inverter power to house. - Page 1
Forum section: electronics / general

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 30, 2015, 07:50:03 pm
content: Hi, Just need a bit of advice on safety.I have a small solar and wind turbine setup charging a battery bank which I set up to power my shed.Winter is on its way and nights are drawing in which means the lights are on longer this time of year. I was thinking that the power in that battery bank would be better served coming into the home to help with the cost of electric. My system is too small to run my whole house, that's obvious but I was thinking of just powering the lights. Living in the UK I have two circuits in my fuse box for lighting, 1 for upstairs and one for down. I don't really need to use the inverter to power the upstairs as they not really on for very long, but I was thinking of disconnecting the downstairs circuit from the fuse box and wire it to the inverter. Ok I know this probably breaks a lot of codes of practice and invalidate insurances but the questions I want answered is "Would this be safe", "what could I do to make it safe" "Is there anything else I should know", "What about earthing?" "Has anyone else done this?".Thanks for listening.

author: ajb
author_rank: Super Contributor
timestamp: September 30, 2015, 08:41:35 pm
content: It's perfectly safe as long as you do it safelyIn the US, it's common when installing a backup generator to move the circuits you want to run from backup power to a new panel installed next to the old one. The new panel is fed from a transfer switch which has one input from a suitably-sized breaker installed in the original panel and the other input comes from the generator. You could do the same thing, except instead of having the transfer switch fail over to the generator when the mains drops out you have it switch to the inverter when it has enough capacity. You may even be able to use the same components that a generator installer would use, which should have the proper type approvals and such, as long as you can control the transfer switch appropriately. Heck, you may even be able to have a generator installer set it up for you. (I don't know how common home backup generators and hence installers are in your area though.) As far as earthing, you should maintain the earthing of the inverter-fed circuits just as you would if they were still mains powered, and the inverter should be earthed as required by your electrical system.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 30, 2015, 08:51:50 pm
content: @ajb I don't want to run it as a back up, I wont to only power the down stairs lighting circuit by by disconnecting the circuit from the fuse box and permanently connect it to the inverter, So the down stairs lights can ONLY be powered by the inverter.

author: German_EE
author_rank: Super Contributor
timestamp: September 30, 2015, 09:18:15 pm
content: You're in the UK, so that probably means that your lighting circuit is a ring main with two sets of cables going into the breaker box for the circuit that you want to power.So.............................1) With the power off disconnect your lighting circuit from the breaker box and pull the cables free.2) Wire the two live wires of the lighting circuit to the common connection of a two way switch.3) Wire one pole of the switch to the original circuit breaker and the other pole of the switch to the live output of your inverter4) Connect together the following four wires; A Neutral wire from your breaker box, the two Neutral wires from your lighting circuit and the Neutral wire from your inverter.5) Connect together the following four wires; An Earth wire from your breaker box, the two Earth wires from your lighting circuit and the Earth wire from your inverter.6) Get an electrical inspector to look over your work and certify it as safe.7) Turn the power back on.The connections in steps (4) and (5) should be made inside either an earthed metal box or a junction box designed for 240V operation.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 30, 2015, 09:43:23 pm
content: you still not getting what I want to do.1st of all UK light circuits are not on a ring circuit.2nd I want to disconnect the down stairs lighting circuit completely from the grid power and use inverter power instead.3rd I know how to do it, just want to know if it's safe.Ill insert a pic of uk wiring.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 30, 2015, 09:47:45 pm
content: So from the last pic to this.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 30, 2015, 10:03:20 pm
content: Sorry German-ee After reading your article again I understand what your saying.What your say is you can switch between grid power and inverter power, just i'll only have one live and one nutral wire instead of two as the lighting is not on a ring circuit. I got you.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 30, 2015, 10:14:44 pm
content: Something like this you mean?

author: Ian.M
author_rank: Super Contributor
timestamp: September 30, 2015, 10:25:07 pm
content: The key to doing this safely is that the switch *MUST* be suitable for transfer switch use. i.e. it must be rated to switch a circuit between two independent supplies. If it ever shorts between the two lives feeding it, its a major safety violation. Also the switch cabinet *MUST* have the correct safety labelling indicating it has more than one independent live feed. It may be preferable to move all the lighting circuits to an auxiliary panel (consumer unit) and connect that to the main panel via an appropriately rated flex cable and plug and a fixed socket fed from the main panel (probably an industrial one to BS EN 60309-2) so that the feed can be manually transferred to a socket fed by the inverter with no risk of cross-connection.Talk to a licensed electrician, preferably one with both domestic and industrial certification and experience of mains installations in recreational vehicles.If you want to avoid all the licensing, insurance and other legal hassles, install a completely independent auxiliary low voltage lighting system, that does NOT use any voltage over 50V.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 30, 2015, 10:50:55 pm
content: So after thinking about it, I come up with this.

author: johansen
author_rank: Super Contributor
timestamp: October 01, 2015, 01:15:30 am
content: usually if it has a plug on it, they can't do anything to you.so take the wiring from the lights, near the fusebox, and install a plug on it.plug this into an inverter. plug the inverter into an outlet.configure the inverter to use the batteries whenever the battery voltage is higher than X, below which it will use the grid.alternatively you can buy an inverter that is code complient. you then screw it to the wall and hardwire the system in place.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 01, 2015, 01:28:35 am
content: Quote from: snipersquad100 on September 30, 2015, 07:50:03 pmYou so can't do this.What voltage is the battery system? Just put in some extra LED DC lights (<= 48V much safer) and don't turn the AC powered ones on unless the battery is low.If you have a mains blackout then you will still have lights too.

author: Monkeh
author_rank: Super Contributor
timestamp: October 01, 2015, 01:43:06 am
content: Quote from: German_EE on September 30, 2015, 09:18:15 pmNo, it most certainly does not. Not only is a ring main never found in a house, but lighting circuits are not ring finals. Ring finals are reserved for very specific configurations and otherwise not allowed. There is certainly no benefit to using one for lighting..Quote from: johansen on October 01, 2015, 01:15:30 amBullshit, it's still fixed wiring.sniper, if you don't know if it's safe, then you don't know how to do it, and you shouldn't.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: October 01, 2015, 09:47:57 am
content: There's quite a bit of dodgy advice floating around in this threadSimon had a thread on there a while ago asking a similar question. If you have a look through it and find my posts (or look through my posts history) it all applies to this set up as well. A selection of issues you will have to deal with:1. Earthing. The output from your inverter is likely floating i.e. not referenced to earth. This is ok for feeding a single appliance but not suitable for feeding a domestic circuit. It will need a neutral-earth link which is switched appropriately so that it's not there when the circuit is powered by the mains. Depending on your supply arrangements you may also need an appropriately installed earth electrode as you can't rely on the electricity supplier's earthing system when using your own power. This may mean either changing the earthing system for your entire house or providing an appropriate switching system to a separate earth when using your inverter.2. Overcurrent protection. In the schematic above there is no overcurrent protection for the 6A lighting circuit when running off the inverter. (Unless you're relying on the inverter being so small it can't overload the circuit). If you add an overcurrent protective device e.g fuse or breaker then you will have to ensure that the inverter can supply sufficient current in the event of a fault to operate the 'OCPD' within the required timeEDIT: sorry you have included a circuit breaker in the second schematic I didn't spot it.3. Phasing. There will be no way to ensure that your inverter is in phase with your mains supply. This will mean that there will be up to 480V rms between the live conductors in different parts of your installation. May or may not be a problem depending on things and reasons4. Insurance. If you do this work yourself it is very unlikely to comply with the 17 edition of the IET regs (and it will be notifiable to Building Control under Part P). Your house insurance company will have a big problem with this.Plus lots of things I haven't thought of yet. You'd probably be better off spending the time and money buying decent LED lightbulbs for the house instead.

author: German_EE
author_rank: Super Contributor
timestamp: October 01, 2015, 10:54:17 am
content: All agreed, the two problems here are that a) my knowledge of UK mains wiring stops in 1985 when I left the country and b) I don't know the current UK regulations. This is why my advice included getting an electrical inspector to check the work before the power was reapplied.I remember that there were ring mains on UK circuits, are they only for wall sockets and not used for lighting?