Formulas

[Graham Coughlan]

2 questions here

First one... I know theres a formula you can use to work out lengths of cables and the csa. I remember it being something like pl/csa but i cant remember the rest so could someone please help me remember this

Second question...

N = E x A / F x UF x MF

I know all the meanings to this formula apart from F so again someone please help with that

Cheers

 

[Richard Burns]

First one

R= rho l/A
resistance(ohm) = resistivity (ohm meter) x length (metre) over cross sectional area (metre squared)

or
L = R S 27.6
Length (m) = resistance (ohm) x cross sectional area (milimetre squared) x 27.6
for copper

no idea about the second one

 

[telectrix]

over cross sectional area (metre squared)

bloody big cable, that is ! LOL.

 

[Graham Coughlan]

so far ive for N = 500 x A / F x 0.6 x 0.8 - I still dont know what F is tho... (Ive got to work out the area still)

The question ive got to answer is....

The designer has requested the sales area at a bench level to be illuminated to a value of 500 lux reapectively as fitted with T8 single flourescent luminaires.

Assuming the MF is 0.8 and the UF is 0.6 demostrate through calculation the number of fittings required.

 

[Silly Sausage]

Ah! Lighting calculations.

A 5 second google search yielded this...
LIGHTING CALCULATIONS, LIGHTING, CALCULATIONS, FORMULAS

Is this what you need, look at step 4.

 

[Graham Coughlan]

Ah! Lighting calculations.

A 5 second google search yielded this...
LIGHTING CALCULATIONS, LIGHTING, CALCULATIONS, FORMULAS

Is this what you need, look at step 4.

Thats what ive been after!!! ive also just found my notes telling me what F stands for as well! lol

Thanks so much

 

[Knobhead]

Graham, this has gone beyond a joke! You’ve gone from cable to lighting calculations. For gods sake give people a clue.
UF = utilisation factor
MF = maintenance factor
Not done lighting calculations since I was an apprentice, but can still remember them.

Better still just scan the entire test and hope someone is daft enough to do it for you!

 

[Silly Sausage]

Graham, For gods sake give people a clue.

Someone needs to start a thread giving the basics of how to do your own research.
(In way a he is by asking on here!)

 

[MarkieSparkie]

F = Total luminous flux (Lumens)

 

[DPG]

Thank flux for that. Daz

 

[SirKit Breaker]

I think i will stick to being thick.

I have only just got my head back around the adiabatic equation after many years of not using it, and that is only cos it can crop up in the 17th edition exam, so i need to be able to explain it to the fare paying public:banghead: