BS 7671 max surface temperature under fault condition ???

[brett reader]

Can anyone give me some clarification on the following.

I am installing some Osram Planon Plus led light panels into a temporary building and have been told the transformers need to housed in an enclosure as they do not have the correct markings for BS7671 "max surface temperature under fault condition".

Im a mechanical design engineer and not disagreeing with the request but want to understand the regulation and why these off the shelf units need additional enclosures in order to be used.

Many Thanks in advance.

 

[Deleted member 26818]

421.1.2 Fixed electrical equipment shall be selected and erected such that its temperature in normal operation will not cause a fire. This shall be achieved by the construction of the equipment or by additional protective measures taken during erection.
The heat generated by electrical equipment shall not cause danger or harmful effects to adjacent fixed material or to material which may foreseeably be in proximity to such equipment.
Where fixed equipment may attain surface temperatures which could cause a fire hazard to adjacent materials, one or more of the following installation methods shall be adopted. The equipment shall:
(i) be mounted on a support which has low thermal conductance or within an enclosure which will withstand, with minimal risk of fire or harmful thermal effect, such temperatures as may be generated, or
(ii) be screened by materials of low thermal conductance which can withstand, with minimal risk of fire or harmful thermal effect, the heat emitted by the electrical equipment, or
(iii) be mounted so as to allow safe dissipation of heat and at a sufficient distance from adjacent material on which such temperatures could have deleterious effects. Any means of support shall be of low thermal conductance.

422.3.2 Measures shall be taken to prevent an enclosure of electrical equipment such as a heater or resistor from exceeding the following temperatures:
(i) 90 °C under normal conditions, and
(ii) 115 °C under fault conditions.
Where materials such as dust or fibres sufficient to cause a fire hazard could accumulate on an enclosure of electrical equipment, adequate measures shall be taken to prevent the enclosure from exceeding the temperatures stated above.
NOTE: Luminaires marked D in compliance with BS EN 60598-2-24 have limited surface temperature.

The symbol referred to in the Note above is a d writhing a triangle pointing down.

 

[brett reader]

Thats brilliant, thanks so much for the reply, it totally clarifies the issue.

 

[brett reader]

One other question. What would be the logo I would look for that covers this on a transformer?.

 

[brett reader]

Also is there a specific reg for surface temp under fault condition

 

[Deleted member 26818]

Sorry, the site plays up so much, that it’s easier to edit a post than to try to write a long one.
The logo is a D in a triangle pointing down.

Regs regarding temperature under fault conditions only apply to conductors as far as I am aware.

 

[snowhead]

Mounting something that has the possibility of overheating, within an enclosure would seem to be completely the wrong choice, it's going to over heat quicker.

I'd be going for mounting in free air as a first choice, if fact I'd can't believe a company like Osram would manufacture something like this so I'd be contacting them and if it is correct looking for an alternative manufacturer first.

 

[Bobster]

Mounting something that has the possibility of overheating, within an enclosure would seem to be completely the wrong choice, it's going to over heat quicker.

I'd be going for mounting in free air as a first choice, if fact I'd can't believe a company like Osram would manufacture something like this so I'd be contacting them and if it is correct looking for an alternative manufacturer first.

Mounting on a large piece of metal would be preferable to free air. It'll act as a heat sink.

However I think it is eluding to, if you install in an enclosure, the component that is going to reach >115 deg C will not be in contact with anything flammable.

 

[brett reader]

The reason I purchased from Osram was because I thought issues like this would be covered.
So frustrating...

 

[westward10]

If the panels have a metal enclosure just sit on top and ensure it is not enveloped by anything. As above I would not personally enclose them as this will restrict heat dissipation and the enclosure will also need to kept away from non flame retardant materials.

 

[Wilko]

Hi - have you got the lamps to have a look at, get the model number etc? I just had a quick look "a brochure" and they seem to be a double insulated 230V light supplied with a flex. No external transformer evident on the model I looked at. Just saying.
https://www.osram-lamps.com/appsinf...60236&vid=PP_EUROPE_Europe_retail_eCat&lid=EN

 

[brett reader]

Yes thats the one but ive got the remote control version

This is the Transformer
https://photos.app.goo.gl/qVx12k3idzjgZSRK6

And link to the complete light unit.
PLANON Plus | OSRAM Lamps - https://www.osram-lamps.com/ecatalog/luminaires/consumer-luminaires/wall-and-ceiling-luminaires/planon/planon-plus/index.jsp#

 

[Wilko]

Ok - I hadn't thought about this before, so I had a quick look out of interest. Looking at your transformer it's missing the inverted triangle symbol with the thermal protection temperature. If you look at the pic below, it's saying 110 C, in line with @spinlondon quote from Regs of less than 115 C. I can't say if it's mandatory to have the symbol, but without it we don't know what it's performance will be under fault conditions. The symbol is referenced in BS7671 Table 55.3 . Scanning a few drivers, some have the symbol and some do not. Another Learning Moment for me .

 

[Deleted member 26818]

What does ta and tc stand for?

 

[Wilko]

My best guess Ta manufacturer's ambient temperature range for normal operation and Tc is temp when cr*p happens .

 

[DPG]

Ian, why the dumb ratings on the posts above? The replies seem pretty helpful to me.

 

[brett reader]

I am still reading your replies but also trying to speak with Osram and get some clarification from them. At present I can not use these, but feel I can mount the Transformer on a aluminium extruded T section away from any combustible material.

 

[Deleted member 26818]

My best guess Ta manufacturer's ambient temperature range for normal operation and Tc is temp when cr*p happens .

Yes, that’s what I’m wondering.

 

[Deleted member 26818]

Ian, why the dumb ratings on the posts above? Seems pretty helpful to me.

He’s decided to rate a number of my posts with either dumb or disagree.

 

[Deleted member 26818]

A lesser known but critical LED light specification is the Ta rating. Ta, or “ambient temperature,” is the reference temperature of the ambient air when the product is tested to deliver the rated performance.

This specification is important in critical or harsh environments. For example, in the absence of specific instructions from the manufacturer, the default testing temperature in a laboratory may be only 25° C.

If the luminaire is to be installed into a harsh environment where the average temperature is 45° C, the 20°C difference will have a significant negative impact on the anticipated life of the product.

Furthermore, the other critical reference is the Tc, which is the hottest point of the luminaire component at the time of testing in the selected ambient temperature.

In the theoretical case above, the Tc point on a driver may be tested at 65°C at a Ta of 25°C.

If the actual installation environment has a Ta of 45°, then it stands to reason that the Tc could escalate well above the reliable operating limit for that device.

In summary, the Ta is an important technical specification that should be carefully explored to ensure the product selected is fit for purpose for the intended installation environment.