Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 31 replies
  • Subscribers 32 subscribers
  • Views 3159 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

I just thought of something

ebee
I know it`s many years ago that I queried the age old saying that was taught in college etc as to the r1 & r2 cross connection to form a double loop and the statement was made that this gave the exactly the R1 + R2 reading of the whole ring when taken from any point on the ring.

My statement was that this statement was not quite right and the word "exactly" needs substituting with "substantially" (I think the error was about 6% which as 6% of an already small number was not a great worry and it was still a very good approximation fit for use).


Anyway to add to that,,it just occurred to me . If we leave connected and test at a spur then it adds the spur value to the (nearly) ring value so that`s usually OK too.

However that`s only for spurs near to ring midpoint.!

If we had a spur nearer to one ring end than to midpoint it would therefore give a missleadingly large R1 + R2 value.

Not normally an issue but in extreme cases too pessimistic and causing a headscratch.


Off course field errors and instrument errors give missleading readings too.


I`d say once we done the fig 8 for the ring we should really connect ring ends together then test R1 + R2 from ring origin to each spur end to get as truer reading.


I know, I should get out more


?
Parents
  • 0
    gkenyon:
    Chris Pearson:



    I still wonder why anybody would use 4 mm² T&E for a ring.




    Minimum tabulated current carrying capacity Iz to be at least 20 A (Reg 433.1.204) and therefore from Table 4D5, Ref Method 101# or, where correction factors (such as grouping or ambient temp) might mess things up a little, Ref Methods A, 100#, 102#.


    As per earlier comment re 6 sq mm .... you might struggle with some products to drop spurs off a 4 sq mm ring at a socket-outlet or other accessory to BS 1363 because of terminal constraints if the product meets the minimum requirements of the standard.




    Graham, thank you. I see what you mean. I had thought do radial instead, but short of going up to 6 mm² (which as you say, is possible only with the better makes of socket) under those circumstances, it would be necessary either to downsize to a 20 A OCPD, or complete a ring.


Reply
  • 0
    gkenyon:
    Chris Pearson:



    I still wonder why anybody would use 4 mm² T&E for a ring.




    Minimum tabulated current carrying capacity Iz to be at least 20 A (Reg 433.1.204) and therefore from Table 4D5, Ref Method 101# or, where correction factors (such as grouping or ambient temp) might mess things up a little, Ref Methods A, 100#, 102#.


    As per earlier comment re 6 sq mm .... you might struggle with some products to drop spurs off a 4 sq mm ring at a socket-outlet or other accessory to BS 1363 because of terminal constraints if the product meets the minimum requirements of the standard.




    Graham, thank you. I see what you mean. I had thought do radial instead, but short of going up to 6 mm² (which as you say, is possible only with the better makes of socket) under those circumstances, it would be necessary either to downsize to a 20 A OCPD, or complete a ring.


Children
No Data

Community Rules & Guidelines