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Grounding Aluminum Siding


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The NEC references this only once that I know of in ART. 250.116 Nonelectric Equipment. It doesn't really get into the subject in the article itself, but it does reference a FPN article that basically says that siding is not electrical equipment so it is outside the scope of the NEC. But the FPN says that by bonding and grounding the siding, it will provide additional safety. My references are the 2002 and the 2005 NEC Handbook. Hope that answers the question.

T.

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Originally posted by inspectort

The NEC references this only once that I know of in ART. 250.116 Nonelectric Equipment. It doesn't really get into the subject in the article itself, but it does reference a FPN article that basically says that siding is not electrical equipment so it is outside the scope of the NEC. But the FPN says that by bonding and grounding the siding, it will provide additional safety. My references are the 2002 and the 2005 NEC Handbook. Hope that answers the question.

T.

If there were a pool or spa nearby (within 5 feet) then the siding would have to be bonded per article 680.

I wonder, though. If someone did want to ground or bond aluminum siding in an effective manner, how he would go about doing it. There are hundreds of separate pieces on a house and while they're snapped together that isn't the same thing as a good electrical connection. It seems to me that, if you wanted to effectively ground it, you'd have to run a jumper to each piece.

- Jim Katen

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Originally posted by Jim Katen

I wonder, though. If someone did want to ground or bond aluminum siding in an effective manner, how he would go about doing it. There are hundreds of separate pieces on a house and while they're snapped together that isn't the same thing as a good electrical connection.

Gotta agree with that. Think of all of the little, short, odd-shaped pieces that you would have to account for, the trim, etc. The only practical potential solution that comes to mind would be some kind of bonding clips to go between pieces at installation, then ground (or "earth", Jim loves that term) in a few different places for insurance. It could be reasonably effective if it were done right (and therein lies the rub of course).

Brian G.

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Originally posted by Brian G.

. . . Think of all of the little, short, odd-shaped pieces that you would have to account for, the trim, etc. The only practical potential solution that comes to mind would be some kind of bonding clips to go between pieces at installation, then ground (or "earth", Jim loves that term) in a few different places for insurance. It could be reasonably effective if it were done right (and therein lies the rub of course).

Brian G.

Actually, in the case of a spa or pool, you would not want to connect the metal siding to the earth. If you did that and there were a lightning strike in the vicinity, you could get a deadly voltage gradient between the siding and the pool or other nearby metal parts. Every piece of metal near the pool or spa should be connected to every other piece of metal and not independently connected to the earth.

- Jim Katen, Oregon

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Most of the homes I see have a piece of coiled aluminum wire attached to the outside silcock and the siding. I have also seen a wire attached to a ground rod however, the majority have the 1st method. I always thought that it was due to electrical items attached to the home such as porch lights, outside power outlets and the like and the possibility that these could energize the siding and present a shock hazard if the siding was not grounded in some fashion. No?

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Originally posted by Terence McCann

Most of the homes I see have a piece of coiled aluminum wire attached to the outside silcock and the siding. I have also seen a wire attached to a ground rod however, the majority have the 1st method. I always thought that it was due to electrical items attached to the home such as porch lights, outside power outlets and the like and the possibility that these could energize the siding and present a shock hazard if the siding was not grounded in some fashion. No?

Well, sure. One of the reasons to bond all this stuff is to clear faults. To do that effectively, you've got to bond to the electrical system. If you were to connect the aluminum siding to the earth, it might or might not clear a fault from a porch light depending on the resistance of the earth connection. If, on the other hand, you were to connect the siding to the electrical service's grounding system, the fault would clear with certainty. (Well, depending on how well each piece of aluminum were connected to each other piece as we discussed before.)

However, I was trying to describe another reason for the bonding that isn't so obvious and has to do with lightning. When lightning strikes the earth, the voltage in the earth 20 feet away from the strike is higher than the voltage 23 feet away from the strike. It could be a *lot* higher. Imagine two metal objects buried in the ground three feet apart. If you were touching both of them when the lightning struck, you'd become part of the path that the voltage followed. ZZZZZap! If, however, there were a wire connecting the two objects, way more electricity would flow through the wire than flow through you. If it were a nice big wire with good connections, you might not feel anything.

Make sense?

- Jim Katen, Oregon

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Originally posted by Jim Katen

Actually, in the case of a spa or pool, you would not want to connect the metal siding to the earth. If you did that and there were a lightning strike in the vicinity, you could get a deadly voltage gradient between the siding and the pool or other nearby metal parts. Every piece of metal near the pool or spa should be connected to every other piece of metal and not independently connected to the earth.

Ah-so. I wasn't thinking of a pool & spa application, just the typical house with aluminum siding, but I agree. But come to think of it, in the typical metal siding situation you would probably still want to bond it rather than ground it though, right?

Actually I just wanted to throw "earthing" in there for your benefit. [:-dev3][:D][:-dev3]

Brian G.

Licensed, Bonded, Insured, and Earthed [;)]

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I usually see (in Boston area):

-AL siding w/o any bonding.

-AL siding with 'ground rods' not 'bonded' to the equipment ground system/electrical system. (Dumb)

-Bonding jumpers at under-side of siding at the corners (to 'jump' the corner pieces). This last one is probably the only 'reasonable' one but of course, there are many potential breaks in the bond.

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Originally posted by Jim Katen

However, I was trying to describe another reason for the bonding that isn't so obvious and has to do with lightning. When lightning strikes the earth, the voltage in the earth 20 feet away from the strike is higher than the voltage 23 feet away from the strike. It could be a *lot* higher. Imagine two metal objects buried in the ground three feet apart. If you were touching both of them when the lightning struck, you'd become part of the path that the voltage followed. ZZZZZap! If, however, there were a wire connecting the two objects, way more electricity would flow through the wire than flow through you. If it were a nice big wire with good connections, you might not feel anything.

Make sense?

- Jim Katen, Oregon

Sure, that makes sense. There is a potential difference between 20 & 23 feet. Also when there is a nice big wire there it becomes the path of least resistance - lower ohms than your body.

Back to the topic of stray voltage from an attached electrical device for a moment though. If the aluminum siding had an earth ground, such as a ground rod, and not attached to a cold water pipe that might be directly used for a electrical ground, would it still trip a breaker in a short condition? After all the cold water pipe is nothing more than a connection to the earth. Also, wouldn't it help more in a lighting strike or would it be more of a hindrance. Example: Lighting hits 50 feet away and you happen to be touching the siding.

What are your thoughts here Jim.

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Originally posted by Jim Katen

Originally posted by Terence McCann. . . Back to the topic of stray voltage from an attached electrical device for a moment though. If the aluminum siding had an earth ground, such as a ground rod, and not attached to a cold water pipe that might be directly used for a electrical ground, would it still trip a breaker in a short condition? After all the cold water pipe is nothing more than a connection to the earth.

It might or it might not. That would depend on the resistance of the ground rod and the earth in that area. (The cold water pipe doesn't trip breakers because its in contact with the ground.) In order to trip a breaker, you've got to complete a circuit. So if the hot wire on a porch light were to slip and touch the aluminum siding, the electricity would have to flow through the siding, through the wire, through the ground rod, through the earth to another grounding electrode (water pipe, ground rod, foundation steel, whatever) and then through a wire to the service neutral terminal bar (or up the pole to the street transformer) (or, by chance, into your neighbor's service panel -- that's a discussion for another day). This path might be so fraught with resistance, that the current would just trickle and not have enough oomph to trip the breaker.

Also, wouldn't it help more in a lighting strike or would it be more of a hindrance. Example: Lighting hits 50 feet away and you happen to be touching the siding.

What are your thoughts here Jim.

I'm on shakey ground here because I don't know anything about lightning protection systems. But it seems to me that grounding the aluminum siding to the earth would tend to attract lightning strikes. Also, if lightning struck 50 feet away and you were standing on the ground, and you touched some siding that was grounded by a ground rod that was 10 or 20 or 30 feet away from you, there'd be a nasty voltage gradient between you and the siding.

Cramer probably knows all about that stuff, he lives in lightning country.

- Jim Katen, Oregon

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Originally posted by Terence McCann

Back to the topic of stray voltage from an attached electrical device for a moment though. If the aluminum siding had an earth ground, such as a ground rod, and not attached to a cold water pipe that might be directly used for a electrical ground, would it still trip a breaker in a short condition? After all the cold water pipe is nothing more than a connection to the earth.

No, connecting to the earth will NOT clear a fault, at least not at the voltages we use in a house. Clearing the fault quickly requires about 5 times the amapacity of the breaker. The resistance of the earth is too high. At 120V you would only have about 1 amp returning to the neutral at the transformer through the earth. You are fooling yourself if you think that a ground rod will clear a fault.

The connection to the metal water piping is NOT just a connection to the earth. The metal water pipe is bonded to the service neutral. That connection allows enough current to flow to enable the circuit breaker to trip.

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