MP200 Installation Manual
26
The method described may also be used quite successfully to size a more complex power supply network, with
ramifications, such as that shown below:
In this case it will be sufficient to identify the points of connection, beginning at the source and calculating for
each single section that is included between the two points.
NOTE: in any case, standards specify that cable section should never be less than 0.1 mm
2
10.2 NORMOGRAM FOR SIZING CABLES
• This technical sheet offers a graphical method that will make it possilbe to calculate cable sizing.
• It is possible to find:
- the voltage drop
V that will occur as a consequence of the length of the line L, of power consumption I, and
section S of the cable used;
- what section S is required to obtain no more than a voltage drop of
V as a consequence of the length of line L
and of power consumption I;
- maximum amount of power consumption as a consequence of the length of line L, the voltage drop
V accepted
and the section S of the cable used.
EXAMPLE 1
• a siren that consumes 2A (2000mA) with a cable section of 1mm must be connected over a distance of 100
metres. What voltage drop will be found at the end of the line?
Solution
Trace a segment that starts from length
L
(100 metres) of the line then intersects
S
(cable section) in
1
(mm
2
)
and extend it to the central line
R
. From this point trace a second segment that passes through power consump-
tion
I
(2000mA) and extends as far as the line
V.
• with this procedure the voltage drop that occurs in a 100 metre line with 1mm section cable and 2A power
consumption has been found and it is 3.7V.
EXAMPLE 2
• On the basis of example 1, the decision is made to accept a maximum voltage drop of no more than 2V.
Solution
Trace a segment that starts from
V (2V) then extends to central line
R
, intersecting
I
in 2000 (mA), which is the
power consumption of the siren when active. From this point trace a second segment that meets at
L
(100
metres). At intersection
S
it will be possible to read the minimum section value for the cable required for the
purpose, in mm
2
, which will be slightly less than 2 mm
2
. This procedure can be used to obtain any other vari-
ables that may be required.
Summary of Contents for MP 200
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