Array frame earthing

[Jimbo2]

Hi, still confused about array frame earthing.

I will be fitting my first install soon on a garage roof, even using the DTI decision tree its unclear as to earthing the frame.

Will be using a electronic ( transformer-less ) inverter from power one ,3kw system.

Decision tree from DTI mentions only Class two panels etc , nothing about inverters. so should i leave it floating ?

Or is it better to earth to main earth terminal, supply is a PEN ?

Any help / guidance would be great

Thanks James

 

[jason121]

Leave it floating, before the new guide came out, most PV installs had to be earthed.

 

[Jimbo2]

Leave it floating, before the new guide came out, most PV installs had to be earthed.

Hi Jason, ok the new guide, are you referring to the new DTI guide at what revision ? im reading that all none transformer inverters must be earthed, if you have a reading under 21Mohms , if its over leave it floating ....... why cant this subject be clear

 

[Worcester]

DTI Guide? that must be version 2 - This one replaced the DTI guide: http://www.microgenerationcertification.org/images/PV Book ELECTRONIC.pdf early 2013 page 40,
The panels will be Class II, you should be using double insulated DC cables anyway, so the only real question is: "Is the PV array frame an extraneous conductive part?" and in most cases the answer will be No.

 

[Jimbo2]

DTI Guide? that must be version 2 - This one replaced the DTI guide: http://www.microgenerationcertification.org/images/PV Book ELECTRONIC.pdf early 2013 page 40,
The panels will be Class II, you should be using double insulated DC cables anyway, so the only real question is: "Is the PV array frame an extraneous conductive part?" and in most cases the answer will be No.

Hi,

I have class 2 and double insulated.

So if i have over 22mohms then on earth is required. even thow its a transformer less inverter .

This subject needs more clarity surely by the DTI i mean .. after talking with the manufacture power one they have advised ( not in writing) to earth the array frame if its easily accessible as you may get a shock, from AC DC leakage etc ......

So bottom line is if i have class two and double insulation and a power one transformer less invert with over 22mohms when testing insulation resistance as per the decision tree im ok not to earth the array is that correct .

Thanks again for all your support

 

[Jimbo2]

further to this i have just read the module install spec sheet from Canadian Solar , they are referring to all modules / panels being grounded. as below . any advice please

5.2 GROUNDING


Although the modules are certified to safety class II, it is recommended that they be grounded and the module installation complies with all local electrical codes and regulations. The earth grounding connection should be made by a qualified electrician. 2Connect module frames to each other using adequate grounding cables, the recommended size is 4-14mm (AWG 6-12) copper wires. Holes provided for this purpose are identified with a green label. All the junctions on the conductive connection must be fixed. The bolts, nuts, flat washers, lock washers or other relevant hardware should be made of stainless steel.


Grounding hardware is not provided by Canadian Solar Inc. Two specific grounding methods are recommended for Canadian Solar Inc. standard modules with 5 mm grounding holes, as described below. Other grounding methods can be acceptable, provided they comply with all local electrical

 

[BruceB]

There will be as many opinions as there are ways to do it. Although the manufacturer recommends it, he does not say 'is to' or 'must', so I think some discretion remains. He also says follow local codes and regulations. Including 7671 and MCS in that category then our UK 'code and regulations' say grounding is normally unnecessary.

In this litigious age it is probably worth making a specific note in the design record of what decision you make and why. As long as it is reasonable and/or you can cite an authority then you will probably be ok. Where you would be at risk is if there was an accident and there was no record of you having considered the issue at all.

 

[Jimbo2]

thanks Bruce, very good advise i will make sure i record all within the design file , just a little question if my resistance is under 22meg during test would i connect to earth as its a extraneous part (dti) ? so say or is there a array fault

 

[BruceB]

I would say yes, connect to earth, because below 23,000 ohms it can be considered extraneous and likely to introduce an earth potential......

However I note that within the last week or so there has been something on one of these forums that NIC are now recommending a value of 7,667 ohms. The former corrsponds to a current of 10mA; the latter 30mA. The 10mA value was chosen because that is the value of current above which most people cannot let go if they grasp something live.

Edit: the discussion on the other forum is here:
http://www.------.org/forums/forum/messageview.cfm?catid=205&threadid=34339
I have not chased down the references

Edit2: not sure how that ref popped up as it is 2010, unless some recent messages were deleted