The right inverter for battery storage and some other Qs

[Stinsy]

Not unknown for the incoming neutral to go to a high voltage when there's a fault somewhere.

Correct. AND... in this circumstance, in a "TN" earthing arrangement, the earth conductor and the metal casing of anything that is earthed ALSO rises to line voltage!

This situation, being possibly the reason for the outage, should be taken very seriously in the event of an outage.

[ducabi]

So what is a good approach to installing an earth rod? I'm on TNCS in early 90s build and my electrician said it's easy to install an earth rod even though my research says that it really depends on what's in the soil (pipes etc).

[Oldgreybeard]

So what is a good approach to installing an earth rod? I'm on TNCS in early 90s build and my electrician said it's easy to install an earth rod even though my research says that it really depends on what's in the soil (pipes etc).

Very easy to put one in usually. Needs to be clear of metal pipes and cables underground, but that's usually easy enough in houses built in the past 40 or 50 years, as plastic piping pretty much took over from iron and galvanised steel from around the 1970's onwards. Off the top on my head I think the absolute minimum distance from an earth electrode and any metal underground pipes etc is 2m, or might be 3m, but if your gas and water are coming in via plastic (pretty much a certainty with a 1990's build) then you really only need to worry about physically hitting something critical when driving the electrode in. If in doubt there are ones you can just dig a hole and bury, now. They have the advantage of not needing to go do deep, plus digging the hole gives an indication of anything else that might be in the way.

[ducabi]

Very easy to put one in usually. Needs to be clear of metal pipes and cables underground, but that's usually easy enough in houses built in the past 40 or 50 years, as plastic piping pretty much took over from iron and galvanised steel from around the 1970's onwards. Off the top on my head I think the absolute minimum distance from an earth electrode and any metal underground pipes etc is 2m, or might be 3m, but if your gas and water are coming in via plastic (pretty much a certainty with a 1990's build) then you really only need to worry about physically hitting something critical when driving the electrode in. If in doubt there are ones you can just dig a hole and bury, now. They have the advantage of not needing to go do deep, plus digging the hole gives an indication of anything else that might be in the way.

How can i be 100% sure they are plastic?

Digging a hole myself is what I'm thinking about. What's the required lenght of the rod?

[Oldgreybeard]

Very easy to put one in usually. Needs to be clear of metal pipes and cables underground, but that's usually easy enough in houses built in the past 40 or 50 years, as plastic piping pretty much took over from iron and galvanised steel from around the 1970's onwards. Off the top on my head I think the absolute minimum distance from an earth electrode and any metal underground pipes etc is 2m, or might be 3m, but if your gas and water are coming in via plastic (pretty much a certainty with a 1990's build) then you really only need to worry about physically hitting something critical when driving the electrode in. If in doubt there are ones you can just dig a hole and bury, now. They have the advantage of not needing to go do deep, plus digging the hole gives an indication of anything else that might be in the way.

How can i be 100% sure they are plastic?

Digging a hole myself is what I'm thinking about. What's the required lenght of the rod?

Just check where your water pipe comes in (that will definitely be plastic - they stopped using metal communication pipes in the 70's) and where your gas pipe comes in and try to get the earth electrode as far away from them as you can.

Rod type earth electrodes come in 4ft lengths (1.2m) usually. Unusual to need more than one, but you can screw them together with a threaded coupler if you need to lower the resistance a bit. Here (North Dorset) the normal reading from a single rod is around 20 to 30 ohms, which is very good. Max recommended is 200 ohms, but in reality anything up to 1667 ohms is OK in terms of tripping a 30mA RCD. The 200 ohms recommendation is to allow for changes due to weather, to try and ensure that even if the soils dries right out an electrode that measured 200 ohms would still be OK and under 1667 ohms if very dry.

The usual way to put earth electrodes in now is to dig a hole for the earth pit, fit that and maybe concrete it in place if needed, then drive the earth electrode down through the lower grommet in the pit using an SDS driver. You can put two nuts locked up on the thread at the tope and bang the thing in with a lump hammer, but it's a hell of a lot easier with an SDS driver, and it is like likely that the thread will get damaged, which is very useful if you do need to fit a coupler and drive down a second one.

[AGT]

Looks good!
They also do a great swa clip too!

[Caesium]

Wow that looks easier than I thought. And CEF sell all the bits for it. Might just have a go myself

I'm assuming adding an earth rod isn't notifiable work?

[Oldgreybeard]

Wow that looks easier than I thought. And CEF sell all the bits for it. Might just have a go myself

I'm assuming adding an earth rod isn't notifiable work?

Changing the installation earthing system does require some safety critical measurements and testing that few DIY'ers will be able to do. The key measurement is the resistance of the electrode to earth. This cannot be measured with any normal multimeter, so needs either a multi-electrode earth electrode resistance test meter (how it used to be done when TT systems were commonplace) or it can be inferred by measuring the earth loop impedance (which includes conductor impedances that are massively lower than the electrode resistance, so is a good enough measurement). To measure the earth loop impedance needs a meter designed to do it, or needs the built-in functionality from one of the commonly used multifunction test meters.

This test gear is too costly for a DIY'er doing a one-off, unfortunately. In addition to measuring the electrode resistance (should be under 200 ohms) there's also a requirement to test that the RCD trips within the right time and at the right current with the TT earthing system. It can't be assumed that because an RCD tripped OK when used with a TN system that it will still be OK with a TT system (it should be, but still needs testing). Again, a multifunction test meter will usually include RCD trip time and ramp trip current test capabilities, and it only takes a minute or so to do these tests with one.

[ducabi]

I took this to mean what it says <I thought it wasn't relevant given I'm not running it in UPS mode>

Then you will need the earth rod, and a 30mA RCD on the output to the critical circuits because the 100mA one on the input isn't sufficient for shock protection. They need to be different to provide some level of fault discrimination.

You don't need the bypass switch (or relay), this is an option if you are worried about the inverter failing. I have manual changeover switches fitted because the whole house is on the UPS side. I might add an automatic relay for the freezer because of the remote likelihood of the inverter failing while I am on holiday.

I've read and watched a bit and now I'm confused how UPS works. Some say they only have it as a socket and you are saying your whole house is on the side. That's what I would want, i.e. my main CU has 2 RCDs at the moment, so I would want everything be on the UPS side or just one of the RCDs.
If someone says only critical load is connected to UPS does it mean it's taken out of the main CU and moved to the new CU or it's just a description of cables running from inverter to the side of the main CU with just critical load?
If the whole house is on the UPS side doeas it mean I don't need another RCD because it's already in the main CU?

Base set:
New CU with the following
RCD 100A 100mA Type A
MCB type C 25mA
SPD


UPS set:
Earth Rod
30mA RCD
Changover switch

btw Solis has nice YT installation manuals, can't find anything as detailed for Sofar but I assume it's not much different.

[sharpener]

I've read and watched a bit and now I'm confused how UPS works. Some say they only have it as a socket and you are saying your whole house is on the side. That's what I would want, i.e. my main CU has 2 RCDs at the moment, so I would want everything be on the UPS side or just one of the RCDs.

You haven't bought the right inverter to run the whole house in EPS mode. From p45 of the Sofar HYD3600-es data sheet it seems all of the inverters in the range have the same 3000VA EPS power output. This isn't sufficient (particularly if you have an electric cooker), you will not be able to boil a kettle if the central heating and a few lights are on. The reason I have been able to do it is that the 5kVA Victron also has a 50A pass-through capability which will allow 12kW of load on the EPS side when the grid is present.

So either you can have a couple of sockets wired to your inverter's EPS output, and run table lamps and small appliances e.g. laptop, phones, router off extension leads. Or, better, to separate the circuits (if it is possible) into critical and non-critical and wire them permanently via some combination of existing and new switchgear

If someone says only critical load is connected to UPS does it mean it's taken out of the main CU and moved to the new CU or it's just a description of cables running from inverter to the side of the main CU with just critical load?

It means it has to be connected electrically like Fig 1 on p1. If you are finding this difficult to interpret then you should consult an electrician with experience of ESS. The mechanical implementation depends on the siting of the various bits, how easy it is to segregate the critical circuits and so forth. As you already have a split board with two RCDs you may be able to rearrange the critical circuits to be on one and the rest on the other.

But since you need extra ways for the extra stuff you have listed below it is probably better to either

(i) move the critical circuits (only) to a new CU connected to the EPS output provided this will leave sufficient space in the old board for the extra bits to feed the inverter, this avoids having to install new meter tails etc.

(ii) failing that, put all the new components in a new, additional split CU and move the critical circuits to the new board

If the whole house is on the UPS side doeas it mean I don't need another RCD because it's already in the main CU?

No, you need at least 3 and probably 4
100mA for the feed to the inverter
30mA from the EPS output to the critical loads which for safety should include some of the lighting circuits
The 2 x 30mA in your existing split CU because you still want to have the circuits distributed between more than 1 RCD

Base set:
New CU with the following
RCD 100A 100mA Type A
MCB type C 25mA
SPD


UPS set:
Earth Rod
30mA RCD
Changover switch

btw Solis has nice YT installation manuals, can't find anything as detailed for Sofar but I assume it's not much different.

A competent electrician should be able to work from what is in the Sofar manual I found on the Midsummer web site above