Givenergy Monitor app | Emergency Backup Power

Managing backup power

Do you have a changeover switch?

The backup power feature is optional, and can be installed in a number of ways:

Not at all.
A socket that will stay live even during a power outage.
Selected circuits that can remain on.
Some form of whole house backup.

This article mainly focuses on the third option where a number of circuits, appliances and devices considered to be "essential" are on a separate supply. Given that the power grid can suffer an outage, but also that the Inverter can fail, it makes sense that these essential devices are not permanently wired to either power source. Hence the need for a changeover switch so that the essential devices can be powered from either the Grid or the Inverter. An alternative to a changeover switch is a Gateway device, which is typically used with the fourth option and beyond the scope of this article.

Let's define some terms and check your equipment

The Maintained Load is all the circuits, appliances, and devices connected to your changeover switch. This typically includes lighting, television, broadband router, computers, games consoles, central heating, fish tanks, and other low power devices. It may include a fridge and/or freezer, but more consideration is needed for metal appliances due to the greater risk of electric shock. Air conditioning only makes sense for hybrid installations where solar generation can continue during an outage, and the air conditioner must be a low-start type (typically with a compressor driven by an induction motor).

The Non-Maintained Load is all the other circuits, appliances, and devices. This will be higher power appliances, such as kettle and toaster, cooker, washing machine, dishwasher, almost anything found in a kitchen, heaters, electric showers, and car chargers.

If your system has been installed with a single earth (more on this later) you MUST HAVE AT LEAST 3 CONSUMER UNITS. One for the maintained load, one for the non-maintained load, and one for the Solar Inverter (which should also contain the energy meter(s)). You may have other consumer units too, for example a separate one for an EV charger. A common error is to wire the Inverter system into the consumer unit for the non-maintained load. This is incorrect because an RCD is shared between the Inverter and non-maintained circuits, so when the Inverter creates a N-E bond, the non-maintained circuits have two return paths, which will cause the RCD to trip when power is (re)applied.

Wow! That last sentence was a bit technical, sorry. If you think it has been wired incorrectly, just test it. Make sure the changeover is in the backup position. Turn the power off, at the Isolator if you have one, or else at your non-maintained consumer unit. Now turn the power back on. Does anything trip? If so call your electrician back, and explain that the Inverter needs to be wired to a new consumer unit, show them the explanation above.

Just because your electrician has a city&guilds qualification from a college doesn't mean they are an expert in solar battery backup technology; this type of equipment isn't covered on standard courses. An expert electrician that has experience with battery backup systems will be in such demand (for mobile phone masts, hospitals, etc), they are unlikely to be doing domestic installations.

Which position should the switch normally be in?

I leave my changeover switch in the GRID position. Partly because over the last year I have had only one short power outage, yet had 3 occasions when I needed to turn the Inverter off. Your experience of power outages may be different, particularly if you live in a rural location. However there is another reason to leave the switch in the grid position...

Power is supplied to your home by electrical cables which can deteriorate over time. The most common fault [often called low voltage by power companies] occurs when the insulation fails and (usually a joint in) the cable corrodes. This can occur regardless of whether the supply is overhead on poles or buried underground, and results in a reduced supply of electricity to your home. Symptoms such as lights dimming when a kettle is turned on are typical, although modern LED lights flicker or flash rather than dim.

Potentially if the voltage falls too low, the Inverter will see it as a power outage and switch to backup. Once the maintained load is running from the backup supply, if there is comparatively little non-maintained load, very little will be drawn from the grid, and the voltage will rise back up. The Inverter will recognise this as power being restored and switch back to using the grid. This will cause the voltage to drop again and the cycle will repeat switching back and forth every few seconds.

Your Inverter contains relays that are designed for thousands of operations. Unfortunately, there are 3,600 seconds in every hour, so if the fault is not attended to quickly, arcing and sparking at the relay contacts could cause your Inverter to fail and need replacing. It is unclear if this situation is covered by warranty or not.

Whether you leave your changeover switch in the GRID position or the BACKUP position is your choice. There is a good case to be made for either choice, as long as it is a properly informed decision.

Useful tip for those in the UK: If you suffer low voltage as described above, call 105 immediately. It will be treated as an emergency because it can be dangerous, it won't fix itself, and it will get worse.

Which rule did your electrician break?

Whenever you post anything vaguely electrical on internet chat forums, you can be sure someone will be along soon to quote some wiring code, rule, or regulation as if it were written in stone. These rules vary from country to country, and are really guidance to get everyone doing things in a consistent way. That said, you should make every effort to follow the local rules as closely as possible. But remember, the electrons haven't read the rules!

There are two rules that are particularly relevant here. One is that in your home neutral and earth must be bonded together AT ONE POINT ONLY, the bonding point is usually close to where the supply enters your house. The second rule is that all metal objects in an equipotential zone must be connected to the same earth. An equipotential zone is any area where someone could touch two conductive objects at once, for example in a kitchen, the sink and the fridge, or in a bathroom the shower and the washbasin taps (remember water can conduct electricity too). Wikipedia covers this in more detail.

When in island mode (during a power outage) your Inverter creates a neutral earth bond for the backup supply. The grid supply earth is NOT CONNECTED TO the backup supply earth within the Inverter. The electrician doing the installation can however choose to connect the two earths together outside of the Inverter.

Here's the dilemma; let's suppose you have your fridge on the backup supply and it's in the kitchen within reach of the (metal) sink. If the electrician doesn't connect the two earths together, then the equipotential rule is broken because the sink is on the main earth whilst the fridge is on the backup earth. If the electrician connects the two earths together, then the bonding rule is broken because there is a second bonding point within the Inverter.

An earth rod is essential, but not a guarantee of safety

Whilst we are on the subject of earthing, an earth rod should be installed. If the backup supply is on a separate earth, then the earth rod must be connected to this backup earth. If the backup earth and the main house earth have been connected together, then the rod can be connected anywhere, but close to the main bonding point would be ideal if possible.

The principle of earthing is simple. Suppose an appliance in a metal case, say your washing machine, develops a fault whereby the live wire touches the case. Without the protective earth, when you touch the machine you would effectively be touching the live wire and get an electric shock. Because the case is connected via a protective conductor to earth (which is bonded to neutral remember) when the live wire touches the case a circuit is made and the high current drawn causes a breaker or fuse to trip cutting off the power.

This works well because the electricity grid can provide A LOT of power to trip the breaker quickly. However a backup supply is limited by the power of the battery and Inverter; in the case of a Gen1 Inverter the battery power is limited to 2600W or about 11Amps. Power circuits are typically protected by 16A, 20A, or 30A breakers, and your Inverter couldn't supply enough power to make any of these trip, so during a power outage they, and the entire backup earthing system, are ineffective.

Different types of power outage

As mentioned before, electrical power is brought to your home by cables. Typically for a domestic supply, there are just 2 wires, which is the minimum needed to make an electrical circuit. One wire is called live and the other neutral and they are not the same. The neutral is bonded to earth at various points in the electrical distribution system, most notably at the substation(s), whilst the live wire is only connected to the power transformers. Hence the neutral is the safe(r) one and the live potentially more dangerous.

Power outages are often due to a failure of the supply at or before the substation, in which case both cables to your home remain intact but carry no power, and are safe. Outages also occur if one or both of the cables between your home and the substation are damaged and broken, and in this case it makes a difference which one. A break in the live will cause no real danger, but a break in the neutral means that your home only has a live supply. Normally this presents no actual danger because everything including the kitchen sink and the fridge is live and there is no way to complete a circuit for electricity to flow.

However if your fridge is connected to a backup supply, it is possible that your kitchen sink is live and your fridge earthed. This presents a real danger of electrocution; let's follow the current flow to see why. Live power arrives from the grid, passes through the non-maintained consumer unit, and passes through a load. This could be anything that is on permanently, such as the clock/timer on your electric oven. The current flows along the neutral but cannot get back to the substation so takes an alternative route along the earth wire to your kitchen sink. If you have one hand touching the sink and the other on the fridge, the current flows THROUGH YOU, the fridge casing, and onto the backup earth conductor which connects to the earth rod. It then flows through the ground to other earth rods until it finds a way back to the substation. There are no protective devices to protect you; the current will be too low to trip breakers, RCDs require power to operate and there isn't any, and the devices in the backup supply are not even in the circuit. It is the grid that is electrocuting you, and death is a possible outcome.

Staying safe during a power outage

As stated before, I leave my changeover switch in the GRID position, which means that in the event of an outage everything goes off. Since outages can be short lived, the first action is to simply wait a few minutes to see if power comes back on. This is a good time to find a torch.

If power is still off, the procedure is as follows. First TURN OFF the main switch at the non-maintained consumer unit. Leave the solar consumer unit on. Go to the Inverter and turn the changeover switch to the backup position.

That's it. The maintained devices can function and the grid is safely isolated. But before getting back to the "essential" games console, check to see if neighbours have power or if street lights are working, then call 105 (in the UK) to report the loss of power. They can often advise how long the outage may last.

It is safer not to have metal appliances wired to the backup supply. Fridges and freezers can stay cool/frozen for many hours without power. In the event of an extended outage; provided the main consumer unit is off to prevent the grid electrocuting you, a fridge or freezer can be powered via an extension cable.

Monitor the outage

Once the router/firewall is back on, and the Inverter/Dongle reconnected to the network, the app (this is a website about an app remember) will show the status.

Whilst the power is off, the grid line will show OUTAGE and the voltage will switch to showing the backup voltage.

Throughout the outage, monitor the battery charge level and the home consumption which should show as EPS. If necessary, turn things off to conserve battery power. If you have a hybrid system, the battery can be charged from solar whilst the grid is off.

Small discrepancies in power measurements are quite normal due to inaccuracies in the measuring equipment. I notice on my inverter, the EPS power reads more accurately during an outage than when the power is on, but always reads less than the true value. The figures are only intended as a guide to help you make informed decisions..

When the power comes back on, allow about a minute for the grid status to return to balanced. Check the voltage displayed on the grid line is in an acceptable range before turning back on the non-maintained consumer unit.

Putting the changeover switch back to the GRID position can be left until a convenient time, when interruption to the maintained load causes less disruption.

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