Hello All- I have an NFPA 780 bonding question. We have a 1" sched 40 pvc conduit routed directly from the roof of a 50' building to a ground rod near the foundation for a down conductor. The conduit is routed within the structural concrete wall and is continuous. The down conductor does not come into contact with the wall. Is the down conductor still required to be bonded at the top and bottom of the wall to the rebar (ie. NFPA 780 - 4.9.13 and/or 4.15.3)? What if the conduit were attached to the exterior of the wall instead of the interior? Any info would be great!
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Lightning Protection Down Conductor Bonding and PVC
- Thread starter breezinuw
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bphgravity
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- Florida
Maybe yes, maybe no. Bonding of the structural reinforcment within the wall is not necessary if the bonding-distance formula calculation indicates the bonding is uncessary. Otherwise, the bonding should be performed or ensured. (See 4.21 - NFPA 780 AND C.2.2 in Annex C)
The installation of down conductors in nonmetallic raceways & enclosures does NOT eliminate the various bonding requirements identified in the NFPA 780...
The installation of down conductors in nonmetallic raceways & enclosures does NOT eliminate the various bonding requirements identified in the NFPA 780...
I think NFPA 4.9.13 doesn't give you any wiggle room. You have to bond it at the top and bottom. Even if you could use the side flash calculations, the result would surely be that you were within the sideflash bonding requirements. And as was already stated, you get no credit for insulating properties of the PVC. NFPA only lets you pretend like it's air or concrete (see NFPA 4.21.2.4 equation.)
bphgravity
Senior Member
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- Florida
The section references "reinforced concrete columns or structural steel columns". Billyzee appears to be referencing a "wall".
You certainly can't "overbond" a LPS, but sometimes bonding is unpractical and truly unnecessary.
The hardest thing about answering questions on a web forum is the details. There are too many "what-if's & what-about's", especially when it comes to the design of an LPS.
You certainly can't "overbond" a LPS, but sometimes bonding is unpractical and truly unnecessary.
The hardest thing about answering questions on a web forum is the details. There are too many "what-if's & what-about's", especially when it comes to the design of an LPS.
corlickmark
New member
- Location
- United States
Hello All- I have an NFPA 780 bonding question. We have a 1" sched 40 pvc conduit routed directly from the roof of a 50' building to a ground rod near the foundation for a down conductor. The conduit is routed within the structural concrete wall and is continuous. The down conductor does not come into contact with the wall. Is the down conductor still required to be bonded at the top and bottom of the wall to the rebar (ie. NFPA 780 - 4.9.13 and/or 4.15.3)? What if the conduit were attached to the exterior of the wall instead of the interior? Any info would be great!
well, if you bond the down conductor thesystem will be balanced. as the conduit is attahced the interior wall i don't think it will be a important matter for lighting protection at all. my question is- " is it the only highest building of that area?" if it is then you should attached the conduit to the interior wall as the chance of inducting voltage will be reduced.
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