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I

iceman

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hi i was doin a minor works 2day on a light circuit on a tt system i couldnt get a reading for Zs cos me metre tripped out to determin Zs do i mesure Ze witch wos 38.8 and me R1 + R2 wos 0.61 = 39.41 this dont seem rite to me cos the tapulated value for a 6A breaker is 7.67 any help would be great cheers ;-)
 
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W

Wotsit

  • Thread Starter Thread Starter
  • #2
Thats fine, maz value would be 1667ohms for your 50v touch voltage. Hence the need for an rcd on tt systems.
 
I

iceman

  • Thread Starter Thread Starter
  • #3
so im right by recording 39.41 for Zs aslong as theres an rcd in place if not id hav to put somethin the remarks collem sugesting action required?
 
W

Wotsit

  • Thread Starter Thread Starter
  • #4
Have a look at table 41.5 page 50 of BRB and reg 411.5

If there is no rcd for a socket circuit on a tt i use code 1 and for others i use a code 2 and if only one rcd is used for all circuits in a property i use code 4

I normally record the value i see although i beleive it is ok to record less than 1667

A value of 1667 is only ok if an rcd is used
 
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I

iceman

  • Thread Starter Thread Starter
  • #5
im this case thn the rcd used was a 100A main switch with a 30mA trip so would state in the collem tht requires improvement
 
W

Wotsit

  • Thread Starter Thread Starter
  • #6
I would put code 4 - not inline with current regulations but not dangerous
 
J

joe kane

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  • #7
this is rght has to be less than 150ohms for ze thats why you ave to use a 100m/a time delay rcd
 
S

Spudnik

  • Thread Starter Thread Starter
  • #8
Ze has to be less than 1667 ohms.

Although anything over 200 is regarded as unstable.
 
I

iceman

  • Thread Starter Thread Starter
  • #9
nice one chaps thanks for ya help ;-)
 
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