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Confusion over table 7.1(i) OSG

When I look at line 10 (B40 mcb on a 6/2.5 twin and earth,TNS system the max circuit length due to zs is given as 23m(no RCD).Yet when I calc R1 +R2 x 23m I get 10.49x23/1000 = 0.24 ohms.Add ze for TNS to this(0.8) gives 1.04 ohms,whilst table B6 gives a max zs of 0.88 ohms for a B40.Wondered where I,m going wrong.

Regards,

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0 AJJewsbury over 3 years ago

Alan Capon:

mapj1:
. . . The mains may be as low as 230V- 10% or 207V. . .
Not quite. The lower limit is -6%, which gives 216.2V at the load side of the meter or isolator (where fitted by the supplier).
Regards,
Alan.
BS 7671 takes a different approach again, saying 230V x Cmin = 230V * 0.95 or 218.5V.
- Andy.
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0 AJJewsbury over 3 years ago

Alan Capon:

mapj1:
. . . The mains may be as low as 230V- 10% or 207V. . .
Not quite. The lower limit is -6%, which gives 216.2V at the load side of the meter or isolator (where fitted by the supplier).
Regards,
Alan.
BS 7671 takes a different approach again, saying 230V x Cmin = 230V * 0.95 or 218.5V.
- Andy.
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Vote Up 0 Vote Down

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Confusion over table 7.1(i) OSG

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