Topic

-1 vote
Do you know if we can use sheet metal screws for bonding?

I am installing a solar system and I want to know if you know if we can use sheet metal screws for bonding?  Do the bonding screws need to be a certain length?

Comments

Martha on June 29, 2012 - 9:38am
mg,
Your local jurisdiction should be contacted to see what they accept. To use any kind of screw, the NEC requires a certain amount of metal to metal contact:

250.8 Connection of Grounding and Bonding
Equipment.
(A) Permitted Methods. .......
(5) Machine screw-type fasteners that engage not less than
two threads or are secured with a nut

A self-drilling screw can probably not engage two of its coarse threads in the thin aluminum module. 

Here are three generally accepted guidelines. Assume all material is solid copper for the conductor, stainless steel for any fastener or washer, and tin plated copper for any lug. If these three rules are followed, a long lasting and effective bonding path can be relied on in most climates.

  • If a self tapping screw is used, it must be fine threaded and matched to its pilot hole.
  • A stainless star washer and / or fender washer should be used to isolate the conductor from the aluminum module frame. NO copper touching aluminum!
  • The conductor needs to be continuous and uninterrupted. Taking it off of one module should not disconnect another - a direct burial lay in lug facilitates this as the equipment grounding (bonding) conductor (ECG) can be lifted out.

Here is further info on array bonding: http://www.civicsolar.com/node/13256
And for lightning protection through good bonding: http://www.civicsolar.com/node/12342