3Phase AC Cable Heat Rise Test

[BendRadius]

Hi all,

I am a recent graduate and have been tasked with creating a test rig for a cablebus system according to a newly drafted CSA No 273 standard. The goal of the test is to measure the heat rise of the cablebus system by injecting the cablebus system rated current into the cablebus. My question is that the diagrams on the CSA standard show that there is a short circuited at the end of the cablebus system. Being that I am injecting a 3 phase AC current into the cablebus system, would the end of cablebus be a wired like a "bolted fault current" in that all three phases will be joined to a single busbar?

Additionally, what sizing of a busbar should I use to connect the cable ends? I have read that the rule of thumb is general 1000A per square inch of surface area. Is there a CSA or NEC standard where I can read up on this?

I appreciate the help!

 

[waross]

Yes, bolted fault.
Jumper the bus bars with a jumper bar the same size as the bars under test.
You may want to consider a return jumper joining the outside bars as well as the two jumpers between the bars.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BendRadius]

Thank you for the response waross!

I was wondering if it would be alright to stack busbars on top of each other to increase the cross-sectional area. We have 1/4 x 8 copper busbars available which is rated for 3450A (65C rise), would stacking 3 of these achieve the same effect as a 3/4 x 8 busbar (5400A @ 65C rise)?

Thanks again

 

[davidbeach]

You’ll get more current for a given temperature rise, or less temperature rise for a given current, with the thinner bars spaced apart to allow air circulation between the bars.

 

[7anoter4]

As davidbeach said the busbar ampacity depends on distance between components. However it depends also on a lot of other factors like relative position: vertical or horizontal ,indoor or outdoor, natural ventilation or forced ,air temperature and other.
Following-for instance-Copper for Busbars by David Chapman & Professor Toby Norris and
Aluminum Electrical Conductor Handbook, bars in vertical position in indoor at 30oC air and 95oC conductor[copper] temperature a single bare of 3/4x8" the ampacity -as calculated- will be 5510 A [it is close to 5400 A as you said] and 3 copper bar of 1/4x8" in vertical position at 1/4" clearance withstand 5222A -total current. If the clearance is 2/4" then ampacity could be 5560 A.

 

[BendRadius]

Thank you both davidbeach and 7anoter4 for your insight, this has helped me tremendously. I'll read up on the two references for more info