CR4 - The Engineer's Place for News and Discussion ®
Login | Register for Engineering Community (CR4)

 Previous in Forum: Capacitive Switch Next in Forum: Tandem Switch
Anonymous Poster

# Current carring capacity of copper bus bar

09/15/2006 1:15 AM

Please let me know the ampere(current carring) capacity of a copper bus bar.

Pathfinder Tags: Bus bar Copper current carrying
Interested in this topic? By joining CR4 you can "subscribe" to
Associate

Join Date: Jun 2006
Posts: 25
#1

### Re: Current carring capacity of copper bus bar

09/15/2006 8:48 AM

It depends on the size of the bar. The web has this info posted and you can probably find the formula for calculating this as well while searching.

Anonymous Poster
#3
In reply to #1

### Re: Current carring capacity of copper bus bar

09/16/2006 3:11 AM

In general it depende from the bus bar manufacturer catalogue, which is specified based on the bus bar working tempereture, number of parallel bars, the alloy components ... ets. For gereal purpose, a a guidance you can take 2 Amper per mm squere.

Anonymous Poster
#17
In reply to #1

### Re: Current carring capacity of copper bus bar

03/11/2008 2:04 AM

Hi,

Please send me that formula that how to calculate it Or how to find area of copper Bus Bar and its current carying capacity.

Example, I have 250amp main breaker and its load is 7Nos MCCB breaker of 30Amp and 5Nos. MCCB Breaker of 20Amps.

Please send me its calculation in detail of Copper bus bar and etc.

Best Regards

Off Topic (Score 5)
Anonymous Poster
#20
In reply to #1

### Re: Current carring capacity of copper bus bar

07/18/2008 4:49 AM

Physical Design Considerations

 Cross Sectional Area Considerations and Determination The required cross sectional area of a copper conductor for a given amperage requirement and a temperature rise of 30° C max from ambient can be determined by the following formula: Formula (2.7) A = 300 x l x [1 + .075 (N - 1)] Sq. Mils Where, l = curent in amperes N = number of conductors For multiple layer bus bars, the cross sectional area calculated for each conductor should be increased by approximately 7½% to account for the decrease in heat dissipation between conductors. This is already accounted for in formula (2.7) above. Conductor Thickness and Width Calculations The width calculation for a given cross sectional area can be determined by selecting an appropriate standard thickness and using the following formula: Formula (2.8) w = A / (1 x 106 ) / t conductor width in inches Where, A = cross sectional area as calculated from formula (2.7) t = conductor thickness in inches selected from the list below Available Standard Alloy 110 Thickness copper conductor: 0.020", 0.032", 0.040", 0.062", 0.093", 0.125", 0.187", 0.250", 0.375", 0.500", 0.750" For a given cross sectional area and taking into consideration the space and structural application requirements, the combination of a very thin and wide conductor, or having a maximum w/t ratio, has the following benefits: • Inductance is minimized; formula (2.5) • Capacitance is maximized; formula (2.4) • Low characteristic impedance pls visit this site http://www.cci-msc.com/Bussco/physical.html
Guru

Join Date: Jun 2006
Location: Toronto
Posts: 3879
#2

### Re: Current carring capacity of copper bus bar

09/15/2006 11:10 PM

Yes, as suggested, look online for this via search.

Use a string like

That will give you some hits. You can choose from those hits what fits your situation

Bus bars can be in open air or enclosed and there will be an allowed rise in temperature in the specs, and for endurance over time, they may require extra capacity to start. A wrapped bar will get hotter at the same current than a bare bar, as the insulation stops heat losses.

__________________
Per Ardua Ad Astra
Guru

Join Date: Jan 2006
Location: Tamworth, UK.
Posts: 1436
#4

### Re: Current carring capacity of copper bus bar

09/16/2006 5:14 AM

A round figure for power distribution is 10 amps per mm2 for copper.

It is a balancing act between heat dissipation + volts-drop (when under-sized) and space (size) + cost (when over-sized).

Whatever the current rating, closely spaced bus-bars need suitable support because they buckle in hot conditions (over-current) due to expansion, and due to electromagnetic forces. The latter can be quite high in fault conditions - made worse by low resistance. This can be seen from Ohm's Law where the current is equal to the voltage divided by the resistance.

So for example in a 240 volt domestic supply with a fault resistance of 0.001 ohms (at the point of the short circuit) the current will be 240,000 amps. Not for long admittedly, but there until the fuse blows.

__________________
When arguing mud-slinging gets you nowhere. Doing so means you lose ground.
Guru

Join Date: Jun 2006
Location: Toronto
Posts: 3879
#5
In reply to #4

### Re: Current carring capacity of copper bus bar

09/16/2006 6:41 AM

I remember in electric machines labs we hed test shorts of 200,000 amps or so for fractions of a second from a rotating energy storage device. I forget what it was called. but in the fraction of a second the current flowed the cable jerked from either repulsion or attraction(depending on the direction of current flow in each one...which we could change).

That 10 amps/mm2 is a good conservative figure to use.

__________________
Per Ardua Ad Astra
Anonymous Poster
#25
In reply to #4

### Re: Current carring capacity of copper bus bar

12/10/2009 7:20 AM

240000 amps only if the driving source impedance is low !! even in heavy power distribution 200 kA is considrered a very high short circuit fault current. With a 1000 kVA feeder transformer the typical load current is 1000 0000 /(3 * 240) approx 1400 amps per phase. For a short circuit take the worst case of twenty times this 28000 amps. And this assumes all the feeder cables to the short circuit are zero ohms.

Anonymous Poster
#6

### Re: Current carring capacity of copper bus bar

09/16/2006 7:35 AM

A lot of factors must be considered, as previously mentioned.However, I do not think merely the surface area is adequate for a current calculation.You need to know the volume of the bus bar.More massive bars will carry more current.Of course I am presuming relatively low frequency and voltage.At high frequencies and voltages, the main current is carried in the outer "Skin" of the conductor, and as such, a hollow tube can carry nearly as much current as a solid one at high frequencies and voltages..in fact several hundreds of amps can circulate thru a 1/4 inch tube, with water circulating internally for cooling.A cap sealer is such an application, for instance.

Also, as previously stated, system capacity(Max Amps Available in short circuit conditions), the ambient temp, spacing,support, and insulation are all factors to consider.

Periodic maintenance of the bus bars is also critical. Proper torque, cleaning, etc.

For these and other reasons, there are no simple answers to your question.

Guru

Join Date: Aug 2006
Posts: 4542
#7

### Re: Current carring capacity of copper bus bar

09/16/2006 12:02 PM

As you've seen, there is disagreement here: some say 2 amps per mm2, some say 10 amps per mm2. If your question is related to a particular situation, then I'd suggest following the advice of the manufacturers of the devices to be powered and of the bus bars, as well as following the recommendations of NFPA. If your application is very new or unusual, then you really need to hire an electrical engineer: when you are dealing with amperages that require bus bars, then you are dealing with very serious safety issues, such as arc blast, fires, etc. etc. Not stuff for amateurs.

__________________
There is more to life than just eating mice.
Guru

Join Date: Jun 2006
Location: Toronto
Posts: 3879
#8

### Re: Current carring capacity of copper bus bar

09/16/2006 1:59 PM

A reference here show that 16 gage insulated wire is rated for 10 amps and has 1.3 mm of area. a bus wire in air has a slightly higher rating at the same size.

SInce this is a very conservative rating, 10 is OK for small bus bars.

http://en.wikipedia.org/wiki/American_wire_gauge

As you get into larger bus bars you must consider the effect of square law.

So if you have a bus 1 mm square and another one 2 mm square you have 4 times the copper in number two, however the 1MM wire has a surface of 4 mm2 and the 2 mm has a surface of 8 mm2(for a 1 mm running length), thus it has twice the heat per unit area to dissipate, so it must be derated to less than 10, to a current where the same relative heat per unit is radiated.. As you get into large busses the derating gets larger. Wire and bus makers have charts for this, as does the UL

__________________
Per Ardua Ad Astra
Power-User

Join Date: Apr 2006
Posts: 261
#9

### Re: Current carring capacity of copper bus bar

09/16/2006 8:07 PM

It varies with cooling considerations, and bracing must be
designed for available short circuit currents.

A good 'rule of thumb` figure is 500A./Sq. In., for L.V. (Under 600V.),
in ventilated enclosures.

.....but you've got to run the numbers for the use contemplated.

(Manufacturers of busways and panels, etc. will supply figures for their
products under varying conditions.)

Guru

Join Date: Jun 2006
Location: Toronto
Posts: 3879
#10
In reply to #9

### Re: Current carring capacity of copper bus bar

09/16/2006 9:28 PM

that is very low, on the order of 1.3 amps per MM2, and would go broke from buying copper/aluminum at that rate of use on bus bars

__________________
Per Ardua Ad Astra
Power-User

Join Date: Apr 2006
Posts: 261
#12
In reply to #10

### Re: Current carring capacity of copper bus bar

09/18/2006 7:19 PM

It's an old rule of thumb from the days when material costs were not as important,
and was intended to be taken as a 'safe` number.
You will find many old switchboards with sizes/capacities in this range.

Use of domestic cable area loadings for interpolation to busbar sizing is not a
good plan . The area/surface ratios, and the insulation on the cables are
factors in cooling. So are expected ambient temp.s, air flow, and even buss
configuration and orientation.

As I said, - you've got to run the numbers.

Guru

Join Date: Jan 2006
Location: Tamworth, UK.
Posts: 1436
#11

### Re: Current carring capacity of copper bus bar

09/17/2006 3:19 AM

I'm back again. I suggested 10 amps per mm2 based on domestic cable ratings in the Uk.

A copper power cable of 2.5 mm2 has a current rating of about 25 amps. The precise figure will depend on the application and can be found in the IEE Regs.

__________________
When arguing mud-slinging gets you nowhere. Doing so means you lose ground.
Anonymous Poster
#13

### Re: Current carring capacity of copper bus bar

10/19/2006 5:42 PM

The National Electrical Code indicates 1000 amps per square inch, for copper and 700 amps per square inch for aluminum. For example a 4 inch wide by 1/4 inch thick copper bus bar can carry 1000 amps.

Member

Join Date: Oct 2007
Posts: 6
#18
In reply to #13

### Re: Current carring capacity of copper bus bar

05/27/2008 4:18 AM

Thank you for the comment, can i know the NEC standard No. In which the rating is specified.

Anonymous Poster
#14

### Re: Current carring capacity of copper bus bar

05/24/2007 11:06 AM

at lower sizes (down to around 25x5mm) you will be at nearer to 3 amps per mm2.

When you get to 2000A the ratings starts to dip under 2A, but 2A is a good call up to there. When you parallel coppers in a standard ASTA support, there is further derating.

You will find that a 100x5mm copper has a better rating than a 50x10 as it has more surface to dissipate the heat despite being the same volume.

steve e

steveenglish.com

Member

Join Date: Oct 2007
Posts: 6
#15

### Re: Current carring capacity of copper bus bar

10/22/2007 5:11 AM

Please let me know the ampere(current carring) capacity of a copper bus bar.

Guru

Join Date: Jun 2006
Location: Toronto
Posts: 3879
#16
In reply to #15

### Re: Current carring capacity of copper bus bar

10/22/2007 6:31 AM
__________________
Per Ardua Ad Astra
Anonymous Poster
#23
In reply to #15

### Re: Current carring capacity of copper bus bar

08/02/2009 9:16 AM

630 Amps at 50 KA shortcircuit level

Associate

Join Date: Jun 2008
Posts: 45
#19

### Re: Current carring capacity of copper bus bar

06/10/2008 10:54 AM

It is interesting to compare these considerations to the standard plugs used in different parts of the world. For example, the standard UK design has robust pins, typically of brass, measuring about 6x4mm, whereas the Australian design (also used in China) uses flimsy pins of about 6x1mm. The examples I have use steel pins. Of course one has to take into account the conductivity of the different metals, and the way the pins are connected in both directions, to assess how well chosen these designs are.

__________________
Elroch
Anonymous Poster
#21

### Re: Current carring capacity of copper bus bar

01/20/2009 2:39 AM

Dear Freind,

For design purpose you should consider the current capacity of copper as 1.6 amp per sqmm.

Shalabh Kesarwani

Jaksons Limited, Noida, India

Guru

Join Date: Oct 2006
Location: India, 200 Km. North of Delhi.
Posts: 1355
#22
In reply to #21

### Re: Current caring capacity of copper bus bar

01/20/2009 4:29 AM

Dear Sir.

Your figures are AtLeast 6times conservative then of normal standard. A transformer is normally wound with the Current density of 3.3 amps/sq-mm.and an open conductor can carry about 3times of that.

Sorry my intention is not to put you down but as 1.6ams/sq-mm can waste lot money of poster.

__________________
Jesus gave me message, Gandhi gave me method, M.L.K
Associate

Join Date: Aug 2009
Location: India
Posts: 25
#24

### Re: Current carring capacity of copper bus bar

09/11/2009 5:03 AM

Roughly 1.5 A/mm2 at ambient temperature of 40 deg C

Anonymous Poster
#26

### Re: Current carring capacity of copper bus bar

02/10/2010 10:48 AM

please send me the copper bus bars ampare carring capacity

thanks & regards.

AsimLatif Bhatti

Off Topic (Score 5)
Anonymous Poster
#27

### Re: Current carring capacity of copper bus bar

05/14/2010 7:20 AM

current carring capacity of copper is 1 sq mm = 1.2 amps.

Anonymous Poster
#28

### Re: Current carring capacity of copper bus bar

07/09/2010 4:04 AM

simplest of all....

120mmX10mm copper busbar can carry 1200A...

simply multiply... and get solution....

amazing... isn't it.???

but just a shortcut... not the exact method...

Off Topic (Score 5)
Power-User

Join Date: Jun 2009
Posts: 221
#29

### Re: Current carring capacity of copper bus bar

04/22/2013 11:23 PM

is the anonymous poster of 2006 still reading?

Participant

Join Date: Jul 2015
Posts: 1
#30

### Re: Current carring capacity of copper bus bar

07/06/2015 3:17 AM

Hello Dear ,

first of all i would like to say its such good plate forum for information .So we want know actually about the bus bar rating according to amperes we using under mention bus bar for modification of 4000 ,60 hz ampere panels so could you please confirm us or suggest bus bar rating for this modification.

we are using 1.5amp/mm2 for 4000 amps please suggest

thanks and regards,

Interested in this topic? By joining CR4 you can "subscribe" to