DC cabling and shielding principles

Considerations for ensuring proper over voltage and lightning protection.

Shielded power feeder cable is always needed for installations when the power feeder length exceeds 4 m (13.1 ft) in an outdoor environment to ensure a properly working overvoltage and lightning protection in the Radio and OVP Module.

The power feeder cable needs to be grounded at both ends and country local regulations for connecting the ground shield to the mast body must be followed. The DC feeder cable type recommended by Nokia is an MCCMK or MCMK shielded cable, minimum shielding 2.5 mm². Also outdoor shielded hybrid cables with embedded fiber and minimum shielding 2.5 mm² are suitable. For indoor environments or outdoor ground configurations with < 4 m (13.1 ft) DC connections, an equivalent locally-supplied unshielded DC cable can be used. Make sure that both ends of the connection to the Radio Module or the System Module are IP65-protected.

External surge protection is always needed for installation with the System Module PDU DC outputs if the output power feeder length exceeds 10 m (32.8 ft) (installed at the System Module end). The same external surge protection requirement applies to DC outputs of FPMA and FPRB AC/DC systems.

External surge protection is always needed for installation with the System Module DC input (FSMF with or without FPFD) if the input power feeder length exceeds 10 m (installed closely to the System Module DC input port).

Some of the legacy RF Modules also require an OVP enclosure (FSES) close to it if the power feeder length exceeds 10 m (32.8 ft). Recent RF Module variants have built-in OVP. See Table Lightning surge requirements for selected RF Modules for more information. External FSES/FSEP surge protection can be used in cases where higher protection levels than Radio in-build OVP is needed.

DC cable extension:

Connection of the long DC cable and Nokia IP65 cable is recommended to be done in an IP65 outdoor weather-protected space, for example in Flexi External OVP enclosure (FSEP).

Tip:

If the diameter of the cable is smaller than 19 mm (0.75 in.), use either self-fusing tape or heat-shrinkable tube to increase the cable diameter to 20 - 21 mm (0.79 - 0.83 in.) to fulfil the IP67 requirement. The distance between the expansion and the stripped part of the cable must be at least 10 cm (4 in.).

Table:

Nokia requirements for a shielded, locally sourced DC cable (3U RF Module), T=20ºC (68ºF)

Cable type	A	R	L
Shielded twisted pair	10 mm²	1.83 Ω/km	-
	16 mm²	1.15 Ω/km	0.3 mH/km
	25 mm²	0.727 Ω/km	0.26 mH/km
	35 mm²	0.524 Ω/km	0.24 mH/km

Note:

In feederless and distributed site installations, Ohm's law cannot be applied alone because inductance must also be taken into account.