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Help NEC Article 500 & ANSI/ISA 12.12

Help NEC Article 500 & ANSI/ISA 12.12

Help NEC Article 500 & ANSI/ISA 12.12

I am looking for fuse and fuse terminal block suitible to be mounted in general enclosure installed in class I Div II ( certified ) location. The  equiment to be used in the curcuit are intruments such as low power soleniod valve, pressure switch and pressure transmitter connected to a PLC I/O module certified for class I DIV II location. The circuit loop power is 24-30 VDC. My company is US-based oil & gas operator. I  would be appreciated if anyone could help me on the following matters;
1. Which NEC 500 subcode which my application application relates to, NEC 501-3 or NEC-501-6?
2. If my application falls within NEC 501-3, does the fuse and fuse teminal block type need to be rated NEC 501-6.(b)(3)  or just general type? According to  ANSI/ISA 12.12 4.4, it states that " Fuses may be housed in general enclusures only when used for overcurrent protection of circuit which are not subject to overloading in normal use "
Fuse used in circuits which are subject to overloading in normal use must be the type suitible for use in DIV 2 locations or housed in an enclosure rated for DIV 1 location.  
Note : This subsection precludes a fuse housed in general purpose from being used in motor circuit where a possibility of a stalled mortor opening the fuse exists, or where there is a possibility of an overload not caused by a fault in the circuit ".
   In the first paragraph of ANSI/ISA does not state that what type of fuse which may be install in the general encloure. But specified in the NOTE that a fuse must be rated NEC 501-6(b)(3) if the circuit is for mortor control.
   My interpretation is  the circuit above falls witin NEC 501-3 and general fuse can be house in a general enclusure. provided that there is a switch ( rated for class I Div, I )  for removing power form the equipment and fuse. But my colleague disagree with my interpretation. He interprets that the application above folls within NEC 501-6(b)(6).
3. What is the differnt criteria or intenton of NEC 501-3 and NEC 501-6?


RE: Help NEC Article 500 & ANSI/ISA 12.12

Are you manufacturing equipment, purchasing equipment or modifing equipment it in the field?

RE: Help NEC Article 500 & ANSI/ISA 12.12

I am designing a junction box for the electrical instrument like pressure, level transmitter and low power in consumpion solenoid valve. All of the instrument above suppied with 24 VDC and certified for class I Div. II.  The instrument devices are connected to PLC I/O modules witch are approved  by CSAH  CSA C22.2 No. 213-M1987 and ULH  UL 1604. My concern is that I would like to select the fuse correctly on my design.  I would be appreciated if you could advise me on the following matter.

RE: Help NEC Article 500 & ANSI/ISA 12.12

Check with Bussmann. Try FNQ-2 Rejection Style 500 vac Rated Time Delay Current Limiting. Use an R Type holder.
Email at hcraig@jwphyre.com

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