NEC 501.30 (B) Exception

[bozosboss]

The referenced article states that the bonding jumper around LFMC may be deleted if :

The LFMC is 6' or less in length with approved grounding fittings

The O.C. protection is 10A or less

The load is not a "power utilization load"

I cannot find the definition of "power utilization load" in the NEC. It appears to me that if the load device uses current at some voltage (any voltage) it becomes a "power utilization load". Is that a correct interpretation?

In the refinery in which I work, the typical method of wiring to solenoids (120VAC), process transmitters (24VDC), switches (24VDC or 120VAC) is with RMC to about 3' from the field device. LFMC is then used to a conduit seal, union and the field device. No bonding jumper around the LFMC and no internal ground wire in the RMC. Is this correct?

 

[rbalex]

Solenoids and transmitters are "power utilization" equipment; switches are not. Essentially, switches are not a ?load? to the power source.

 

[bozosboss]

Exception

Exception

So even a process transmitter (4 - 20mA device at 24VDC) that utilizes LFMC must have the bonding jumper and cannot rely on the LFMC as a ground return path?

 

[rbalex]

That's correct. The 4-20ma is simply the output of the transmitter; however, the transmitter itself is a load to the 24VDC system.

 

[bozosboss]

Thanks for the information. What concerns me is that for the past 20 years or so I have worked in a number of Gulf Coast refineries, many operated by major oil companies with their own R&D, Corporate Engineering, etc. Most of these folks have a set of standard I/E details that they issue to contractors working in their plants. I have yet to see a standard instrument wiring detail for a process transmitter or solenoid which indicates the required bonding jumper across the LFMC.
I have woked on a number of these devices over the years and rarely see an internal equipment ground. Grounding of the process instrument is solely dependant on the LFMC.
Could this be that these corporations see themselves as being the "authority having jurisdiction" and elect not to utilize bonding jumpers across LFMC used with process instrumentation?