Technical information

4. batteries;
5. Current transformers: CCN XODW2 (UL506 ”Specialty Transformers”);
6. Current transformers with 5 A secondary: approved or otherwise.
1.7.2 Overcurrent Protection
To assure that the circuit power is limited it is necessary to install an overcurrent
protection down line from the supply dimensioned as in 43.1 of UL508A
It is known that in the calculation of the maximum protection size the peak value
of the voltage should be applied (V
P
) and not the effective value (V
RMS
).Thus for a
24 V circuit we should consider two cases:
–direct current:V
P
= V
RMS
= 24 V
–alternating current:
and therefore
Circuits down line from the current transformers with (TA) with 5 A secondary
are considered self protected.
It is not required for each Low-Voltage Limited Energy circuit to have its own
power source but it is sufficient that the power of each is limited.
EXAMPLE
Let’s say there is a 24 V control circuit in direct current with absorption of around
10 A.The components of the circuit are partially non approved
A choice should be made: replace all the non approved components with
equivalent approved components or place them in Low-Voltage Limited Energy
circuits.The first solution is usually not possible while it is generally possible to
split loads over several different circuits (for example coils on one circuit and
solenoid valves on another).
In this example it is assumed that the components are split up into three circuits.
To enjoy the advantages of the Low-Voltage Limited Energy it is not necessary to
CONTROL CIRCUITS
82
RMSRMSP
VVV ⋅=⋅= 41,12
A3
34
100
≅
VV
P
342441,1 ≅⋅=
100
24
≅ 4,17A
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