Zeusmatt67
Member
- Location
- Arizona
- Occupation
- Electrical contractor
I’ve been following Mike Holt for a long time but just recently signed up for the forums so this is my first post. I’m a 30 year electrical contractor and I’m fairly well versed in code but I can’t find a definitive answer to the scenario I’m about to describe. This is also the same scenario I’m now running into non a second job.
I just recently finished a government building for a medical clinic where one of the last requirements was to measure ground resistances to all surfaces within a 72 inch radius of the main service. During the course of construction the general contractor installed the building exterior finish before the main service was installed. The exterior finish consisted of metal lap siding. The siding is rectangular sheets of metal with folded edges that hold it 1/4 or more off the building framing or moisture barrier, the sheets lap over each other and cover the entire structure all the way up to and over the roof parapet walls. The siding is also in contact with the metal staircase running from the first floor to the roof.
I had asked the general contractor to have the metal siding behind the switchgear left out and to either stucco or use wood siding where my gear was going to be attached to the wall. The general contractor or refused to comply and told me to just bolt my gear to the siding which I did. The inspectors for the facility were “in house” federally hired inspectors and did not see a problem with the installation although they did say they were only looking at items the feeeral agency was concerned with.
There is no way to effectively ground metal lap siding covering the entire surface of the building and my concern is that any kind of atmospheric event like lightning or any kind of fault in my equipment could be extended to the metal siding or staircase. Anyone touching any of the surface of the building could suffer injury or worse in the event of a catastrophic fault. I took my meter to the siding and its surface is conductive over the entire structure of the building.
Does my bolting the main switch cabinet to the siding count as an effective ground fault path even though there is no mechanical connection between siding plates?
Sone information I should have given at the start:
Building service is an 800 amp 277/480 volt service with a step down transformer sitting next to the stand up section. The stand up section is bolted to the wood wall and nipples from the gear extend into the electrical room panels directly behind the gear itself. There is a 277/480 to 120/208 150 kva transformer sitting next to the outside gear that has conduit extending through the metal siding to panels in the electrical room behind both the gear and the transformer.
This installation is in the bottom of the Grand Canyon on a Native American reservation and was inspected by independent inspectors hired by the customer.
No one seemed to care about the grounding issues I was raising except for me.
I’m just trying to determine what the best solution for the issue would have been. The job is done and gone so this isn’t about fixing something it’s about what to do the next time I encounter this situation as metal siding seems to be the way some customers are choosing to go currently. Can anyone offer a specific code that addresses this issue or point me in the right direction? I can’t find anything specifically regarding this in 250 at all.
I just recently finished a government building for a medical clinic where one of the last requirements was to measure ground resistances to all surfaces within a 72 inch radius of the main service. During the course of construction the general contractor installed the building exterior finish before the main service was installed. The exterior finish consisted of metal lap siding. The siding is rectangular sheets of metal with folded edges that hold it 1/4 or more off the building framing or moisture barrier, the sheets lap over each other and cover the entire structure all the way up to and over the roof parapet walls. The siding is also in contact with the metal staircase running from the first floor to the roof.
I had asked the general contractor to have the metal siding behind the switchgear left out and to either stucco or use wood siding where my gear was going to be attached to the wall. The general contractor or refused to comply and told me to just bolt my gear to the siding which I did. The inspectors for the facility were “in house” federally hired inspectors and did not see a problem with the installation although they did say they were only looking at items the feeeral agency was concerned with.
There is no way to effectively ground metal lap siding covering the entire surface of the building and my concern is that any kind of atmospheric event like lightning or any kind of fault in my equipment could be extended to the metal siding or staircase. Anyone touching any of the surface of the building could suffer injury or worse in the event of a catastrophic fault. I took my meter to the siding and its surface is conductive over the entire structure of the building.
Does my bolting the main switch cabinet to the siding count as an effective ground fault path even though there is no mechanical connection between siding plates?
Sone information I should have given at the start:
Building service is an 800 amp 277/480 volt service with a step down transformer sitting next to the stand up section. The stand up section is bolted to the wood wall and nipples from the gear extend into the electrical room panels directly behind the gear itself. There is a 277/480 to 120/208 150 kva transformer sitting next to the outside gear that has conduit extending through the metal siding to panels in the electrical room behind both the gear and the transformer.
This installation is in the bottom of the Grand Canyon on a Native American reservation and was inspected by independent inspectors hired by the customer.
No one seemed to care about the grounding issues I was raising except for me.
I’m just trying to determine what the best solution for the issue would have been. The job is done and gone so this isn’t about fixing something it’s about what to do the next time I encounter this situation as metal siding seems to be the way some customers are choosing to go currently. Can anyone offer a specific code that addresses this issue or point me in the right direction? I can’t find anything specifically regarding this in 250 at all.
