Chapter 2: Installation
98-141368-A 36
To calculate the maximum cable extension, do as follows:
1. First measure the source impedance in the ship installation as shown in Measuring the
ship source impedance on page 34.
2. Then find the resistance per meter for the cable type you are going to use.
For 4 mm
2
/AWG 11, the value is 4 mOhm/m at 20 °C
For 1.5 mm
2
/AWG 15, the value is 10 mOhm/m at 20 °C
For other cable types, refer to the data sheet for the cable.
3. Calculate the maximum allowed impedance in the extension cable as follows:
Max. allowed impedance in extension cable = max. total impedance - (measured source
impedance + impedance of the supplied cable).
4. Then calculate the max. extension cable length as follows:
Max. impedance in extension cable (from step 3.)
Max. length = 0.5 x impedance/meter (from step 2.)
The length is multiplied by 0.5 above because there are two conductors in the cable.
Example:
Ship supply voltage: 12 V DC
Ship source impedance (measured): 50 mOhm
Extension cable type: 4 mm
2
(AWG 11)
Max. cable extension =
In this case, the power cable can be extended with up to 3.12 m.
If you need a longer cable, you can double the maximum allowed length by connecting two
cables instead of one, or you can use a cable with a larger diameter.
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