Grounding, Bonding and Lightning, three buildings.

islandguy · July 2013

Ok, Now i've done it . . .

Looking for advice on the present set up at this off Grid location.

The Generator shed, small cinder block building with a cement floor, is about ten yards from the main house. Has a copper ground driven in right next to it. The cable from the shed is buried to the house.

In the main house there are two Load centers. Both are tied into the house ground. As well as 'Bonded' to the copper water pipe ground.

There is a separate circuit for the well pump inverter. this is a direct burial cable that runs about 100 yards to the well pump. Got hit by lightning last year and fried that inverter. Since replaced. Want to put some lightning protection in a small circuit box and keep that - Well pump - Inverter - charger -batter bank - system seperate from any and all house equipment as much as possible. Should this get a separate earth rod for grounding at the house end?

There is also a barn, about 50 yards from the house. Fed by a 20 amp wire along the ground. Kinda buried. This building has a small mains load center and a ground rod. There used to be an 8k diesel here but it has since been retired.

Lastly I am planing to mount a Gudcraft 400 watt windmill on the roof of the main house. This will be on a ten foot metal pole, probably seven feet above the ridge. I'd like to add some kind of lightning protection to it.

Questions:
Lightning protection, I picked up a couple of those small cube ones that go right into the mains, SquareD model. Do these actually work? Can I add one to the well circuit?

At each location, Gen shed, House and Barn, I have a ground rod. Should I dump the ground wire at that location? In the case of the Gen should it be grounded there even if the neutral goes into the house load panel? Or Do I ground it both locations?

Thanks!

mike95490 · July 2013

Re: Grounding, Bonding and Lightning, three buildings.

Do not put a windmill on a house. The sound and vibration will reverberate throughout the house, and you will not like it. And it would be a lightning magnet, so you would have to have it properly protected.

BB. · July 2013

Re: Grounding, Bonding and Lightning, three buildings.

Oh boy... Lets start with some basic information from other posts/experts on lightning:

BB. wrote: »

A couple threads about Lightning:

Off Grid Grounding Technique?
Another Question, this time about Lightning

Note, the above are discussions, not a do A, B, and C--and you will be "safe". There probably is no such thing with lightning. Several different techniques are discussed--and a few of those posters even have experience with lightning. :cool:

And our host's consolidated FAQ page:

www.windsun.com
Lightning Protection for PV Systems

From other past posts here, Windsun (admin/owner of NAWS), he said that most of lighting induced failures he saw were in the Inverters' AC output section.

Towards the end of this thread is a very nice discussion of proper generator grounding.

Next, a metal "box" around the electrical components is going to do a pretty good job of keeping anything inside "safe" (see Faraday Cage). Placing a couple of lightning rods on top of the building and running grounding down the outside of the building (opposite walls, opposite four corners, etc.). to earth all works well.

The problem is the wiring that leaves the building. So, you want those cables to not bring energy into the building and cause damage.

One way is to put the cables in a buried metal pipe (shielding). If the wiring is either in the building or in the pipe (grounded to the metal conduit at the edge of the building), it will not "receive" any lighting energy. But most of us cannot justify the costs/pain to do that.

Remember there are two types of energy in cables... Differential voltage (+ to -, Hot to neutral, Hot to Hot, etc.) and Common Mode (all cables to earth, etc.).

For the most part, common mode voltage is "easier" on electrical equipment. For example, the average electric appliance is designed to withstand 1,800 VAC (~2,400 VDC) of common mode voltage on the AC line cord (at the factory, each appliance is supposed to be high pot tested at 600 VAC rated voltage * 3 = 1,800 VAC before it leaves the door). In theory, 600 VAC and any amount of current is supposed to be "safe".

The "difficult" voltage to protect against is the Differential Mode Type. You would not expect a 12-48 VDC or a 120/240 VAC device to accept more than its rated voltage and survive.

And this is were the "real world" vs "ideal" comes to blows... When you follow the NEC (US National Electric Code) and ground bond the Neutral to Earth at your homes Main Panel, you now have converted (typically) common mode lightning energy (all cables "go up and down" together) to differential energy (neutral is "at ground" and the hot leads have lightning energy on them). This now is read to "do damage" to all of your electrical appliances. A few countries (at least years ago) would require a "ground screen" in appliance transformers so that the lightning energy would hit the ground screen rather than go through to the appliance (and go through the green wire to earth). But, for the most part, you can assume double insulated with 600 VAC of insulation between AC input and local appliance use (tested to 1,800 VAC for one minute at factory).

Note that NEC "requires" (suggests is their term) that you use a DC GFI which puts a ~1 amp fuse between DC Return and Safety Ground. If you do this, you need to install a two circuit surge suppressor on both + and - lines. A single + surge suppressor will not "protect" if there is enough energy to pop the 1 amp DC GFI detection fuse/breaker.

So, your protective strategy is is to prevent that differential energy from getting into the power system (direct lightning energy away from electrical system). And for any energy that enters, the power lines and gets "converted" to differential voltage, use surge suppressors to divert that differential voltage to earth ground (same point as the neutral bond ground) with surge suppressors at the "edge" of the building (usually service panel, breaker/switch box, etc.). Once that energy has been diverted, then the equipment "should be safe".

Because lightning has a tremendous amount of energy available--Equipment surviving a direct strike is difficult to guarantee--But keeping people safe and lightning away from the electrical lines is a good start.

Midnite makes some very nice surge suppressors (which should work, on average, better than the standard Delta brand "spark gap+sand" type device). However, these (and any) devices can be damaged by nearby/direct strikes, so you have to have them inspectable to make sure all is still OK (the Midnite units have LEDs that indicate proper functioning).

Metal Oxide Varistors mounted in PV junction box?

https://www.youtube.com/watch?v=vkeFYuHxJoU

Now--To your questions (sorry, lots of typing so far on the "basics"). Using Lightning rod(s) to keep lightning energy away from electrical stuff. And using surge suppressors from AC (and/or DC) power lines to local earth. In your case, the ideal method would be to put surge suppressors at both the pump shed and the home/AC power source. You want to protect both sets of expensive equipment (well pump and AC inverter).

Part of my "evolving" thinking of lightning energy control would be to Earth Bond the neutral at both the main AC panel (home) and the AC neutral at the out building/pump shed. This means that you cannot use any sort of GFI breaker from the AC main panel out to the well pump building... But install any GFI outlet/breaker at the well building itself to prevent "false" GFI trips at the main breaker panel.

This appears to violate the "one neutral AC to earth bond" rule... And it does. However--from a lightning point of view--Your well pump and home are completely different locations. And both need lightning control. So, both need any lightning energy directed to local ground and any AC/DC power lines need to have "zero volts" on them with respect to their "local grounds" (i.e., a ground at the house may be a zero volts when a strike hits near the home, but the home's ground may be hundreds to thousands of volts above the "pump ground" do to voltage gradient from home to pump building (voltage drop as lightning energy dissipates through the earth). Having the pump building with no local ground is of no help to the building electrical devices.

So, shunting to local ground home "excessive voltage" and pump building "excessive voltage" is the best bet--And not worry about the voltage drop across the AC cables between the two buildings (the cables are also tested to 1,800 VAC minimum during manufacturing). If the cables are in plastic or metal conduit--you will get some additional protection... But if there is a lightning strike that went through miles of air--a few millimeters of plastic or metal is not going to make much difference.

I have to go right now--so have to end the post here at the moment... I am sure you will get some other ideas--and even suggestions to do something different. I am certainly no expert in this stuff and respect that there are differing opinions on the matter.

-Bill

islandguy · July 2013

Re: Grounding, Bonding and Lightning, three buildings.

@BB, Thanks! Quick Question, since the well pump is in water, doesn't that count as a ground? the pump is the Franklyn 1/2 HP 220v. Last year the lightning strike fried the inverter but the pump survived. Luck?

@Mike95490 - If a tower isn't really an option where would you suggest? In this case the Gudcraft 400w is a pretty small windmill. The plan was to bolt the pole to the wooden ridge. 2x12 Ridge. I couldn't find any information on lightning strikes and rooftop wind turbines. Thanks for the input.

mike95490 · July 2013

Re: Grounding, Bonding and Lightning, three buildings.

islandguy wrote: »

@Mike95490 - If a tower isn't really an option where would you suggest? In this case the Gudcraft 400w is a pretty small windmill. The plan was to bolt the pole to the wooden ridge. 2x12 Ridge. I couldn't find any information on lightning strikes and rooftop wind turbines. Thanks for the input.

Look into how Ham Radio Operators ground their rooftop antenna masts. That would be a good start. A heavy ground wire bolted right on the mast/pole with no sharp bends, gently wending it's way to it's own beefy ground rod. But the blades of the turbine, bolted to the shaft, which goes right into the windings, is taller than the mast it's mounted on, so at the least, you could expect the turbine to be toast, and most likely, any charge controller connected to it. The battery bank may soak up the strikes' surge, and maybe your inverter would survive. But who can tell how the plasma that just traveled a mile through air, will spend it's last 100 feet with metal all around. It's easy to keep most of it out of your house, but the effects will impinge on anything connected to the wires.

BB. · July 2013

Re: Grounding, Bonding and Lightning, three buildings.

Regarding the pump--Several reasons it could have survived.

The well casing itself is a metal shield + grounding rod (probably much better than an 8 foot copper/steel rod). And the cable going down the well gets some capacitance with the pipe... Lightning is an "RF" event (radio frequency ~7 kHZ maximum frequency) so that helps to "filter out" the RF energy of the strike. And lightning energy will (again roughly) travel a few 10's of feet down typical power cabling--So the farther the device is from the strike, the less the effects.

Also, a motor is "inductive" which tends to "resist" differential current and is not very sensitive surges (copper wire windings in Induction Motors). An AC inverter contains transistors which are very sensitive to over voltage events (the dimensions between terminals/across junctions are very small, so a few hundred volts can easily puncture through the semiconductor/across the lead frames). And transistors are easily damaged by high voltage/static charges which will cause early life failures down the road.

Regarding the wind turbine--They are very easy to damage by lightning strikes and not very easy to protect with a lightning rod. Turbines with on-board electronics are probably more prone to lightning damage (semiconductors are not very rugged with static electricity/high surge voltage environments). The wind turbine is typically the highest object around and one of the first items struck. Having the electronics (rectifier, charge controller, etc.) on the ground at least makes it a bit easier to protect against lightning and easier to repair.

Another issue with turbines on the roof revolve around the mechanical and wind flow...

Wind flow--The turbine probably needs to be at least 30 feet above the home/roof line to get into clean airflow (laminar flow). Wind turbines in turbulent wind produce almost no useful amounts of power.

Another is noise--The cogging of the wind turbine (and gear box/blade noise) is usually easily conducted into the building and pretty irritating. And the stresses from the tower/guy cables can damage a stick frame home (loosening nails/etc.). As well as possible lightning attraction.

And there is the problem that wind turbines are known for shedding parts/blades/falling nacelles. You really do not want turbines of any size/mass near where people live, work, and play. Really recommend not doing building mounting.

Multiple articles about Roof Mounting of wind turbines from Wind Works site

-Bill

islandguy · July 2013

Re: Grounding, Bonding and Lightning, three buildings.

@BB, Quick question as I am still working my way through the material. Why do you recommend GFCI at the endpoints? With old wire and wet locations I expect this to be problematic. What I was looking at were the Schneider Electric SDSA1175, My plan was to mount one of these at each location, where the wiring enters the building if there is no panel for that circuit.

@mike95490
Thanks. The blades on this windmill are plastic. So that's not a consideration. In thinking this through I am equating it to a large TV mounted antenna that every house used to sport. While it should increase the probability of a lightning strike, I'm not sure it will be by a significant amount.

BB. · July 2013

Re: Grounding, Bonding and Lightning, three buildings.

The surge suppressors at each building wall would appear to be a good solution. The Schneider has both 120 (phase+neutral) and 120/240 (L1+L2+Neutral to ground).

The question is do you connect Neutral at the building to Earth Ground Rod (and well casing, if present) at each out building or just use the above surge suppressor at the outbuildings to dump neutral surges to earth ground. Your choice (as I said, I have mixed feelings about that. That you are installing MOV's at each location probably makes this less of an issue (either should work well enough--although MOV's do have their maximum current limits). Multi-point bonded neutral to earth bonds have better lightning grounding...

Regarding antenna--In a lightning prone area, you are going to have a lightning arrestor before the wiring goes into the home and you can do the same with the turbine wiring too (turbine itself at the top of the tower--Not much you can do to better protect any on-board electronics/rectifiers in the nacelle over/above what the mfg. may have done). But--Yes, both are going to attract lightning to similar degree (assuming similar elevations).

-Bill

Grounding, Bonding and Lightning, three buildings.

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