ICC 500 Interpretation - Grounding fixtures to the Host Building

[steve66]

Can anyone interpret what they mean by this, because I have no idea what they are asking for:

307.2 Electrical grounding of shelters. Exposed metal interior surfaces of shelters which are electrically grounded and electrical fixtures wihthin shelters shall be grounded only to the host building external grounding system.

Here is their definition of a host building;

HOST BUILDING. A building which is not designed or constructed as a storm shelter that totally or partially encloses a storm shelter.

I don't know why they say "only"? Like we are supposed to intentionally isolate all the lights, outlets, and conduits from the storm shelter metal structure?

Also not sure how this would be any different than standard branch circuit wiring with a ground or in metal conduit?

 

[LarryFine]

Can anyone interpret what they mean by this, because I have no idea what they are asking for:

307.2 Electrical grounding of shelters. Exposed metal interior surfaces of shelters which are electrically grounded and electrical fixtures wihthin shelters shall be grounded only to the host building external grounding system.

It sounds to me like they don't want the shelter to have any separate electrodes.

 

[steve66]

It sounds to me like they don't want the shelter to have any separate electrodes.

I could buy that, but I still don't understand why.

The host building could get sucked away in a tornado, along with Dorothy and Toto, while the shelter remains in place with emergency power and no grounding.

 

[steve66]

Now that I think about it, what if we had a standalone storm shelter that doesn't have a host building?

I'm completely missing the point.

 

[hbiss]

307.2 Electrical grounding of shelters. Exposed metal interior surfaces of shelters which are electrically grounded and electrical fixtures wihthin shelters shall be grounded only to the host building external grounding system.

I don't know why they say "only"? Like we are supposed to intentionally isolate all the lights, outlets, and conduits from the storm shelter metal structure?

That's not what they are saying at all. Sounds like any room or space within a building. You wouldn't build out a space in a building and provide it with separate grounding. Everything gets bonded, including any part of the "substructure" likely to be energized, back to the main structure.

I really don't know why they feel that they have to make this distinction.

-Hal