Just for information when designing the CTs and wiring: 1. If you double the length of wire you will
double the resistance of the wire. 2. If you double the cross sectional area of the wire you will cut its
resistance in half. Most effect is in that if you use 1A secondary instead of 5A, all burdens will drop to
level smaller to portion of 5A
2
e.g. 1/25.
Now normally copper cables are used to connect CTs to relay, anyway in below table is presented also
Aluminum resistivity and conductivity properties.
These values in this table present the resistivity in the given tempe20ºC. For calculation of the
conductor resistivity in other temperatures use following formula:
These values in this table present the resistivity in the given tempe20ºC. For calculation of the
conductor resistivity in other temperatures use following formula:
For example copper resistivity in +75 would be calculated as follows:
With this given value most common used copper wires resistance per meter in 75 are:
1.5 mm
2
2.5 mm
2
4 mm
2
6 mm
2
0.0135 Ω/m
0.00812 Ω/m
0.00508 Ω/m
0.00338 Ω/m
These values were calculated with formula:
Suggestion is that for calculating the CT burden the worst case scenario is used. For most cases these
75ºC values can be used. If in your application ambient temperature is higher than 75ºC , then the
resistance should be calculated for that temperature.
AQ-T257
Instruction manual
Version: 2.00
159
© Arcteq Relays Ltd