New Zealand Volt drop cont.

[Monkeyblaine]

Ok I have another VD question. I'm installing 9 LED floods around my friends garden which totals at just over 100m in length. Obviously for each branch the VD varies so for argument sake I worked It out as if all the cable would be taking all the load (rather than dropping relevant current after each light, worse case scenario) the load is minimal being LEDS but to be safe I'm putting 2.5mm 3c hightuf in to cope with the distance and to help for the zs reading. Now I am also using a wise box control box (wireless switching) now am I right in thinking I can supply this box from the CU with a length of 1mm t+e as this is a very short distance and is my thinking correct that as long as no voltage has been dropped through the 1mm to the wise box then I have a full 230v (give or take) for the garden circuit and as its run in 2.5mm it will stop any VD issues. Basically what I'm asking is, whatever voltage you have at a certain point regardless of cable size, then that's what you have from that point onwards. I.e if I lost 3volts through initial 1mm cable then I'm down to 227v at wise box (for example)

 

[telectrix]

your thinking appears logical, but for what it costs, i'd run from CU to wise box in 2.5mm T/E.

 

[Monkeyblaine]

Yeah I thought that would be the general consensus. I was just trying to get my head round it. You could technically run it in 1mm until the voltage started to drop then up the cable size to reduce resistance and VD. Ohms law. It's just as a design point it would be best to keep it all the same.

 

[kingeri]

If you want to reduce volt drop then increase the CSA from the origin of the circuit, for example I added a heavily loaded 10amp lighting circuit to a very big house the other week, DB was at opposite end of house, and ran the feed in 2.5mm to an adaptable box then came off that in 1.5mm to the individual parts of the circuit. The load on the 2.5mm was terminal, so the whole length was subjected to the full effect of the voltage drop, whereas the individual branches were not.

 

[Monkeyblaine]

Yeah like I was saying your voltage at any given branch is subject to what has been lost from the origin. So providing there is no major loss from origin you have 230v(ish) for all branches and then subject to what current each branch is taking x length of cable, each branch will have its own VD subject to those factors. So you could run supply to garden in 1mm with no real VD. Then use 2.5 for long lengths to combat any VD. it's a backwards way of doing it and not great from a design point of view. But it would work the same. Ohms law.

 

[Outspoken]

Ok I have another VD question. I'm installing 9 LED floods around my friends garden which totals at just over 100m in length. Obviously for each branch the VD varies so for argument sake I worked It out as if all the cable would be taking all the load (rather than dropping relevant current after each light, worse case scenario) the load is minimal being LEDS but to be safe I'm putting 2.5mm 3c hightuf in to cope with the distance and to help for the zs reading. Now I am also using a wise box control box (wireless switching) now am I right in thinking I can supply this box from the CU with a length of 1mm t+e as this is a very short distance and is my thinking correct that as long as no voltage has been dropped through the 1mm to the wise box then I have a full 230v (give or take) for the garden circuit and as its run in 2.5mm it will stop any VD issues. Basically what I'm asking is, whatever voltage you have at a certain point regardless of cable size, then that's what you have from that point onwards. I.e if I lost 3volts through initial 1mm cable then I'm down to 227v at wise box (for example)

You need to work out the volt drop across the entire circuit, so you need to know how much power the LED floods will use combined and then any power for the control box, then you can calculate the volt drop correctly and accurately. Guesstimates are for bodgers.

 

[kingeri]

Most sparks just prefer to use the same CSA cable throughout a circuit. As do I, but there are times when I've upped a cable size for a specific reason just for part of a circuit.....voltage drop is an example, but also when there is a reduction in CCC of the cable due to external factors for part of the run, e.g. cable passing through insulation of through a higher temperature area.

 

[Monkeyblaine]

Outspoken I understand that completely and I've gone fully worse case scenario so I know everything is fine and no VD problems with this particular situation. I was just seeing if my thinking was correct and providing no VD from origin cable then you have full 230v for branch cables of circuit.

 

[telectrix]

you will get VD on the 1.0mm once you load the circuit

 

[Monkeyblaine]

I know that too but If you worked it under full load conditions and as run to wise box was minimal (very low resistance) so at the wise box we were still getting 230v(ish) then you would have that 230v(ish) for all your branch circuits. Then they would VD individually, respectively of their load/length factors.