I've had this question about padmount transformer arc flash protection for awhile and I haven't had anyone able to answer the question. Here it is....
Typically anytime you are working on the secondary side of a transformer, and more specifically for my question a padmount transformer, there is a large amount of incident energy available and therefore the arc flash boundary is fairly large. If you are tasked with verifying the absence of voltage at a padmount transformer with a 480v secondary you will have to open the door to the secondary which exposes you to the exposed parts of the secondary terminations.
NFPA 70E 120.2 (A) says "Electrical conductors and circuit parts shall not be considered to be in an electrically safe work condition until all of the requirements of Article 120 have been met."
NFPA 70E Table 130.5 (C) Estimate of Likelihood of Occurrence of Arc Flash Incident
- This table list the likelihood of an occurrence of an arc flash as "yes" for two applicable scenarios when working on a padmount transformer:
1. Opening hinged doors or covers to or removal of bolted covers (to expose bare, energized electrical conductors and circuit parts).
2. Application of temporary protective grounding equipment, after voltage test.
Depending on the transformer's incident energy a 40 cal, 65 cal, or even greater PPE would not be sufficient.
Some would say go downstream of this transformer and check on the load side of an overcurrent protection device and then return to the transformer to install the personal protective grounds. Even then you still can't be sure that the conductors are de-energized.
Ultimately the question is how can you work safely on the secondary side of a transformer to verify the absence of voltage when the arc flash boundary could possibly be 10'+?
Any thoughts/insights and experience on this would be appreciated. Thanks.
Follow Us
