Why let through energy of cable is calculated and compared against protective device let through energy, when adiabatic equation and disconnection time check is used to verify the cable sizes? or this let thru energy verification is applied only for current limiting breakers / fuses?
Though both the equations are same (just rearrangement) but the I2t value comes from the manufacturer in case of verifying the let through energy. Now my question is can we use this let through energy value (received from the manufacturer in the form of curve) to apply in this adiabatic equation S=(I√t)/k, to find out the minimum required CSA of conductor
That's the point, the expression you stated does not include the term (I2t), which is the value quoted by the mcb/RCBO manufacturer, or from BS EN 60898 or BS EN 61009.
The minimum S in the case you stated would have to be given by:
S={√(I2t)}/k
The different ways in which the adaibatic formula or adiabatic criterion is presented in BS 7671 is not helpful.
For example, have a look at the following Regulations:
434.5.2 (for current carrying conductors) uses both of the following (depending on device type) but does not print the first one as an equation-type expression, it's in the words of the 2nd para of the Reg
k2S2≥I2t
t=(k2S2)/I2
543.1.3 (for protective conductors) uses only S={√(I2t)}/k
Though both the equations are same (just rearrangement) but the I2t value comes from the manufacturer in case of verifying the let through energy. Now my question is can we use this let through energy value (received from the manufacturer in the form of curve) to apply in this adiabatic equation S=(I√t)/k, to find out the minimum required CSA of conductor
That's the point, the expression you stated does not include the term (I2t), which is the value quoted by the mcb/RCBO manufacturer, or from BS EN 60898 or BS EN 61009.
The minimum S in the case you stated would have to be given by:
S={√(I2t)}/k
The different ways in which the adaibatic formula or adiabatic criterion is presented in BS 7671 is not helpful.
For example, have a look at the following Regulations:
434.5.2 (for current carrying conductors) uses both of the following (depending on device type) but does not print the first one as an equation-type expression, it's in the words of the 2nd para of the Reg
k2S2≥I2t
t=(k2S2)/I2
543.1.3 (for protective conductors) uses only S={√(I2t)}/k
