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A response to Chris Rolph


Dr. Geoff Archenhold's right to reply...

Dear Chris,

Thank you for your Letter and it raises some rather interesting issues with the current standards for LED drivers and more particularly with the interpretation of standards amongst the lighting community. As you will have heard me say many times previously, the LED articles are created to provide a brief overview of what is happening in the LED industry and to provide a focus on specific sections and not to be treated as a replacement for years of research, development or detailed experience for each specific topic.

Therefore, the contents of each article should be verified and understood further by the reader or indeed to contact me for further explanations and reference materials.  

However, I do agree entirely with your first comment regarding my terminology and what I actually tried to elude too very poorly may I say is that the Standard IEC 61347-2-13 was actually new in terms of being fully adopted by 1st July 2009 rather than it being a new standard per say.

Many LED companies that were selling 3rd party LED drivers as part of their service had not even heard of this particular standard and what I wanted to highlight to the general reader is that they should be asking for the document to ensure the source of the LED drivers are complaint to these standards.

Prior to this standard there were several other standards that LED driver manufacturers would get their products approved to and hence why the IEC 61347-2-13 was created as it was deemed more applicable.

The very positive aspect that I have seen since the other competing standards to the IEC 61347-2-13 standard were withdrawn is a large number of customers asking for the IEC 61347-2-13 documentation and CE certification. Before the 1st of July I had witnessed a large number of manufacturers undertaking CE-self certification and although some companies may have the considerable expertise to do this internally their numbers are small.

Therefore, I would always recommend that you ask your LED driver supplier to provide validated CE and standards documents from reputable 3rd party test houses. This will ensure that your products are tested to known standards correctly and provide you with a high degree of assurance.

The second useful aspect of gaining these documents is they should highlight the owner and manufacturing sites used to construct the product. 

In terms of using an RJ45 as an output connector to LED fixtures the advice I have had from various test house experts are that the use of RJ-45 may be unsafe for certain aspects of an LED driver and therefore it is very confusing or infact potential dangerous to use RJ-45 for LEDs. The following are some reasons why RJ-45 connectors could be unsafe for LED lighting:

• Not all RJ-45 connectors are rated for high current applications: RJ-45 connectors were created for low current applications such as network port connectors and not designed to carry 350mA average current.

• RJ-45 connectors are single isolated: This does cause specific issues for the standards depending on what the LED forward voltage is of the LED fixture. This will be discussed below in more detail.

• Confusion of RJ45 connector ratings: The end-user cannot determine what the current rating of the RJ-45 is once it is installed so how do they know if each connector is rated for 500mA maximum (not average) current or if it is higher. This would provide no comfort to the driver reseller or end-user especially if the wrong current rated part was used.

• Issue of common anode fixture connection: I have seen several companies connect the LED fixture in a common anode format to reduce the number of LED fixture cable cores from 6 to 4 (for R,G,B LED channels).  In common anode mode all of the 3 channels have the anodes wired together and they share a common ground return line. In this mode, the current passed across the ground line is 3 times the standard current ie; 1050mA average. If the RJ-45 connector is not rated at well above 1A then there could be a safety issue. Obviously this issue would become even worse if either more channels eg; 4 were wired together or if there was a higher forward current used on each channel.

• Potential confusion of RJ-45 connector: There are some LED driver manufacturers that use RJ-45 connectors for DMX in and out. There is a potential for end-users to inadvertently connect an RJ-45 connector incorrectly if they use different LED drivers.  RJ-45 have been used for DMX connectors which is a low power application and is in the respective ESTA standard.

Unfortunately, RJ-45 connectors have become a defacto standard from the early days mainly due to the fact that most electricians had an RJ-45 crimp tool in their toolkit. Unfortunately, in my view they are wholly inadequate for high power LED fixture design and that is why many companies are starting to us different connector systems for the LED fixture to driver interface. These connectors provide a much higher current safety rating eg, 4, 8 and even 16 amps per pin allowing for common anode and channel bonding capabilities.

In terms of the IEC 61347-2-13 standard I refer readers to section 8.2 of the standard which states “Output circuits of SELV- or SELV equivalent control gear may have exposed terminals if:
-    The rated output voltage for constant voltage control gear or minimum output voltage for constant current control gear under load does not exceed 25V r.m.s
-    The no load output voltage does not exceed 33 V r.m.s. and the peak does not exceed  33 √2 ( =46.67V)

This clause goes on to state the following “Control gear with a rated output voltage above 25V shall have insulated terminals.”
Now this is where the issue is with RJ-45 connectors as they do not have insulated terminals so it is quite easy to make contact with multiple pins within the connector.

Therefore, according to this section of the standard as long as the LED voltage on the LED terminal is less than 25V the product with an RJ-45 connector would pass (providing all other aspects such as current rating etc pass the relevant standards). Therefore, many of the LED driver I have seen with RJ-45 connectors are able to drive LED forward voltages up to 48V which exceed this part of the standard.

Off course, LED drivers can have higher forward voltage levels but they must use double-insulated connectors of which RJ-45 are not.

It is important to note that even if a 48V capable LED driver has an LED fixture with say 24V of LEDs connected to a driver then it will still fail as when the load is taken away the majority of the anode pins will return to the approximately 48V level and so would still fail the standard if the connector was single insulated.

This is my interpretation after I have received guidance from a certified safety test house although I must stress that I am not a safety expert which is why I always suggest you ask the LED driver supplier to provide you with independent 3rd party test information on the product you wish to purchase.

Therefore my interpretation is that if you have an LED driver with an RJ-45 connector to power the LED fixture then as long as the LED output voltage is less than 25V it will pass the standard but if it is more than 25V I do not believe it will pass this standard unless there is a different double insulated connector and RJ-45 isn’t used. This assumes the current rating of the RJ-45 is suited to the application which is difficult to determine if you do not have a guarantee of the components fitted.

I would be delighted to widen the debate and hear from readers who are a part of an authorised test laboratory as they will be able to provide far more qualified advice.

The positive news is that several well known lighting organisations are taking part in a new lighting standards forum which will be held at the LED & Light Fair show alongside the established euroLEDs conference and exhibition taking place in Birmingham next year.

This forum will be ideal to inform and provide guidance and interpretation of LED and lighting related standards. For more details about the forum and event please email the conference team at info@euroled.org

I have not received the third party approval or CE approval documentation for any of the products sold  by Tryka LED Limited in the letter but I am sure the documentation will be freely available on request for validation as discussed previously.

Best regards
Geoff Archenhold

 

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