- Joined
- 27 Jan 2008
- Messages
- 25,350
- Reaction score
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- Location
- Llanfair Caereinion, Nr Welshpool
- Country
The problem in real world is if one makes a minor mistake like forget to add minus when squaring J or as I did miss off three zeros then the results can be costly so we tend to used spread sheets or other programs where the program can be tested and ensured error free which removes the chance of expensive errors.
On the Falklands someone in PSA miss read the annual rain fall by a factor of 10 and as a result monsoon ditches were built either side of the road. As well as the expense of making the ditches it also means if a vehicle leaves the road it will normally turn over. Which has cost quite a few lives mainly military as contractors and locals don't use soft top Landrovers.
All because of an extra 0! Can you imagine what it would have been like in Roman times with no Zeros!
But even BAS example got some answers well out and this is a problem where we do not normally calculate. For example if I wanted to run in an extra long ring main I could try to calculate the length.
We know for 2.5mm how many meters is now allowed. So I will give 4 lengths one of which is correct if we used 4mm cable instead:-
a) 109 meters
b) 174 meters
c) 179 meters
d) 197 meters
Now if you Spark123 had to decide if any of those results looked right you could most likely pick the correct figure.
I built a spread sheet to work out length for 2.5mm cable which gave same results as the guy in IET lecture stated was maximum length and to get results for 4mm I had only to change two figures. Current carrying capacity moved from 20A for 2.5mm to 27A for 4mm and the mV/A/m changed from 18 to 11. So I am very unlikely to have made any errors.
So how many can select correct select the correct answer? In other words if something went wrong with your calculations would you notice? Two of the figures have been arrived at by entering wrong information i.e. a real mistake likely to be made. I have also tested using 26A for design current for cable as it shows 21A in table but we use 20A in calculations and the answer to 3 sig figures is the same.
If I ask for a guess then no one can be shamed for getting wrong answer.
On the Falklands someone in PSA miss read the annual rain fall by a factor of 10 and as a result monsoon ditches were built either side of the road. As well as the expense of making the ditches it also means if a vehicle leaves the road it will normally turn over. Which has cost quite a few lives mainly military as contractors and locals don't use soft top Landrovers.
All because of an extra 0! Can you imagine what it would have been like in Roman times with no Zeros!
But even BAS example got some answers well out and this is a problem where we do not normally calculate. For example if I wanted to run in an extra long ring main I could try to calculate the length.
We know for 2.5mm how many meters is now allowed. So I will give 4 lengths one of which is correct if we used 4mm cable instead:-
a) 109 meters
b) 174 meters
c) 179 meters
d) 197 meters
Now if you Spark123 had to decide if any of those results looked right you could most likely pick the correct figure.
I built a spread sheet to work out length for 2.5mm cable which gave same results as the guy in IET lecture stated was maximum length and to get results for 4mm I had only to change two figures. Current carrying capacity moved from 20A for 2.5mm to 27A for 4mm and the mV/A/m changed from 18 to 11. So I am very unlikely to have made any errors.
So how many can select correct select the correct answer? In other words if something went wrong with your calculations would you notice? Two of the figures have been arrived at by entering wrong information i.e. a real mistake likely to be made. I have also tested using 26A for design current for cable as it shows 21A in table but we use 20A in calculations and the answer to 3 sig figures is the same.
If I ask for a guess then no one can be shamed for getting wrong answer.
