Top of pole mount conduit routing

Macaw

What is the most common way to route the conduit from a top of pole mount down to the ground? I see lots of photographs of the PV panels on the top of the mount but can't find many images of how the wire is routed down to earth. Should I weld conduit supports to the pole? Hose clamps maybe? I noticed a hole in the top of the top of pole mount structure that might allow routing of the wires down the inside of the support pipe but then they would have to egress out somehow at the bottom which would require a hole... which would result in a stress concentration and require additional structural reinforcement.
This is a Direct Power and Water mount that will be mounted 14 feet up on a 10 inch to 8 inch schedule 40 pipe supporting 205 square feet of panels.

halfcrazy

Re: Top of pole mount conduit routing

i have done it 2 ways the first is to use stainless hose clamps around the steel pipe and conduit. which worked well. The other way was to drill and tap the pipe for conduit straps

icarus

Re: Top of pole mount conduit routing

Self drilling, self tapping TEK screws.

Tony

Macaw

Re: Top of pole mount conduit routing

icarus--
Your location looks very intriguing from this end being that I used to have salt water in my blood but now it is much diluted. I have lived on remote islands in the past but probably not as secluded as yours. (they both had electricity from the mainland) I suspect that those self tapping TEK screws wouldn't do too well in 1/2 inch thick walled steel but thank you for pointing them out to me as an alternative. Halfcrazy is not too off-center with his advice on either drilling and tapping or using SS hose clamps so I thank you both. I like the drill and tap approach, wet installing the fasteners for improved corrosion protection. By wet install I mean sealing the fastener and entire fastener interface against moisture so there is minimal chance for galvanic or aerobic corrosion to occur.

More questions regarding routing the conduit down and out--

Can I use regular EMT to go down and underground and bury it in the concrete base of the top of pole mount? That is, will there be a chemical reaction between the caustic concrete and the zinc galvanized EMT, also know as CORROSION, that will eat the conduit up before my 40 year planned design life is exceeded?

What about waterproofing? Are there special EMT connections that are designed to keep the water out of underground conduit and out of concrete encased conduit for 40 years? I hope the licensed electrician that I have yet to hire will be able to answer all of these questions but have learned from experience to assume the experts don't necessarily know all of the answers.

I am trying to keep with metal conduit for lightning protection, and it will be passing though the crawlspace of a dwelling where EMT is required anyway, but still wonder how to keep water out of this 60 foot run from the back yard to the garage service panel for FORTY YEARS.

Thank you all for reading and your comments.

niel

Re: Top of pole mount conduit routing

that's a tough one. even if you prevent the corrosion from the concrete the condensation is liable to kill it too, not to mention if there are any problems in the future it is permanently inaccessible. if i may suggest to place the conduit into 2 or 3 inch pvc with something to hold the conduit near the top of the pvc so it doesn't sit in any of the collected condensation. that could also be something attached around the pvc itself to lift it off of the bottom while still allowoing moisture to pass. a large pvc raceway for the conduit to pass through would also make it possible to access things in the future if something should go wrong.

n3qik

Re: Top of pole mount conduit routing

Gray PVC from pole underground to house. At house place a fused disconnect. From there, do either EMT or PVC.

Thin walled metal conduit, buried, is not going to last.

icarus

Re: Top of pole mount conduit routing

We used to use Tek screws attach fire rated dry wall to steel ibeams for fire rating. With the proper Tek screw and drill speed they will run right into steel pipe, or beams or what have you.

No salt here,, we are 400 km from salt on Hudson's Bay.

T

halfcrazy

Re: Top of pole mount conduit routing

n3qik wrote: »

Gray PVC from pole underground to house. At house place a fused disconnect. From there, do either EMT or PVC.

Thin walled metal conduit, buried, is not going to last.

I will second this statement.

Ecnerwal

Re: Top of pole mount conduit routing

Macaw wrote: »

Can I use regular EMT to go down and underground and bury it in the concrete base of the top of pole mount? That is, will there be a chemical reaction between the caustic concrete and the zinc galvanized EMT, also know as CORROSION, that will eat the conduit up before my 40 year planned design life is exceeded?

What about waterproofing? Are there special EMT connections that are designed to keep the water out of underground conduit and out of concrete encased conduit for 40 years? I hope the licensed electrician that I have yet to hire will be able to answer all of these questions but have learned from experience to assume the experts don't necessarily know all of the answers.

I am trying to keep with metal conduit for lightning protection, and it will be passing though the crawlspace of a dwelling where EMT is required anyway, but still wonder how to keep water out of this 60 foot run from the back yard to the garage service panel for FORTY YEARS.

There's EMT, and there's much thicker stuff, more like plumbing pipe - threads and all. Use that. Might be called RMC (Rigid Metallic Conduit ?)

Code assumes that all underground conduit will be operating full of water. Unless you seal it pressure-tight and fill it with dry nitrogen under pressure, code is right. Use properly rated wire insulation for wet locations, and it should be fine.

The thicker galvanized conduit is similar to galvanized water pipe in lifetime under soil, I'd assume. Bolt some magnesium blocks to it and you should get even longer life. In any case, do not allow direct contact between the concrete and the conduit - wrap it or sleeve it. I still prefer PVC underground, but you have different considerations/concerns.

icarus

Re: Top of pole mount conduit routing

As far as I know,, you don't have to inclose the entire underground run in pipe,,, just use direct burial wire. Lead into a entrance El into the house conduit,,, and the pole mount. I'm not sure I see a reason you couldn't use the pole itself as the conduit,,, assuming it was the proper pipe diameter or larger to comply with NEC, and you entered and exited the pipe with proper bushings etc. You could put an elbow on the bottom of the pipe, cast it in the concrete, (with proper wrap) and kill two birds with one stone.

Having said that,, I know next to nothing about grid tie assemblies, so I will defer to others on those merits.

Tony

BB.

Re: Top of pole mount conduit routing

Personally--I like to direct bury 2-4" or larger ABS sewer pipe (or whatever you have handy)... And use direct burial wire inside the pipe and leave a pull rope behind to allow new runs to be pulled.... I am not sure if it meets code--but it is certainly a lot easier to pull new wiring from point to point without having to dig up the ground to run a new set of wires (say a little digital interface or remote on/off inverter control wire, alarm wire, --etc.).

Also provides a bit of warning if somebody is digging a drainage trench and they hit the ABS first instead of the direct burial wire...

-Bill

niel

Re: Top of pole mount conduit routing

that might be a better idea bill, but would certainly test the insulation's ability to keep the water out and away from the wire itself as it will accumulate in the pipe. underground use is not quite the same as under water, but i think it'll work. now the question is is there a special nec wire designation for being in water or is it covered under the burial type?

icarus

Re: Top of pole mount conduit routing

Try using perforated drain tile,,, either black flex,, or rigid PVC light weight sewer grade. We used to use it for Radio antenna coax all the time,,, allowing us to pull a new wire any time we needed one.

Tony

n3qik

Re: Top of pole mount conduit routing

To meet NEC the pipe must be gray PVC or metal. The wire should be THHN.

Building Wire - THHN Wire Approvals:

* UL listed Stds. 83 & 1063 as: Type THHN Wire 90°C in dry locations, Type THWN Wire 75°C in wet locations.
* A-A-59544, NEMA WC-5, UL-758
* CSA approval upon request

niel

Re: Top of pole mount conduit routing

ken,
does that wet designation cover submerged in water too?

tony,
drain tile may still back up with water unless it has an outlet in which that water can drain out of. if the pvc pipe with no water outlet is all below ground level, that water will sit in the pipe without someplace else to go and although the holes may allow some escaping of the water it could also allow the water into it if the ground is saturated.

dagr51

Re: Top of pole mount conduit routing

I'm a bit perplexed. In a properly sealed pvc conduit, how is water going to enter? I've dug up old pvc conduit that had been buried for years and was bone dry. Although I still think uf wire should be used, it seems to me a properly detailed underground pvc conduit would be the perfect solution. No?

BB.

Re: Top of pole mount conduit routing

I believe direct buried rated cable is OK with standing water (wet location)--as in ground, during the winter, the water table may be well above the buried wire at times anyway (18" minimum wire depth in ground?).

The NEC should state the uses very clearly (I do not have copy of the NEC to check).

Yes, usings ABS (or other non-rated pipe) would not be legal for THNN, etc., wire. However, for Direct Burial wire (and other small signal wire for alarm and digital communications) I would believe that ABS + Direct Burial would meet the intent of the code as Direct Burial cable needs no conduit anyway.

If you want to be really "code aware"--lay two ABS pipes side by side... Put your Direct Burial AC and high voltage Solar panel DC wires in one pipe. And place the small signal stuff in the second (alarm wiring, digital signalling, cable TV, antenna cable, etc.)... Might also be a good idea if you have lighting in your area to keep your AC/DC Panel lines separated from your small signal stuff.

If I recall correctly, all wiring sharing a single conduit must have the same minimum voltage rating (600 VAC for typical "house wiring") which would make it impossible to share a single "conduit" with both AC wiring and CTV cabling (as an example).

Regarding water in PVC/metalic conduit--I have seen it can be very easy for water to enter the conduit through external fitting subjected to rain if not done correctly--so I would follow the "wet" conditions requirements unless the installation is "inside" a house.

-Bill

n3qik

Re: Top of pole mount conduit routing

Niel,

Will look, manufacture just stated what I pasted in my post

Bill,
Any electric should be in gray PVC. This is for someone digging without knowing what is there. If they see yellow, GAS !!!!! If the see black, drainage. White is for water. I am now seeing orange for communication wire/cable.

Edit: Forgot about this. One can use this Underground Cable and Pipe Warning Tape:
http://www.mcmaster.com/#60005t29/=1flcx8

dwh

Re: Top of pole mount conduit routing

Ack!

Okay, first of all - NEVER USE EMT UNDERGROUND. It's not legal and it sure as hell won't last long.

Use the gray schedule 40. It's cheap, easy and tough. And in *most* areas it's also legal (there are some municipalities which have never had a HUD loan, and thus have never had to accept the "lower" standards of the NEC. They often have codes which are MUCH stricter than the NEC would allow for). Also, I use a separate purple primer and glue - I've found it holds better than the "blue glue". YMMV.

As to water...well I've seen old buried pipes that are bone dry, and I've seen them pour out a solid stream of water when they were opened. Either way they usually still work. I wouldn't worry about water. Most problems I've seen in underground wiring failure are either due to poorly made connections, or a root (or bonehead) breaking the pipe.

As to how water gets in...well condensation is one way. A not-quite-perfect joint is another. Boxes above (or below) ground come with a foam or rubber gasket...which rarely actually stops water from getting in. Again, if the connections are done right, water is rarely a problem except for, of course, eventually corroding the metal parts of the system.

For connections in wet areas (anything "outside" automatically gets treated as a wet area in my book), I either buy the wirenuts with Noalox in them (for large wire - #10 or bigger) or for smaller wire (#12 or smaller) I make my own by just using an acid brush to fill a standard wirenut with Led Plate or Noalox. I then tape around the wire and nut and place the connection with the wirenut pointed UP so it won't form a cup that fills with water. For even bigger wire of course, I usually use split bolts, paint with a coating of Led Plate or Noalox and then wrap with rubber tape, plastic tape and then friction tape.

(BTW, I prefer Led Plate and I use it all over the place. Great stuff!)


As to the wiring running down the pole. The OP mentioned welding tabs to the pole, and if there is access to a welder, that would be what I would do. NO WAY would I drill that pole if I could avoid it. Drilling and tapping a really thick piece of steel is a colossal pain in the butt (even with a press, but most especially by hand), AND you can be absolutely certain that no matter what you do, Murphy WILL make that screw or bolt rust into the hole so that when you try to remove it - it will break.

Having said that however...I have drilled poles like that. Not to mount conduit to the outside, but in order to run the wires down the inside. Sign poles and parking lot lights are where it's usually done. There, you drill (well, actually I use a holesaw) and tap a hole for either 1/2" or 3/4" PIPE. You use a pipe nipple screwed into the pole then mount either a box or LB (LR, LL, etc.). It's still a huge pain.

I would go with welded tabs with holes in them, and then bolt (not screw) EMT conduit hangers to the tabs. This way, if the conduit hangers had to be replaced, you can break off the rusted bolts, and just bolt on a new one.

http://www.grainger.com/Grainger/items/6XC37

This also keeps all the wiring on the outside of the pole where A) it's easy to get to, and you don't have to worry about the insulation getting nicked up by the pipe nipples (poles flex in the wind, and the wire WILL rub - even a nicely rounded off nipple end will eventually grind down the insulation).

dagr51

Re: Top of pole mount conduit routing

Okay, I'll bite. What is "Led Plate"?

BB.

Re: Top of pole mount conduit routing

Looks like Lead based oil+grease anti-seize compound (MSDS)

Vendor page.

-Bill

n3qik

Re: Top of pole mount conduit routing

2X

Google found this:

http://www.setonresourcecenter.com/msds/Docs/wcd00006/wcd00665.htm



Edit:
BB: You beat me to it.

BB.

Re: Top of pole mount conduit routing

n3qik wrote: »

2X

Ken, great minds think alike... What accounted for this?

-Bill

dwh

Re: Top of pole mount conduit routing

Wow. How strange. I never searched for Led Plate before - there's really not much on the net about it.

Yea, it's an electrically conductive, (uh oh...I'm surrounded by engineers...I better qualify that statement - I think it's conductive...at least I treat it like it is), anti-seize and anti-corrosive. I buy the 1 lb. cans, not the "brush top" cans because cleaning the brush is a pain so I prefer to just buy a bunch of little tin-handled acid brushes and throw them away when they get dirty.

Basically, it's like plumber's pipe dope - for electricians. I have only found a couple of electrical wholesale houses that *didn't* carry Led Plate. Normally I just ask for it and they have it.

Led Plate is great stuff. It goes on with the consistency of thin grease, and over time will stiffen up a bit - but I've never seen it truly harden and it takes a lot of heat to make it run. It looks exactly like what you would picture if someone said, "lead grease" to you.

I've dug up rigid pipes that were installed years before, and even when the pipe had rusted so badly that there were actual holes in it - I was able to easily unscrew the couplings that had had the threads coated with Led Plate (I know they did, because I installed the pipe originally).

I use it all over. In my earlier example, I use it to make my own little "waterproof" wirenuts. I use it on terminal blocks. I use it on the battery connections in my truck. I use it on any threads I think might corrode. I most especially slop this goop everywhere when doing outdoor electrical installations.

Anyone who has taken apart a "bell box" which has corroded knows that the little 6-32 screws will always break off - but NOT when they were coated with Led Plate before being screwed in. Even years later when the box itself had rotted away - the screws will come out. Even better the box (or it's remains) WILL unscrew off the pipe.

I wouldn't use it on potable water lines of course, but it says on the can it works for steam fittings. Or high pressure air lines.


Had a carpenter on a job once ask me about a problem he was having. He had an old (30's I think) restored motorcycle, and said he was constantly having wiring problems - especially with the generator connections. Said he'd tried silicone (d'oh!) and caulk (double d'oh!) and something else but nothing worked. I handed him a can of Led Plate that was about 1/3 full (and a new acid brush) and told him to try that.

(I also explained that you do NOT use regular silicone on electrical connections.)

Saw him on another job maybe two years later, and he said he owed me a beer, since that goop I'd given him worked perfectly. He cleaned all the connections, painted them with Led Plate and hadn't had *any* electrical problems since - even when he rode the bike from Los Angeles to Sturgis and back.

Macaw

Re: Top of pole mount conduit routing

Thanks to all for your valuable responses. My installation is on temporary hold while all hardware for top of pole mount of twelve 205 watt Evergreen panels is sitting in the yard. All except the steel pipe and conduit and wire that is. I also need to buy a deep hole to install in the back yard to pour concrete into. So far all of the online sources of holes seem to come from Nigeria and the price is relatively high but shipping is cheap. I'll do my best to photo document the installation in high enough quality for a magazine article. Led_Plate !! I'm gonna load up on that stuff !

dwh

Re: Top of pole mount conduit routing

Actually, a 1lb. can of Led Plate will probably last you a long time. A thin coat is all you need for most things.

A little dab'll do ya.


EDIT: Just remembered another handy use for Led Plate - paint your tap with it and it will not only lube the cutting operation, it'll catch the metal chips as well.

Macaw

Re: Top of pole mount conduit routing

An update here from the pay-first-install-later department at homestead Alabama--
The 2.4 kW nameplate power top-of-pole-mount installation is moving along briskly at a snails pace. Today on 12-17-2009 there is a 12 X 8 X 5 foot deep hole in the back yard and the civil engineer approved the new mechanical installation drawing which addressed the difference between the ACTUAL depth of the bedrock and the originally "measured" and assumed depth of bedrock. (5 ft -vs- 32") The pad for the (now 15 ft above ground level) steel mast is designed to sit on bedrock. I have been taking pictures for a future mag article or posting here but nothing to show so far except whole pictures of holes.

The welding shop has completed welding the 18 foot structural steel support mast and I expect they will finish priming and painting in time for delivery just before Christmas ! (10 inch schedule 40 A500 Grade B 42 ksi yield with a short piece of 8 inch to mate with the Direct Power and Water support hardware)

So here is (we hope) some useful information for the forum: The weld shop has many contracts for billboard structures in the local area. The weld shop boss told me " we welded on a couple of angle irons on the bottom of the post so it wouldn't turn in the concrete" He explained to me that "those things will turn in the concrete if the wind gets to blowing" I told him that I have had several installers ask me, and have in turn asked civil engineers and read all the issues of Home Power Magazine and looked at all the pictures of solar PV masts that I could ever find, and nobody, and no photograph, ever indicated that any type of anti rotation or anti-pull-out features need to be added to a steel pipe encased in subterranean concrete.

His reply was -- "you know why? 'CUZ it ain't in the BOOK!" heh heh heh. He implied that engineers wouldn't call for anti rotation on a steel post because they couldn't find it in a book. Humph.

Bottom line-- Experience says to weld a couple of angles to the bottom of your top of pole mount mast to increase turn resistance in the concrete. Weld the 2 foot long by 1-1/2 inch angles up the side of the pipe parallel to the centerline. The cross section of the pipe at the bottom then will look like this: <0> but the angles will be much smaller with respect to the diameter of the 0 shown above.

Item # 2
"do you want us to weld a cap in the top of the pipe so it does not fill up with water?"
That is what they do with all (most?) of their big signpost installations. Good idea I figure so I present it to the forum.

The Direct Power and Water top-of-pole mount hardware I have has a substantial weldment designed to mount to the top of a 8" pipe. It has a hole in the top with a loose fitting plastic plug that will undoubtedly be totally degraded and blown away within 10 or less years. After that, the pole will slowly fill with water in this neck of the woods. Maybe I should haul the top-of-pole pipe mount down to the weld shop and have them weld the hole shut. Seems like common sense. But I did spend some time in college so maybe I am missing something. The weld shop boss's common sense approach to totally seal up the top of the pipe sounds reasonable to me. In the end it may not be important depending on how the rain comes off the array. I'd rather design around the possibility now, than deal with the repercussions in the year 2031 (approx 20 years from now when I'm finally making money off this array). Every design decision I make on this PV project as well as my earlier domestic hot water project is tempered with the realization that this equipment and installation will be around for 20-40 years (we hope).

niel

Re: Top of pole mount conduit routing

both points of base vanes and a cap seem sound and reasonable to me. is the cap totally air tight or just an open cover? i'm thinking of the condensation that could form inside of the pipe. it's more likely to happen exposed to outside humid air, but will also evaporate more readily into that outer air with an unsealed cap.

mike95490

Re: Top of pole mount conduit routing

I really think, that once the cement sets in a day or 2, it would not rotate. Course, I punched a couple 2" holes in the base of the pole, for the concrete to flow into, locking the pole.
And the engineering, I'm now more concerned about the whole thing sinking into the ground ala "China Syndrome", it's a huge slug of concrete, nearly 30" di in spots where the auger was chewing up the dirt. But the plans called for 10' deep. 8" schedule 40 pipe. 12' above. But i now will think about a cap on top, maybe just one of the white plastic anti-seagull pileing toppers used at marinas. Or maybe the array bracket will cover it well enough.

a0128958

Re: Top of pole mount conduit routing

dwh wrote: »

... (I also explained that you do NOT use regular silicone on electrical connections.)

I'm curious as to why this is the case (what problems result), and if use of silicone inside wirenuts is actually prohibited by the NEC.

Thanks.

Best regards,

Bill

dwh

Re: Top of pole mount conduit routing

a0128958 wrote: »

I'm curious as to why this is the case (what problems result), and if use of silicone inside wirenuts is actually prohibited by the NEC.

Thanks.

Best regards,

Bill

There is a special silicone for electrical connections; dielectric silicone - usually sold as a form of grease but I've seen it as an RTV as well.

Wirenuts that are factory-filled, will normally be filled with dielectric silicone grease, but some are filled with a NoAlox type compound.


As I understand it, regular RTV-type silicone has a few problems when used with electricity:

*It's not a good insulator. Shorts can bridge through it more easily, and it's easily punctured.
*It doesn't bind tightly to the metal, thus allowing corrosion by moisture penetration or even encouraging corrosion by holding in moisture.
*Something in the solvent can also cause corrosion (I'm not a chemist so I can't say what).
*It's generally not UV rated.
*It's not easily removed or cleaned off to allow for inspection of connections.