Grounding metal roof with PV system EGC?

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
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Consulting Electrical Engineer - Photovoltaic Systems
pv_n00b said:
I found a couple of photos of one way to ground the roof panels. If you don't mind drilling some holes. My guess is that the same kind of thing could be done under the peak cap. This does look pretty nice though, it won't allow water into the roof, and it has minimal obstruction for snow, leaves, or other matter from getting off the roof.

View attachment 20455
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Whether it seems as though it won't cause a leak and whether it will void the roof warranty are two different and virtually unrelated issues.
 
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pv_n00b

Senior Member
Location
CA, USA
I've been taking a closer look at 250.110 to see what it actually applies to. Here's the wording from the 2017 NEC.

Exposed, normally non–current carrying metal parts of fixed equipment supplied by or enclosing conductors or components that are likely to become energized shall be connected to an equipment grounding conductor under any of the following conditions:

Let's break this down.


  1. Exposed, normally non–current carrying metal parts
  2. metal parts of fixed equipment supplied by or enclosing conductors or components
  3. metal parts ... that are likely to become energized

To be required to be grounded all three of these would need to be true for a metal part. Number 1 would apply to the metal roof pans. Number 3 might, if a conductor was damaged and fell on the pan then it would energize it. These seem to be the two items that most people focus on but number 2 would not seem to apply. The roof pans are not supplied by or enclosing conductors or components. Number two is intended to restrict the application of equipment grounding to electrical equipment that houses current carrying conductors or houses a load supplied by conductors. This is intended to exclude all the random metal in an area that just happens to be next to some conductors but not part of the electrical system.

This is specifically overridden in some code sections, such as the requirement that fencing around high voltage electrical equipment is grounded but that is a specific inclusion that is called out. I think this provides further indication that just being metal and adjacent to an electrical system is not reason enough to believe the metal has to be grounded.

What do you think?
 
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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
pv_n00b said:
I've been taking a closer look at 250.110 to see what it actually applies to. Here's the wording from the 2017 NEC.

...

What do you think?
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I think you are right that this section does not require the roof to be bonded.

What about 250.104(C)? I think it does not require a metal roof to be bonded if it is not "interconnected to form a metal building frame". I'd say that if the metal roof is attached to metal building framing, the framing should be bonded/grounded. But this whole discussion is over a non-issue in that case!:lol: But if the metal roof is attached to wood framing ... then I don't see a code section that requires it to be bonded.

FWIW, this thread was never about a code requirement; the OP was about best practice. So far I've not been forced by any AHJ to bond a metal roof because I was installing solar. So fingers crossed I don't have to remember these code citations anyway...
 
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SolarAlternativesDesign

Senior Member
Location
Soulsbyville, California, USA
William L said:
I see that 2017 690.43 lists the specific metal parts and metal roofing is not included and the phrase "likely to become energized" was removed.
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However 2017 250.4(A)(4) still states "normally non-current-carrying electrically conductive materials that are likely to become energized shall be connected... in a manner that establishes an effective ground-fault current path."
 
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pv_n00b

Senior Member
Location
CA, USA
jaggedben said:
I think you are right that this section does not require the roof to be bonded.

What about 250.104(C)? I think it does not require a metal roof to be bonded if it is not "interconnected to form a metal building frame". I'd say that if the metal roof is attached to metal building framing, the framing should be bonded/grounded. But this whole discussion is over a non-issue in that case!:lol: But if the metal roof is attached to wood framing ... then I don't see a code section that requires it to be bonded.

FWIW, this thread was never about a code requirement; the OP was about best practice. So far I've not been forced by any AHJ to bond a metal roof because I was installing solar. So fingers crossed I don't have to remember these code citations anyway...
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Kind of, the OP brought equipment grounding conductors and ground rods into the question which makes it code related. They also asked what was acceptable as well as best practice, and determining acceptability is part of the code.

The code does not define the term "structural steel" but my take it that if it is not a structural component then it can't be structural steel. Cladding, windows, doors, and roofing materials are not structural since the structure will stand without them. Beams and other load bearing members are. Steel I-beam, that should be bonded in.

To take this out of a code context and just look at it as a best practice, it is possible for metal roof pans to be energized by a PV conductor falling from the array. That's not much of a stretch. That being the case we should want to ground the pans. Can we add the pans to the EGC system? Not easily, there are no products that are designed to do this without modifying the roof. The roofing manufacturers won't allow physical modifications. So we are kind of stuck.

SolarAlternativesDesign said:
However 2017 250.4(A)(4) still states "normally non-current-carrying electrically conductive materials that are likely to become energized shall be connected... in a manner that establishes an effective ground-fault current path."
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NEC 250.4 lists very general requirements, the following sections provide the more specific prescriptive requirements to comply with 250.4. Read the text right under 250.4.
The following general requirements identify what grounding​
and bonding of electrical systems are required to accomplish.​
The prescriptive methods contained in Article 250 shall be​
followed to comply with the performance requirements of this​
section.

​
The later sections in 250 add more definition to the general requirements.
 
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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
pv_n00b said:
For a commercial roof, any penetrations usually have to be done by, or at least approved by, the roofing company behind the warranty for the warranty to remain in effect. I'm not sure how much that applies to residential roofs.
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It works the same, except that in my experience a homeowner is less likely to care, or to know what the warranty is, or who is responsible for it.
 
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