Short Circuit Current

The heating effect is given by the term I² x t, where I is the current in the conductor and t is the time.

For the first case, I²t = 15² x 1 = 225

For the second case, at 50Hz, I²t = 50² ÷ 100 = 25 (and it's even smaller for 60Hz).

So the 15kA for 1 second gives about five times as much heat.

If you want to meet the spec, don't take your supplier's offer.

Every piece of electrical apparatus has a short-circuit withstand rating. It can carry only so much current for so much time before it is damaged. For example, bus duct may have a short-circuit rating of 50,000 amperes for three cycles. If 75,000 amperes were to flow through the bus for three cycles, it might be damaged. Or. If 50,000 amperes flow for 12 cycles, it might also be damaged. Nationally Recognized Testing Labs such as UL often take short-circuit withstand ratings into account when they test products. In the example above, the short circuit test on the busway would likely include the overcurrent device. So, the busway might be tested at 100,000 amperes when protected by an 800 ampere Class L fuse. If the busway passed the test, it would be marked as suitable for use on a circuit capable of delivering 100,000 amperes when protected by a Class L fuse of no greater than 800 amperes.

So where does that leave you. A fault current of 15 ka for 1 second is not likely. It will be more like 50 ka for 1/2 or 1 cycle at the main switch. Depending on the protection, the OC device should interrupt the fault in less than 1 cycle. You need the fault current level at the location of you equipment to size it correctly.

My dear friend calculate time per cycle either 60 or 50 cycles you have the answer for your question

crm

Quote [Specifications says busbar to with stand 15KA for 1 sec however supplier is confirming 50KA for 1/2 cycle.]

This is the first time I've seen SC current specified in cycles. Are you sure this is not a typo? Normally, SC current is given in seconds so if it read "50kA for 0.5 secs", no problem but 50 kA for 10mS (1 cycle = 20mS@50Hz, 1 cycle = 16mS@60Hz)? Unheard of!!!

If it's 50kA for 0.5 secs, then your ok.

50² x 0.5 = 1250