EGC in each conduit?

[mr_rhino]

Greetings. This is my first post to the forum; I've been very impressed by the general level of knowledge and professionalism here compared to other forums. I truly believe that folks here are trying to help others.

I'm in the process of installing several conduits between a motor controller and a pump unit. Looking to verify if either NEC (or individual's) recommendations indicates a need for an Equipment Grounding Conductor in Conduits "A", "B", and "C" (or other changes) under the following conditions:
1. Power to a motor controller is supplied via one branch circuit. All voltages used by the controller (and equipment external to the controller) are derived within the controller.
2. Conduit "A" contains all six motor conductors and the only EGC. The motor is driven by a Wye-Delta starter in the controller. This conduit includes a 3' section of greenfield at the controller end and 3' of non-metallic flex at the pump end, with EMT between. Voltages are between 208VAC and 600VAC. EGC is connected at controller and at motor/pump, and is sized same as the individual motor conductors.
3. Conduit "B" contains several pairs of 18AWG conductors used to operate solenoid valves. All voltages are 120VAC; load on any given pair will not exceed 1.2A. Conduit setup is similar to Conduit "A" except smaller. Presently no EGC is proposed to be installed in Conduit "B".
4. Conduit "C" contains a multiconductor cable (24AWG x 8) that carries signals up to 24Vdc at <10mA. Conduit "C" is comprised of FMC (Greenfield) from motor/pump unit to the controller. No additional EGC is installed in Conduit "C".
5. Grounding Bushings are installed inside controller for Conduit "A" and "B".

The configuration is intended to address potential EMC issues. Have I overlooked anything (especially regarding NEC Article 250)? Any recommendations or or comments from the experts? And especially important, why?

Thanks in advance,
Jeff

 

[Smart $]

The only concern I would have is no EGC for the solenoids. You will have 120V at the solenoids. Doesn't matter what the load is, the concern is for safety... and as stated Conduit B setup is similar to Conduit A... so I'm taking that as a soloenoid end being LFNC or device-cable connected, deducing to lack of grounding continuity. Simply stated, if the solenoids provide an EGC terminal or EGC in the cable, use it!

 

[don_resqcapt19]

If the raceway system is all metallic, none of the conduits are required by code to have an EGC installed in the raceway because the raceway itself is an EGC. However, Smart$ brings up a good point about the EGC connection to the solenoids. If you are not using a metallic raceway system that extends to the solenoids, you will have to make provisions for the EGC connection to the solenoid itself. We use LFMC for the solenoid connection and rigid pipe for the raceway and we do not pull a green wire in these conduits. All power conduits get both a green wire and a bonding jumper around any flexible conduits.
Don

 

[petersonra]

3. Conduit "B" contains several pairs of 18AWG conductors used to operate solenoid valves. All voltages are 120VAC; load on any given pair will not exceed 1.2A. Conduit setup is similar to Conduit "A" except smaller. Presently no EGC is proposed to be installed in Conduit "B".
4. Conduit "C" contains a multiconductor cable (24AWG x 8) that carries signals up to 24Vdc at <10mA. Conduit "C" is comprised of FMC (Greenfield) from motor/pump unit to the controller. No additional EGC is installed in Conduit "C".

These sound like they might qualify as limited energy circuits. Is an egc required for such circuits?

5. Grounding Bushings are installed inside controller for Conduit "A" and "B".

The configuration is intended to address potential EMC issues. Have I overlooked anything (especially regarding NEC Article 250)? Any recommendations or or comments from the experts? And especially important, why?

What EMC issues?

 

[charlie b]

What EMC issues?

"Electro Magnetic Compatibility." It's a more modern term for what use to be called "Radio Frequency Interference," or "RFI."

I guess the concern would be that a rapid change in, let us say, the power circuits (motor turned on or off) might, through transformer interference, cause one of the control circuits to actuate.

 

[Smart $]

These sound like they might qualify as limited energy circuits. Is an egc required for such circuits?

120V energy-limited circuits? Perhaps, but I don't think so. What is the circuit potential current have to be limited to for 120VAC... something like 1A? ...and the OP stated 1.2A.

Regardless, I am inclined to run an egc as long as there is a terminal for such at the other end, and in some cases even provide the terminal if it is not already there. Let us not forget that the wiring originates in a control panel which has potentially lethal energy available when energized.

 

[mr_rhino]

Followup from Original Post/ Responses to Q's

Followup from Original Post/ Responses to Q's

What I failed to identify in my original post is:

1.To Smart $: The common 120VAC feed to the multiple valve solenoids (Conduit ?B) is protected via a 2A fuse in the motor controller assembly. No more than 2 solenoids can normally be actuated simultaneously, limiting normal operating current to less than 1.2A.

To petersonra: I wouldn?t consider the valves/solenoids to be a limited-energy circuit, though the signals in Conduit ?C? would likely qualify.

2.To Smart $ and don_resqcapt19: Unfortunately there is no obvious place to connect a ground to the valve solenoids. However, the UL/CSA-approved solenoids themselves are encased in plastic, and all metallic conduits and enclosures that the solenoid leads encounter are grounded via appropriately sized EGCs.

In addition, the hydraulic valves themselves (that the solenoids operate) are electrically connected to the pump/motor assembly via hydraulic pipe. The pump/motor assembly IS directly connected to its own EGC, a 12AWG to 3AWG (depending upon motor HP and line voltage) green conductor that is connected back to the motor controller.

Does it still make sense to run a second EGC (for the solenoids via Conduit ?B?) even though I have no place to terminate the EGC at the valves/solenoids?

3.To petersonra & charlie b: Regarding questions about EMC, maybe I should have identified that my customer is very concerned about its impact on other sensitive equipment nearby. While my proposed conduit and grounding approach may appear somewhat unorthodox, it serves it purpose by:

a.Eliminating potential ground loops ? Providing one and only one path for possible leakage and/or motor/solenoid fault currents back to the controller, which in this configuration is via a dedicated, appropriately-sized green EGC (instead of multiple-conduit paths) eliminates ground loops.

b.Ensuring long-term reliability as an EGC ? Many folks like myself feel more comfortable not having to rely on conduit as an EGC should the conduit connections loosen/corrode over time, or if not installed properly initially by someone other than myself.

c.Providing suitable shielding to contain the electric and magnetic fields caused by large (motor running) currents, and starting/stopping transients. ? using grounded metallic conduit (at the controller-end only) on all but a 3? section (LFNC) near the solenoids and motor helps to contains these fields. If you?ve got a customer concerned about EMC, think twice before installing LFNC for anything other than several feet.

I appreciate the time that everyone has taken to respond, and welcome additional input and rationale.

Thanks-
Jeff

 

[Smart $]

Does it still make sense to run a second EGC (for the solenoids via Conduit “B”) even though I have no place to terminate the EGC at the valves/solenoids?"

No. Sounds like your solenoids are "double insulated".

You appear to have the situation well under control...