The vast majority of the worlds population take street lights for granted - in most cases not even knowing that they are there. But a common query is, how are street lights connected?
You can be forgiven to think that all street lights are supplied the same and this surely means the cables supplying them are the same also. However, it is common for street lights to be fed either by a private supply (local authority supply) or a DNO supply (Distribution Network Operator).
In this post we look at the various ways the humble street light is powered:
Connection types:
DNO - Distribution Network Operators
A street light can be connected to the DNOs mains electricity cable - the same cable that could be supplying your property. Effectively they joint onto one of the mains cables and connect it to the street light.
These supplies are considered unmetered supplies - this is because the supply cannot be metered as this would be uneconomical to provide a meter in every street light - to track energy use the DNOs are provided with an UMSUG code for the street light - you can learn more about UMSUG codes here.
The cabling for this type of connection is typically concentric - a cable that has one core with the neutral and earth combined surrounding the inner core.
Private Supply - Local Authority
In some areas street lights are powered by a cable belonging to the local authority; this cabling could be single or three phase.
The cable is usually connected to a feeder pillar or lighting column that has a DNO supply.
The cabling and ducting differs to the DNO connection and will usually be Steel Wired Armoured (SWA) with 3 cores - live, neutral and earth - and be laid in orange HDPE ducting. It is common for the steel wiring surrounding the cores to be used as an earth.
Private supplies are usually found in areas a DNO supply would be uneconomical such as motorways, dual carriageways, remote footpaths etc.
5th Core Supply
We have rarely come across lighting columns supplied by the 5th core of the electricity boards cable. But they do exist.
A few decades ago some cabling had a 5th core which was a dedicated supply for street lights. Why use this 5th core?
The 5th core was used to enable the switching of the street lights on and off - a time clock would be located at the sub-station to switch the 5th core on and off at set times. Compared to todays street lights which are typically switched via a photocell (monitoring light levels) or a remote monitoring system.
The above are a few ways street lights are powered to keep our roads safe at night. For futher information on how they are correctly billed, take a look at are article on UMSUG codes here.
This is a general guide and cables cannot be guaranteed to be what we assume they should be - we've surveyed cables that appear to be private but in reality they are a DNO supply. Always consult with a specialist.
All the best,
Peter