RmS wrote:
I would indeed be most eager to get hold of some "Test" questions -
(these may have suffered a bit from being cut and pasted... note read
Ohms where you see "W". Answers in brackets at the end)
1. A single-phase circuit is to be wired in 70°C PVC-insulated and
sheathed multicore cable to BS6004 with copper conductors. The cables
are to be installed single in conduit without insulation. The nominal
design current of the circuit is 30A, ambient temperature is 50°C. If a
BS88 gG fuse of rating 32A has been selected, determine the minimum
cross sectional area of these cables that can be used. [10mm2]
2. A single-phase circuit has a nominal design current of 17A and a
BS3036 semi-enclosed rewireable fuse of 20A rating has been selected.
Ambient temperature is 45°C and the cable is installed with 4 similar
cables all clipped direct. BS6004 70°C PVC-insulated and sheathed
multicore cables are employed. Determine the minimum cross sectional
area of the cable to be used. [10mm2]
3. Six similar single-phase circuits, each designed for 8A and protected
by a 10A miniature circuit breaker are wired in BS6004 70 °C
PVC-insulated and sheathed copper multicore cable. The cables operate at
an ambient temperature of 45°C and are totally enclosed in thermal
insulation with a derating factor of 0.5. Determine an appropriate cross
sectional area for the conductor. [6mm2]
4. A single-phase a.c. circuit is wired in single core 70°C
PVC-insulated non-sheathed cable to BS6004 having copper conductors of
10mm2 cross sectional area in conduit (CR1). If the nominal design
current is 40A and cable length 33m what voltage drop is experienced
down the cable? [5.8V]
5. A 240V single-phase a.c. circuit is wired in multicore 70°C
PVC-insulated and sheathed cable to BS6004 with copper conductors. The
circuit length is 20m with a design current of 25A. The cross sectional
area of the cable is 6mm2. The circuit is taken from a distribution
board supplied with 240V single-phase cable, again to BS6004 with cross
sectional area 25mm2 and design current 100A over length 30m. All cables
are clipped direct. Determine the voltage at the point of utilisation.
[231.1V]
6. Eight similar single-phase circuits are grouped together,
clipped-direct, each having a nominal design current of 24A and
protected by a 30A BS3036 semi-enclosed, rewireable fuse. The circuits
are run in 70°C PVC-insulated multicore, sheathed cables to BS6004. If
ambient temperature is 30°C and the cable run is 70m what is the minimum
cross sectional area that can be used and what is the voltage drop? [16
mm2, 4.7V]
7. A single-phase circuit is run in single core 70°C PVC-insulated and
sheathed cable clipped-direct and not bundled with other circuits. The
conductors are copper with a cross sectional area for the line conductor
of 4mm2 and protective conductor of 2.5mm2. The length of the cable run
is 45m and Ze=0.35W. Assuming an earth fault at the load with a loop
impedance for the cable of 16mW/m calculate the earth fault loop
impedance and the fault current that would flow with a 240V supply.
[1.07W, 224.3A]
8. In an installation which is part of a TN-C-S system a final circuit
is fed from a sub-distribution board. The distribution circuit from the
main board to the sub-distribution board is run in single-core 70°C
PVC-insulated cables having copper conductors. The live conductors being
25mm2 and protective conductor 16mm2 and a loop impedance of 2.59mW/m.
the distance between the distribution boards is 27m. The final circuit
is run in 6mm2 twin conductor with CPC with a loop impedance of 14.48
mW/m and length 22m. If Ze= 0.35W calculate the earth fault loop
impedance, a) at the sub-distribution board, b) at the final circuit
board. [0.42W, 0.74W]
9. A 240V single-phase circuit is run in BS6004 multicore cable with
main conductors of 16mm2 and protective conductor of 6mm2 and loop
impedance of 5.84 mW/m. the cable has a length of 40m, operates in an
ambient temperature of 30°C and has Ze=0.35W. Use the adiabatic equation
with K=115 to calculate the maximum disconnection time allowable for a
protective fuse. [2.8s]
10. A 240V single-phase circuit is run in 6mm2 two core with a 2.5mm2
CPC for a length of 35m. The cable has an earth loop impedance of 14.48
mW/m and Ze=0.35W. The circuit is protected by a 40A MCB (type B) which
offers a disconnection time of 0.1s. Check that the adiabatic equation
condition is satisfied if K=115. [78482856]
Thanks. - And i will certainly try to get the OSG.
One of the cheaper sources:
http://www.amazon.co.uk/exec/obidos/...ternodeltdcomp
--
Cheers,
John.
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