Frankenstein’s Wife and Getting Wired

Proof that The Man from Salford doesn't eat too much!

Proof that The Man from Salford doesn't eat too much!

Some strange crackling and fizzing has been emanating from the generator room, sparks are flying and electricity is wildly arcing.  What has The Man from Salford being doing?  I suspect he is building a new wife.  A wife who will let him eat steak whenever he wants. A wife who will let him have a cat and a Rhodesian Ridgeback puppy (and let that eat steak whenever it wants.)  And a wife that doesn’t accidentally spill her vile comfrey tea all over his clean overalls.

As I’m pondering the advantages of such an arrangement, (perhaps she can do all the housework?) I fear we might both become widows before we’ve sorted out the exact details.  Any minute now The Man from Salford will be lit up from the inside like an x-ray cartoon of himself and I will have to figure out how everything works on my own. 

I have spent the best part of the last forty years happily watching televisions, using phones, being transported in cars, tapping at keyboards and generally getting what I want at the flick of a switch and I am ashamed to say I haven’t got the foggiest clue how all these things actually work.  I really do marvel at humankind’s ingenuity.  Yet, if you are thinking of living off-grid then it is probably a good idea to start getting to grips with some of the basics as it is likely you will have to carry out at least some routine maintenance yourself. 

Whatever kind of off-grid system you have none of it will be much good to you until it is properly wired and connected together.  We have, as I’ve mentioned before, a 24v Trace inverter, a battery bank consisting of 12 two volt deep-cycle batteries and an 18kw diesel generator.  In addition to this we have a 12v back-up lighting system.  12v back up systems are becoming increasingly popular choices, even for those on the grid, as extra security in the event of intermittent mains power supplies.

Our 12v system is very rarely used except by visiting guests who have no idea what they’re switching on.  As this system was put in first the switches get pride of place by doors, you have to grope around in the dark to find the AC appliances. On very dark, moonless nights we sometimes use the 12v to help us find my our way from the bedroom door to the bed! 

Cabling installation for low voltage DC systems doesn’t vary wildly from those for standard mains, however, some extra consideration should be given to cable size and type, and you need to give some thought to durability and how you will protect cables from damage.  

In most conventional domestic electrical installations cable is simply selected on its current-carrying capacity.  With low voltage systems the current for any type of appliance will be much higher than an equivalent mains appliance so the cable needs to be much thicker in order that extra current can be carried without overheating.  

Resistance from the copper in any cabling system causes ‘volt drop’ and here is another difference between conventional mains systems and low volt systems.  As current travels along a cable some power is lost along the way due to this copper resistance, the higher the current and the longer the cable the greater the volt drop. 

Low voltage systems require much thicker cabling than you might suspect, not just to carry current without overheating but to allow for voltage drop.  A voltage drop of 2v in a mains 240v system wouldn’t even cause a flicker, but a drop of 2v in a 12v system is unacceptable.  Appliances will not function properly or, as if often the case with TVs, not at all.  In a twelve volt system you cannot afford a drop of more than 0.6v.  Typically a cable of 10m length for a circuit up to 288W with a 24amp current requires a minimum cable size of 16mm², increasing to 35mm² for a cable length of 30m.

 What kind of cable should you use?  As always cost will be a factor. PVC twin core cable is the cheapest option and a popular choice for indoor DC wiring, but even indoors requires protection and should be carefully routed or covered with protection strips.  Multi-strand cables give a better defence against conductor damage and should be used where cables may experience movement.  Sunlight does eventually degrade PVC and outdoor cables can be placed inside polythene water pipes.  Steel-wired-armoured cable, while very expensive, is probably the best choice for outdoor cabling and can be sunk into the ground.

I eventually pluck up the courage to stick my head into the generator room and ask The Man from Salford what exactly the problem is.  Mice have eaten through our cable!  This wouldn’t be quite so bad if the expansion tank into which we pump water wasn’t also leaking all over the place.  I’m guessing we don’t have steel-wired-armoured cable.  So what sort of cable do we have?  ‘Cable, cable?’ shrugs The Man from Salford.  Perhaps I should let him have a cat after all, in place of a regular maintenance routine this may be our best defence against damaged circuits!

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3 comments to Frankenstein’s Wife and Getting Wired

  • This is funny, I was just thinking about this yesterday. For some weirdmotive I stumbled to this article lol. I’ll be coming back here. This really is a good discovery….rare for me to stumble on new websites :)

  • Love the article – hope you keep updating it. I nearly installed an off grid system myself 10 years ago it ened up cheaper to give the electricicty board a huge wad of money. I have recently been looking again with the introduction of FITs at installing a wind turbine as the quotes that installers give you demonstrate you won’t only save the planet but also make a load of cash tax free as well. I decided to analyse my location’s wind speed and found the government’s average wind speeds (which the installers go on)to grossly over estimate.. When I looked at power generation figures over a 6 month period I found that the real power power generated was in the region of 40% to 45% of the estimate given by installaion companies.
    I edit a website and I have published my findings within our wind power section. I am very pro renewable energy and believe the world must work towards sustainable living but we cannot base our figures on incorrect data. Please take a look at the article and give me your views.

  • goo

    Hi Chris thanks, I will be heading over for a read and I hope other readers do too. Generating your own power seems to be fraught with uncertainties, as you say not always helped by those with vested interests. Without reliable data people are bound to be put off.

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