Domestic EESS, island mode and island mode isolator

Do you plan on having EPS output power supply a dedicated consumer unit, independently connecting your essential circuits, separate from the main household consumer unit ?

The inverter’s EPS output, active during both normal operation and island mode, inverter creates a neutral-earth bond in power cuts. The EPS connects to a 100 mA time-delayed RCD, feeding a dedicated consumer unit with RCBOs for essential circuits, independent of the main household consumer unit. The other option is using a Gateway for complete installation backup.

Yes this is correct :)

Thank you and this confirms my understanding - if the EPS output is only supplying dedicated CU/circuits then we can rely on the inverter to disconnect and isolate from the grid in island mode.

Downdraft said:

then we can rely on the inverter to disconnect and isolate from the grid in island mode.

I would caution, that I have been made aware that some inverters do not disconnect from the grid using devices that BS 7671 would recognize as providing 'isolation'. See Regulation 826.1.1.1, last para, which states 'A switching device suitable for isolation according to Chapter 53 shall disconnect all live conductors from the public distribution network.'

It's also worth remembering the provision in Regulation 21 of ESQCR [Regulation 22 of ESQCR(NI)] which conains the requirement that 

21.  Where a person operates a source of energy as a switched alternative to a distributor’s network, he shall ensure that that source of energy cannot operate in parallel with that network and where the source of energy is part of a low voltage consumer’s installation, that installation shall comply with British Standard Requirements. 

(British Standard Requirements means BS 7671 in the ESQCR.)

Hi Graham. Is this the best way to ensure compliance to check the inverter model on the ENA Type Test Register (via the Energy Networks Association website) for G98/G99 certification. Also perhaps, contact the manufacturer, ask Does their  inverter provide Chapter 53-compliant isolation per 7671 Reg 826.1.1.1 & ESQCR Regulation 21.  Do you have any additional advice or steps we should consider?

I agree that it is very likely that relays are being used inside of the hybrid inverters that do not comply with chapter 53. I will ask the manufacturer and I will share the information.

What may be tripping me up is that without battery storage my understanding is that these internal relays meet the requirements of G98/99 for anti islanding. So if we are using the EPS for dedicated circuits only why can we not rely on this relay?

AMK said:

 Is this the best way to ensure compliance to check the inverter model on the ENA Type Test Register (via the Energy Networks Association website) for G98/G99 certification.

G98 certification doesn't cover island mode operation.

G99 might have been gained on "connected mode" operation only? Even if it does cover both, it might not necessarily cover the requirements of BS 7671 in this regard.

AMK said:

perhaps, contact the manufacturer, ask Does their  inverter provide Chapter 53-compliant isolation per 7671 Reg 826.1.1.1 & ESQCR Regulation 21.  

That might be the way to go. But ... I would add that there are ways you can, for example, build Product A into Product B, and "defeat" some of the provisions of the safety standard for Product A. If the safety standard for Product B doesn't have a way of verifying the provisions of Product A have not been defeated, that could be an issue.

Downdraft said:

What may be tripping me up is that without battery storage my understanding is that these internal relays meet the requirements of G98/99 for anti islanding. So if we are using the EPS for dedicated circuits only why can we not rely on this relay?

Anti-islanding is the ability of the inverter to stop squirting power into the grid, when it stops converting.

If it starts converting again, for island mode, is there any way power can "leak" (AC or DC) from one side of the converter to the other when you re-earth the "IPS" side ? This depends on a number of factors, and the particular topology ... but in some cases, there may well be a problem.

There are also some considerations for multipole vs single-pole switching devices that might need to be considered.

AMK said:

 Is this the best way to ensure compliance to check the inverter model on the ENA Type Test Register (via the Energy Networks Association website) for G98/G99 certification.

G98 certification doesn't cover island mode operation.

G99 might have been gained on "connected mode" operation only? Even if it does cover both, it might not necessarily cover the requirements of BS 7671 in this regard.

AMK said:

perhaps, contact the manufacturer, ask Does their  inverter provide Chapter 53-compliant isolation per 7671 Reg 826.1.1.1 & ESQCR Regulation 21.  

That might be the way to go. But ... I would add that there are ways you can, for example, build Product A into Product B, and "defeat" some of the provisions of the safety standard for Product A. If the safety standard for Product B doesn't have a way of verifying the provisions of Product A have not been defeated, that could be an issue.

Downdraft said:

What may be tripping me up is that without battery storage my understanding is that these internal relays meet the requirements of G98/99 for anti islanding. So if we are using the EPS for dedicated circuits only why can we not rely on this relay?

Anti-islanding is the ability of the inverter to stop squirting power into the grid, when it stops converting.

If it starts converting again, for island mode, is there any way power can "leak" (AC or DC) from one side of the converter to the other when you re-earth the "IPS" side ? This depends on a number of factors, and the particular topology ... but in some cases, there may well be a problem.

There are also some considerations for multipole vs single-pole switching devices that might need to be considered.

Presumably all these (potential) issues are common with a typical UPS setup...? (which is what the inverter is behaving as in EPS mode)

   - Andy.

AJJewsbury said:

Presumably all these (potential) issues are common with a typical UPS setup...? (which is what the inverter is behaving as in EPS mode)

Not at all. In a UPS, the arrangement is selected, and the product fully conforms to, relevant parts of BS EN [IEC] 62040 series.

A UPS never exports to the grid, and there is no possibility of "back-feed" to the grid. Bypass switching may be provided for faults downstream of the UPS, or to take it (or part of it) off line for maintenance.

In this case, the inverter (often completely transformerless) operates in parallel with the grid, and when grid power fails, can provide a backup supply for use in island mode ... this is a Prosumer's Installation arrangement according to Chapter 82 of BS 7671 and Regulations 21 and 22 of ESQCR [Regulations 22 and 23 of ESQCR(NI)]

Is it a case of confirming the inverters relays are multipole (switching both phase and neutral), tested for low leakage currents (<5mA)  

External to the inverter, lockable isolator installed on the EPS output side before the dedicated consumer unit.

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