Domestic EESS, island mode and island mode isolator

AMK said:

So, purchasing a MCS registered inverter would likely meet UK-standards - 7671 & ESQCR for safe disconnection of live conductors (including neutral) no external device required for EPS mode

You would have to ask MCS about their criteria, and whether it covers island mode capability.

A UPS never exports to the grid,

Never deliberately for sure (but neither would the EESS in EPS mode) - but whether that's the same as providing "reliable isolation" between the locally powered installation and the grid perhaps isn't obvious. Some of the "line interactive" designs of UPS are a long way from the traditional double conversion types - some in effect just having a pair of relay contacts to separate the two sides during grid fail (ignoring some early designs of US origin that deliberately left N connected though in the hope that the N-PE link on the grid side would provide earth reference/ADS on the protected side!)

I do take your point that the interior functioning of any equipment is subject to its own equipment standard rather than BS 7671 - so as long as the equipment is selected appropriately (according to BS 7671)  it's entirely possible that it's internal functions could be done in ways that BS 7671 itself wouldn't have approved of (thermostats in the N of heaters, exposed live wire elements in toasters come to mind).

So I guess there's a possibility that a simple relay, controlled by fallible electronics, could be acceptable for the purposes of isolation according to some equipment standards.

If that were the case, provided the EESS, including its EPS function, fully complied with its appropriate equipment standard, the equipment had been appropriately selected according to BS 7671, then the ESQCR would be satisfied, even if the internal means of isolation didn't align with chapter 53 or any other part of BS 7671?

   - Andy.

AJJewsbury said:

So I guess there's a possibility that a simple relay, controlled by fallible electronics, could be acceptable for the purposes of isolation according to some equipment standards.

Not to the best of my knowledge.

There are some basic criteria in IEC 61140 that the product standard should conform to.

AJJewsbury said:

If that were the case, provided the EESS, including its EPS function, fully complied with its appropriate equipment standard, the equipment had been appropriately selected according to BS 7671, then the ESQCR would be satisfied, even if the internal means of isolation didn't align with chapter 53 or any other part of BS 7671?

Well ... not really, but even if you went down that line of thinking, ESQCR still requires the installation to conform to BS 7671.

Regulation 826.1.1.1 means the installation does not conform to BS 7671.

I suppose an intended departure is possible ... but that's like declaring the installation doesn't conform to BS 7671, and the legislation does not say "or is no less safe".

Does the internal switching over to EPS in island mode need to meet regulations 537.3. Are these requirements for isolation purposes only and does not apply to the active operation of island mode as it’s a functional switching requirement governed by G99 standards. This switching being managed by the inverter’s semiconductor or relay devices, not compliant with Regulation 537.2.2 but deemed acceptable for this specific purpose. 

Isn’t 826.1.1.1 to ensure that prosumer installations have manual isolation meeting 537.2.2.1

AMK said:

Does the internal switching over to EPS in island mode need to meet regulations 537.3.

That is up to the designer of the installation to determine.

AMK said:

Are these requirements for isolation purposes only and does not apply to the active operation of island mode as it’s a functional switching requirement governed by G99 standards.

The installation needs to meet the requirements of BS 7671, and the legislation demands this.

The requirements of products standards can go where they will ... that is an issue for the product standards committees. However, it's also true that, for a particular product, more than one standards may apply if the product meets multiple criteria, or its usages extend outside the scope of just one standard ... the manufacturer or importer is responsible for assessing the standards conformity requirements for the product based on this.

AMK said:

Isn’t 826.1.1.1 to ensure that prosumer installations have manual isolation meeting 537.2.2.1

Chapter 82 is functional requirements, but in this case, functional can't be divorced from safety ... hence, we have the notion of "functional safety ".

I'm sure the Electrical Equopment (Safety) Regulations wouldn't support the view that "one Designated Standard = compliance" when others may apply.

So in EPS mode, supplying a dedicated consumer unit, if the inverter’s internal relay does not meet Table 537.4’s isolation requirement then an external automatic isolation device (island mode isolator)  that complies with Table 537.4 is required

If Manufacturers have confirmed relays ( BS EN 60947-5-1) doesn’t meet Table 537.4’s isolation requirements. Have you asked the manufacturer to provide evidence that the relay meets isolation criteria, is it combined with another switching device to achieve safety compliance in the UK market ? 

A note from electrical design of a domestic battery storage system- island mode switching arrangement: Because network arrangements, conditions and legislative provisions are different in every country, it might not be possible to use certain features of certain international battery enabled inverter products. Other products might require installation of additional UK specific compatible equipment to provide some functionality

So for a configured system where the inverter’s EPS setup powering a dedicated consumer unit, are we also required to install an external to the inverter, automatic, Line & N  island mode isolator on the inverter’s incoming side to ensure, auto disconnection of all live conductors during island mode, to comply with 826.1.1.1

As I understand it, EPS mode is normally "automatic" - i.e. keeps the power on continuously to the critical loads - so there's little or no opportunity for manually operating a simple isolator at the appropriate time. Any automatic scheme (e.g. a appropriately rated contactor) would need some kind of signal to operate it - and if we're not trusting the inverter to disconnect reliably where can we get such a signal from?

   - Andy.

Yes I agree on the EPS operation. single-phase voltage monitoring relay can control contactor to open on grid voltage loss, isolating the inverter’s line and neutral in,  to prevent backfeed during EPS mode. 

But if the inverter fails to disconnect from the mains - won't it'll keep up the very voltage the voltage monitoring relay is looking at? (presuming it's a nice clean break on the supply side with little or no other loads present on your side of the break - maybe unlikely on a conventional power cut, but could arise if your service cable is severed or a deliberate disconnection (say at your cutout). 

  - Andy.