Maybe I should have made it a Debate rather than a question as I can see what is for me, incorrect. And having put together a Tech Talk for a dozen electricians on the omission of supplementary bonding in a location containing a bath or a shower and the correct determination of potential extraneous-conductive-parts. I realised whilst putting this talk together that after more than 20+ years of staring at this equation that for me I now see it as an incorrectly conceived and lazily written working example of the equation (6.1).

Looking at equation (6.2) as with the others, it's not so clear that everything to the right of the (=) in the middle of the equation is the same equation just with the bracketed part of the equation completed. This surely should have been the symbol for 'equivalent' or 'is equivalent to'? Like an equals symbol but with three lines?

Why is this simplification or staged aproach required?

If followed mathematically then the outcome would be incorrect...

(230 / 0.0005) -1000 = 459 000 - 1000 = 458 000Ω (not 459KΩ)

Surely written correctly it should be:

(230 / 0.0005) - 1000 / 1000 = 459kΩ

It's just messy and if assumes that the person reading it needs help with the bracketed part of the equation, but then goes on to jump from 459 000Ω to 459KΩ without any further guidance for those that required help with the bracketed part of the equation as to how we got from Ω to KΩ.

It's just my opinion of course ;0)

sae70 said:

If followed mathematically then the outcome would be incorrect...

(230 / 0.0005) -1000 = 459 000 - 1000 = 458 000Ω (not 459KΩ)

Surely written correctly it should be:

(230 / 0.0005) - 1000 / 1000 = 459kΩ

That is not correct at all.

Why have you in the first example subtracted 1000 (Ω) twice, and divided by 1000 in the second?

I would prefer to have each = sign starting a new line.

I disagree with your 'correctly written'. I hope from school you will recall

BODMAS

Brackets, operators (sin cos tan etc), division, multiplaction addition, subtraction

For the order of evaluation of nested expressions.

"(230 / 0.0005) - 1000 / 1000 = 459kΩ"

Let us break that down

Brackets

230/0,0005 = 460 000 = 460k  (read all the "=" sign as 'is the same as' with a slight Yorkshire accent.)

no ops,

Division

1000/1000 = 1k/1k = 1

 no addition, but one subtraction

460 000 - 1= 459 999

rather a  long way, well 999 ohms to be exact , from the right answer...
 here 'k' is short for 3 zeros, or multiply bu 1000,  and if we had it M would  be short for 6 zeros = multiply by million etc.

I'm concerned

Mike

mapj1 said:

BODMAS

I usually use "BIDMAS" where "I" stands for "Indices", i.e. powers or roots, but it can be "O" for "orders".

Ok, other and maybe more helpful acronyms exist, it probably depends on who taught which set for  O level maths ;-)

edit In the US apparently it is PEMDAS (Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction)

But my point is that functional operators like sin cos tan need doing immediately after brackets too - but indices/orders   and functions are sometimes mixed - beware of things like tan^-1 meaning arctan(f), not 1/ (tan(f))

And then of course the sparking favourite of indices within unbalanced units

kA²s

- let through energy

or nVHz^-1/2  

Noise voltage per unit bandwidth - but noting that power, not voltage, scales with bandwidth.

My point was really  that there are dragons to catch  those who do not follow  the rules in order - and I think the OP has been bitten by that.

I also agree the text book could be made clearer.

Mike.

Ok, other and maybe more helpful acronyms exist, it probably depends on who taught which set for  O level maths ;-)

edit In the US apparently it is PEMDAS (Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction)

But my point is that functional operators like sin cos tan need doing immediately after brackets too - but indices/orders   and functions are sometimes mixed - beware of things like tan^-1 meaning arctan(f), not 1/ (tan(f))

And then of course the sparking favourite of indices within unbalanced units

kA²s

- let through energy

or nVHz^-1/2  

Noise voltage per unit bandwidth - but noting that power, not voltage, scales with bandwidth.

My point was really  that there are dragons to catch  those who do not follow  the rules in order - and I think the OP has been bitten by that.

I also agree the text book could be made clearer.

Mike.