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#176924 - 04/16/08 08:06 AM Electrode?
JValdes Offline
Member

Registered: 06/03/07
Posts: 308
Loc: South Carolina
I installed a aluminum and steel gazebo on an existing concrete pad just outside of my home. It is not attached. I ran a single 20 amp branch circuit in schedule 40 PVC to the gazebo.It is GFCI protected. 3 recepts and 1 fan.
I wanted to know what you all think regarding a ground rod. There is no sub panel just the single 20 amp circuit. I thought for lightning protection some sort of an electrode would be a good idea? I would drive the rod about 4" from the structure and attach it to the mounting bolts on one post? If this were your project what size wire and rod would you use, or would you consider this a waste of time........Thanks John


Edited by JValdes (04/16/08 08:07 AM)

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#176925 - 04/16/08 08:54 AM Re: Electrode? [Re: JValdes]
mikesh Offline
Member

Registered: 06/07/06
Posts: 614
Loc: Victoria, BC, Canada
First I don't know how many lightning strikes you get in your area but I would not bother. A couple of really long bolts into the concrete and I'd be happy.
If lightning is a real probability. IE there are regular strikes near or on your property then a rod closer than 4' is OK but to do it right I think you need 2 down conductors and that might require 2 rods. The lightning down wires should be as free from bends as possible and the rods should be located very close to the building. Lightning does not tend to turn corners and will just as likely follow the skin of the building. You also need to bond the lightning ground rods to the main electrical electrodes. I might be inclined to install a tvss at the circuits entry to the house or on the service.
Is your house lightning protected? is a tvss installed in your service panel?
I doubt the gazebo is any more likely to be struck than your house or the hydro poles or any trees in the area.
My advice is tempered by the fact that lightning is rare where i live but even in Alberta Where we got lots of lightning I would not have bothered. All of this is subject to the highest point disclaimer. If the gazebo is built at the top of a hill all bets are off.

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#176927 - 04/16/08 09:05 AM Re: Electrode? [Re: mikesh]
JValdes Offline
Member

Registered: 06/03/07
Posts: 308
Loc: South Carolina
I tend to agree with you mikesh. Never had a strike YET. But did have some concern for safety. There is no way to tie into the existing service, so it would just be a stand alone electrode. I can get it very close and it will be a straight run......Thanks

PS....The gazebo is mounted with four inch long red heads. Total of 16. None penetrate the concrete pad or in contact with the earth.


Edited by JValdes (04/16/08 09:08 AM)

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#176929 - 04/16/08 09:13 AM Re: Electrode? [Re: mikesh]
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
JValdes,

If the gazebo isn't grounded in any way, I'd drive a ground rod to prevent a static charge from building up and reduce the chance of a lightning strike. If you can bond it to the ground wire in your branch circuit, that should be fine for this purpose, and I wouldn't bother with an additional rod. Best thing you can do is solidly bond the gazebo to the IMC/RMC you ran the wiring in, as it will double as a supplemental grounding electrode.

The rod might help a small bit, but rod or not, if the gazebo takes a direct strike, everything electronic in your house will be fried, including the TVSS- they're great against a hit down the street, but simply can't withstand the magnitude of a direct strike. Even if the gazebo isn't connected electrically, the lightning will arc to it, and it's close enough that the EMP will couple right into every wire in your house and fry it from the inside.



Edited by SteveFehr (04/16/08 09:16 AM)

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#176935 - 04/16/08 09:38 AM Re: Electrode? [Re: SteveFehr]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
Your concrete pad is a fairly good electrode but you just don't have much connecting the gazebo to it. I suppose the direct contact and 60 odd inches or red head will give you some connection tho.
Everything will probably be wet when the lightning hits and that will help.
I do disagree with Steve on the effectiveness of the TVSS. A well designed TVSS system will save you from some pretty scary lightning hits. I took one on the air terminal above my weather station and only lost the serial port on the laptop that collects the data and the sender in the weather station. Lightning has hit the 250kv lines behind my house several times with no other effect than my UPS beeping.
_________________________
Greg Fretwell

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#176940 - 04/16/08 02:04 PM Re: Electrode? [Re: gfretwell]
BPHgravity Offline
Member

Registered: 04/08/03
Posts: 141
Loc: Port Charlotte, Florida
Installing a ground rod at the structure will serve absolutely no purpose. You will receive no benefit or added safety with a ground rod.

As stated by others, perform a risk analysis as outline in the NFPA 780. If the level of risk indicates the need of an LPS, only that as designed and installed per the NFPA 780 will provide any mitigation from the effects of a lightning strike.

Keep in mind, a conventional lightning protection system short of a surge protection device does not protect premise wiring. The addition of an LPS or lack there of does not change the probability or likelyhood of a strike occuring at a building or structure.
_________________________
Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter

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#176949 - 04/16/08 05:01 PM Re: Electrode? [Re: JValdes]
KJ Offline
Junior Member

Registered: 11/08/01
Posts: 53
they dont have to touch the earth, the entire concrete pad is suffiently 'bonded' to the earth, unless the pad floats in the air, or is isloated from the dirt under it.just make sure that your equip. ground conductor from the service that feedsthe outlets and switch, is at some point physically jumpered to a point of the gazebos steel.

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#176951 - 04/16/08 05:09 PM Re: Electrode? [Re: KJ]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5299
Loc: Blue Collar Country
If it only has one circuit, there is no code requirement to bond the structure, or plant an electrode. Though doing so will cause no ill effects.

Different electrodes in the same system need to be part of the same grounding network. This is accomplished by having the electrode, at some point, be connected to the ground wire. You only need to wire 'rod to rod' when the additional rods are intended to reduce the resistance of the ground electrode.

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#176952 - 04/16/08 05:13 PM Re: Electrode? [Re: renosteinke]
KJ Offline
Junior Member

Registered: 11/08/01
Posts: 53
im not talking electrode, not required,
im talking branch circuit bond.

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#177029 - 04/19/08 10:01 AM Re: Electrode? [Re: KJ]
JValdes Offline
Member

Registered: 06/03/07
Posts: 308
Loc: South Carolina
The gazebo is physically bonded via the EGC to the frame including #10 self tapping screws for mounting the boxes, Very secure chase nipples behind and through the frame of every box, every box grounded with the ground screw provided, 16 - 4" red heads and an unbroken path to the sub panel grounding bus.
I am not driving a rod. To bad I'm not a good carpenter, then I would have built my own gazebo with WOOD.

Note: There is a point on the very top for decoration.

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