Remote Earth

[mbrooke]

As I'm reading article 250, the NEC does not seem to show concern about about remote earth remaining accessible to occupants within a building?

 

[ptonsparky]

As I'm reading article 250, the NEC does not seem to show concern about about remote earth remaining accessible to occupants within a building?

?? I know this is a loaded statement or question, so what is the concern?

 

[mbrooke]

?? I know this is a loaded statement or question, so what is the concern?

I want to know the NEC's stance on the matter- curious if you will.

I say this because the IEEE and others seem to indicate that elimination of remote earth within a building provides essential protection against elevated N-E voltages as coming from the utility or NFPA 780 lightning protection.

However, the NEC seems to forgive not bonding of concrete rebar, selection of bonding of earthed objects and disconnection of earthed objects for mitigation of objectionable current.

At the same time, from a fault clearing and touch voltage perspective, remote earth vs main disconnect ground bar reference makes little difference in occupant safety as nearly all of the voltage division during a fault takes place on the final branch circuit. So as long as prompt disconnect exists, remote earth is not a hazard.

 

[mbrooke]

From a fault clearing perspective, the user being exposed to remote earth makes little difference, 222 amps clears the breaker in 2 cycles, faster than what 60 or 55 milliamps can do to the human body.

https://imgur.com/00QHekg

In summary the extra 50 ohms pathways to the X0 makes little difference in clearing time, while the slight reduction in voltage is only slight making no difference compared to the fast clearing time of the OCPD.

In a fault clearing sense exposing bulding occupants to remote earth inside a building does not pose an elevated or latent danger.