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Posted By Topic: Tesla Powerwall 2 and RCD protection

Solarman
Aug 21 2017 10:30

If you install an approved battery inverter (such as a Tesla Powerwall 2) that provides household back up power and stores surplus solar power for self consumption at night, do the existing household circuits need to be upgraded to include RCD protection? The existing circuits are MCB's only.
http://www.tesla.com
   

pluto
Aug 21 2017 10:46

Solarman Aug 21 2017 10:30

If you install an approved battery inverter (such as a Tesla Powerwall 2) that provides household back up power and stores surplus solar power for self-consumption at night, do the existing household circuits need to be upgraded to include RCD protection? The existing circuits are MCB's only.
http://www.tesla.com


My comments
Approved by whom?
I know of no NZ approvals body or requirements.

RCD protection would typically be required on the input to the battery system for the inbuilt battery charger/inverter and it is most likely that a normal RCD (type A) will be unsuitable due to the amount of d.c. in the current flowing in the mains input connection. Typically a type F or B RCD is usually required.

If the existing house protection does NOT have RCDs, the grandfather provisions of the ESR 2010 does NOT require retrofitting of RCDs, but if doing major work on the switchboard and if requires being replaced the AS/NZS 3000 section 2.6 requires that RCDs be fitted as for a new electrical installation.
   

AlecK
Aug 21 2017 10:53

Sounds as if you want to use the energy both as co-generation (while mains power is also supplying) and also as "back up" when mains power is not available.

There are currently NO approved guidelines for doing this, and the requirements of each are pretty much mutually exclusive. Certainly no off-the-shelf inverter is capable of doing both functions by itself while complying with mandatory Standards - additional equipment will be required.

Not sure what you mean by "approved" inverter; but the basic current requirements for a grid-connect co-generation are that the inverter comply with AS 4777.2 and have a grid-protection device.
The basic requirements for an alternative supply include full isolation between all sources.

However neither mode of operation would require installation of RCDs to circuits that don't already have them.

More to the point is to ensure that any RCDs that are fitted will operate correctly on the inverter's output waveform.


   

Solarman
Aug 21 2017 11:44

This model inverter is approved to AS/NZS4777:2015 as of April this year. These units are being installed in Australia now and have been since June this year I believe.
The initial response deadline to the first draft of AS/NZS5139 closed last week and I understand that there have been thousands of submissions. The final version may be some time away yet.
Thank you for your prompt replies to the question.
   

evanh
Aug 21 2017 11:44

The way I've seen the wiring diagrams of these hybrid type inverters, to achieve both co-generation and back-up, is they provide a limited secondary output for an independent sub-circuit that effectively becomes a UPS.

The primary output is the regular grid connected method with the usual anti-islanding feature.

   

pluto
Aug 21 2017 11:46

Recent extensive studies by me show that the correct RCD selection is based on the loading being supplied and the d.c. currents (both pulsating and constant) that are present in the load input current t is many times more critical that than the inverter output waveform when selecting the correct type of RCD to use.
   

pluto
Aug 21 2017 12:04

Solarman Aug 21 2017 11:44

This model inverter is approved to AS/NZS4777:2015 as of April this year. These units are being installed in Australia now and have been since June this year I believe.
The initial response deadline to the first draft of AS/NZS5139 closed last week and I understand that there have been thousands of submissions. The final version may be some time away yet.
Thank you for your prompt replies to the question.

My comment

The approval you quote is the Australian Clean Energy Council approval for AUSTRALIA only, it does NOT cover use in NEW ZEALAND.

The only approval in NZ is currently AS 4777.1 which does NOT covewr this type of Inveter system at all.
   

Solarman
Aug 21 2017 12:57

It is my understanding that AS4777.1:2005 was superceded and changed to a joint standard by AS/NZS 4777.1:2016 in March this year, with a note in the preface that 6 months after the publication date (September 2016) ie March 2017, this standard may be adopted despite the fact that it has not yet been mandated by the regulators in NZ.
HOWEVER, if this standard is utilised for an installation from March 2017 in NZ, the later version (ie AS/NZS 4777.1:2016) MUST be clearly specified in the Coc.
Within this standard, there is a reference (Sect 2.3) to any inverters utilised shall comply with the requirements of AS/NZS 4777.2:2015.

   

pluto
Aug 21 2017 13:27

In NZ the approval of any electrical standard can only be approved by the Electrical (Safety) Regulations 2010 is schedule 2 of those regulations.

Currently, this is AS/NZS 4777.1.

What is written in the Standard does NOT and can NOT overrule schedule 2 of those regulations.

   

Solarman
Aug 21 2017 13:58

If it is a published NZ standard and approved by the NZ Standards Approval Board (as it was on 17th August 2016)
AS4777.1:2005 was not a joint standard. AS/NZS4777.1 2016 is a joint AS/NZS standard.
I recognise the fact that this version is not yet published in schedule 2, but my understanding is that only means it cannot be enforced exclusively. Ie the 2016 version cannot be mandated, but it does not mean it cannot be used, provided you specify the later version on the Coc.
   

AlecK
Aug 21 2017 15:30

You're corr5ect that a later edition (in this case AS/NZS 477.1) can be used despite not yet being cited in schedule 2... BUT only provided such use does not contravene any provision of the cited edition 9in this case AS 4777.1: 2005.

Such conflicts are not common, but they can happen; so it's important the cited edition be checked, and not to blindly follow the later one.
   

Solarman
Aug 21 2017 16:32

Thanks for all your comments today. I would like to think that a standard published 11 years after the previous version is an improvement all round from a safety and methodology perspective. However, your point about not blindly following the later version (AlecK) is valid and I appreciate you raising it.

Incidently, the supply companies have been robustly 'encouraging' the industry to adopt these new standards sooner rather than later, since there are several benefits and opportunities to them from a 'grid stability' perspective.

However, it can be unfair to impose them too soon if the equipment specified within the standard is not yet universally available from the equipment suppliers.
   

Sarmajor
Aug 21 2017 19:20

It is a complete waste of time for suppliers to encourage industry to adopt newer versions of standards.

What they should be doing is lobbying the Regulator to get the new standards included in Schedule 2 of ESR's.

Then we can all move on and use the newer versions without having to refer to multiple documents and the difference between them.

This of course applies to all of the standards that we use in our daily work.

It would be a great thing if as soon as the new version of 3000 is completed it could be used, after a suitable short transition time.

From memory the original version took almost 7 years to be adopted.
   

Solarman
Aug 25 2017 16:08

As a last word on which version of the standards may be used, please find below official response from ESS on this:

"The cited standard must always be used and quoted for certification purposes

If the standard has been amended it may be used if the installer can assure that it still meets the requirements of the cited standard, although they will still quote the cited standard.

Normally an amended standard will contain improvements, although there may be the odd case where these cause an unrealistic requirement. In this case the amended standard may not be cited at all or cited with regulatory conditions"

I hope this helps anyone reading this conversation
   

Sarmajor
Aug 25 2017 21:31

Which is ES speak for if you get it wrong you're screwed.
Use the correct version of the standard and stop listening to people telling you what is coming in new versions. It will never end well.