Grounding of aluminium plates on building facade

[zlovenac6]

My first post, hello everyone
We have to put several dibond signs (two sheets of aluminum with a solid polyethylene core sandwiched between) with safety at work warnings at our factory.
These quite large signs (~100 sqft) will be mounted on different building facades.
My question is whether we should bond them to our grounding system, and if yes, what is the most suitable method to do it (taking into consideration that we have two different materials Al (dibond) and Cu (ground conductors).

 

[Fred B]

My first post, hello everyone
We have to put several dibond signs (two sheets of aluminum with a solid polyethylene core sandwiched between) with safety at work warnings at our factory.
These quite large signs (~100 sqft) will be mounted on different building facades.
My question is whether we should bond them to our grounding system, and if yes, what is the most suitable method to do it (taking into consideration that we have two different materials Al (dibond) and Cu (ground conductors).

Welcome, a few considerations not addressed by your post when determination to bond or not to bond. First to preface is your location would likely have codes different than that here with the NEC, but principles of why our codes might indicate bonding would apply.
1. What is the building facade constructed from if a concrete or wood structure it would be different from a steel structure. (Steel or metal structure enclosure most likely needs to bonded as well as any other metal attached to structure that has a possibility to become energized). If structure is not likely to become energized or non conductive, bonding might increase risks (NEV) if no other reason to bond signage are present.
2. Is power coming to the sign, as in sign lighting.
3. What is the possibility of incidental contact with energized source, such as other lighting damage energizing surrounding materials.
4. Potential of personnel contacting signage if it were to become energized.
To address your question about bonding to system grounding, if your sign IS or meeting a reason to bond then yes it would likely need to be bonded to the "system" grounding for any incident that may energize the sign (fault current) to clear and breaker trip. Putting a separate ground to earth will do nothing for safety concern of signage becoming energized.

 

[zlovenac6]

Fred, thank you for your explanation. Let me try answer your questions:
0. We are quite a specific facility, so to some degree we also follow NEC.
1.I am talking only about concrete buildings.
2. No power is coming to sign.
3. There are some down conductors, all more than 1 m away. No other installations are close to signs.
4. There is low probability of contact. The aluminium signs will be mounted on different locations, some of which are accessible to people, while other will be out of their reach.

The thing is simply that suddenly we have a substantial surface of buildings covered with conductive sheets, and therefore I am not sure if there is any code requirement or any other concern, which would require bonding of these plates.
Of course all these buildings have lightning rods installed, so I did not recognize a problem that could be introduced with new signs regarding it (isolated plates shouldn't be the preferred path for the lightning).

 

[LarryFine]

I would say that metallic surfaces that are likely to become energized are normally considered bonded by the EGC of the source likely to do the energizing. Since you have no electrical sources, you have no need to bond. The concrete is more than adequate.

 

[mopowr steve]

Maybe your question is better suited for lightning protection codes not NEC. (Can’t remember what the NFPA code number is for lightning protection) if those large metallic surfaces happen to be in some kind of “sphere of influence”