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#201755 - 05/13/10 05:08 PM Re: Whole house surge protector [Re: MarshAviator]
ILBob Offline
Old Hand

Registered: 02/05/10
Posts: 776
Loc: Northern IL
Originally Posted By: MarshAviator
You will also want to make certain your grounding electrode (ground rod) is sized correctly and has low impedance (The NEC allows in some cases 25 ohms) but you need around 2 ohms maximum.

Nowhere in the NEC does it mandate any such thing. Getting your ground impedance under 2 Ohms is very difficult (25 Ohms is not all that easy), and serves no real purpose in any case, at least in a residential or industrial setting. For certain types of transmissions lines, yes, but not typical users.
Warning - I am not an expert on anything having to do with this forum, but that won't stop me from saying what I think. smile


#201776 - 05/13/10 09:33 PM Re: Whole house surge protector [Re: ILBob]
Art_in_FL Offline

Registered: 09/01/07
Posts: 2432
Unfortunately there is a lot of misinformation out there on this subject. Grounding actually has very little effect on how surge suppressors work. Lightning arrestors are a little different, and grounding is an issue with them.

MOVs do not "absorb" energy, they are not energy sponges, they are in fact voltage dependent switches connected to ground. When activated they form a simple voltage divider with your equipment on one side and the the ground path on the other. The lower the impedance of the ground path the more effect they are. Part of the materials fuse inside every time they cross the voltage threshold but they do not dissipate any significant amount of energy on their own.

They also do not have a "shelf life" they do not degrade over time on their own. They are worn down by activation and more energy they pass the more they are damaged. They are expendable. Which is why it is good to replace them on a schedule and not to depend on the little indicator light, typically triggered by a fuse, to tell you it is used up.

Also the grounding system is very much vital to most, but not all, power conditioning systems. These are more or less dependent on a ground system of some sort. Most need a least a nominal ground system to work at all and ultimately use the ground system to discharge and as reference.

Such conditioning systems that operate partly independent of a ground are pretty common in areas where soil conditions make earth grounding difficult. Sand hills and areas with non-porous rock, particularly if the climate is very dry, can be problematic to effectively ground.

Many of those systems are large, heavy and expensive. Pretty much beyond the scope of what people are likely to install. People are not going to install even a relatively cheap $5000 conditioning system in their house. On the other hand, assuming earth grounding is possible and the system is solid a $100 whole-house surge arrestor can provide a measure of protection. And if combined with a $60 plug-in surge arrestor it can go a long way toward protecting your $1000 computer or $3000 home entertainment system. Most quality surge suppressors have an array of chokes, coils and capacitors to help smooth the passed waveform so the functions are not mutually exclusive.

Nothing likely to be installed by a homeowner is going make much difference with a direct lightning strike. But even a moderately priced surge arrestor array can help with the much more common small spikes from distant strikes, POCO switching, and noise from neighboring equipment sharing the transformer.

Note that a whole-house surge protector is covered in the NEC under "Article 285 - Transient Voltage Surge Suppressors: TVSSs"

And yes, the NEC, at least for "rod and pipe electrodes", does mandate the 25 ohm resistance as the dividing point between using one or two grounding electrodes. It mandates that if you cannot meet a 25 ohm standard with one electrode it "shall be augmented by one additional electrode". (NEC 250.56) Note that it does not specify what the resulting resistance might be.

The other grounding methods, such as a concrete encases electrode, are assumed to be at least as effective as two ground rods 6' apart. Reference NEC 250.50 for further information. We pretty commonly drive one or more well pipes down to ground water to meet engineering specifications.

I'm looking at a 2005 edition, what I have immediately available, but suspect this hasn't changed in the current edition.

#202061 - 05/19/10 12:16 AM Re: Whole house surge protector [Re: MarshAviator]
pezhead Offline

Registered: 05/18/10
Posts: 76
Loc: Minnesota
We watched an episode of Holmes on Homes & he added one to a house he was remodeling. Several years ago I had a amp for my stereo go out from a surge (lightning storm). Now when we have a
storm certain items get unplugged when we're home.

#202418 - 05/24/10 11:43 PM Re: Whole house surge protector [Re: Art_in_FL]
MartinFocazio Offline


Registered: 01/21/03
Posts: 2155
Loc: Bucks County PA
Surge strips should be marked with the month and year so you know how long they have been in place. It is really easy to plug one in and then forget about it for a decade. They need to be replaced regularly. How often you replace them depends on how tough they are, how many and how large the spikes they absorb are, and how expensive the gear they are protecting is.

I do have a "storm protocol" for summer thunderstorms - unplug the file servers, disconnect the cable internet feed - but I can't always be home for that.

Is there any test to see if the suppressors are still working? I sank some serious $$ into high-end surge protection strips (big metal units) but that was close to 10 years ago (as you said, set & forget). We don't have a lot of lightning strikes that come close to the house, but we do have enough line hits in the summer that we see some noticeable wallops on the lights, followed by 15-20 seconds of brownout and then dark.

I presume my suppression gear is kaput...

#202426 - 05/25/10 01:18 AM Re: Whole house surge protector [Re: MartinFocazio]
Art_in_FL Offline

Registered: 09/01/07
Posts: 2432
I would think ten years is plenty long. If those units use MOVs as their main mechanism I would go ahead and demote them. You say you spent a good amount of money.

Do these units have some sort of function indicators? If the indicator is telling you it is still okay, and you have a lot of faith in the brand and model, and that the indicator is telling you the truth, you could keep them in place and ride on.

There is no practical way of testing such units. So your operating on faith, company reputation, perceived risk, and how lucky you feel.

Then again ten years is a very long time in technology and consumer electronics. After ten years you might consider that you have got your moneys worth.

If you wanted to split the difference you could transfer the older units to less important equipment and bring in newer units to protect your most important electronics. There is some benefit to having surge arrestors on many circuits.

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