New Zealand Volt drop cont.

[telectrix]

liken it to a bus load of 60 passengers. bus drops off 10 at the first load. so it's now got 50. at the 2nd load it drops off 5 more. so now its lost another 5 on top of the 10 already lost and now has 45. . and so on.

 

[Monkeyblaine]

That is exactly what I'm saying In my earlier post. With a circuit with say 5 joints down its length with lights coming off joints it's dropping volts at every joint. So the VD will be at its worse at the last joint. It's what I said and outspoken said that's not right???

 

[Outspoken]

That is exactly what I'm saying In my earlier post. With a circuit with say 5 joints down its length with lights coming off joints it's dropping volts at every joint. So the VD will be at its worse at the last joint. It's what I said and outspoken said that's not right???

Because it is not right!!

 

[Monkeyblaine]

I give up. How is That any different to the bus and passenger thing?

 

[telectrix]

the lowest voltage will befoundat the kast load, but the biggest vd is on the 1st section, as that section from the ocpd will be the only part of the circuit carrying the full load.

 

[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.......