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topic 50556p2

Copper Bus Bar Sizing for DC low-voltage high-amperage



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A discussion started in 2008 but continuing through 2020

September 24, 2012

Q. My existing plating tanks have undersized cathode bars (3"x .75", 4000A rectifier) which cannot be upsized. During plating the cathode bar gets so hot you cannot touch it. Currently, bussing is only connected to one end of tank. Will connecting both ends of the cathode bar decrease the resistance through the cathode bar to the 40 plating racks evenly spaced on the bar? Does this essentially double the current carrying capacity of the cathode bar (almost like having 2 shorter cathode bars end-to-end each with 2250A current capacity)?

Joe Smith
chrome plater - Portland, Oregon


September 24, 2012

A. Hi Joe. Yes, exactly. This will work, and it should be done immediately before you risk catching the tank liner on fire. Don't forget to check the ampacity of the anode rod when you fix the cathode rod.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



Are my bus bars properly sized?

May 28, 2015

Q. Good Morning
I need to reinstall some bus-bars in our factory.
Distance from rectifier to tank is 10.5 m.
I order 38 x 6 mm copper bus-bar / line.
Maximum current 400 A on 8 ~ 10 V DC.
It is enough dimension for new copper ?
Old bus bars are 52 x 14 mm (installed maybe 40 years ago). I cannot reuse them and I don`t want to. There are too heavy and dirty.

Best Regards
Mike

Mihai Popa
- Walton On Thames, Surrey, UK


May 2015

A. Hi Mike. If there is something you don't understand on this page, we'll be happy to try to explain it in different words until it is completely clear. But the voltage has little to do with it (in this limited context of bussing a plating tank that operates at the usual industrial levels). The length of the run is not totally irrelevant, but for typical plating shop runs, like 10.5 m, it's not real important. My own thumb rule, which was already a well established guideline at the plating equipment manufacturer I went to work for in 1967 is simply 1 square inch (645 square millimeters) of cross sectional area in the bus bars for every thousand amps you want to carry. This gives you measurable but not excessive voltage drops, and warm but not hot bus bars. So you would need 645 * 400/1000 = 258 square millimeters, and you've only got 228.

My opinion, and that's all it is, is that you should have ordered 6 mm x 52 mm (1/4" x 2") bars. The rectifier terminal often implies what size bus bar the rectifier manufacturer feels is appropriate. But whether you should proceed or start over may be a different question, and I suspect that most people would advise you to just continue :-)

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


May 29, 2015

A. Good day Mihai.

Ted has a good point about the calculations, but this is not written in stone. Your busing is 12% short of IDEAL calculations. I feel you can proceed with what you have.
I would, however, like to make a suggestion.
If you are leading each end of your cathode/anode bars from the MAIN busbar, I found that these leads from the MAIN busing should be of the same length.
You can measure the amperage along the length of the cathode bar on each rack/fixture with a tong tester/ammeter to verify the amperage is consistent.
Hope this helps.

Regards,

Eric Bogner
Lab Tech. - Whitby, On. Can.



September 19, 2015

Q. How to calculate the copper busbar size for a given DC current rating ?

I have a rectifier it gives output 24 volts DC and 15000 amps at source to load in distance 6 m, 5 m, 2 m, 1 m. At what size of busbar(or) cables are taken my application and what type of insulation I prefer to the bus bus at safe conditions.

I don't have any knowledge of busbar size calculation; please send me choice of a correct busbar sizes for required current rating.

shiva shankar
- hyderabad,india


September 2015

A. Hi Shiva. I think you may need to retain an experienced electrician, electrical engineer, or plating consultant -- someone who has worked with this stuff and is familiar with the concepts being discussed. How to size this stuff has been explained numerous times just on this one thread alone, and if you can't follow it sufficiently to do the arithmetic yourself, you don't understand enough to install bus bar without guidance. Although voltage drop is proportional to the length of the bus bar, it's not conventional to use different cross-sections of bus bar for lengths of 6 meters vs 1 meter.

Safety issues are tricky at best. Is this a manually operated installation? I am long familiar with open bus bar systems which have no insulation at all, and which have been used for many decades in plating shops -- but I've also seen movement toward people no longer accepting open bus bar systems as being safe, especially as we get to higher voltages like 24 V. Welding cable sized at 1000 Amps/square inch can be used as an alternative to open bus bar, but doesn't fully address the issue of people working with live 24 v systems. A metal tool accidentally shorting out a 15,000 Amp power supply can be a spectacular event! In any case, you obviously should minimize potential exposure to live circuits even though they are only 24 V, and people in the area should clearly understand the situation. Sorry that it's hard to be of much more help from such a distance.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



November 4, 2015

Q. Thank you for very useful information; I have question as I work only in AC and I'm managing project for DC busbar with the following data: length 100 m, Current 2000 A, Voltage 48 V, size 1600 mm2. After calculating voltage drop (V 10.2, please correct me if I'm wrong) the loss in voltage first will result in not getting required voltage at the bus end and heat dissipation will be high (about 20.4 KVA again correct me if I'm wrong) even if I adjusted the source voltage to compensate for the voltage drop the heat is high. and as stated above it's in line with 1000 Amp/sq.in. Please advise.

Thank you

Khaled Bader
- Melbourne, Florida


December 2015

A. Hi Khaled. The resistance of the bus bar is calculated as: R = ρ x l / A
The resistivity of copper bus bar is about 1.68 x 10-8 ohm-m, so I get as the resistance of your bus bar:
1.68 x 10-8 ohm-m x 100 m / (1600 mm2 x 1 m2 / 1,000,000 mm2), so:
R = 1.05 x 10-3 Ω

And V = I x R, so I get: V = 2000 A x 1.05 x 10-3 Ω = 2.1 Volts

That's a lot, and it would apply to each pole if they're both 100 m long. Then again, 100 m is pretty long for a DC bus run.

The KVA waste sounds like 2000 A x 2.1 V /1000 = 4.2 KVA.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



January 16, 2016

Q. Hello dear Ted,
I have a question for you: what's the whole voltage drop, cross section and short circuit current computing procedure of a DC busbar?

For example: A DC busbar with 38000A current, 200 v dc

Sincerely yours,

Hojat radmehr
- yazd.iran


February 2016

A. Hi cousin Hojat. Sorry, but we'd just run in circles and never get anywhere if, after 30 postings on a subject, instead of asking for specific clarifications people just say "start over and tell me everything" :-)

I don't see how the voltage drop and cross section calculation you wish to do is any different than Khaled's example which I just worked for you. Sorry, I don't know the codes regarding short circuit protection (if any) in your situation, and my main experience is with low voltage busbar, not 200 V busbar. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



May 3, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am looking into the ratings for the Bus bar that is used on my anodizing tanks. I have always understood that the Rise in Celsius is the rise over ambient or resting temperature. I currently have 1/4" x 3" Buss bar on my tanks, which according to the charts, is rated at 1500 amps at a 65 degree Celsius rise? But I have not found a chart stating whether that is AC or DC. In stating that, my questions are simple. Using my current bussing, what are my limits on DC Amperage, and what is the temperature rise above ambient that I should factor in?

Thank You

Danny Ferguson
- Thomasville, North Carolina, USA


May 2016

A. Hi Danny. 1/4" x 3" bus bar is rated 750 Amps, not 1500 Amps, based on 1000 A/sq.in. If you are speaking of an anode rod or cathode bar on top of the tank, yes, it's capacity could be 1500 Amps if it is bussed from both ends (750 A coming in from each end).

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



February 14, 2018

Q. Is cable advisable to use for 700 Amps Oil Cooled rectifier for Nickel plating or it should be Copper bar only. And what should be the Jumpers sizes for carbon brush holders.
Also, How many carbon brushes to be used at each side. These are for rotogravure cylinder plating machines.

ANAND VAIDYA
- Lagos Nigeria


February 2018

A. Hi Anand. Sorry, I don't have any experience with carbon brushes, so you'll have to wait for input from others on that. I've already offered my opinion on cables and the sizing criteria I use twice on this page; maybe someone will offer a second opinion.

Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



Protecting bus bar from corrosion in a plating shop

March 9, 2018

Q. Good afternoon. My name is drew and I would like to know if conductivity of copper buss bars degrades with the accumulation of green corrosion. And if this loss of performance is enough to change or clean the buss bar. I know that the surface corrosion will have a very small impact but that the connections could be significant. We electroplate zinc onto ordinary Link chain at 9 VDC @ 3000A. I have read your thread and would like to know what you have to say regarding the corrosion and its effect on conductivity as well as any experience you have with cleaning the buss bars and methods to minimize the accumulation of green corrosion. Are there ways to make the corrosion more manageable. Thank you in advance.

Drew

Andrew Ryan
Apex Tool Group - York, Pennsylvania USA


March 2018

aff. link
"No-Ox-Id" Compound

A. Hi Drew. There should be no decline. I have seen plating shops clear coat or lacquer their bus bar runs (except for the connections of course) and it does seem to hold up well and to look better than streaky green stained copper.

Bus bar connections are actually supposed to be silvered or tinned. I visited a GE or Westinghouse bus bar plant decades ago where they hung bus bar vertically and dipped it 4"-6" deep into the plating solution to plate the ends. Bus bars are also supposed to be clamped together rather than bolted, I believe. But in my own experience, plating shops rarely use plated ends or buss bar clamps: they just drill holes, and wire brush No-Ox-Id compound onto the joint area before bolting together. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



January 8, 2020

Q. I made 200 amp switch with tin coated copper busbar. At 200 amps the joints are heating to 70+ °C.
What could the heating be due to?
All joints (male/female ) are firm and good contact.

ajay gahlaut
- noida, up, India


January 2020

A. Hi Ajay. Are all components at least 1/4" x 3/4"? There should be no spot on the switch where the cross sectional area of the copper is less than 1/5 in2 because the current carrying capacity of copper is 1000 A/in2.

Are you sure the copper is all hard drawn electrolytically pure? The current carrying capacity is drastically reduced with even a very small amount of alloying materials. Did you wire brush the joints and apply conductive joint compound?

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



January 14, 2020

Q. How to calculate DC bus bar current carrying capacity with respect to temperature.
e.g.: I have copper bus bar width = 14 mm, thickness= 6 mm, temperature 100 degrees -- so how to calculate current carrying capacity.

virendra Kushwaha
student - Bangalore,Karnataka,India


January 2020

A. Hi Virendra. Generally, the allowable temperature rise is fairly low and it doesn't do much good to design to a higher allowable temperature rise anyway -- because conductivity is inversely proportional to temperature. So you will see that empirical numbers are used instead. Here in the USA and in the electroplating industry, the nice round number of 1000 Amps per square inch for open bus bar was universally accepted long before I entered the industry, and that was over 60 years ago :-)

The allowable current carrying capacity of enclosed bus bar in bus ducts is a little bit lower because of lack of cooling; since bus duct is a standardized product, you'll see the numbers in product literature and electrical codes.

According to my method, your 14 mm x 6 mm bar can carry 130 Amps in open air.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha

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