The sooner we're into the 17th edition the better.
security lighting and zs query
- Thread starter steveth
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I'm going a week on wednesday 
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Did mine in April.
Got one question wrong....
Got one question wrong....
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Purely from a circuit theory viewpoint ----
It's a bit more complicated than I first thought. For the worst case analysis of a single fault condition in the lamp, the ring should be assumed to be carrying its rated current because this will reduce the voltage at the FCU. With this lower voltage as a starting point, use the 3 amp fuse characteristics to calculate the maximum wiring resistance.
It's a bit more complicated than I first thought.
For the worst case analysis of a single fault condition in the lamp, the ring should be assumed to be carrying its rated current because this will reduce the voltage at the FCU. With this lower voltage as a starting point, use the 3 amp fuse characteristics to calculate the maximum wiring resistance. I see it that the circuit ends at the live side of the fused spur, the fused spur being a distribution point. The outgoing side being a separate circuit protected by a BS1362 fuse.
When completing EIC with a fused spur fed off a ring final I create a separate 'Schedule of circuit details / test results'. At the top of the schedule I would put the fuseway that protects the ring final at the source of supply, BS88 32A for example.
That way, there's a clear line between the two circuits.
Imagine having a TN-S property with an external impedance of 0.8ohms and a ring final with an R1+R2 reading of 0.4ohms, Zs would read the maximum allowed for a B32 MCB (1.2ohms corrected), parellel earths omitted.
That would leave no headway to connected a fused connection unit and run 20M of 1.5mm cable around the garden for lighting (class 2 with no E-C-P), adding another 0.6ohms to the Zs value (if you count this as part of the ring final).
As circuits are now separated I see no issue with using a 0.4s disconnection time for the ring final and feed side of the fused spur and 5s disconnection time for the outing circuit.
As for max Zs figures of BS1362 fuses, no I haven't seen the source but use a document created by a member on the IET forums which lists both 3A and 13A figures for both 0.4 and 5s.
When completing EIC with a fused spur fed off a ring final I create a separate 'Schedule of circuit details / test results'. At the top of the schedule I would put the fuseway that protects the ring final at the source of supply, BS88 32A for example.
That way, there's a clear line between the two circuits.
Imagine having a TN-S property with an external impedance of 0.8ohms and a ring final with an R1+R2 reading of 0.4ohms, Zs would read the maximum allowed for a B32 MCB (1.2ohms corrected), parellel earths omitted.
That would leave no headway to connected a fused connection unit and run 20M of 1.5mm cable around the garden for lighting (class 2 with no E-C-P), adding another 0.6ohms to the Zs value (if you count this as part of the ring final).
As circuits are now separated I see no issue with using a 0.4s disconnection time for the ring final and feed side of the fused spur and 5s disconnection time for the outing circuit.
As for max Zs figures of BS1362 fuses, no I haven't seen the source but use a document created by a member on the IET forums which lists both 3A and 13A figures for both 0.4 and 5s.
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