Let's talk voltage rise during a transient - I would love some insight from the pros!

Scenario - Metal clad 13.8KV switchgear mounted on a concrete floor that has a properly installed 4/0 ground grid within the concrete floor. Grounds come up from the grid to the grounding bar in the switchgear. For argument's sake, let's say that the gear has 18 kA available fault current on the line side of the gear.

The gear is part of a local industrial plant distribution system, and is in an outage - this gear is opened, verified, LOTO, and grounded per 1910.269 section M and N.

In this condition, if somehow the gear was either backfed while grounded, or the line side switch intentionally switched back on (insert disgruntled employee here), how much voltage would be present from the concrete pad to a phase? Would there be significant voltage rise during the fault (which would be extremely short duration obviously with a fully-shorted and grounded system). Would this potential rise be if a person was touching a phase insulator for replacement at the exact time that power was applied to the system?

Consider this ala 1910.269 Section (n) that requires T&D grounding and creation of an equalized potential zone (1910.269(n)(3) as part of the grounding protocol.

By the way, this question came up at a data center duringa training session. The location has indoor distribution switchgear ranging from 13.8 kv to 35 kv.

Regarding the application of power to the system while a person is touching a phase insulator, it is essential to follow proper safety protocols to prevent electrical hazards. The equalized potential zone (EPZ) requirement you mentioned, as per 1910.269 Section (n)(3), aims to create an area of equipotentiality during grounding operations. This zone helps minimize potential differences and the associated risks of electric shock during maintenance or equipment replacement. Adhering to these protocols helps ensure the safety of personnel working on the system.

Exactly - hence the question. What IF the site was LOTO and grounded and the EPZ step was missed? With the worker standing on concrete/asphalt, during that extremely short transient, would the worker get shocked?

I’m thinking the maximum voltage rise is dependent on the size of personal grounds and max available bolted fault current when a ground grid is present under the concrete or asphalt.

Is it ballpark 30 volts maximum, or 100 volts maximum across the worker?