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)

 

[Monkeyblaine]

Ok. I think we're on the same page. So max VD is from CU to first joint/light/fitting. Still hard to grasp as last light will have dropped more volts but If that's the way you have to do it.

 

[telectrix]

no. max. vd for the circuit is from ocpd to last load. the biggest vd is from ocpd to 1st load.

 

[Monkeyblaine]

Haha ok so do you calculate by adding all loads and assume they are going through entire length of cable used in circuit. Rather than working out legs separately with deducting their load as its lost along lengths?

 

[Outspoken]

Monkey, Look at this FFS..



The maximum voltage dropped it at the START of the circuit because this has the HIGHEST load placed upon it.

 

[Monkeyblaine]

There's conflicting information going on here. Outspoken info understand what your saying and just because at the start of the circuit is the max VD as it has the most load upon it. Doesn't mean it's not going to drop more by the time it reaches furthest point and got operation of things working, that's what im interested in. So an accumulation of volts dropped by the time it reaches last point. Which is surely what the regs require us to obtain.

 

[Monkeyblaine]

Not just what the max VD is for a circuit. Surely it's what voltage is left at end so lights/equipment work correctly.

 

[Outspoken]

There's conflicting information going on here. Outspoken info understand what your saying and just because at the start of the circuit is the max VD as it has the most load upon it. Doesn't mean it's not going to drop more by the time it reaches furthest point and got operation of things working, that's what im interested in. So an accumulation of volts dropped by the time it reaches last point. Which is surely what the regs require us to obtain.

Monkey, FFS, the calculation of the TOTAL voltage drop across the entire circuit tells you the voltage at the END of the circuit FFS....

If the Volt drop is calculated at 4V (Thus dropping to 226V) the the voltage at the end of the circuit is ...Yep, you guessed it 226V ...it is not Rocket Science!

 

[telectrix]

i'm bowing out before i suggest that you got 10V to play with anyway as we have 240V at source, but calculate VD from 230V. courtesy of the meddling euro rats in brussels.

 

[Monkeyblaine]

I'm not stupid and I do get what you are saying. I know how to calculate the entire load of a circuit then use VD calcs to obtain total VD. I was always taught that you had to work out each leg individually. As the way your explaining it is assuming the total load is at the end of the circuit rather than it branching off at various points. Do you not see my point. But I will go with everything you say as you clearly have worlds more knowledge/experience. And if in your examples is correct way to
Determine total VD for a branch circuit, then I will leave it as that. As its a simpler way to calculate.

 

[Outspoken]

I had considered pointing out that if you measure voltages in the UK the averages for single and three phase are 236.7V and 415.8V respectively...but realised he was confused enough as it is!!

 

[Outspoken]

I'm not stupid and I do get what you are saying. I know how to calculate the entire load of a circuit then use VD calcs to obtain total VD. I was always taught that you had to work out each leg individually. As the way your explaining it is assuming the total load is at the end of the circuit rather than it branching off at various points. Do you not see my point. But I will go with everything you say as you clearly have worlds more knowledge/experience. And if in your examples is correct way to
Determine total VD for a branch circuit, then I will leave it as that. As its a simpler way to calculate.

Monkey, FFS, whoever taught you that is a frigging idiot as you will always end up with incorrect figures, that is why i gave you the example I did, to PROVE you MUST calculate the total maximum demand on the maximum length of the circuit to establish the true maximum volt drop you may experience. Obviously in the example I gave this will be variable as lights are turned on and off on various branches, thus you need to calculate the worst case scenario, if this is within the permitted levels with BS7671 then everything else is a pointless waste of your time!

 

[Monkeyblaine]

Thank you. I do understand. And sorry for all the frustration. Bad training.

 

[Monkeyblaine]

Haha this could of been over a lot earlier if I'd seen this sentence at the beginning.

you MUST calculate the total maximum demand on the maximum length of the circuit to establish the true maximum vd

 

[44ALLAN]

Monkey, FFS, the calculation of the TOTAL voltage drop across the entire circuit tells you the voltage at the END of the circuit FFS....

If the Volt drop is calculated at 4V (Thus dropping to 226V) the the voltage at the end of the circuit is ...Yep, you guessed it 226V ...it is not Rocket Science!

Well put and better than a thousand diagrams

 

[kingeri]

Monkey, Look at this FFS..

View attachment 19415

The maximum voltage dropped it at the START of the circuit because this has the HIGHEST load placed upon it.

Couldn't be spelled out to folk any clearer than that! And yet still it continues.......