150V on rails!

[infinity]

Went to a job today, had been installed about 4 days ago, apprentice went up ladder ( bungalow) and got a tingle, when i checked rails to the ladder which was earthed in garden below there was 150V present!
Install was a 3600TL sma, checked AC side and all seemed ok, was late so going back tomorrow. array not earthed which i said is first port of call and left all switched off.

Surely the TL cannot pass 150v into rails in normal conditions? even if rails are earthed it doesnt seem right.

More investigation in daylight tomorrow!

 

[yorkshiremike]

It's possible due to capacitive coupling and discharge. This is a possible factor when using transformer-less inverters and certain designs of panel (particularly with conductive back surfaces etc). I wasn't able to post the links for the SMA reports, but try a google on "Capacitive Discharge Currents"

 

[infinity]

Ah i see il take a look, they were 16x sanyo hit n 240 panels so maybe thats the answer. thanks

 

[whinmoor]

There have been compatibility issues with the Sanyo/SMA combination. Search on this forum for some lengthy debates. Several times the installer has had to replace with a different brand of inverter. Both SMA and Sanyo of course claiming it's not their fault. Mainly related to disappointing output though.

 

[infinity]

Really? why such a bad combo? Well il earth array, test and thats all i can do.

 

[whinmoor]

Dunno - long thread about it here - maybe only HF and not TL inverters.

http://www.electriciansforums.net/p...compatability-issues-sma-hf-sanyo-panels.html

 

[SolarCity]

Are you saying that the array is not bonded?

If not then it should be. Do an IR between the frame and your strings and make sure you haven't trapped a cable. If all is good then bond away and you should be all good.

 

[infinity]

Bonded it today down to a stake as tncs. Starnge as couldnt be a pinched cable it was AC voltage i was getting not DC!

Rcd hasnt tripped either so i have no idea what was causing that.

 

[BruceB]

As suggested earlier it will be the capacitive effect between the panels and roof/framework

 

[moggy1968]

why is it AC then?
Is it some kind of backfeed?

 

[BruceB]

ac because the voltage in the panels is oscillating at mains frequency and at some voltage between 0 and mains voltage. Backfeed would be one way to describe it. The dc voltage produced by the panels is superimposed on that. Only the ac voltage in the panels is relevant to any capacitive coupling effect.

 

[mdovey]

Dunno - long thread about it here - maybe only HF and not TL inverters.

http://www.electriciansforums.net/p...compatability-issues-sma-hf-sanyo-panels.html

I think it is just the HF series. However, the problem here is with the MPP tracking somehow losing the peak output, and I believe that there is a workaround of updating to the latest firmware and enabling global optipeak. I doubt that this is related to AC leakage onto the panels.

 

[edexlab]

The Ac present is due to it being a TL inverter as Bruce and some of the others have stated, installation manual and DTI guides decent textbooks , all say to bond the array and this is done only to discharge the potential on the array ,irrespective of any issues about extraneous/exposed parts which is a different matter
as I've posted on another thread if you test for voltage between the array/and earth when a Tl system is turned on you'll see something like 100v or more and I've done this on around 80 TL systems , recently did a console job immediately next door to another company fitting exactly the same system ,went over to have a chat over the hedge and was asked why I had bonded every panel together and all down to a couple of rods (2 deep) so told him the story and he disagreed said it was'nt necessary ,and decided to not bother ,following day their apprentice got a small shock (better him than the customer I suppose) , then spent a few hours bonding it all together.
another good reason for bonding the array is in some cases not bonding and earthing the array effectively can lead to the internal Rcmu in the inverter recording high discharge currents on the DC side and the inverter shutting down .

( I've even heard about installers telling customers its a means of lightning protection! and then they did'nt install it anyway )

 

[moggy1968]

I wonder if the weay it is wired affects this. If you run your DC in a big loop will that tend to produce this effect more if you wire to the end, then run a long cable back the same route?
I haven't explained that very well, but hopefully you get the gist.

 

[SibertSolar]

You're right Moggy, the way the DC cable is routed can have an impact on inducted voltages. I think it only really applies if the +ve and -ve branches are routed in such a way that they don't run next to each other though.....which hardly happens I'd imagine. I could be wrong but I have an inductive loop picture in my head from a document/guide somewhere along the way, maybe the MIS document? Can't check it right now....

That said, I think this "issue" with potential differences detected on the array frame is more related to the parasitic capacitive AC leakage current generation of the array and TL inverters as mentioned above.