Cut Outs & Isolators | The Street Weapon In Street Lighting Safety by Lucy Zodion
Published 04 Aug 2021
Street Lighting Safety
Cut Outs & Isolators
An industry leader in the design and development of street lighting control products, Lucy Zodion offers a range of solutions that span from the ground up; encompassing in-ground feeder pillars right through to cloud based IoT street lighting management. In the Highways industry, one of the key ranges Lucy Zodion offers is fused products.
Fused products or cut-outs and isolators have an important job that is often taken for granted – they terminate a supply cable and provide electrical protection for the light on the column, improving safety for those maintaining and upgrading lamp post infrastructure.
Greater awareness of safety & quality
Lucy Zodion understands that certain measures and standards should be met in order to ensure the safety of street lighting columns, where the independent testing of fused products contributes to their suitability in the field. From the materials such products are made with, to the way they are engineered to function, all are considerations before they can be used and installed.
The quality and manufacture of fused products contribute to their safety and reliability in the field. This is something that carries great impetus and should be understood by all in the industry. This paper explores what is currently known about fused products (from a manufacturing point of view) and the quality measures that are currently in place, to assure safety and quality.
What we know
To comply with a British Standard indicates that a company/organisation takes its responsibilities seriously; compliance is often taken as evidence of due diligence.
By following the processes recommended in a Standard, it implies that impetus is made on doing things properly. It is important to highlight that standards aren’t the same as regulations; following a standard doesn’t guarantee that the relevant laws are met, due to the fact that legislation could change within the lifetime of the Standard. But, companies that follow the standard give customers and collaborators confidence that measures are being taken to provide a high level of quality in the products they produce.
In respect of the context of this paper, reference is made to the BS 7654 Standard, which is for single phase street lighting cut-out assemblies for low-voltage public electricity distribution systems – 25A rating for highway power supplies and street furniture. This is a standard which covers the whole of the product and not just parts. From constructional and performance requirements, normal service and mounting conditions over all sizes, the Standard requires the designed unit to pass the tests prescribed within it. This is to ensure firstly that the unit is safe.
A large part of the Standard is the type testing that the designed unit has to pass; these tests will prove that the unit will be fit for purpose in service.
Such tests include:
Terminal Torque Test
This is a test which proves that terminals have the strength to be tightened to a given torque onto a copper rod, for a period of one hour and to show no signs of cracking or distortion; thus proving its durability in the field.
In regards to the material /design of the terminal – it states which material cannot be used, to the minimum amount of threads (all screw holes with pinching screws shell contain at least three full threads conforming to BS 3643).
In reference to the design of the unit – a simple part of the Standard gives the layout of the terminals, stating that Phase Neutral and earth shall be positioned from left to right and viewed from the front, so that an operative will instinctively know their way around the cut out unit.
Where the standard does not cover the requirement in full, it will refer to other standards that will. This Standard also covers the IP levels required (IP22), again safeguarding the operative material choice is one area which is heavily scrutinized by the standard – this is covered by several tests:
This prescribes how the test is to be carried out. Impact energy of 0.25J, 2 Sets of units (6 in each); Test 1 at room temperature and Test 2 after the units have been at a temperature of -25°C for a period of not less than 18 hours, and is struck the amount of times as prescribed in the standard (three times).
This will prove the suitability of the given material and design; it proves both its durability and that the given materials will not shatter and expose dangerous parts. Clearances and creepage distances are also stated and are to be a minimum of 6mm.
The flammability test should be in accordance with BSEN 60695-11-10 test method A, which is a horizontal burn test.
Hot Ball Test
This is when a piece of apparatus with a 5mm diameter ball is pressed against the material surface with a force of 20N. and placed into a heating cabinet; this can be at different temperatures depending what the material is specified for:
- 125°C for insulating materials which retain current carrying parts,
- 70°C for other insulating material not necessary to retain current carrying parts in position
After a period of 1 hour, the test material is immersed in cold water at which point the diameter of the impression by the ball shall be measured.
Resistance to Tracking
This tests the material which in itself involves a series of tests, carried out in accordance to the Standard BS EN 60112.
In principle, this test requires the upper surface of the test specimen to be supported in an approximately horizontal plane and subjected to an electrical stress via two electrodes. The surface between the electrodes is subjected to a succession of drops of electrolyte, either until the overcurrent device operates, or until a persistent flame occurs, or until the test period has elapsed.
The individual tests are of short duration (less than 1 h) with up to 50 or 100 drops of about 20mg of electrolyte falling at 30 second intervals between platinum electrodes, 4mm apart on the test specimen surface. An AC voltage between 100 V and 600 V is applied to the electrodes during the test, where specimens may also erode or soften, thereby allowing the electrodes to penetrate them.
Resistance tracking is an important part of the testing process and pins down the characteristics of the materials used, as well as their ability to withstand environments similar to those in the field. Without such testing and the supporting certification, safety and performance cannot be assured.
One of the main parts of the type test is the section on the performance side. These tests are designed to test the units in operation, temperature rise testing at maximum rating. Temperature rise test is when the unit is loaded to the maximum of 25A and is left on until it reaches a stable state; testing that the temperature limits stated for this test are not exceeded.
Cyclic loading of the unit puts the unit on test for 1h on/1h off, for a period 2000 cycles. At every 100 cycles a standard temperature rise test is carried out (this test alone can take approximately 6 months to carry out).
The BS 7654 Standard is extensive and the above information is not exhaustive of its entirety, however highlights the attention to detail that is required in certain aspects of the Standard.
Cut outs are needed in every Distribution Network Operator (DNO) supplied streetlight in the UK. A cut out has its own British Standard, BS 7654 (as detailed above), which covers all aspects of the cut out from the materials it’s manufactured from to a series of tests relating to temperature, ingress protection, current, mechanical strength; it even states its physical size. Manufacturers must be able to prove this with an independent certification and this is something that those buying the product should always ask for.
The cut out comes with a set of terminal blocks, designed to accept cables up to 25mm² and has a suite of accessories that include extension pieces, brass and plastic cable entry plates, to suit different types of cable and to make installation as easy as possible.
The fuse in the cut out is contained within the cover of the unit, the action of removing this cover disconnects the fuse (so it can be replaced) which also isolates the load from the supply. Higher quality cut out designs (such as Lucy Zodion models) have a lever cam action handle on the cover, which improves operator access to cables. Although the terminals are isolated, removing a cover from a cut-out to change the fuse should be done in a safe and responsible manner that complies with the responsibilities under organisation and legislative policies.
Cut outs only come in either a single or twin fuse version; the option of using digital timers or RCCD’s to control or give additional protection aren’t covered by the Standard.
Isolators are used for secondary isolation and add an extra layer of electrical safety; they are not required in all street lighting columns, unlike cut outs. The main body or casing of an isolator isn’t covered by the same BS as a cut out, however there are other British Standards that relate to them, which the switch and fuse carriers must meet (BS88). To assure quality, manufacturers should produce the body to the relevant BS for isolators (BS EN 60947-3:2009+A2:2015 and BS7671) and independent certification should be available.
The isolator provides a switch-disconnector which can be operated in order to isolate the load, allowing maintenance and for the fuse to be replaced. This makes changing fuses and isolating circuits simple and helps prevent risks of injury. Additionally, to increase safety, covers can be made lockable. Most isolators have an interlock device that automatically slides over the fuse carrier(s) when the isolator is moved to the ON position, ensuring that a fuse carrier cannot be opened with the circuit energised.
Both isolators and fuse carriers should be independently tested by a third party, in KEMA laboratories or the equivalent, to meet the relevant Standards. Factors like a high tracking index and self extinguishing plastics are vitally important when it comes to safety. Using robust and durable thermoplastic enclosures with high anti-tracking properties, well manufactured isolators often have a safe and transparent front access cover to offer clear visibility, reducing the need to open up the isolator.
Typically, the isolator comes with a 32 amp isolator and a fuse carrier, however, if the product has a DIN rail different arrangements and components can be used, e.g. digital timers, MCB’s, RCBO’s, RCCB’s, contactors, push buttons, etc. An isolator can form the basis of a unit used for Festive Decorations, for example.
The isolator usually has a DIN rail that can accept products like MCB’s and fuse carriers, which have a total of four modules in width, or less; however they are available with a capacity of more than four if required. Should the isolator include a DIN rail, a module with no more than 17.5mm width is to be used, almost like a mini distribution board.
The isolator typically has a suite of accessories that include extension pieces, brass and plastic cable entry plates to suit different types of cable and to make installation as easy as possible. Something the installer should consider is that terminal blocks sometimes need to be added to the final assembly to aid installation; this, in some instances, makes it quite long in length.
Lucy Zodion Fused Products
The Lucy Zodion range of fused products follows the requirements under the respective Standards highlighted in this document. With an in-house Quality Team, it means that products can be tested at every stage of assembly – from initial design to completion – implying due diligence throughout each step of the manufacture process.
Additionally, each of Lucy Zodion’s products is independently tested by a third party, in KEMA laboratories, to ensure such measures meet industry Standards. As a responsible company Lucy Zodion has its own Quality Policy that covers operations throughout the whole company, as well as the manufacture of street lighting and power distribution products. It provides the approach necessary to ensure the requirements of ISO 9001:2015, and any regulatory/statutory requirements, are achieved in full and are improved where possible to ensure that customer requirements are met in full by the business.
Should Lucy Zodion customers wish view certification relevant to any aspect of the Standards and Policies stated above, Lucy Zodion is obliged to share and confirm the responsible steps have been taken to assure quality and safety.
- Street Lighting Cut Outs – Lucy Zodion DNO Approved Cut Out Listing
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- Northern Powergrid Approved | Cable Joints, Terminations & Electrical Equipment
LUCY ZODION – DISTRIBUTORS, STOCKISTS & SUPPLIERS
Thorne & Derrick provide competitive prices and fast delivery from stock for the complete range of Lucy Feeder Pillars, Isolators and Cut Outs.