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inverter plus shorepower

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i have on board a 1000 watt inverter which can be a very handy piece of kit at the right time.

the problem being i am advised to run the engine when it is in use, which, as we all know is a little awkward, especially

at night or early morning, and rightly so.

i therefore have decided to add shore power.

question; how do i connect the 240 to the inverter wiring and does it have to go through a consumer unit, or is it easier or necessary to put extra sockets in for the sole use of the shore power


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Depends on the invereter, some kick out when they sense shorepower connected, check the manual or ask the manufacturer. Even if not, then it is possible to wire an inline isolator on the AC side but you will have to be certain it is switched before pluging in the shorepower. If in doubt when working with mains voltage then have a qualified marine electrician either install or at least check it out after you have installed it. Use only multi strand cable (none of this solid core stuff) in any new circuit.

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yes, thanks dave

at first i thought it was a job i could tackle with confidence, if it was a straight forward ring-main affair, but now i am thinking it may be wise to let a qualified sparky do the job


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Hi Alan

We had the same dilemma with our boat when we installed a 1000 watt inverter. I have wired this to a ring main with 4 double sockets around the boat, and then wanted to add shorepower. Having spoken to Brian Ward's in Brundell, there are basically two alternatives to the issue of switching. They sell a manual change-over switch which selects between the inverter and the shorepower for around £35. The more expensive option (over £100 I think) is an automatic changeover switch, which detects which source is providing power and automatically switches to that.

I haven't yet got round to installing the shorepower, just bought all the bits, but I also am not sure about where to put the RCD and consumer unit in the circuit. I am assuming it needs to go after the changeover switch so that the ring main is protected whether on inverter or shore supply, but as the inveter can only supply about 4 amps I'm not sure about this.

With regard to running the engine when the inverter is on, it really depends on what you are powering. Our LCD TV runs from the inverter, but is only 60watts and therefore uses not a lot of battery. However a microwave will knacker a battery in 10 minutes, and hence we split our battery bank so the inverter ran from a dedicated battery. Even if that one goes flat, there are still 2 domestic batteries for the lights & fridge etc, and the engine battery is separate as well.

If you are ever in the area of Ludham, and wany to see what I did with our boat, let me know and you are more than welcome aboard!

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Hi Rod

We did the Waveney over the Whitsun holiday week. Found a lovely mooring on the way to Beccles which was called Aldeby Staithe. Lovely location on the main river, but backs onto some day ticket still waters if you are into fishing (no idea how good they are though). It's a nice spot for an evening Barbie and a spot of owl watching too.

We also went to Geldeston Locks for a pint, and then back the other way towards the Geldeston village moorings. I wouldn't recommend that one though, as there only seemed to be a public mooring for one boat. It was a bit tight but not too bad for turning though. ALso spotted a kingfisher along that stretch, but the weed being only inches from the surface was a bit worrying!

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You guys enjoy it as well.

Where are you planning to go this time?

We are looking at spending some time re exploring the Waveney and are hoping to get up as far as Geldeston. before returning back to the North.


Sorry for the tread drift Alan,

We're off to do the Walton backwaters Rod, Tichmarsh, Shotley, Levington, Ipswich, also Woodbridge, maybe a bit further down to Brightlingsea and if all goes well and there is a window we all like the look of then over to Neiwport for some Mules & Frit, if not then possibly even try for St Kat's, it's all fluid :-D

As ever the whole thing is governed by the weather so maybe none of it :oops:

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Firstly if in any doubt, then you should consult a qualified marine electrician.

The output from the invertor should never be allowed to connect to the ring main at the same time as shorepower, therefore you will need to isolate the two sources. This can be acheived via a maual switch or an automatic switch. Most of the automatic switches have prioritised inputs, so if both invertor and shorepower are available at the same time, it will switch to shorepower. Some also have a third input for a generator. In that case it will use shorepower first, genny second and then finally invertor. After you have sorted out the source switching, you should then have a consumer unit and RCD to protect the mains sockets. This should be after the switch, so that the user is protected whether you are on invertor or shorepower. A 1000w invertor may only supply 4amps, but that is still enough to kill, so always ensure a rcd is installed.

A word about battery chargers. If powered of the ring main to keep the batteries topped up, make sure you remember to switch them off before switching over to invertor power. The law of rapidly diminishing returns, means that you will flatten your batteries faster than ever, if trying to use them to run an invertor, to run a battery charger, to top up batteries being used to run an invertor, to run a battery charger and so on :-) Some of the automatic change over switches have a battery charger isolator circuit, so that if you are running on shorepower, the battery chargers work. If running of invertor power, the battery chargers become isolated and turned off.

Finally, back to my first point, if in any doubt, then you should consult a qualified marine electrician.


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i dont want you guys out there worrying about hijacking my thread, no problem.

i really do appreciate the advice i have been given, and i am now trying to digest every piece.

many thanks


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just a thought,

we will be coming to norfolk on wednesday evening for a fortnight and planning to do some time on the south side

so look out for an ex royall bathtub.

and mark, yes, i would love a look at what you have done.


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