12 / EN
WORKED EXAMPLE
tundishThe example below is for a G 1/2” temperature & pressure relief valve with a discharge pipe (D2)
having 4 no. elbows and length of 7 m from the tundish to the point of discharge.
From Table 2
Maximum resistance allowed for a straight length of 22 mm copper discharge pipe (D2) from G 1/2” T &
P valve is 9 m.
Subtract the resistance for 4 no. 22 mm elbows at 0.8 m each = 3.2 m.
Therefore the maximum permitted length equates to: 5.8 m.
As 5.8 m is less than the actual length of 7 m therefore calculate the next largest size.
Maximum resistance allowed for a straight length of 28 mm pipe (D2) from G 1/2” T & P valve equates
to: 18 m.
Subtract the resistance for 4 no. 28 mm elbow at 1.0 m each = 4 m.
Therefore the maximum permitted length equates to: 14 m
As the actual length is 7 m, a 28 mm (D2) copper pipe will be satisfactory.
d) ELECTRICAL WARNING:
The appliance must be earthed
The electrical installation must be in line with the current IEE wiring regulations.
A mains supply of 240 VAC 3 kW.
Heat resisting cable, round 3 core 1.5 mm (to BS 6141 table 8) should be used to connect to the electri
-
cal supply through 20 amp double pole switch (conforming to BS EN 60669-1).
The appliance must have a dedicated incoming supply that must be protected by an industry stan-
dard MCB compliant with the current IEE wiring regulations.
The cable enters the terminal compartment through a tube embedded in the foam insulation, the
entrance to this tube is on the rear right hand side at the bottom.
Flexible cables are colour coded as follows:
Brown .................................................................live
Blue ..............................................................neutral
Green and yellow ....................................... earth
Valve
outlet
size
Minimum size
of discharge
pipe D1*
Minimum size of
discharge pipe D2*
from tundish
Maximum resistance allowed,
expressed as a length of pipe
(i.e. no elbow or bends)
Resistance crea-
ted by each elbow
or bend
G 1/2 15 mm
22 mm
28 mm
35 mm
Up to 9 m
Up to 18 m
Up to 27 m
0.8 m
1.0 m
1.4 m
G 3/4 22 mm
28 mm
35 mm
42 mm
Up to 9 m
Up to 18 m
Up to 27 m
1.0 m
1.4 m
1.7 m
G 1 28 mm
35 mm
42 mm
54 mm
Up to 9 m
Up to 18 m
Up to 27 m
1.4 m
1.7 m
2.3 m
Table 2 Sizing of copper discharge pipe “D2” for common temperature valve outlets.
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