Island Mode N-E Bond Relay, How do inverters manage this?

[nowty]

Just to jump on this, the Alpha ESS battery systems operate in this way (at least the Smile B3).

When in backup mode, i can measure 120V between L&E and N&E and 230V between L&N. I contacted them, they told me it was because of capacitors between the various connections when in backup mode.

I asked about adding a N-E bond, and it was a firm “do not do this”. I raised this with their UK distributor, who told me that the backup ideally needs to supply either a double socket or a separate consumer unit (as is my case) with an earth rod outside (which I also have to supplement the PME).

If you compare this to Tesla and others, their backups are not UPS’ as such, in that they fail over for a few seconds and this N-E bond is created. I would add that personally my view, as this is for backup purposes only, there is little risk (I am feeding a socket and my lighting circuits). I am sure this would open a debate elsewhere, however regulations are constantly changing, look at EV chargers! I am keeping an eye on this subject.

Alpha didn’t really seem to understand, and I actually purchased the inverter/battery having checked with them beforehand, and I was given the wrong information (they told me it created a TN-S output from memory, when in actual fact (after testing / install) it appears to be more aligned with an IT type earthing system).

I agree it sounds like an IT earthing type system but with the added capacitors, should be safer than without them.

[vantech2022]

Just to jump on this, the Alpha ESS battery systems operate in this way (at least the Smile B3).

When in backup mode, i can measure 120V between L&E and N&E and 230V between L&N. I contacted them, they told me it was because of capacitors between the various connections when in backup mode.

I asked about adding a N-E bond, and it was a firm “do not do this”. I raised this with their UK distributor, who told me that the backup ideally needs to supply either a double socket or a separate consumer unit (as is my case) with an earth rod outside (which I also have to supplement the PME).

If you compare this to Tesla and others, their backups are not UPS’ as such, in that they fail over for a few seconds and this N-E bond is created. I would add that personally my view, as this is for backup purposes only, there is little risk (I am feeding a socket and my lighting circuits). I am sure this would open a debate elsewhere, however regulations are constantly changing, look at EV chargers! I am keeping an eye on this subject.

Alpha didn’t really seem to understand, and I actually purchased the inverter/battery having checked with them beforehand, and I was given the wrong information (they told me it created a TN-S output from memory, when in actual fact (after testing / install) it appears to be more aligned with an IT type earthing system).

I agree it sounds like an IT earthing type system but with the added capacitors, should be safer than without them.

Are there any restrictions on using an IT system within a domestic dwelling?

[Stinsy]

Are there any restrictions on using an IT system within a domestic dwelling?

I don’t believe so. Shave sockets are IT. It is just exceptionally unusual in the UK to have ordinary lights/sockets in an IT arrangement. I’ve heard of IT being used in some scientific and computing environments but I’ve never understood the reason IT was chosen for that application.

My understanding is that you need to ensure the neutral doesn’t drift too far from Earth so an Earth-Neutral resistor is required.

[Swwils]

I think there are some real concerns with IT in domestic dwelling - normally you see it in critical care and safety critical places like that since all equipment is easier to make sure is compatible.

IT system is not permitted for a low voltage public supply in the UK because the source is not directly earthed. Think it's in Electricity Safety, Quality and Continuity Regulations 2002.

I have had confirmation from lux there is no N-E bond relay - their suggestions to "fix" this were borderline hilarious.

I am having trouble finding a suitable spark that is remotely interested in checking my designs so I can roll it out to several interested users. My local lux installer is also interested.

Would be good to see what myenergi is doing with the libbi, since it's a rebranded USTAR ESS.

[vantech2022]

I think there are some real concerns with IT in domestic dwelling - normally you see it in critical care and safety critical places like that since all equipment is easier to make sure is compatible.

IT system is not permitted for a low voltage public supply in the UK because the source is not directly earthed. Think it's in Electricity Safety, Quality and Continuity Regulations 2002.

I have had confirmation from lux there is no N-E bond relay - their suggestions to "fix" this were borderline hilarious.

I am having trouble finding a suitable spark that is remotely interested in checking my designs so I can roll it out to several interested users. My local lux installer is also interested.

Would be good to see what myenergi is doing with the libbi, since it's a rebranded USTAR ESS.

I think the world is changing and the regulations are based on aged methods that are applied to physical mechanical generators.

The Alpha products are certified to UPS standards, and comply with all of the other grid tie standards like G98 and G99. The only part that doesn’t really add up is the system when in UPS mode. I suppose you could compare this to a combustion generator being added to a property during a power failure. It’s a temporary supply. The UPS would shut down when it detects faults (overload/short circuit).

My battery is installed, working perfectly and I really have no desire to pay to have the UPS disconnected. BS7671 allows for a single piece of equipment to be powered from an IT source, and this clearly could be a class 2 or a class 1 appliance. What difference does it really make for a few lighting circuits and a backup socket, during the rare power outage?

Fully appreciate the regs say different but this is absolutely something that’s impacting many home owners with ESS/Solar.

[Oldgreybeard]

Large areas of Norway have been using IT for decades, as do almost all users of portable generators, running things like market stalls, caravans, motor homes etc, and now we have a few EVs that have a V2L capability that is also IT.

It's not inherently unsafe, but is slightly less safe than the earthing arrangements we're more used to in the UK. As a backup only supply, used with RCD protection, I don't see a particularly severe risk in using IT. It's no worse than staying in a holiday let in Norway, for example. There are many other electrical risks that are significantly more serious than running an IT supply for a few occasions when grid power fails.

[Swwils]

It's not that complicated to get an earth rod installed and then a changeover switch that also bonds N-E.

The telsa is capable of seemless switchover, via gateway as is the lux, but many wouldn't want that or do it since it's a much bigger install job. Esp since "backup" mode (aka BS HD 60364-8-2 "island mode") is not "UPS" unless the product is certified to BS EN 62040.

The floating socket is not encouraged anymore.

"It is not recommended that such a socket-outlet is provided with a means of connection to an electrical
installation or a permanently installed item of equipment"

Previous discussion on bigger and unknown gear:

https://engx.theiet.org/f/wiring-and-re ... ry-storage

[Oldgreybeard]

It's not that complicated to get am earth rod installed and then a changeover switch that also bonds N-E.

The telsa is capable of seemless switchover, as is the lux, but many wouldn't want that.

Except for the case mentioned where the manufacturer specifically prohibits having a N to PE bond in EPS mode, perhaps. Hard to see why they should be concerned about this, given that such a bond will be there when not in EPS mode, via the grid connection, but if the manufacturer has stated that it shouldn't be done then I think we need to assume they have a good reason for stating this.

Seamless switching, or a continuously available EPS supply like the hybrid Sofar models, seems a better arrangement, but doesn't necessarily solve the issue of making the thing TN-S when in EPS mode. Frankly, I'd not lose any sleep over having an IT emergency back up, as long as it had RCD protection and earth provided via a local earth electrode.

I think we can get VERY hung up on UK regs that have evolved independently of regs and methods in other countries, and often we seem to have an almost "ruling empire" view that the ONLY safe approach is ours, and that all other systems, regardless of their track record in the countries in which they are used, are inferior.

[Marcus]

Are there any restrictions on using an IT system within a domestic dwelling?

IIRC
IT is considered ok for a single appliance in a stand alone system - eg running an appliance of a portable generator, as it's a simple system with few parts to go wrong, and a single fault to earth in the system will simply turn it from IT to TN, and the chances of multiple faults developing in such a simple system is quite low.

It becomes an issue when you have multiple appliances (or circuits) running from an IT source, with single pole protection devices such as fuses. For IT systems generally double pole protection devices should be used. Single pole protection in TN is always used in the live conductor.

In an IT system, a single fault will turn it into TN by grounding whichever 'live' conductor has the fault, but a second fault to the other live may cause a fuse or single pole MCB to disconnect. Depending on where the two faults are relative to the open protection device this could leave the earth of some connected appliances connected to one live and others connected to the other live. I.e. you may wnd up with two earthed appliances with 230v between their earths (or between appliance and earthed plumbing). An RCD near the source will likely not trip as both faults are downstream of it.

You may take a view on the probability of that scenario, but IT systems should be avoided where multiple earthed appliances or single pole protections are used.

[vantech2022]

It's not that complicated to get an earth rod installed and then a changeover switch that also bonds N-E.

The telsa is capable of seemless switchover, via gateway as is the lux, but many wouldn't want that or do it since it's a much bigger install job. Esp since "backup" mode (aka BS HD 60364-8-2 "island mode") is not "UPS" unless the product is certified to BS EN 62040.

The floating socket is not encouraged anymore.

"It is not recommended that such a socket-outlet is provided with a means of connection to an electrical
installation or a permanently installed item of equipment"

Previous discussion on bigger and unknown gear:

https://engx.theiet.org/f/wiring-and-re ... ry-storage

Funny that this is obviously a very closed conversion. There are many installers of alpha products on YouTube showing the connector of the backup connection.

The Alpha ESS smile B3 is certified to 62040… it’s a true UPS. The Tesla range and others are not true UPS’ and cannot be used for guaranteed failover.

I think this is where the N-E issue comes in perhaps. Does the 62040 standard allow for N-E bonding on its output? How many desktop and larger UPS’ provide power to computers and servers in big metallic cases on power failure? Tones, everywhere…