usual question - pv array earthing!

[paulsamuel1984]

I am currently carrying out a design for a 4kW system, using class 2 modules, cables and connectors. using sunnyboy 3.8kW (with isolation transformer).

Having read the dti guide i am sure I am to leave this system floating (TNCS earthing system). i.e. I will not connect/bond the rails, frame etc, and will then not connect to new earth spike.

can someone confirm if this is the right thing to do?

 

[BruceB]

That looks correct. Is there any reason you think not?
Regards
Bruce

 

[malcolmsanford]

If the frame is not an extraneous conductive part then there is no need to bond it and no need to earth it if the invertor is a transformer type and therefore has seperation.

 

[paulsamuel1984]

Thanks for this. The reason I am second guessing myself is because I have been speaking to a fellow installer who bonds framing / mounting structure etc. together even though the array is left floating. so, in short everything is bonded together but there is no connection to either earth rod or met.

Am I missing something? there is no merit in carrying this process out unless you are connecting to earth. correct?

 

[malcolmsanford]

Basically he as got a lot of pretty Yellow/Green cables between the frames and the brackets, so totally useless

 

[paulsamuel1984]

Exactly the point I made to him, maybe he finds it aesthetically pleasing!

 

[ihugs]

Earthing of the array is not required,also earthing for lightning protection is not required. you only have to earth the array if the inverter does not have an isolating transformer between AC and DC parts or any conductive part of the array and frame is in the equipotential zone.

 

[malcolmsanford]

Earthing of the array is not required,also earthing for lightning protection is not required. you only have to earth the array if the inverter does not have an isolating transformer between AC and DC parts or any conductive part of the array and frame is in the equipotential zone.

Why would you want to earth a class II installation or bond a non extraneous conductive part, even if it is within an equipotential zone?

 

[ihugs]

If the inverter does not have an isolating transformer between AC and DC parts, like i said in last post.

 

[SolarCity]

Is there no merit in bonding the rails together, without then bonding this to the MET?

 

[paulsamuel1984]

that is my question. i cannot see any merit in bonding the rails together if there is no connection to earth. anyone agree or disagree?

 

[SolarCity]

How large is the risk that one rail could have a negative fault to it and another rail have a positive fault to it?

 

[malcolmsanford]

How would these rails develop a fault, they are not exposed conductive parts because the panels are Class II equipment, and unless there is a chance of the rails being at a different potential and therfore a extraneous conductive part, which is highly unlikely on a floating rail, then earthing and bonding can be more dangerous, as you could transfer a fault from the equipotential zone onto the frame work.

 

[SolarCity]

Perhaps a fault on the cable? Perhaps from damage from vermin or birds?

I just think there is a special risk with PV in that the installation is hidden from view yet not shielded from damage. These systems are likely to be on a roof for a long time.

I'm not saying bonding the rails together is the right thing to do, I'm just asking other opinion.

 

[malcolmsanford]

Perhaps a fault on the cable? Perhaps from damage from vermin or birds?

I just think there is a special risk with PV in that the installation is hidden from view yet not shielded from damage. These systems are likely to be on a roof for a long time.

I'm not saying bonding the rails together is the right thing to do, I'm just asking other opinion.

Not sure if birds would attack it Briggs but I do see your point about vermin or squirrels. Is there in corelation between Panel double insulated tails and vermin attack.