Digital Design Process 5.

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Prototypes

By using this design guide the designer and manufacturer is expected to improve the accuracy of porotypes and should aim for a ‘right first time’ approach.

Fundamental to this approach is the re-use of approved parts, either dc or retailer approved and to this end we recommend using the dc design library for components and parts.

During the briefing the designer is expected to establish the display review and approval process and when dc testing will be carried out.

The testing must be carried out before production as the certification provided will be for ‘type’ approval and therefore every unit thereafter will need to match the certified display.

In order to complete a thorough analysis before the final approval it’s recommended to trial units instore or in application in order to get feedback from instore staff, users and customers.

Mock-ups

During the Creative Design process there may be a need to create a mock-up of the display equipment to ensure its dimensionally correct and ergonomically fit for use. At this time there may be no electrical equipment and the materials used may not be as specified for production.

Consideration should be given to the materials used for mock-ups so they can be easily recycled later.

Prototypes

As the design develops through the Engineering Design stage there will be a need to test that the design meets all the basic requirements of form and function as well as the technical requirements set out for dc certification.

The prototype should be made with all the intended production materials and electrical components required.

The key areas of assessment will include:

• Material finishes
• Lighting brightness
• Functionality
• Test results

It may be determined after full assessment and testing that the display does not pass all criteria and therefore a pre-production display must be created before production.

 

First off’s

It’s recommended that before a full production run a ‘First-off’ of the display is created. This may be due to small design changes following the protype but also due to tooling or materials.

The designer or manufacturer may decide that due to limited time or production capability, mock-ups and protypes are not needed and they may go straight to first off.

Key considerations:

• Is the prototype packing representative of the production packaging?
• Will be protype be delivered as it will be received instore?
• If the display requires assembly will the installation be timed to asses roll out timings?
• Who will be installing the prototype, and will it be the same company as for production?

 

Factory testing

Before carrying out any electrical inspection and testing a risk assessment should be carried out to identify any dangers present and enable any necessary precautions to be taken.

Test equipment should be constructed, maintained and used correctly to prevent danger. GS38 HSE publication gives suitable guidance on this.

Before you begin the inspection and test you will need all the necessary information including schematics, technical drawings, load calculations and intended environment of the equipment under test (EUT)

All work should be carried out in a safe manner. You should use a suitable test area where the risks can be controlled, making sure you have enough space, adequate lighting and proper access to the EUT.

All personnel carrying out the inspection and testing should have relevant training, skill and experience to prevent any danger during the inspection and testing process.

Electrical testing should only be performed by a person who is competent in the safe use of the test equipment and is able to interpret the results correctly.

 

Visual Inspection

A visual inspection must proceed testing, before the unit is energised.

Regulation 642.3 of BS7671 provides a list of items that should be included as a minimum

Further advise is available in the IET Guidance Note 3, Inspection & Testing publication and the IET code of practice for in-service Inspection and Testing of Electrical Equipment

 

Testing

The tests required for Design Conformity are,

1. Earth Continuity Test (Class 1 Fixtures)
2. Insulation Resistance Test
3. Protective Conductor current/or touch leakage test
4. Function test including Load test

Earth Continuity

The earth continuity test will apply to almost all fixtures designed using Design Conformity Guidance as the majority will have earthed metal gear trays as part of the design. This test should be carried out to all exposed conductive parts of the fixture, this may require multiple continuity tests with the highest reading being the one recorded. Due to the nature of many led power supplies it may be necessary to carry out a “soft” test which uses a test current in the 20mA to 200mA range

Acceptable results would be 0.1Ω + the resistance of the supply cable.

For example,

If we take a fixture supplied by a 3M length of 1.5mm 3 core flex, from Table VI.1 of IET code of practice for In-service Inspection we can see the protective conductor resistance at 20°C is given as 39.9mΩ, so in this example any reading in excess of .14Ω would need to be investigated

 

Insulation resistance test

The insulation resistance test will normally be carried out by applying a test voltage of 500V dc and measuring resistance.

This may not be possible on some fixtures that contain LED drivers or SMPS which may contain EMC filters or Surge protection devices. In this case the test voltage should be reduced to 250V dc. A note should be made on the test certificate by the inspector that the test was carried out at the reduced voltage for this purpose.

 

Productive conductor test

This test is a complementary test to the insulation resistance test and is especially important where a reduced voltage had to be used because of problems with EMC filters or SMPS or in the case of lower than expected readings during the Insulation resistance test.

The equipment should be switched on for this test and will be operating at supply voltage for the duration of the test. The person carrying out the test should take all the necessary safety precautions highlighted in their initial risk assessment of the inspection and testing procedure before initiating this test.

 

Substitute Leakage Test

Some Portable appliance testers(particularly handheld devices) carry out a substitute leakage test.

This is not a suitable replacement to the protective conductor/touch current test and is not recognised as an alternative to the insulation resistance test due to limitations in the way the instrument carries out this test.

Design Conformity will not except this test as an alternative to the protective conductor/touch current test.

 

Load Test

When previous tests indicate it is safe to proceed, a full load test should be carried out on the EUT. The results, usually given in KVA must be included in the test results provided to Design Conformity

(This test is often combined with the protective conductor/touch leakage test when using a Portable Appliance Tester to carry out the tests).

The easiest way of carrying out these tests would be with a downloadable Portable Appliance Tester; this ensures test results are easily available if required for future testing/maintenance purposes.

If you have any doubts concerning inspection and testing, we recommend you consult a qualified electrical engineer who will have both the necessary experience and correct equipment required to carry out the task safely.

 

Labelling of Electrical Display Units

• All display units and systems powering luminaires must be clearly marked or labelled.
• Marking/labels have to be visible, legible, durable and clearly accessible to the person undertaking installation and maintenance tasks.
• Information must be provided in text not smaller than 2mm high.
• Tamperproof labels should be used rather than paper printed labels as these can be damaged by cleaning agents and or UV damage.

Information to be Included on Labels/Marking
1. Manufacturers identification and contact details (mandatory)
2. Manufacturers batch number of product for tradability (mandatory)
3. Test date and initials of person conducted test (mandatory)
4. Voltage rating of the unit (mandatory)
5. Rated maximum ambient temperature, if not 25°C.
6. Symbol for class II luminaires, where applicable.
7. Symbol for class III luminaires, where applicable.
8.IP rating, if greater than IP20.
9.The relevant symbol for suitability of direct mounting on combustible or non-combustible materials.
10. The unit rating (Watts).
11. Termination points. These should be marked to indicate polarity. For ELV cables, use red for live and black for neutral.
12. The earthing connection point.
13. The maximum number of luminaires that can be interconnected.
14. Nominal operating frequency.

 

Certification

Once the unit is ready to be inspected a dc appointed inspector will conduct a visual inspection and test the pre-production display equipment.

 

dc label and reference number

Manufacturers that pass inspection and obtain a dc certificate of conformity also gain the right to use the dc logo on their test label only when in conjunction with the dc certification number.

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