250.21 (1) Industrial Electric Furnaces
- Thread starter tester730
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pierre
Senior Member
- Location
- Westchester County, New York
Re: 250.21 (1) Industrial Electric Furnaces
There are some processes (usually in industrial applications) where the ground is not a good idea, because the ground fault opening a protective device could stop the process which would introduce a greater hazard. These types of installations usually are in premises where highly qualified people will have an alarm system that alerts them to the fault and they will try to fix it before another fault occurs.
There are some processes (usually in industrial applications) where the ground is not a good idea, because the ground fault opening a protective device could stop the process which would introduce a greater hazard. These types of installations usually are in premises where highly qualified people will have an alarm system that alerts them to the fault and they will try to fix it before another fault occurs.
rcwilson
Senior Member
- Location
- Redmond, WA
Re: 250.21 (1) Industrial Electric Furnaces
In the aluminum and chemical industries, some furnaces for refining operate on high currents (100,000 Amps) but low voltages per furnace (3-5V)- sometimes called a "cell" or "pot". The pots are series connected together into potlines with rectifier banks feeding the series circuit at 500- 1000 VDC, 100 -200 kA.
NEC Article 668 describes this type of furnace and the special precautions needed.
The steel and carbon structure of each furnace is part of the circuit. Potline workers are trained in safe methods of working the furnaces while energized. The low DC voltages to adjacent equipment make it a safer environment than it sounds. Since the system is floating, voltage to ground varies from 700V to 0V. Introducing a ground anywhere in the vicinity of the potline creates a hazard. Great care is taken to not short out any portion through an unintentional ground.
In the aluminum and chemical industries, some furnaces for refining operate on high currents (100,000 Amps) but low voltages per furnace (3-5V)- sometimes called a "cell" or "pot". The pots are series connected together into potlines with rectifier banks feeding the series circuit at 500- 1000 VDC, 100 -200 kA.
NEC Article 668 describes this type of furnace and the special precautions needed.
The steel and carbon structure of each furnace is part of the circuit. Potline workers are trained in safe methods of working the furnaces while energized. The low DC voltages to adjacent equipment make it a safer environment than it sounds. Since the system is floating, voltage to ground varies from 700V to 0V. Introducing a ground anywhere in the vicinity of the potline creates a hazard. Great care is taken to not short out any portion through an unintentional ground.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Re: 250.21 (1) Industrial Electric Furnaces
Sounds like a situation where a high-impedance connection can ruin one's day. I wonder what the 310.16 conductor requirements are for 100Ka? Mine doesn't go quite that high.
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