What follows are some general observations on the type of protection devices/fuses/cutouts used for streetlighting. There will obviously be differences due to regional variations, suppliers and contractors preferences. The termination/cutout connected directly to the service cable is technically the property of the electricity board.
The earliest form of cutout was often no more than a ceramic fuse holder with a re-wireable fusewire type fuse, often housed in a bracket control box especially for pole mounted brackets fed from an overhead supply. Surprisingly original examples can still be found, often 60 or more years after they were first installed. By today’s standards they offer very little electrical safety in terms of shrouding of live connectors or their current breaking capacity in the event of a fault.
In the image above there is a 2nd fuse, possibly for a sign light.
For underground supplies, it was common practice for lead sheathed service cables just to be sealed with pitch, the cable tails being the terminations, with the live side just being connected into a ceramic fuse carrier. Despite being totally unacceptable today, one such installation was glimpsed through a partially open door in 2012 in West Sussex, totally unchanged from when it was installed over 60 years ago.
The red wire on the left goes into the pitch sealed end of the service cable.
By the late 1950s a more robust/higher breaking capacity cutout was required to meet the electrical standards of the day and also to cope with the higher inrush currents that mercury ballasts and sodium leak transformers generated. The “black” MCO40SL Lucy style cutout was typical of this period, especially for use with lead sheathed service cables and remained in use until the 1980s. The carrier allowed the use of a BS88 HRC ceramic replaceable fuse cartridges (although I have seen some fitted with fusewire). This style of cutout also allowed termination of the neutral and earth conductors in one self contained unit. The design of the carrier also allowed increased clearances to prevent “electrical creepage” compared to earlier re-wireable fuses, as well as hand protection in the event of an arc being struck when the carrier was removed “on load”.
The earth terminal block is also the neutral block. In the UK neutral and earth are (generally now) connected at supply origin.
The cutout also contained loop in terminals for the service supply, yet was also compact enough to fit in the previous generation of control boxes or column bases that contained the control gear for the lanterns. Similar designs of cutout were offered by competing suppliers. Often a secondary ceramic fuseholder was still fitted in series “upstream” of the cutout.
This was often used for circuit isolation rather than removal of the main cutout. It also meant that the “board cutout” could be left untouched. In some areas the cutout was fitted with lead seals or paper tamper tape.
By the 1980s, electrical standards improved, which required the use of shrouds for live terminals. In the case of the Lucy MCO40SLC cutout, a red plastic shroud was fitted to the incoming service terminal and the moulding changed to white plastic. The fuse contacts were also changed to be on the same side rather than offset.
This type of cutout was again very popular, being fitted until the 2000s. By this time, the use of a secondary fuseholder had often been discontinued (as a cost saving).
To reduce contact resistance and maintain good contact pressure over time, increased terminal clamp forces were required, this however necessitated lever assisted carriers for removal. The Lucy MCO40SLE carrier made from ABS plastic and with a removal lever is shown below -the main housing is missing the lower cover.
Changes to electrical standards post 2000 required live and neutral isolation of the supply for servicing. In many areas streetlighting contractors met this with a double pole switch often combined with a miniature circuit breaker for overload protection, housed in a small enclosure. This effectively returned to the previous arrangement of having 2 circuit protection devices. Fortunately, the move to integrally geared lanterns freed up the necessary column backboard space to mount the enclosures.
Cutouts were later modified to provide a neutral link in the carrier so that its removal, also isolated the neutral supply. The TOFCO F144 cutout shown below (used by the Portsmouth PFI) is one such device.
For the South Coast PFI, SEC have used a Lucy MCO40SLFcutout with neutral isolation.
Both devices are manufactured from ABS plastic. In both cases this is the only form of circuit protection/isolation used – not surprising given that the additional cost of fitting double pole switches/MCBs would be considerable given the number of installations being fitted.