Can a 600Y/347V Circuit Breaker Be Used on a 480V Delta System?

Hello all,My question: Will a 600Y/347V rated circuit breaker handle 480v delta?I am a mechanical engineer by trade. At my current place of employment, we recently lost our only electrical engineer (for this location). I am quickly becoming the guy who picks up his slack. Lets just say that NEC, google, and forums like this have been my best friend lately. I should probally also mention my company is Japanese and none of the other electrical engineers speak english. 
Today I am hung up on what I would have called a simple question compared to what I have been digging through, it is driving me crazy!
I have very little experience/knowlege of delta vs wye power. I understand the voltage from each leg to leg, or leg to ground are different but thats about it. I've been reading articles, trying to calculate and playing with online calculators all morning but just cant grasp it. I have recently been updating our circuit breaker selection chart, and come across a slash rated breaker: 600Y/347V. It's my understanding that this means it is rated for 600v from leg to ground, and 347v leg to leg (wye only). When trying to calculate, I just couldnt make sense of my results. Any help would be greatly appreciated!

Taylor, a simple formula to convert from Phase-Neutral voltage to Phase-Phase voltage for 3-Phase systems is to multiply by the square root of 3 (1.73 for practical purposes).  So a 240V phase-Neutral voltage implies 240 * 1.73 = 415V Phase-Phase.  Now 347 * 1.73 = 600 so I think you hit the nail on the head there, except you got it the wrong way round, the 600V is Phase-Phase (what you call Leg-Leg) and the 347 is Phase-Neutral (your Leg-Ground).  This is simple trig and I can find something with the math if you're interested.The Y may just indicate 3-Phase and imply a Phase-Phase voltage. You should try and get the full specifications of the breaker to make sure of its ratings.Of more interest to you is the current carrying capability of this breaker; once you have determined that you can switch the voltages required, it also has to handle the current drawn by the load.  Circuit breakers are a pretty vast subject and include the fault current breaking capability (6KA or 6000 Amps is a common value for domestic breakers), which is important when you have the possibility of large fault currents, and the tripping curve - ie how quickly it will trip for various overloads.Motors will often have starters which start them in Y mode (ie using the neutral) and then switch to Delta mode (ie no neutral) once the motor is up to speed.  Y gives better starting torque and Delta is better for running.You can google "3-phase power tutorial" and there are a few sites that may help your understanding of this.Back to your original question:Will a 600Y/347V rated circuit breaker handle 480v delta?     Yes it will, if the 480V delta is truly Phase-Phase voltage (this implies 277V Phase-Neutral).  But take into account other factors above.I'll end by saying: it sounds like you are dealing with some fairly heavy machinery and electrics here.  BOTH CAN BE EXTREMELY DANGEROUS! Do take care and if you're not sure what you are doing, seek professional advice.  Better to pay someone who knows what they are doing than to suffer injury or loss of life.Do take care.

Hi David, 
Thank you for your reply. I understand much better now that I am not trying to calculate backwards haha!
I also contacted the circuit breaker manufacturer and they too confirmed it will be ok for 480V Delta. 
Yes, breaking capacity and panel SCCR is one reason I'm having to change our motor protection. Don't worry, with me taking over these projects with no experience all of my work is checked by real electrical engineers. The problem is they are in Japan and it takes a few days to get any feedback (after translations are confirmed), so I try to confirm any uncertainty's before sending them my report. 
Just wanted to take a second to thank you again, this site has helped me quite a few times!

Taylor, thanks for your thanks, much appreciated, we don't get a lot!It sounds like you are well across this both generally and in your particular case.Cheers // David