Grounding of Module Frames with transformerless inverters?

[jerriais]

Hi all,

I heard somewhere that with the new transformerless inverters from SMA and others there is a need to ground all the modules and mounting structure.

Can anyone shed any light on this?

Thanks!

 

[SolarCity]

That's right. If the inverter is transformerless then the array must be earthed.

 

[jerriais]

So that would be a lot of extra work on the roof, not sure if it's worth getting the TL inverters then, and they're more expensive than the regular Sunny Boy inverters.

 

[SolarCity]

Also, if the incomer is PME then you have other issues. I don't really see the point of transformerless inverters but I'm sure there must be some point to it.

 

[dansk]

We use these transformerless inverters with electrical seperation built in.

 

[jerriais]

It's nice that they have 2 MPPT trackers so even if one string is shaded the array can produce decent power, good for E-W roofs for example but with all the extra hassle I don't think I'll be trying them. Steca do a double tracking inverter which isn't transformerless (I think) so that might be a better bet. Thanks for the info Biggs!

 

[jerriais]

So does that letter give you official clearance to install without grounding the modules?

 

[TedM]

Is there a typo in that letter where they mention 300mA in 0.3s in the text but have 30mA at 0.3s in the table?

 

[dansk]

It gives official notification that the inverter has built in protection and therefore complies with the electrical seperation issue and RCD class B, and if your complying with that then everything else concerned with it drops into place.

 

[dansk]

So does that letter give you official clearance to install without grounding the modules?

No its just saying anything over 300ma must comply to 0.3s (thats the way i interpret it)

 

[JulianC]

I've seen that letter before. The RCD, as far as I can tell, does not comply with the requirements of BS61008, or whatever the BRB specifies in section 712 (don't have the book to hand). And even if the RCD is suitable, it does not provide electrical separation.

There are two separate requirements for using transformerless inverters and both are required:

-Type B RCD, if there is the possibility that in the event of a fault, DC could be injected onto the grid (incidentally, most SMA transformerless inverters are, by design, unable to inject DC onto the grid, therefore the RCD is not required)

-Array frame bonding. Required if there is no electrical separation between AC and DC within the inverter.

Simply fitting an RCD does not remove the need for bonding the array

 

[dansk]

Well actually reading the letter about 10 times now, it isnt really an RCD, its a monitering device built to Class B standard, therefore it would prevent any direct injection of DC into the grid - but as you say its not technically "electrically seperated", its more "DC injection in AC protected" if that makes sense.

Anyhow its a usefull feature.

 

[erf151an001]

Is this going along the same lines?

I have fitted 2 of these Europa 1500 inverters supplying 2 strings. I have left the array frame floating as per what I thought you did. What they go through with you on the install course etc.
[FONT=Calibri,Bold][FONT=Calibri,Bold]

Declaration​

[/FONT][/FONT]

Integrated Redundant Protection in the EUROPA InvertersEuropa Series inverters (which contain the EUROPA-1500, EUROPA -2000, EUROPA -3000,EUROPA -4000 and EUROPA -6000) are equipped with a device for protection against groundfault in accordance with the German Standard VDE V0126-1-1:2006-02 (par. 4.7), Italianstandard CEI 11-20 (2004-08) e all normal ENEL DK5940 Ed. 2.2 (April 2007), Spanish standardRD1663/2000, United Kingdom standard G83/1 (September 2003 and Amendment 1 June 2008)and other country standards. All the Europa inverters sold in Europe are equipped with theprotection.The Europa inverters are equipped with redundant hardware providing fault-resistant reading ofthe leakage current to earth, and sensing of DC and AC currents and voltages. The measurementof the leakage current to ground is performed simultaneously and independently by 2 differentprocessors: it is sufficient that one finds an anomaly to trigger the protection, with theconsequent detachment from the network and stopping the conversion process.There is an absolute threshold of 300mA of total leakage current AC + DC with intervention timeof 300msec max. In addition there are three other levels with thresholds at 30mA/sec,​

60mA/sec and 150mA/sec to cover “quick” changes of the fault current caused by accidental​

contact with active parts in dispersion. The intervention time limits reduce progressively withthe increasing of the fault current changing speedy: starting from 300msec/max for a 30mA/secvariation, are reduced at 150msec and 40msec for variations of 60mA and 150mA.Please note, however, that the system integrated on the inverter protects only against groundfaults occurring upstream of the inverter AC terminals (that is towards the DC side and so tophotovoltaic modules). The leakage current that can occur in the AC line from the gridconnection to the inverter are not detected and need a additional protection system.For the protection of the AC line, the CEI 64.8, par. 712.413.1.1.1.2 second paragraph says:​

“When an electric installation consists of a PV system​

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​

​

without – at least – a basic separationbetween the AC and the DC side, the differential device – installed to prevent from indirectcontacts by means of an automatic stop – must be of Type B according to IEC 60755/A2. If theinverter in not able to inject ground fault DC in the electric installation, the differential device​

type B according to IEC 60755/A2 is not required.”​

From what described above concerning the differential protection integrated in the SolarEuropa inverters, the installation of a differential device type B is not required for protection ofthe AC line.​

Bob Tsai​

Safety Manager

 

[erf151an001]

I have supplied my inverters via a 16amp type B MCB installed into an existing consumer unit. The existing consumer unit was installed as per 16th edition. TT earthing system, so 100 mA time delay main switch for the fixed equipment and a 30 mA for the socket outlets.

I have installed my MCB into the fixed side of the consumer unit which gives it 100mA RCD protection. The cable is run externally in non metalic conduit from ground floor consumer unit then up into the loft space where it is clipped direct and supplies the isolators.

The way I see it I dont need to provide it with 30 mA protection as its not buried in a wall or the inverter is not in a special location.

The array I have left floating and not connected to earth in any way.

 

[BruceB]

Too many words. He is dissembling. He has incorrectly quoted a regulation, the correct one is 712.411.3.2.1.2.And he has not used the precise words from the regulation. What you need is one sentence from Bob Tsai:

"The inverter is by construction not able to feed dc fault currents into the electrical installation."

Otherwise you need a type B rcd (if an rcd is required at all).

Regards
Bruce

Edited to add: You must have posted whilst I was typing. I see an rcd is needed. You have to make a judgement on whether you think the inverters meet the exemption. His letter could be clearer. And if it is transformerless then as I read the DTI decision tree, with TT you bond array to MET.