Do I use zdb or ze when calculating zs values on am2?

[DPG]

This is how I was told to validate:

Let’s say my r1 is 0.20 rn is 0.20 r2 is 0.30

R1+Rn = r1+rn/4
R1+Rn = 0.20+0.20/4
= 0.40/4
= 0.10 ohms
So R1+Rn = 0.10 ohms

Then repeat for r1+r2 to validate the R1+R2 reading

I was not told to put anything in brackets

You've done the sum by doing the addition first. But in mathematical hierarchy (BODMAS) division is done before addition.

So thought you have done it in the correct order, it is actually written incorrectly.

 

[Uplight99]

You've done the sum by doing the addition first. But in mathematical hierarchy (BODMAS) division is done before addition.

So thought you have done it in the correct order, it is actually written incorrectly.

This is exactly how they told me to write it out on my revision day. Not sure what’s right/wrong now

GSH electrical have also done it the same as me and they’re college tutors

 

[Aaron b]

GSH have written it as a fraction which is just another way. If you make sure you do the addition first, it will work or if your calculator lets you lay it out as GSH has. The equation is technically wrong without the brackets and all written on one line.

What you have written "R1+Rn = 0.20+0.20/4" = 0.25ohm

 

[DPG]

This is exactly how they told me to write it out on my revision day. Not sure what’s right/wrong now

GSH electrical have also done it the same as me and they’re college tutors

You don't need brackets when it is written with items above and below the line as they have done. But the way you wrote it is incorrect, ie. R1 + Rn / 4

 

[loz2754]

This is exactly how they told me to write it out on my revision day. Not sure what’s right/wrong now

GSH electrical have also done it the same as me and they’re college tutors

That drawing is not the same as writing the equation in a straight line. In the drawing, the sum of r1+ rn is written above the divisor, which makes it obvious in which order to evaluate the equation.
When written in a straight line, we need to follow the rules of what order to do the evaluation, which is summarised using the acronym BODMAS, or BODMAS.
Just to back this up, page 66 of guidance note 3 shows the equation as (r1 + r2)/4, which clearly shows the use of brackets.

 

[Uplight99]

You don't need brackets when it is written with items above and below the line as they have done. But the way you wrote it is incorrect, ie. R1 + Rn / 4

Ok.

So I would write R1+Rn = (r1+rn)/4
Then lay it out like I previously did

 

[DPG]

Ok.

So I would write R1+Rn = (r1+rn)/4
Then lay it out like I previously did

Yes that would be a correct format.

 

[Uplight99]

Yes that would be a correct format.

Thanks for the help