impression its not really much of an issue. And when I bought the wire at Home Depot, I was informed they don't even carry the AWG #6 in THHN (it's all rated both THWN and THNN).
 

Bill25cycle

Member
Mar 31, 2011
103
69
Ok, so you're better than most. But we can't all ensure such levels of quality. That's why code says that underground conduit must have wet rated wire. For instance, THWN, instead of THHN. Unless your conduit is pressurized, you cannot guarantee water will not intrude.


Uhh, Chief! THHN and THWN are the same wire... Just depends where you use it.
 

Bill25cycle

Member
Mar 31, 2011
103
69
I plan on using duct seal on both ends of the conduit to reduce the chances of condensation (not that I think it would cause a problem, but...). Interestingly enough, even though this installation is in a rain forest, the water table is at least 100 feet below the surface. 8,000 years ago a nearby 8,000-foot mountain (monolithic bedrock upthrust) fractured and collapsed. The fractured rock moved with so much momentum it flowed like a fluid, which formed "rapids" with standing waves of fractured rock boulders that remained when the slide came to a halt. Over the years earthquakes have settled the slide debris such that it is stable. Roads and building sites are prepared by topping with smaller rock and gravel. My site happens to be on top of one of the standing waves and water passes right through.

But what is with all this talk about water in the conduit? I was under the impression its not really much of an issue. And when I bought the wire at Home Depot, I was informed they don't even carry the AWG #6 in THHN (it's all rated both THWN and THNN).

Home Depot carries #6 Copper THWN building wire and also #6, and #4 XHHW aluminum building wire. If your closest store doesn't have it, order it on line and they'll ship it to the store.
 

Daniel in SD

Well-Known Member
Jan 25, 2018
6,551
9,298
San Diego
Could you do the whole thing with flexible PVC conduit? Or maybe you could just use a small section of flexible PVC? Those connections can be unscrewed.
 

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