MCC One-Line Symbol Question

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robgrant3

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I have a symbol on a oneline diagram for a 600V MCC, and I am unsure of what the numbers next to the symbol mean. It is 2 squares, stacked. The lower square has an X in it, and the left and right pieces of the X are dark, like an exit sign with a left & right arrow. Next to the symbol are 2 numbers, ie 30A/15A or 30A/3A (these are the numbers I am unsure of). In the bottom left is the NEMA size for the device. I know the device is a combination motor starter w/ circuit breaker. If anyone can help, I would really appreciate it. :grin:
 
30A/15A or 30A/3A
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Typically this would represent the size of the switch and it's associated OCPD. For example a feeder from a 400 amp switch fused at 250 amps would look something like 400a/250a.
 
Any symbol can be defined in any way the creator wants..... with that in mind I'll guess that 30/3 could indicate 30 amp 3pole. The 30/15 I would usually think of as a 30 amp switch fused at 15 amps but since we know it is a breaker I guess it is a 30 amp frame size breaker with a 15 amp trip?
 
Here are some standard size disconnects: 30, 60, 100, 200 etc. Refer to Bussman for available fuse sizes. If it is a new job, I would also suggest that you put in an RFI for further clarification.
 
robgrant3 said:
I have a symbol on a oneline diagram for a 600V MCC, and I am unsure of what the numbers next to the symbol mean. It is 2 squares, stacked. The lower square has an X in it, and the left and right pieces of the X are dark, like an exit sign with a left & right arrow. Next to the symbol are 2 numbers, ie 30A/15A or 30A/3A (these are the numbers I am unsure of). In the bottom left is the NEMA size for the device. I know the device is a combination motor starter w/ circuit breaker. If anyone can help, I would really appreciate it. :grin:
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The symbol that you describe is not an standard symbol in accordance with any IEEE, ANSI, or IEC published documents. There are some guesses that could be made, such as the 30A/15A or 30A/3A probably means it is a 30A rated fused disconnect with 15A and 3A fuses, respectively. The box with the "X" in it should indicate a combination motor starter, but they may be wanting fuses ahead of the breaker.

Engineering practice is that if the symbols used are standard published symbols, then it is not necessary to supply a legend sheet. But, if the symbols used are not industry standard, then the engineer should provide a legend sheet. If one was not provided, it is within your responsibility to ask for clarification. It would be best to not assume.
 
Your guess is as good as anyones, but why guess? You need to contact the person that provided the drawing and ask for clarification.

Please re-read previous post!
 
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