Fronius TL inverters

[Markc]

I was talking to a Fronius rep today at Eco Build about their range of TL inverters.

Apparently they are the most efficient out there but I raised the point about Class B RCD protection and boning of array frame via stake.

He told me there is no need for Class B RCD protection as they are built in to the inverter. Not seen anything about it on their promotional material and not having much confidence in what he was telling me I thought I'd ask here.

We have not installed one of these yet but do have a design in place for one and we have included bonding and Class B RCD anyway and will install it if we get the job.

 

[SolarCity]

Not sure about this. Does he mean there is literally a Class B RCD in the inverter itself? Or is he talking about equivalent protection from the inverter itself? If it is the latter then I'm not sure it'd be enough.

I think you're probably best off installing the seperate RCD and cover yourself. Out of interest, which manufacturer are you using?

 

[Markc]

Not sure about this. Does he mean there is literally a Class B RCD in the inverter itself? Or is he talking about equivalent protection from the inverter itself? If it is the latter then I'm not sure it'd be enough.

I think you're probably best off installing the seperate RCD and cover yourself. Out of interest, which manufacturer are you using?

If the job comes off I will be using Class B RCD and bonding anyway. I'm not 100% happy with Mr Rep's answers. I have been looking at the ABB "PV RCD" from RS. Do you know of any more?

 

[SolarCity]

No, haven't heard of any more. My wholesaler got spectacularly confused when I brought it up last time.

 

[Markc]

No, haven't heard of any more. My wholesaler got spectacularly confused when I brought it up last time.

You're not alone there! I was told a Time delay RCD would do! Good old Electric Center.......!

RS was the only place I could find them when I web searched it but I'm sure someone else will do them by now. Just need to find where.

 

[Ramjam]

My understanding is that if the inverter is capable of injecting DC into the grid then that is one problem with TL inverters and the galvanic isolation or lack of it with regards earthing RCDs etc. The Fronius rep will be referring to the built in DC breaker boasted on the data sheet. I understand that they have isolation between the AC and DC sides and it can be argued that this is enough but that some authorities remain unconvinced.

Why go for TL? I was going to offer TL inverters and in the end went for the SMA HF range as they are smart looking, efficient and look robust. The fact that the fronius TL brochure boasts about the ease of swapping PCBs makes me worry. To my mind how easy the swap is is insignificant compared to the call out and the reputational damage of having kit go wrong!

 

[Markc]

The TL is what the client want's. He's read the web blurb and feel for it. We had to design the system around the TL inverter more's the pity. He's on a TNS arrangement so the bond can go back to the MET and not stake which is an advantage. I would hate to see a stake on a array. The Class B RCD within a standalone board will go in if we get the job regardless of what the Rep has said. I would rather be criticised for installing one over not installing one.

 

[TJLinks]

Are you sure the RCDs from RS are type B and not type AC or A, type AC are sensitive to pulsed DC and type B are sensitive to smooth DC?

 

[Markc]

Are you sure the RCDs from RS are type B and not type AC or A, type AC are sensitive to pulsed DC and type B are sensitive to smooth DC?

RS call them a PV RCD? I have not checked or used one form RS just found them as a web search.

I have however got this from ABB.

When I need one I will order it form our wholesalers and not RS. I have issues with RS anyway after them not refunding over £150 on an item which was damaged on delivery? Long story!

 

[TJLinks]

I rang ABB technical today and for their F202 type B 25A 30mA RCCBs they gave a list price of over £400!!!!!!!!

 

[SolarCity]

400 quid?! Christ on a bike! I hope they offer decent discount.

 

[BrummyGit]

I recently had a Fronius IG TL installed in my home and initially it was connected via the 30ma RCD in my consumer unit. This caused repeated tripping and has since been wired to the non-RCD side, but this gave the opportunity to read the manual which I thought might help:

The design and function of the inverter provide a maximum level of safety
during both installation and operation.
The inverter provides operator and equipment protection through:
a) RCMU
b) monitoring the grid

RCMU = Residual Current Monitoring Unit
The inverter is equipped with an RCMU according to DIN VDE 0126-1-1.
It monitors residual currents from the solar module up to the inverter grid
connection and disconnects the inverter from the grid when an improper
residual current is detected.
Additional residual current protection may be needed depending on the
protection system of the installation or the requirements of the utility company.
In this case, use a residual current circuit breaker with a release
current of at least 100 mA.


I hope this is useful.