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PostPosted: Thu Jun 14, 2012 3:10 pm 
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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.

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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.

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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”.

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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.

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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.

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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.

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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.

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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.

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For the South Coast PFI, SEC have used a Lucy MCO40SLFcutout with neutral isolation.

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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.


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PostPosted: Thu Jun 14, 2012 8:58 pm 
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Interestingly, in old swan neck brackets I have seen double fuses used where there is protection on both the live and the neutral. Also to be found are bare 'links' used for the neutral conductor which can be loosened to break the circuit if required. All bare brass/porcelain construction!


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PostPosted: Thu Jun 14, 2012 10:55 pm 
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The protection of the live incomer is the key point that I've seen for York's cutouts. By far the most common type is the black Lucy type (which are a pain to try and get the supply side open if you get one, as all the bitumen inside seals the whole thing up and the bakelite just snaps), but I have seen a few examples of columns made redundant (mostly sign columns) where the door has fallen off and gone missing and the cutout inside has had the carrier removed but no protection around the exposed live incomer.
Whilst there's one or two intermediate types used, York moved on to Bill SL type cutouts (I'd have to check the ones I've got for the actual type number) which still only offer single pole isolation... but the strange thing is that some of the columns with Bill ones in used to have a black Lucy type, and at some point had it swapped for a Bill type - which would have required the electricity board/contractor out to disconnect the supply to achieve the swap over.
I haven't looked inside a just-connected brand new column to see what's in there, though I know Lucy isolator modules are used for downstream isolation of the circuit. The fitting of Isolators seems to have happened from the mid 1990's onwards, as any column with a ZX lantern, 2600, 2000, Arc, etc has an isolator in the base, as do some with minicelled Philips XGS103/4 lanterns but not those with the NEMA celled versions. Generally TOFCO isolators were used, with some of the very last concrete columns ever installed having had Charles Endiret (sp?) units fitted (and some metal columns from the same period also got one too). There doesn't really seem to have been much consistency in what type of TOFCO isolator was used though, as some columns would have the slimline unit which could hold maximum 2 modules (2 pole MCB and a fuse carrier) whist the next column along in the same street might have the next size up, capable of holding 3 modules. Then there are one or two columns spattered around that have 'the daddy' in the base, a TOFCO 4 module enclosure with a B22 extension box - one typical example had the primary 2 pole MCB for everything, a fuse for the street light (up) a second fuse for a signlight on the column (up) and a 3rd fuse for a slave circuit such as a zebra crossing beacon or a standard pole down the road with a sign light fitted (down).

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PostPosted: Sun Aug 05, 2012 2:33 pm 
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mazeteam wrote:

Attachment:
File comment: Note the gas bottle right by the far set of excavations just to the right of the van - I believe the gas is used when cutting the supply cable through.
DSC_5172.jpg
DSC_5172.jpg [ 429.73 KiB | Viewed 14156 times ]



Well, not quite.

The cut out end of a lead sheathed service cable looks like this once the cut out is removed.

Image

The part above the grommet is what would be in the base of the cutout, the 2 twisted copper conductors are visible, sealed with pitch.

The earth connection is also visible as the soldered "lump" beneath the grommet.

It all becomes a lot clearer when you look at the construction of the cable.

Image

At the bottom of the image can be seen the 2 copper conductors. These are insulated with layers of waxed paper. They are covered with an overall thin lead sheath. Over that is pitch soaked woven fabric "string". Over that are two layers of steel tape covered by pitch soaked tape.

So referring back to the first image. The solder bulge, connects the earth wire to the inner lead sheath. This is what the gas bottle is for - a gas soldering iron to produce enough heat to make this soldered connection. Between the solder bulge and the grommet, the lead sheath has been covered with fabric tape. Beneath the solder bulge, more fabric tape secures the outer steel tapes and pitch soaked tape.

The cutout is filled with pitch to make sure the wax paper over the conductors is sealed.

A problem with lead service cable is that when it is overloaded due to a fault for instance or insulation breakdown, it can quite literally burn along its length, the string, pitch and wax paper proving ideal to maintain combustion.

This type of service cable was in use to around the mid 1970s, when it was replaced by the much simpler PVC insulated cables.

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In these for a single phase cable, there is only one "wire" surrounded by a copper braid which forms the function of both earth and neutral - in the UK a neutral conductor is provided from the earth connection at the supply point origin. Connections are often made using “crimp and heatsink ” joints. A termination is shown below.

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For 3 phase connections a “potted” connection is often employed – connections are crimped and then sealed in a enclosure filled with epoxy resin. The new single phase connection is the thin black wire coming from the right hand end of the enclosure. Above the housing can be seen another 3 phase lead cable, the spiral of the outer tape being visible. It is laid in an earthenware pipe, the broken end is just visible at the right of the hole.

This has seen the end of the blowtorch except for the final stage of the heatshrink joints, with a much quicker and easier jointing process.

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PostPosted: Sun Aug 05, 2012 11:35 pm 
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What happens with connections at the moment is the old cable is cut off outside of the column, a junction enclosure fitted, and a new PVC cable from the junction to the cutout - and then no pitch/bitumen is required inside the cutout... I presume the lead soldering over the wax paper type supply cable is still required for doing connections like that?

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PostPosted: Mon Aug 06, 2012 7:07 pm 
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All new cabling is of the modern type shown above, lead sheathed cable is not used for new installations hence there is no need for pitch in the joints. Pitch had to be used in the past to make sure the wax paper was protected otherwise if it got damp/wet it would be no good as insulation. Very effective as an insulator but a messy and hazardous method - pouring hot pitch.

It looks like your way they must still be making solder connections to the lead if the gas bottle is there. Down here I suspect they are using simple earth clamps (like the types used for earthing metal water pipes). That is possible as the clamp is inside the joint box and sealed with epoxy - you couldn't do that otherwise. I haven't spotted a gas bottle with SEC jointers for years.

The joint below has a lead sheathed cable entering on the left - under the S&L door, and a modern PVC cable emerging from the right. The putty seals round the cables and keeps the epoxy in the enclosure until it sets hard. It is poured through that square lid on the top - note the "cream" overflow which is the epoxy and the stone to hold the lid on until it sets.

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PostPosted: Mon Aug 06, 2012 10:41 pm 
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Interesting... it still seems odd that a supply cable can be cut and jointed when it's still live, even modern PVC type cables. (I was always instructed that wiring is always done on dead cables!)

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PostPosted: Tue Aug 07, 2012 4:16 am 
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Not practical to turn off entire streets. Having seen it done with the use of insulated tools and rubber gauntlets over the hands it is not that different. The use of PVC cables and heatshrink joints means that the live connection is very quickly and easily made. Planning the order of the work also helps - the cut out can be made up on the dead end of a new cable before the other end is connected to the supply


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PostPosted: Tue Aug 07, 2012 9:49 pm 
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Very interesting as I have never seen a service transfer actually taking place. Most installations my way are fed from overhead and can be switched by the council operatives.

One thing to note about the old lead cables is the damage that can be caused if they are accidentally struck by other road workers as they become brittle overtime and literally explode when a cable strike happens.


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PostPosted: Sun Aug 12, 2012 10:35 am 
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versalift09 wrote:
Interestingly, in old swan neck brackets I have seen double fuses used where there is protection on both the live and the neutral. Also to be found are bare 'links' used for the neutral conductor which can be loosened to break the circuit if required. All bare brass/porcelain construction!

Well here is an example of that, neutral link on the right.

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