fronius IG-TL 3.6

[SPARKY51974]

Hi all bit of advice needed first time using these inverters, does the array need earthing when using these inverters the system is on a PME supply?

 

[binky]

On PME you treat framework at 'Extraneous conductuive part' only if it can be touched through say a Velux window. In which case you earth frame through earth rod not the incoming supply. Other than that I would not earth frame.

 

[SPARKY51974]

No velox windows present so your saying that the array needs roding

 

[Manator]

I think I understood Binky's reply to mean that IF you could come into contact with the frame through a velox window for example then the frame would require bonding, this bonding would go to a ROD though and not the incoming supply.

So? No velox windows, no possible means of touching the frame, no need to bond.

Well that's what I read into his post.

 

[SPARKY51974]

Yes I see your right there seems I mis read the first reply just seems to be a big grey area with earthing on solar pv everybody I speak to says don't earth here s one though if u have a velox window and can touch the frame then surely you could possibly make contact with two different earth potentials PME and TT

 

[steptoe]

:slap

do you really have PME? then its not a problem,

but are you saying PME and really you mean TNCS?

---------- Post Auto-Merged at 18:14 ---------- Previous post was made at 18:13 ----------

oh, and you cannot have a TT system simply by putting a rod to your array,

TT refers to a system of earthing in regards to your supply,

 

[SPARKY51974]

Yes it's TNCS which is same as PME isn't it and surely if you put a earth spike down you are going to have two different earth potentials

 

[Manator]

Earthing is still one of the main stumbling blocks for all electricians, its normally because we seldom question the relevance.

We all tend to over complicate earthing, and to be honest the basics are very very easy to understand, its just that we all think it is more complicated than it really is.

The primary reason for any earth is to supply us with a route for any fault that is or could be present so to protect us and buildings from harm, by dissipating any currents directly away from the installation. It is also used within the installation to equalise any raised voltage which could be harmful due to potential differences.

Farraday showed the possibilities of having no reference to earth, and his concept is still used today in some specialist installations, Testlar was another genius who developed some startling results and on of his experiments if you could duplicate today could win you a fortune. It even has a cult following of scientists who are trying to solve the mystery.

Think of earthing like this:-

A motorway has a crash which closes all the lanes, up ahead two people are trapped in their vehicle, the emergency services use the hard shoulder and reach the trapped people in the car, free them, remove the blockage and reopen the motorway.

Thats the basics of what an earth does, it uses the hard shoulder to remove the fault, free the potential for harm, and eventually when the fault is clear, re-opens the path.

 

[SPARKY51974]

Yes that is understood so u are saying arrays need connecting to earth rod only if they can be touch from within the equipotential ie from a velox window

 

[Manator]

Yes that is understood so u are saying arrays need connecting to earth rod only if they can be touch from within the equipotential ie from a velox window

I would use my own personal assessment based on risk and probability. We have to remember placing out of reach is not allowed for domestic installations, with that in mind could you possibly ignore the regulations? I do like grey areas, they are inbuilt due to the complex issue of proper design that ticks all the boxes.

 

[SPARKY51974]

Thanks will consider what you have said, and yes these grey areas always seem to throw up problems as you have people sat on either side of fence with there own views on the subject And who's to say which is right and which is wrong as everybody has there own interpretation on the regs. One last question on these inverters do they require type B RCDS for pure dc faults or just follow regulations for BS7671 for circuit installed in armoured on surface

 

[Manator]

I have no idea about any solar installs, never done them. Our members who have, will be happy to give you their views.

Remember at the end of the day each and every one of us has to do what we are comfortable with, I sometimes go over the top, but its because I want to, or even sometimes unsure, so I do it as a belt and braces just to cover me backside.

We can never be totally 100% right every time.

I like to think I am close, but I am not.

 

[steptoe]

Yes it's TNCS which is same as PME isn't it and surely if you put a earth spike down you are going to have two different earth potentials

NO,

its not.

a common misconception from people,

do you understand how earthing arrangements are designed, and what the actual letters stand for?

 

[SPARKY51974]

Sorry to be deviating away from original question Yes I understand earthing arrangements and understand what the letters are for correct me if I am wrong please T is terra French if I can remember for earth which means direct connection to earth second letter N is for neutral and it denotes how metal work of an installation is earthed the last two C combined and S separate indicate functions of neutral and protective conductors. So a TNCS system is basically a TNS but sheath or core is also neutral ie forms a combined neutral and earth and these are separate conductors on the installation side system also know as Protective multiple earthing

 

[Manator]

PME was used to denote Points of Multiple Earthing, which as you can see is different by definition to TNCS.

 

[steptoe]

Sorry to be deviating away from original question Yes I understand earthing arrangements and understand what the letters are for correct me if I am wrong please T is terra French if I can remember for earth which means direct connection to earth second letter N is for neutral and it denotes how metal work of an installation is earthed the last two C combined and S separate indicate functions of neutral and protective conductors. So a TNCS system is basically a TNS but sheath or core is also neutral ie forms a combined neutral and earth and these are separate conductors on the installation side system also know as Protective multiple earthing

again, NO, maybe mistaken for, but not the same,

try a search for simplified earthing systems

---------- Post Auto-Merged at 19:44 ---------- Previous post was made at 19:43 ----------

or arrangements , I cant remember which it is, :|

 

[Manator]

http://www.talk.electricianforum.co.uk/student-learning-zone-c-g-2330-levels-2-3-c-g-2381-c-g-2391-other-co/15480-simplified-earthing-arrangements.html

 

[binky]

Getting back to the question, the roof is considered outside the equipotential zone for the house,(assuming not steel frame and metal sheeting) unless you have a velux window which you can reach out of and touch the array. Generally this means no frame bond needed even if on PME / TN-C-S. Fronius transformers are 'isolating' too, also no earth path. Not all transformers are the same....check before fitting.

Micro inverters are usually AC and do need bond, albeit there is some argument about what size is required

 

[SPARKY51974]

Thanks for the help unsure on these inverters as first time used them and I'm sure the TL means they are transformer less all electronics inside also unsure about RCD protection on these things type b for pure dc protection I'm thinking as sure from when I did my course they said as transformer less dc faults can transfer to ac side and normal RCD cannot detect pure dc only pulsating dc

 

[binky]

TL is indeed transformer-less working on the principle of Galvanic Isolation (whatever that is). For DC to get to AC side would require major fault in inverter which would probably have caused the house to burn down!! No RCD fitted before the inverter is ever going to see any DC faults, anything that could cause such a major catastrophy would have tripped any RCD anyway from AC defects or tripped MCB on the circuit. Shutting down AC side on inverer then shuts down DC side of inverter

Fronius units have in-built earh fault detection (as have most decent transformers - it's part of start up cycle which checks cable insulation) and has effectively a built in RCD.