Connection of lightening protection

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STAR87

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IN one of our projects i face problem now about lightening protection
this project is a building its height 32m and its area is 3500m2
the top of this building there is a canopy( decoration shape of aluminum)
we now in stage of finishing and its the time to make the lightening protection
i am confused about the connection between the air terminal rods
off course the connection will be a bare copper cable according the shop drawing
this bare cable will pass throw this canopy which its made from aluminum
my question is there any problem if this bare copper cable pass throw this canopy????????
some might that its forbidden to pass bare copper cable throgh any steel or aluminum and others said that its nornmal and when the lightening will occure current will pass throw the easiest way
i am confused and want definite answer
 
G

G._S._Ohm

Senior Member
Location
DC area
STAR87 said:
so it must avoid passing in steel or aluminum ????????????/
Click to expand...
Sounds like yes

"Each lightning rod should have two paths to the ground by way of the lightning cabling. These paths should be downward, or horizontal in the case of using radials. The cables should be straight, without any bends that create a "U" or "V" pocket, which could cause unintended discharge of lightning between the two points that are bent. The cables should not be bent around corners or located near air ducts or metal venting systems.

Read more: Proper Routing of Lightning Cabling | eHow.com http://www.ehow.com/info_7850243_proper-routing-lightning-cabling.html#ixzz1EAPyJwzV"

but I don't know how credible this info is.

With 30 kA passing down the cable, the cable voltage with respect to ground may be quite high for the duration of the strike. Also the inductance of the cable is important.

Answering this may take quite a few Web searches.
 
Dennis Alwon

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I am no lightning expert at all but my guess is that one would sleeve the conductor through areas where you pierce metal.

As stated you only want one path to ground. Lightning is one thing that has a mind of it's own and trying to predict it's path is a tough one. I would try and eliminate all possibilities that you can.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Some lighting protection systems use the steel columns as the down conductors, so I don't see an issue with the lightning current passing through the steel or aluminum.
You will need to bond the aluminum and steel to the lightning protection conductors to avoid "side flashes".
There will be an issue with the corrosion if the aluminum and copper are actually touching each other. Some times aluminum lighting protection conductors are used to prevent this problem.
 
Z

ZoneOfProtection

Member
Aluminum materials should be used on aluminum surfaces. The change to copper at the roofline can be made with an approved bimetallic connector. A minimum of two paths to ground is required by all standards for lightning protection. The total number of grounds required is based on the protected footprint of the building with an average 100' spacing for cable downleads and 60' spacing if the steel columns are used instead of cable downleads.
 
B

bphgravity

Senior Member
Location
Florida
It's important to first know what regulatory body / standard you would be designing the system under. Based on your description, this is not a US system (UL96 / NFPA 780) but more likely IEC or some other international standard for LPS design.

Based on your question, it is advisable that you consult a true LPS design engineer or certified installer that can best analyize the situation and circumstance of the installation. There are simply too many variables and so much more information needed to make a suitable response.
 
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