Message Board Thread - "Buss bar severity criteria questions"

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Buss bar severity criteria questions Scott Willits 9/7/2004
Generally speaking, what severity criteria should apply in a heavily loaded buss bar? I'm looking at one rated for 3000A, but currently with 2000A fuses installed. With emissivity set conservatively at 0.70, I get a rise over the ambient temp inside the cabinet on the order of 46°F, and greater than 60°F compared to ambient room temp. The B phase is slightly warmer than the others, but not by more than a few degrees.

This is in a creamery that operates 24/7, with virtually never a scheduled shutdown -- this being the main plant switchgear, it's highly critical, but a forced shutdown would be extraordinarily expensive for them.

I did not have the means to measure such high loads, but I am given to understand that it was running at about 70 to 80% of peak at the time.
another pic Scott Willits 9/7/2004
Here's a visible image of what I was shooting, where you can see the hottest spot is down in a cavity.
Re:Buss bar severity criteria questions Manuel 9/7/2004
Hi Scott..

i have no read nothing for rated 2000 or 3000 amp buss bars or fuses.

only i can guess is two things, nothing will be more expensive than unprogramed shutdown.

if the cremery can shutdown, periodic infrared scans will be necesary to keep record of temperature rise.

good luck
roberto cruz
Re:Buss bar severity criteria questions Terry 10/6/2004
Scott, The heating does not appear to be bus bar but possibly conducted heat from a bolted pressure switch (probably a Main Service Disconnect). This could be much more serious than is indicated in the image you have captured. Did you take mV drop readings across the contacts of the switch to compare?
Re:Buss bar severity criteria questions Scott Willits 10/11/2004
Hi Terry,

Thanks for the response. No, I didn't take such measurements, as I'm not an electrician and in this instance feel far from qualified to go poking around in there. The electrician who accompanied me on this survey wasn't too thrilled with the idea either.

I will certainly take your suggestion into consideration, though. It would be a very good idea to break out the drawings and work with the plant staff to see what other tests we can safely perform to determine whether they have a serious issue with this component.

Re:Buss bar severity criteria questions Bob Berry 10/11/2004
As you are not an electrician you did the right thing in not taking measurements. However you must remember that you are also far from qualified make a decision on severity criteria or priority. You need an electrician to make this decision with you.

With your image there is a couple of clear cavity radiators located at the hottest spots. These would typically be good emmitters, and the best indication of actual temperature of the components. Change your emissivity setting to 0.9 and measure the hottest spots again, this should be a more reliable measurement.
Re:Buss bar severity criteria questions huffsw 10/13/2004
What advantage will that give him over the 0.70 Emissivity setting? He needs to show this image to an electrician. There is probably no need for concern, just work with somewone that can help with this buss bar.

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