Help in re-wiring a long 350m outdoor run
- Thread starter bobfleming70
- Start date
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Do you need to have 3 Kw available at any time and if so what for.
If it is for heating then consider a well insulated heat store that is trinkle heated ( 500 watts or less ) until full of heat. Then when the shed needs heating use the heat store to warm the shed.
A heat store system could be made from a hot water tank with small immersionheater, a fan blown finned radiator and an electrically operated valve to prevent hot water circulating through the radiator when heat is not required. Water could be circulated by gravity or pump depending on layout of pipe work.
If it is for heating then consider a well insulated heat store that is trinkle heated ( 500 watts or less ) until full of heat. Then when the shed needs heating use the heat store to warm the shed.
A heat store system could be made from a hot water tank with small immersionheater, a fan blown finned radiator and an electrically operated valve to prevent hot water circulating through the radiator when heat is not required. Water could be circulated by gravity or pump depending on layout of pipe work.
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Someone has already mentioned a "voltage optimiser". These reduce the voltage by connecting the secondary of a 230/12V transformer in series with the supply, bucking the voltage. By crossing the connection to the primary or secondary windings, the transformer would boost the voltage by 12V.
That would offset 12V's worth of losses.
That would offset 12V's worth of losses.
Be simplier and more efficient on a lighting ( and other light ) loads to use an auto-transformer to up the voltage.
You can use a transformer with tapped inputs 220 230 240 etc as an auto transformer and ignore the low voltage ouput provided that the load is less than half the rated wattage of the transformer. Even then some care is needed to ensure the transformer is not over heating ( due to abnormal eddy currents in the metal core ).
Feed the incoming 220 into the 220 tap and take 230 from the 230 tap. Neutrals to the 0 volt end.
But better to buy a proper auto transformer.
You can use a transformer with tapped inputs 220 230 240 etc as an auto transformer and ignore the low voltage ouput provided that the load is less than half the rated wattage of the transformer. Even then some care is needed to ensure the transformer is not over heating ( due to abnormal eddy currents in the metal core ).
Feed the incoming 220 into the 220 tap and take 230 from the 230 tap. Neutrals to the 0 volt end.
But better to buy a proper auto transformer.
Just put the right ******* cable in. 
The problem with using an autotransformer, or Stoday's suggestion of a 'voltage optimiser', are that these both result in 'dumb' fixed increases in voltage (~10V and ~12V respectively), regardless of the supply voltage.
The load due to lighting could easily be very low, quite possibly less than 100W (<0.5A), so in itself would result in little voltage drop (<0.5V) in the supply cable; the large voltage drops we've been talking about result of 13A being drawn mainly by non-lighting loads.
The worst case supply voltage is 230V + 10% - i.e. 254V. Add a fixed 10V or 12V onto that, and one ends up with ~265V. Although very unlikely, that theoretically could happy if the only load was the lighting - and I'm not sure that would be compliant with regs or necessarily safe. The comments I made earlier related to more 'intelligent' voltage stabilising or voltage-tolerant approaches. I still think that ELV lighting (even if only 12V DC lighting from a car battery floated across a 'voltage-tolerant' charger) could be the simplest option if one decided to take this sort of approach.
Kind Regards, John.
It doesn't matter what sort of lighting you install, if it's supplied by that 350m cable then the lighting circuit voltage drop limit applies.
Just put the right ******* cable in.
Just put the right ******* cable in.
I don't think that's actually true. As I wrote recently, sticking to the 'voltage drop limit' specified in Appendix 12 is simply one way of satisfying 525 (per 525.3). If one can demonstrate that one's lighting equipment is being supplied with an adequate voltage for proper functioning, then one can satisfy 525 via 525.1 and/or 525.2.
This is not just an academic discussion. When one is talking about 350m, 'putting in the right cable' to keep within Appendix 12 VD limits for lighting represents a very large additional cost, so I think it's worthwhile considering alternative strategies.
Kind Regards, John.
It is possible to purchase automatic voltage regulators of various sizes, in the simplest form they are a powered variac with control circiutry and are used extensively in countries with power supply problems.
Of course as they boost the voltage on the output they increase the input load (so can lower the input voltage) to cope with this so need careful design considerations.
http://www.ashleyedison.com/AC-Auto...gulators.htm?gclid=CKeB3cu2takCFQNP4Qod1iIHLA
Of course as they boost the voltage on the output they increase the input load (so can lower the input voltage) to cope with this so need careful design considerations.
http://www.ashleyedison.com/AC-Auto...gulators.htm?gclid=CKeB3cu2takCFQNP4Qod1iIHLA
VERY careful design otherwise the system can suddenly become unstable and the voltage varies wildly.
If you do consider this put the automatic variac at the source ( where the supply voltage is not affected by voltage drop along the cable ) and use a second pair to bring the far end voltage back to the controller. The second pair are zero current so can be small cable.
True, but I suspect they're expensive and probably represent overkill for shed/workshop lighting.
As I've said, why not just ELV lighting running off a stabilised, input-voltage-tolerant, power supply - or even my car battery approach (in which case there is no LV lighting circuit, and the battery charger is allowed a 5% voltage drop).
Kind Regards, John.
It's occurred to me that a simple, and probably cheaper, option would be to use an 'online' ('double conversion') UPS designed for computers. Such devices commonly have an input voltage range something like 150V-280V (hence presumably compliant with at least the spirit of 525.2) and provide a constant 230V (or whatever) output. Although more expensive than the more common 'line interactive' mode UPS units, this could still represent a cost-effective solution (in comparison with 350m of larger SWA).
Just a thought!
Kind Regards, John.
The op has not been heard from for a while now, I reason that he had about 30 quids worth of cable ran across to his shed, this discussion is probably shocking to him since we all discussing how many thousands of pounds the materials will cost.
Bet he will just replace the chewed cable with a new one
Bet he will just replace the chewed cable with a new one
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