Matt Black paint inside busduct enclosure

[ravindranathan]

In a typical conventional LV busduct, Matt black paint is painted on busbar as well as inside of busduct enclosure.
While black paint on busbar shall help in radiation of heat from the busbar towards outward direction.
I feel black paint on inside of busduct enclosure too shall radiate heat in outwards direction which mean it will flow towards busbar. This somehow looks contradictory..i.e heat will flow from either of them to each other.This doesn't make any sense.Pl advise..

 

[jghrist]

The black inside will absorb heat from the bus, making the enclosure hotter. The hotter enclosure will radiate outward more than cooler enclosure. You won't get heat radiated from the inside to the bus unless the enclosure is hotter than the bus. Black on the outside would radiate out more that bare metal, but would also absorb radiant heat from the sun, or any other radiant source hotter than the enclosure.

 

[LionelHutz]

What was posted above. The black paint reduces the air to metal thermal resistance which allows the heat energy to transfer from the hot side to the cold side easier. Hot bus -> air inside the duct -> duct enclosure -> air outside the duct.

I talked to a bus manufacturer that said the color the bus is painted doesn't matter. They were running it through their enclosure paint line putting the same color as the finished enclosure on it (it was either beige or grey).

 

[ravindranathan]

jghrist and LionelHutz --Many thanks for your valuable inputs.

 

[che12345]

Dear Mr ravindranathan

Q." In a typical conventional LV busduct, Matt black paint is painted on busbar as well as inside
of busduct enclosure....."
A. No. A typical conventional LV busduct [does NOT have] Matt black paint painted on busbar as
well as inside of busduct enclosure; unless under {special request, with extra charge}. The busbar
are usually [bare] i.e. [without] any painting on it. The metallic enclosure (inside) are usually
[bare] i.e. [without] any painting on it. The (outside) are usually painted according to the
practice of the manufacturer, but (NOT) black.
In most usual indoor installations, the (loaded) busbar temperature would be t1 > inside
surrounding air temperature t2 > enclosure inside surface temperature t3 > enclosure outside
cooling air temperature t4.
The heat transfer is by [radiation] i.e. from the hotter surface to the cooler surface; from t1 to t2...t4. The (air temperature between the busbar and the enclosure inside) does not resist the
radiation from the hotter busbar to the cooler enclosure inside surface. The enclose inside surface
t3 is < t2 and t1. Therefore it does [NOT] radiates back to the hotter busbar, (even if) it is
painted matt black. Note: it is usually [NOT} painted.
FYI: In theory, painting the busbar and the enclosure [outside NOT inside] matt black would assist
in the heat radiation from the busbar to the outside cooling air; therefore (increases the current rating). But in practice, the increment in current rating is [minimal], therefore it is usually
[NOT]implemented due to (additional labour and material cost involved).

Che Kuan Yau (Singapore)

 

[ravindranathan]

Hello Che,

Many thanks for the input.
All busducts supplied to our site is as mentioned by me and hence the query.
I will definitely take up with them to see if we can save on costs as suggested by you.

Regards
R.R.Nair

 

[LionelHutz]

If they are painting it then the paint is likely required.

It might not make a big difference, but it will be required if it made the difference between passing or failing the temperature rise tests during the listing process. The manufacturer I mentioned failed testing with bare bus so they painted it and it passed. That means they can't sell the product with the UL mark unless the bus is painted.

 

[che12345]

Dear Messrs ravindranathan, LionelHutz

If the test is conducted with busbar and enclosure in side painted matt black, this must be observed in the subsequent product.

Precaution: It would be (prudent) to check the test certificates that the [temperature-rise} and the [short-time short-circuit current kA rating] tests (are) carried out [with the same matt paint] on the busbar and on the in side of the enclosure only. While the enclosure out side is not painted with matt black paint.

Caution: The matt paint applied in the busbar must not only withstand the temperature-rise (say total temperature of around 100 deg. C , depending on the material Al or Cu, tinned or silver-plated etc.) but should also withstand the [temperature] resulted by the short-circuit current (i.e. the kA rating). In most cases the busbar temperature of the short-circuit kA test; irrespective of whether Al or Cu may reach [close to 200 deg].

Attention: The short-circuit (temperature) is neither measured nor reported in the short-circuit test certificate, but should be taken into consideration. Therefore, the paint applied on the busbar [shall not be damaged or catch fire ] on the short-time shirt-circuit kA rating test.

Che Kuan Yau (Singapore)

 

[LionelHutz]

The manufacturer I was talking with was powder coating, so I doubt they have much concern with those temperatures.

 

[cranky108]

I believe powder coating is more likely, as that is used in switchgear in the US. However, most powder coating I have seen is red (Maybe the voltage thing).

Painting the inside of the duct sounds like more of an inspection thing, as the flat black would make it easier to see debre, and arcing pits.