Ground Check Wire Color?

[OhioAviator]

Hi All,

We are starting to design a system where the motor control center is feeding power to various motor and other loads at 480Vac. The difference is, we want to include an insulated non-current carrying conductor that will serve as a 'ground-check' conductor. The idea is to land one end of this 'ground-check' conductor on an unused terminal in the MCC bucket and connect the load end of this same conductor to a ground lug in the motor terminal box. The reason for this? Once per year we are required to measure the resistance of the grounding conductor of the motor circuit cable. This 'ground-check' conductor will serve as one-half of the ground/ground-check loop. Knowing the resistance of the ground-check conductor, we can subtract that ground-check conductor resistance from the total resistance to determine the resistance of the ground wire itself.

Since the usual colors for 480V circuit conductors are Brown, Orange, Yellow + Green (ground), what color should this ground-check conductor be?

Thanks!


J.R.

Galatians 2:20

 

[resqcapt19]

Type G power cable with a ground check conductor typically uses yellow for the ground check conductor. For your application, it could be green with yellow stripes, or it could just be green as it will be a smaller size that the actual equipment grounding conductor.

 

[waross]

It is good practice to land the check wire on a terminal at the MCC bucket, but not to ground it.
When the check wire is grounded at the both ends it will share ground fault current with the service grounding conductor.
In the event that the service ground develops high resistance, the check wire will take a disproportionate share of any fault current.
Solid #14 AWG will fuse at around 140 Amps.
That is not very much when considering fault currents.
It is common to connect the check wire to the motor housing.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[OhioAviator]

Thank you, resqcapt119 and waross. I think we will settle on making the ground-check conductor green with a yellow stripe to differentiate it from the actual grounding conductor. We will connect the ground-check conductor to a ground lug inside the motor terminal box and land the mcc end of that same conductor on an unused terminal in the mcc bucket, which will not be connected to ground or anything else, i.e. left floating, as waross suggested.

J.R.

Galatians 2:20