georgestolz said:
Roofs and siding do not require grounding or bonding.
They can be bonded or grounded if desired.
georgestolz said:Well, sorta.
I'm saying there is nothing to energize the siding/roofing, so there is no need to bond it.
250.104(C) requires structural metal to be bonded if likely to become energized. Siding and roofing are generally not structural, they are not supporting the weight of the structure.
What are we envisioning energizing the siding/roofing?
georgestolz said:
Roofs and siding do not require grounding or bonding.
They can be bonded or grounded if desired.
wbalsam1 said:What about "Holiday Lighting" attached to the metal eaves, or a conduit service mast thru the metal roof...? would the egc of the lighting branch circuit and the grounded conductor in the riser satisfy the code's intent to carry the fault currents? and would the code consider these scenarios "likely to be energized" and therefore require additional bonding/grounding?
When lightning strikes a (dry) metal roof, it will leave a burn mark which may
develop into a hole. Also, the area surrounding the contact point will show
"blistering" because of heating effects. On the other hand, when lightning
strikes a body of water or soil, and considering that the medium is mostly
non-uniform, the current will flow in discrete radial channels. This is best
exhibited by a photo of a lightning strike to a golf course that was published
by Professor E.P. Krider in the June 1977 edition of Weatherwise, Vol. 30, No.
3, pp. 111 and the cover.
A sheet metal roof is usually supported by a frame of larger cross section
beams. The current of the stroke terminating on the water above it will tend to
flow radially as in case of strikes to deep water. However, the shallow depth
(a couple of inches) causes the current to flow instead radially along surface
of the metal. This pattern will be distorted by the attraction effect of the
frame beneath it. The metallic filaments being heated are subject to the
cooling effect of the water on the upper surface and no such cooling on the
lower surface. The difference in this "adiabatic expansion" between the top and
bottom surfaces can cause the metall to be ripped along the channels in which
the current is concentrated. This would then explain what you observed.
Abdul M. Mousa, Ph.D., P. Eng., Fellow IEEE
wbalsam1 said:What about "Holiday Lighting" attached to the metal eaves, or a conduit service mast thru the metal roof...? would the egc of the lighting branch circuit and the grounded conductor in the riser satisfy the code's intent to carry the fault currents? and would the code consider these scenarios "likely to be energized" and therefore require additional bonding/grounding?
RUWIREDRITE said:Hi all,
I would love seeing a change in the new nec code to bond any metal structures in residential that exceed a certain size...
bphgravity said:Ryan Jackson sent in a nice proposal for just this and it was soundly rejected by CMP 5. See proposal 5-228 of the ROP.
Florida has amended the Florida Building code to require bonding of metal studs in any building. See E3303 of the FRC, and 2704 of the FBC.