Earthing for an EV Charging Point

[uksparks]

I cheated lol I used Tony's XL spreadsheet to calc the N current

Simon above did it long hand

i did it this way and got a different figure...

Im=√((8-0.5(25+68))²+(0.866(25-68))²

I wonder if i am typing it wrong on the calculator?

Can someone else try this method please.

 

[spark 68]

I have an Excel spreadsheet as well. Wanted to show the way to calculate it though. Either way its the same answer

I have enough trouble posting on here normally with IE11 lol without trying to insert symbols lol

 

[Simonslimline]

I have enough trouble posting on here normally with IE11 lol without trying to insert symbols lol

i use this Type mathematical symbols - online keyboard

 

[Simonslimline]

i did it this way and got a different figure...

Im=√((8-0.5(25+68))²+(0.866(25-68))²

I wonder if i am typing it wrong on the calculator?

Can someone else try this method please.

Can do it like this as well

In=√((Ia²+Ib²+Ic²)-((Ia*Ib)+(Ia*Ic)+(Ib*Ic)))

OR

x = A cos 0 + B cos 120 + C cos 240
y = A sin 0 + B sin 120 + C sin 240
N = √(x²+y²)

 

[Simonslimline]

i did it this way and got a different figure...

Im=√((8-0.5(25+68))²+(0.866(25-68))²

I wonder if i am typing it wrong on the calculator?

Can someone else try this method please.

Must be how you are typing it mate. What answer are you getting?

 

[uksparks]

Il so going on it being 53.57A on the neutral, using the calculations in the book...

70 / 53.57 - (70/230) x (8 + 25 + 68) = -29

it says if it is greater than zero it will need an earth rod, unless I'm being thick (tell me if I am) -29 is less than zero.

 

[spark 68]

I worked the bits in brackets out first, ie 0.3 * 101

 

[shanky887614]

I worked the bits in brackets out first, ie 0.3 * 101

remember bodmas

brackets over divide multiply addition subtraction

 

[uksparks]

Are we accepting 53.57 then?

 

[spark 68]

I ended up with 70/ 53.6 - 30.3

in my rough calc I think just rounded either up or down to the nearest whole number, =>5 up, =<4 down, after all it was just a quick calc, to get a ballpark figure

 

[GB.Kayak]

Im=√((IL1-0.5(IL2+IL3))²+(0.866(IL2-IL3))²

I got 53.57 Amps.

Your equation here is missing a closing bracket. Depending upon where it has been missed from or its location has been assumed to be, the answer may come out very differently.

 

[uksparks]

I'm out at the moment so haven't got the BYB in front of me to look at it again, I think it's just a typo above as the calculation would not work if the brackets were not even.

 

[uksparks]

You have typed an extra bracket at the start just after the root symbol that's all

 

[Simonslimline]

Your equation here is missing a closing bracket. Depending upon where it has been missed from or its location has been assumed to be, the answer may come out very differently.

I got the same answer using an Excel spreadsheet. I understand what you are saying though.

 

[GB.Kayak]

i did it this way and got a different figure...

Im=√((8-0.5(25+68))²+(0.866(25-68))²

I wonder if i am typing it wrong on the calculator?

Can someone else try this method please.

Please see previous post ... closing bracket missing. This will result in discrepancies depending upon where the bracket is assumed to be.

 

[Simonslimline]

Well spark68 came up with the same answer a swell using Excel spreadsheet. Im confident it is correct.

 

[uksparks]

Ok so now we have the correct figure for Im, that means we can now accurately calculate the next one that tells us the answer.

so for the purpose of moving on we shall accept that 53.57 is correct.

 

[Simonslimline]

You have typed an extra bracket at the start just after the root symbol that's all

It does not work without typing that on my Casio fx 85GT PLUS.

 

[spark 68]

The reason I just rounded the figures up and down is because you will not be able to get an Ra smack on the calculated anyway, this calc only gives you the highest permissible figure,ideally you want to be a bit lower

 

[GB.Kayak]

If the extra bracket has been inserted before the sqrt then your answer is correct. Correct equation should be confirmed. When I was doing structural analysis, stress calculations, for a company making actuators primarily for the aircraft and rail sectors, MS Excel was seriously frowned upon as an analytical tool. The very good reason for this is that the method of gaining the result is hidden from the user and is not expressed in the form that it would be mathematically presented.