LV Switchgear - Bus Bar Temperature rise - IEC

Dear Mr. NickParker (Electrical)(OP)28 Apr 22 15:04
" ... The specification says, #1. " LV Switchgear Bus bar temperature rise shall not exceed 45°C under rated current". The ambient temperature is around 40°C. #2. Does it mean maximum permitted temperature rise is only 40 + 45 = 85°C? #3. Not many local vendors can achieve this? #4. Am I correctly interpreting the specification? as IEC allows temperature rise till 105K."
#0. The relevant IEC standard is IEC 61439-x. Note: Different permissible temperature-rise for Copper or Aluminum.
#1. The specification can specify what he thinks is best for his installation; taking into consideration of the cost, material (Cu or Al), surface treatment if any, indoor or outdoor etc., etc.
#2. Yes. It means maximum permitted temperature T= (40deg C + 45K) = 85deg C.
Note: Temperature-rise is 45K.
#3. Enquire your local vendors what is their problem to comply with the spec. Go for more knowledgeable vendors. Usually ALL vendors CAN comply without any problem. It is understood with a higher price.
# 4. NO. IEC does NOT state that Temperature-rise till 105K. See IEC 61439-x. Attention: Total temperature = (T ambient + T rise). Total temperature is NOT = T rise.
Che Kuan Yau (Singapore)

IEC 60694 Edition 2.2 2002-01
Common specifications for high-voltage
switchgear and controlgear standards
4.4.2 Temperature rise
The temperature rise of any part of switchgear and controlgear at an ambient air temperature not exceeding 40 °C shall not exceed the temperature-rise limits specified in table 3 under the conditions specified in the test clauses.

@ 7anoter4 (Electrical)29 Apr 22 06:14
"... IEC 60694 Edition 2.2 2002-01, Common specifications for high-voltage
switchgear and controlgear standards. 4.4.2 Temperature rise...The temperature rise of any part of switchgear...".
NickParker (Electrical)(OP)28 Apr 22 15:04
"... The specification says, " LV Switchgear Bus bar temperature rise shall not exceed 45°C under rated current...".
I presumed the post is regarding " LV Switchgear Bus bar temperature rise ....". The relevant IEC standard for LV is IEC 61439. NOT IEC 60694, which is for HV, which means >1kV ac.
Che Kuan Yau (Singapore)

According to IEC 61439-1, table 6. under clause g, it is 105k as temperature rise.

Two things with that table, Nick.

1) It assumes a maximum ambient of 35 K (see the two-line statement below "Discrete arrangements of plug and socket ...".
2) The items you highlighted also require the application of Note "f" - which means the gear manufacturer has specifically indicated the maximum allowable rise (having taken into account all the OTHER criteria in the table).

Note "g" simply states that IN NO CASE will the rise exceed 105 K (above the 35 K ambient condition). It doesn't require that conductors be allowed to operate at that temperature level.

Converting energy to motion for more than half a century

Bare copper can work continuously at 105 degC without loss of its properties.
The 85 degC stipulation is to take care of the busbar joints etc. I suppose!

Dear Mr. NickParker (Electrical)(OP)29 Apr 22 08:39
" According to IEC 61439-1, table 6. under clause g, it is 105k as temperature rise".
Following are my personal opinion
1. Per table: a) Terminal for external insulated conductors: Temperature-rise 70K.
b) Busbar and conductors: Limited by [ mechanical strength of conducting material........For plug-in contacts,...surface treatment of the material]*
c) g assuming all criterial [xxx]* are met, a maximum temperature-rise of 105K shall not be exceeded. Note The 105K relates to the temperature above which annealing of copper is likely to occur.
2. In realty, most busbars in LV boards are enclosed with say >IP22, busbar holders are not rated for (35degC + 105K), clearance between the heated busbar and other devices are say 30mm etc.
It would be difficult/impractical that all criterial [xxx]* are met. Take particular attention to where the busbar is connected to insulated conductors, where temperature-rise is 70K.
3. Therefore, temperature-rise of 105K shall NOT be exceeded and with stick limitations.
Che Kuan Yau (Singapore)

@ Dear Mr. Gr8blu (Electrical)29 Apr 22 13:48
".... It assumes a maximum ambient of 35 K ...... Note "g" simply states that IN NO CASE will the rise exceed 105 K (above the 35 K ambient condition). It doesn't require that conductors be allowed to operate at that temperature level..."
FYI: 1. Thermodynamic temperature in SI unit is degree Celsius (symbol [sup]o[/sup] C ) . NOT in kelvin (symbol K); e.g. ambient temperature of 35DegC, NOT 35K.
2. Kelvin is the unit for temperature difference and intervals. Temperature-rise is the temperature difference, therefore the SI unit is kelvin (symbol K) ; e.g. 105K.
Note: 1. e.g. temperature-rise 105K, NOT 105DegK. NOT 105k or 105Degk.
2. 1K=1DegC scale unit.
Che Kuan Yau (Singapore)

@ Dear Mr. RRaghunath (Electrical)30 Apr 22 04:29
"...#1. Bare copper can work continuously at 105 degC without loss of its properties. #2. The 85 degC stipulation is to take care of the busbar joints etc. I suppose!...".
FYI
#1. Agreed. " Bare copper can work continuously at 105 degC without loss of its properties"
Note: It is NOT only the [mechanical properties]. The busbar holders thermal rating, effect on nearby devices and especially where there are insulated conductors connection etc.,(see IEC 61439-1) MUST be taken into consideration.
#2. Reference IEC 61439-1. This standard does NOT stipulates " 85 degC is to take care of the busbar joints etc "
Note: A good (clamp/bolt+nut) join along a length of busbar [can be] lower temperature than the bar. The possible reasons being additional material (copper plates/ clamping hardware) being added at the join. These additional items add to the area of material. The result is lower the resistance (lower I[sup]2[/sup] R loses) and an increase in cooling surface. Therefore, possible lower temperature have been noted/observed empirically.
Che Kuan Yau (Singapore)