2 exam questions discuss/answer

[Lee321]

the max permitted earth loop imp for a 30a 3036 supplying a final circuit is:

a)1.09ohms

b)1.84ohms

c)2.64ohms

d)3.83ohms

the max permitted earth loop imp for a 30a 3036 supplying a distribution board is:

a)1.09ohms

b)1.84ohms

c)2.64ohms

d)3.83ohms

 

[Andy™]

depends on your disconnection times.

0.4 will be 1.09 ohms, 5s will be 2.64 ohms

 

[Lee321]

you need to decide what DT you should have for that type of circuit

 

[Andy™]

if TT, both would be 0.4, so 1.09 ohms.

if TN, final circuit would be 0.4s so 1.09 ohms

distribution would be 5s, so 2.64 ohms

well, i think thats right

 

[Lee321]

[quote name='Andy

 

[Andy™]

i think he is wrong - 411.3.2.3 states ' Im a TN system, a disconection time no exceeding 5s is permitted for a distruibution circuit and for a cicuit not covered in 4113.3.2.2.

411.3.2.2 states 'the maximum disconnection times stated in table 41.1 shall be applied to final circuits not exceeding 32A'

411.3.2.2 does not mention distribution circuits and a distribution circuit is not a final circuit, so the must be covered under 411.3.2.3, which says 5s

 

[Lee321]

[quote name='Andy