SMA 3000hf bonding the array?

[solar-spark]

Hi, guys does anyone know where to bond the array too? using the SMA 3000hf inverter I have never used these before so I am a bit unsure. I was told by my supplier just to bond it which I assumed was to the existing installation but after reading posts on here am I to bond it to the installation or a separate earth spike/rod?. I normally use the sunnyboy with the isolating transformers so I have never had to bond them before.

 

[coomers]

I would use a earth stake if tncs (pme) if tns (cable sheath) back to main earth terminal or if easier use stake.

 

[solar-spark]

hi,yes its a tns system i was also told that i dont have to use a type b rcd because sma inverters dont feed back residual currents in D.C and that i would be ok using a normal type a rcd is that true? i am only using the 3000hf because everwhere is out of stock with the standard sunnyboy 3000.
thanks lee.

 

[BruceB]

Surely the HF means high frequency transformer, therefore as there is a transformer they are galvanically isolated, therefore leave the array floating?
Regards
Bruce

 

[solar-spark]

thanks bruce the supplier told me i needed to bond the array he must have been confused with the TL version i start the install tomorow and will leave it floating as i do with the standard sunnyboy ones.

 

[coomers]

I agree! missed hf in original post....wheres my glasses

 

[gjcone44]

how many of you still bond the array, then bring back the earth, to leave isolated near the invertor,for i/r tests, only.? so it is still left floating. but easy for testing?

 

[ExtremePV]

Solar spark...I'd be looking for a new supplier if they can't get a basic thing like this correct.

 

[pvguru]

Hi All

i've read many of these threads and still don't understand why the array needs earthing / boding, can someone explain this to me please?

Thx

 

[Worcester]

@pvguru

See my comments on the Segen conference in Brum and the flowchart in the DTi Guide.

It relates to transformless inverters where there is no galvanic isolation.

 

[pvguru]

Hi Worcester

Thanks for coming back to me, i have read the DTI Guide, but (isnt there always a but)

i dont understand what protection is being provided, also in the guide they seem to complicate things by calling it earthing and bonding, i always thought these were different things?

thanks again

 

[Worcester]

Hi Worcester

i dont understand what protection is being provided, also in the guide they seem to complicate things by calling it earthing and bonding, i always thought these were different things?

thanks again

Earthing and Bonding are different (3rd Edition should clear this up )

Read the threads about Transformerless Inverters and Earthing this has been covered in great detail and depth elsewhere.

Oh and just to throw a spanner in the works

From the DTi Guide 2nd Edition:

"Bold text in blue against a shaded box with two ticks indicates mandatory and/or broadly recognised requirements (‘must’).
Text in blue with one tick indicates recommended practice (‘should’)."

It doesn't have two ticks in the DTi guide !!

Meaning that it isn't a MUST

Aaaaaaarrrggghhhh!

 

[pvguru]

OK

So I have a TL inverter wired to a PME (TN-C-S) supply - the DTI guide seems to contradict BS7671?

I install a "spike" (I presume they mean an electrode) and connect to the array frame

Then what - how and what am i testing for when checking the electrode, and how does this electrode provide protection against a fault on the dc side?

i have read many threads and I just don't get why an array frame is potentially more dangerous than any other system that relies on double or reinforced insulation?

what am i missing?

 

[Worcester]

By earth spike they do indeed mean an earth rod.

You are checking that you do indeed have an earthed connection (usual proecedure for testing earth rods - see Ramjam's posts on that!)

Because the array COULD get become charged, through faults and capacitive discharge.

An electric shock may be experienced from a capacitive discharge – a charge may build up in the PV system due to its distributed capacitance to ground. Such effects are more prevalent in certain types of modules and systems, namely amorphous (thin film) modules with metal frames or steel backing. In such circumstances, appropriate and safe live working practices must be adopted. An example of where such hazards may be encountered is the case where an installer is seated on earthed metal roof wiring a large PV array. In such circumstances the installer must touch the PV cabling and can get an electric shock to earth. The electric shock voltage will increase with the number of series connected modules. The use of insulated tools and gloves, together with insulating matting to stand or sit on, can mitigate this hazard.

An electric shock may also be experienced due to the PV array developing a ground leakage path. Good wiring practice, double insulation and modules of Class II construction can significantly reduce this problem, but in any installed systems, leakage paths may still occur. Any person working on a PV system must be aware of this and take the necessary precautions.

Or an aerial installer, or someone cleaning the panels etc.

 

[pvguru]

Hi

IMHO The standard earth electrode test (C1P1 - C2 & P2) is completely useless in this case as in normal circumstances we are checking the resistivity of the earth so that in the event of a fault we can have some assurance that the electrode will have sufficient contact with the earth to reduce the potential difference from the electrode position and that in some cases a suitably low resistance is achieved back to the supply Tx to allow disconnection (either with or without Rcd)

if I apply this test what values am I meant to achieve and how do I know that these are acceptable?

if my panels develop a fault that allows dc to leak to the array frame, what protection does the bonding provide as there is still no connection at this point to earth at the other side of the circuit, am i attempting to create an "local earth free equipotential bonding" ?

As I understand it BS7671 only allows for protection against first fault conditions, in order for the array frame earthing to provide any level of protection then surely there would need to be more than one fault present?

As far as capacitive discharge goes, I get it for amorphous systems as many of those function much better by having one of the dc legs earthed but cant see it for standard ploy pr mono panels?