Electroendosmosis Underground PV Circuits

System

All

FPN at the end of NEC 310.13 states that "thermoplastic insulation where used on dc circuits in wet locations may result in electroendosmosis between conductor and insulation."

I know that FPN are only recommendations but does this mean that I should be specifying thermoset type insulations for underground conduit runs in Solar PV applications? This would be an increased cost to the overall system and so I would like to make sure that electroendosmosis is a serious concern for 600V and below systems.

Does anyone have any good articles or white papers on this topic? Or even some good comments/suggestions?

Thanks

audredger

Re: Electroendosmosis Underground PV Circuits

electroendosmosis now that's a word to draw for... this is one of the reasons aluminum wire is not recommended for DC circuits!

Wouldn't putting wire in conduit lessen this effect? Less moisture.

russ

Re: Electroendosmosis Underground PV Circuits

That is truly a 3 dollar word!

Cariboocoot

Re: Electroendosmosis Underground PV Circuits

I would suggest the use of UG rated wire inside the conduit would be precaution enough.

Vic

Re: Electroendosmosis Underground PV Circuits

Code books are really intended for SHELF DISPLAY, not for detailed study.
OH, just kidding .... Vic

tallgirl

Re: Electroendosmosis Underground PV Circuits

Make sure the conduit is liquid tight and not subject to condensation.

"Electroendosmosis" is a very big word for "DC makes it absorb water". If I understand the physics correctly, the electric field around the wire causes water molecules to align in such a way that they can seep through plastic they wouldn't ordinarily be able to seep through.

halfcrazy

Re: Electroendosmosis Underground PV Circuits

tallgirl wrote: »

"Electroendosmosis" is a very big word for "DC makes it absorb electricity". If I understand the physics correctly, the electric field around the wire causes water molecules to align in such a way that they can seep through plastic they wouldn't ordinarily be able to seep through.

So that's where all my power has been going to Electroendosmosis Heck I can not even say that word rather worry about it.

tallgirl

Re: Electroendosmosis Underground PV Circuits

halfcrazy wrote: »

So that's where all my power has been going to Electroendosmosis Heck I can not even say that word rather worry about it.

Heh. This is one of the risks of touch typing -- typing so fast I can't be sure I type the correct words

System2

Re: Electroendosmosis Underground PV Circuits

Thanks all for the help, I have been trying to do some research around this and have not found much on electroendosmosis but on "water treeing" on high voltage cables. I am not sure if they are the same but they seem very related when reading about water treeing. The few places that I have read about water treeing it seemed like this was only a problem for high voltage cables and dc hipot testing on them, no mention of low voltage systems. If this is the case then I do not think this will be a problem for our low voltage (600 and below) systems.

Thanks again, and let me know if you have any other comments/suggestions around this. For now I am going to stick with installing THWN-2 in underground DC circuits to save on the cost of thermoset insulation

thenderson4

Re: Electroendosmosis Underground PV Circuits

After 36 years doing traffic signal work (a lot of underground conduit) I have yet to see moisture stay out of underground conduit. Even when sealed the way you do water pipe, condensation takes place, it will build up and collect until you swear there is a bad joint.

When you drive down the road and see the compressed bottles of liguid nitrogen hooked to telephone cables, moisture is the reason. The nitrogen being dry keeps dampness from causing problems with connections. I have been told they even keep the presure slightly higher than atmospheric pressure.

Direct burial type cable is good, so is Underground Feeder (UG) Another type which is good is type USE.

Tom

solarvic

Re: Electroendosmosis Underground PV Circuits

thenderson4 wrote: »

After 36 years doing traffic signal work (a lot of underground conduit) I have yet to see moisture stay out of underground conduit. Even when sealed the way you do water pipe, condensation takes place, it will build up and collect until you swear there is a bad joint.

When you drive down the road and see the compressed bottles of liquid nitrogen hooked to telephone cables, moisture is the reason. The nitrogen being dry keeps dampness from causing problems with connections. I have been told they even keep the pressure slightly higher than atmospheric pressure.

Direct burial type cable is good, so is Underground Feeder (UG) Another type which is good is type USE

I have lots of problems with groundhogs here. They seem to like Satelite Coax cable. I replaced it 3 times already. Last time I put new cable in, I buryed car litter with it. That was about 5 years ago. When I did my solar wireing I buryed some used cat litter under my inverters to keep thee groundhogs away. S:Dlarvic

niel

Re: Electroendosmosis Underground PV Circuits

solarvic,
was it the fact it was cat litter that worked (aka clay) or was it because the cat litter was used?

solarvic

Re: Electroendosmosis Underground PV Circuits

Niel I think it is because it is used. I keep chucking it down groundhog holes and they don,t use again. Seems to be a preety good deterent. so is lead poising or just 1 bite works too. Solarvic

Kamala

Re: Electroendosmosis Underground PV Circuits

Mark yer territory with yer own stuff or that of yer pets. All the same to me.

russ

Re: Electroendosmosis Underground PV Circuits

'I think it is because it is used. I keep chucking it down groundhog holes and they don,t use again.'

They don't use the cat litter again? Or the hole?

niel

Re: Electroendosmosis Underground PV Circuits

russ wrote: »

'I think it is because it is used. I keep chucking it down groundhog holes and they don,t use again.'

They don't use the cat litter again? Or the hole?

i think the key here is that they go somewhere else.:p

solarvic

Re: Electroendosmosis Underground PV Circuits

Yes I had 4 different groundhog holes from 1 ft to 10 ft. from house. Now they arent going near the house anymore. My Gti Inverters had a groundhog hole right under where I put them so after the electrician got done I poured a buckit in the hole before I covered it with dirt. Don,t know if groundhogs are afraid of cats or they just don,t like the smell. I do know but the stuff is a preety good repellent.
S:Dlarvic

nadakal

Can anyone comment to ELECTRO END OSMOSIS impact on DC cables and how to qualify insulation systems? Are there any tests to verify insulations are OK... Thank you.

Dave Angelini

Never had any problems with 600V UL rated wiring in liquid tight armored conduit. One system is still working from the late 1970's.

I can get 2KV rated wire now so I would think this effect would be lessened if anyone had it.