Arc Flash Forum :: View topic - Main SG analysis ok or total needed ?

1. Our mcc's have some sq. d mph or mpl cb's 800amps @ 50ka with adjustable instan. They are used as tie breakers and main cb in mcc.

2. Our main 4000amp switchgear station and mostly 600amp breakers are rated @100ka and 85ka .

After along discussion with safety about labeling and a analysis they sort of agreed on analysis on the main swichgear only. [ #2 ]

Where does that leave the mcc panels as far as using the tables ?

They want to use osha where they can and say to use the 70e tables for the tasks . I explained about being in the parameters for using 70e.

Would'nt the size of mcc cb's [ #1] require a analysis also? Do not know the clearing time of them either.

Author:	PUCKMAN [ Sun Feb 21, 2010 6:22 am ]
Post subject:	Main SG analysis ok or total needed ?
1. Our mcc's have some sq. d mph or mpl cb's 800amps @ 50ka with adjustable instan. They are used as tie breakers and main cb in mcc. 2. Our main 4000amp switchgear station and mostly 600amp breakers are rated @100ka and 85ka . After along discussion with safety about labeling and a analysis they sort of agreed on analysis on the main swichgear only. [ #2 ] Where does that leave the mcc panels as far as using the tables ? They want to use osha where they can and say to use the 70e tables for the tasks . I explained about being in the parameters for using 70e. Would'nt the size of mcc cb's [ #1] require a analysis also? Do not know the clearing time of them either.

Author:	Zog [ Sun Feb 21, 2010 10:12 am ]
Post subject:
PUCKMAN wrote: 1. Our mcc's have some sq. d mph or mpl cb's 800amps @ 50ka with adjustable instan. They are used as tie breakers and main cb in mcc. 2. Our main 4000amp switchgear station and mostly 600amp breakers are rated @100ka and 85ka . After along discussion with safety about labeling and a analysis they sort of agreed on analysis on the main swichgear only. [ #2 ] Where does that leave the mcc panels as far as using the tables ? They want to use osha where they can and say to use the 70e tables for the tasks . I explained about being in the parameters for using 70e. Would'nt the size of mcc cb's [ #1] require a analysis also? Do not know the clearing time of them either. I think I follow you, your plant decided not to do the study on the MCC's and use the tables instead right? The 800A breakers are the mains feeding the MCC's? They based this assumption, that they can use the tables on the AIC rating of the breakers? Do the 800A breakers feeding the MCC's have an INST trip?

Author:	PUCKMAN [ Sun Feb 21, 2010 11:39 am ]
Post subject:
The 800amp 50KA cb in mcc have a instantanous setting low to high. And they said they will get a analysis on the main SG. We'll see.

Author:	Zog [ Sun Feb 21, 2010 6:21 pm ]
Post subject:
PUCKMAN wrote: The 800amp 50KA cb in mcc have a instantanous setting low to high. And they said they will get a analysis on the main SG. We'll see. If they have an INST trip and are properly being applied within the 50kA rating, the tables should be able to be used. But the term low to high for INST settings is throwing me off. Usually they are multpliers like 10x, 12x, etc...

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