Dti Guide..... When will it be released??

[matt25]

Hi, does anyone know if there is a proposed release date for the 3rd edition??

 

[TedM]

It is supposed to be sometime in January.

 

[matt25]

Thanks Ted

 

[The Solar King]

Would confirm Ted's comments. Draft 3.8 is available to download. Lots of useful changes.

 

[matt25]

If it says no need to earth tl's im gonna top myself lol. Could you tell me the website to download this pls?

 

[SolarCity]

I can't understand all the despair surrounding bonding an array frame. It's not exactly the most labour intensive, expensive or complicated job, is it?

 

[matt25]

No Biggs it isnt, not now ive learnt from my mistakes anyway lol. Do you know where to download the draft from?

 

[edexlab]

the draft is on a thread here somewhere

But I agree with Biggs and don't understand why people have an issue with it, in normal Electrical work you have to do the bonding etc whats the difference

Also I read the draft a couple of months ago and to me it was addressing if you should bond the array depending on whether or not its an exposed / extraneous conductive part or not
unlike the current guide it does'nt mention the use of a TL inverter in this section (I know, its not finished yet)

Earthing the array is a in the case of a Tl inverter is a different issue and manufacturers guidelines recommend you do this
since doing my first TL and i've done about 70 I've checked the voltage between the earth wire and rod/Met on most systems installed just to see and on a good day its usually around 100v Ac in lower light conditions it can fall to around 50v (I've never checked the current though my clamp meter won't do mA )
which I would say is not good for you and in my view makes the case for earthing TL systems

 

[matt25]

I wonder how many people would still earth the array if the new guide doesnt make refererence to the Tl's, like it does at present?

 

[The Solar King]

DTi guide here

 

[BruceB]

edexlab, I can well imagine that you could measure significant voltage on an array framework with a modern high resistance digital meter. You really need to see what current you can draw from it to see whether there is in reality any risk of shock. I can remember when I first moved into this house I could measure the same voltages (50V - 100V) on unterminated wires here caused by capacitive effects, but they were not be able to generate a significant enough current to give me a shock.

Regards
Bruce

 

[edexlab]

Bruce B
I can safely say it is enough of a poke to make you flinch away from the contact point which could be dangerous if you are at height eg on a ladder, but as I stated I have'nt as yet measured the current as my clamp meter does'nt register milliamps
I posted that I've been testing the Tl arrays for some time now this was because on the first one I turned the system on and was checking what voltage if any there was between array and earth rod and accidently touched the rod and earth wire while the system was on, daft thing to let happen I know but there you go (curiosity killed the cat) , anyway without knowing the current level present it certainly made me jump.

Incidentally I've just finished our first console job today 4000TL sanyo 250's and next door the neighbour is having an identical system
the installer is new to the game 3rd job and asked why I had run a cpc between the panels and earthed via rod so I explained the reasons why and he did'nt seem convinced that it was necessary, I went there to commission this morning ,afterwards went over to have a chat with the other installer who was not there but his apprentice was working at the house , the first thing he said was that their system was turned off after he received a belt off the panels ,and that they were now going to earth and bond them together
This installer seemed to be competent but he has had some quite bad advice from his training provider and he said from the technical helpline of the MCS who both told him that a 90 metre run in 6mm swa would be ok for the current the system would produce and that there was no need to earth any array
With 5 <4kw systems nearby, 3 of which I've done myself , I've noticed the local voltage regularly over 250v I told him to expect the system to shutdown at some point and also a large difference between the meter and inverter totals

 

[Scott H]

Has anyone heard anything about the new competant person scheme for 'renewables' ???

 

[solarsavings]

Yeah, they want more money out of us. There's only so much they can take...................

 

[Scott H]

well, once it comes out, no more self certification until the CPS is sorted ... lets hope we all get on well with our Building Control Departments ....

 

[JulianC]

Is it just me, or does getting a belt from an array frame carrying class 2 modules connected in double insulated cable seem a wee bit worrying? I mean, wtf?

 

[BruceB]

I can safely say it is enough of a poke to make you flinch away from the contact point which could be dangerous if you are at height eg on a ladder,......

Thanks. Interesting. Draft version 3.8 of the Guide would suggest do not bond/earth as I read it. It will be interesting to see where it ends up.

 

[edexlab]

Is it just me, or does getting a belt from an array frame carrying class 2 modules connected in double insulated cable seem a wee bit worrying? I mean, wtf?

The way you have worded this reply seems to imply that there is a short circuit or wiring fault of some kind on the frame, this is definitely not so, all my jobs get tested thoroughly and if there is any doubt I'm not afraid to tell the roofers to take panels off so it can be checked properly,( this happened once when the roofers damaged a cable causing a short and I was not popular but it was justified).
when it first happened I spoke to SMA as I thought it could be caused by some kind of damage while the install was being carried out and they said this was why the TL systems needed grounding, I'm sure you will have read the pdf on this at some point, as I know from your posts that you are knowledgeable , and also the double insulation of the panels and cables does not prevent this potential from transferring to the array frame and is just basic protection
Also as I have posted before its an Ac voltage not Dc .

I would say test one you have done yourself and see what you find seeing is believing


Sma's pdf How does a capacitive discharge occur:

"During operation, the PV module is connected to the alternating current grid via the inverter. Thus, depending on the device type, a portion of the alternating voltage amplitude arrives at the PV module.
At this point, two cases must be distinguished (see illustration):1. Transformerless inverter In almost all transformerless models, half the grid amplitude is operationally passed on to the module.
The set up oscillates with 115 V / 50 Hz. This applies to Sunny Boy / Sunny Mini Central devices with "TL" in the product names.
2. Inverter with transformer In devices with a transformer, the voltage within the PV module fluctuates with a so-called "ripple" of just a few volts.The fluctuating voltage constantly changes the charge state of the parasitic PV capacitor. This is associated witha displacement current, which is proportional to the capacitance and the applied voltage amplitude."

 

[SolarCity]

Thanks for the info from SMA's PDF. With that in mind, I can't see how anyone can really say that bonding the array frame is not desirable. The safety benefits surely outweigh the problems?

 

[JulianC]

The way you have worded this reply seems to imply that there is a short circuit or wiring fault of some kind on the frame,

Not at all. Not doubting your workmanship or observations for a minute. Far from it, I am more amazed that this is considered normal by the likes of SMA etc.

What I cannot get my head around is:
- How an AC voltage of sufficient magnitude to pass on a tingle is present on a frame that is isolated from the modules and cables. It's been a (loooooong) while since I learned about stray capacitances etc. and I will own up to having forgotten pretty much all I learned. However I am amazed that the effect is of such a magnitude.
- How having a transformer in the inverter somehow manages to block this AC transfer, when transformers are generally quite good at transferring AC from one side to the other? I guess it's just a totally different inverter topology....

Me no likee

Do Froniuses (Fronii?)also suffer from this?