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External Mount Grounding Requirements
When the Main Electronics Module is mounted outside the premises, the National Electrical
Code (NEC), the Rural Electric Association (REA) and state/local codes require that the
MEM be properly grounded. In this application, a proper ground is one that bonds the
module to the buildings primary earth electrode. Extreme care must be taken when attaching
the ground connectors to the utility (earth) ground rod. If the ground is interrupted or
disturbed in any way, an unsafe condition will exist.
Internal Mount Grounding Requirements
The primary method of grounding in this application will be to bond the mounting bracket
to the homes electrical ground circuit. It is at this point that the power utility is also bonded.
The bonding conductor used must be a # 14 AWG copper or equivalent.
Grounding Method
NEC and Grounding
A very important aspect of ONT installation is to comply with the National Electric Code
(NEC), as well as all state and local codes. Article 800 of the NEC requires the ONT to be
grounded according to Article 250.56 of the code. To be properly grounded, the ONT must
be directly bonded to the building’s AC utilities earth ground electrode using a #6 AWG
copper conductor. The earth electrode can be a metallic cold water pipe or a copper clad
steel rod that has been driven into the ground to a depth of at least 8 feet. Metallic cold water
pipes that run under ground for a distance of at least 10 feet are considered the best ground
electrodes. The NEC requires that if cold water pipes are used they must be within 5 feet of
the outside wall that the ONT has been mounted on.
In the event that the ONT is installed more than 20 feet from the building AC utility earth
ground electrode, a suitable secondary ground electrode must be provided. The secondary
ground must be bonded to the building’s primary earth electrode. A bonding jumper of #6
AWG copper must be used between the two electrodes.
Grounding Purpose
Providing proper grounding to the ONT has two different perspectives. First of all
grounding provides for the safety of the intended user and maintenance personnel. The
grounding requirements of the NEC do provide a degree of safety in the event that the outer
metallic case of the protected device should become energized by a current carrying
conductor. In this event, the grounded case would cause the over current device to trip
thereby removing the power to the device.
