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

[Oldgreybeard]

Middle OFF seems very sensible to me and I don't like those 4 module changeovers with no mid position.

Stipulated in the manuals for some inverters, too, as mentioned in this post in another thread: https://camelot-forum.co.uk/phpBB3/view ... 200#p21768

Sofar HYD3600 manual EPS switching.jpg (83.04 KiB) Viewed 981 times

[Swwils]

So what are people's thoughts of just bonding N+E with the island mode isolator?

A 4 pole changeover switch with middile off could make this quite easy rather than have the additional complexity of a relay.

[Oldgreybeard]

So what are people's thoughts of just bonding N+E with the island mode isolator?

A 4 pole changeover switch with middile off could make this quite easy rather than have the additional complexity of a relay.

Makes a great deal of sense for a manual changeover, IMHO. My only concern would be the case where the inverter manufacturer seems averse to making an N to PE connection in EPS mode, although for the life of me I can't understand why this could be a concern, given that N to PE will most probably be linked when the inverter is running in grid connected mode.

[Swwils]

I've not seen any indication of this for lux.

Not that I think what they sent is even able to be done within regulations:



Can't see this being sensible at all.

[Stinsy]

By far the simplest solution is for E-N to be linked out when running off-grid. If your inverter has a UPS output then all is good. If your inverter has an EPS output then you need the link only to be active in grid-down condition. However some inverters seem to have circuitry that wouldn’t like an E-N link, and the point of an E-N link is to ensure that if an earthed casing become live it would immediately trip the overcurrent protective device and that is far form certain with many inverters…

[ducabi]

I'm now worried what to do with my Sofar HYD3600ES. I'm in a not-old estate (late 80s), so being 5-10 away from the house means I'm outside my plot. I need TT for EPS and also for commando socket (for EV charging). I could use PEN protection like matt:e for commando but it won't help with EPS for inverter.
My worry comes from watching John Ward on YT which says it's not easy to do good TT on TNCS whereas by (other) electrician says it's a simple £100 job.

[Stinsy]

I'm now worried what to do with my Sofar HYD3600ES. I'm in a not-old estate (late 80s), so being 5-10 away from the house means I'm outside my plot. I need TT for EPS and also for commando socket (for EV charging). I could use PEN protection like matt:e for commando but it won't help with EPS for inverter.
My worry comes from watching John Ward on YT which says it's not easy to do good TT on TNCS whereas by (other) electrician says it's a simple £100 job.

The “easiness” of a TT depends where you live and how much you care about a good result. The whole reason you’re now allowed (questionable in some cases) PEN-fault detection in stead of an earth rod is that in some areas earth rods are problematic. EG around Bristol you’re on solid rock, in London the risk of hitting something (sewer, gas main, someone’s basement, etc. is too high).

If you’re more rural and have a convenient flowerbed you can wallop a rod into then you’re good. You might need a 2nd or 3rd rod if you don’t get a decent reading off the first though.

[ducabi]

The “easiness” of a TT depends where you live and how much you care about a good result. The whole reason you’re now allowed (questionable in some cases) PEN-fault detection in stead of an earth rod is that in some areas earth rods are problematic. EG around Bristol you’re on solid rock, in London the risk of hitting something (sewer, gas main, someone’s basement, etc. is too high).

If you’re more rural and have a convenient flowerbed you can wallop a rod into then you’re good. You might need a 2nd or 3rd rod if you don’t get a decent reading off the first though.

I'm Bristol area. 99.5% of the time the house will be using grid earthing, so I don't want to move from TNCS to TT in case TT earthing is questionable.
So, the issue is a good earthing for EPS + good earthing for commando socket. I could probably do a PEN protection for commando socket, TT for inverter and leave TNCS for normal use. Question is if it makes sense.

[Oldgreybeard]

It takes maybe ten to fifteen minutes to bang in an earth rod and see what value of Ra you can get. My experience has been that it's really unusual to not be able to get below 200 ohms. When I put in a rod for our garage supply the value of Ra measured was 26 ohms, when the charger installer checked our main earth rod Ra was 24 ohms (there's about 40m between the garage rod and the incoming supply rod).

A 3/8" earth rod without the enclosure etc costs less than a fiver, so it might be worth just banging one in (in a safe location away from other services) as a test, then asking an electrician to come around and measure the test electrode Ra for you (will take minutes to do). That way you would know whether TT for the whole supply is a viable option or not. If it turns out that Ra is OK (under 200 ohms) then you're good to go with a proper TT installation. If it's a bit marginal you can try swapping the 3/8" rod for a 5/8" one, or joining two together with a coupler and driving it down deeper.