DM2-Inc
Senior Member
- Location
- Houston, Texas
I'm trying to get a better understanding of BONDING and GROUNDING requirements for instrumentation.
Background on systems:
Questions with regard to NEC 2009:
Background on systems:
- These systems we're inspecting use what I believe to be Class 2 circuits. The voltage is less than 30 volts (26 VDC actually), and the circuits use renewable fuses some upwards of 10 amps, but most are closer to 2 amps.
- The devices are connected to a 75 Amp power supply / battery charger using a 208 VAC. The battery supply is 1600 amps.
- Due to voltage drop issues, the cable to junction boxes in the filed (some + 500 feet of cable), can be as large as 4 AWG.
- In these remote junction boxes, there are a number of devices that connect to an 8 channel I/O module, with no device drawing more than 1 Amp of current at 24 VDC, and the module itself drawing less than 1 amp.
Questions with regard to NEC 2009:
- For the junction boxes in the filed, I'm assuming section 250.102 should have been used to size the equipment bonding jumper, and 250.122 [ref 250.102(D)], Is this correct?
- If the fuse is set to less than 15 Amps, can the bonding jumpers from the door of the junction box, to the box, to the back pan of the junction box be 14 AWG?
- At the source (i.e. same enclosure as the power supply) there are shielded cables from several instruments, which are tied together and than connected to an "Instrument" buss bar. Where in the NEC does it specify how the wires that connects the drains to the buss bar, should be sized?