Ping Larkin

Yes. Been in one when it was hit. Responsible for its computing systems.

Sounds like a shoddy build quality then doesn't it? Concrete in a finished building should not be damp internally. The surface may be wet.

Seems quite likely. UK buildings have dampcourses to avoid wet walls and most large industrial buildings have lightning conductors on them.

The building that I worked in took a direct hit once. The lightning didn't go down the official lightning conductor as some scrote had nicked it for the copper. So it found the next nearest thing which was the telephone wire cluster trunking and vapourised most of that down to the ground. The secretary in reception was very upset afterwards and the wiremen took a few days to fix it but damage was very localised and largely superficial. The strangest thing was that we were not the tallest thing around - a super grid pylon was no more than 200m away. I expect the large area shallow angle metal roof made us a target.

The computers expensive terminal drivers died saved the cheap surge arresters and the part of the computer that is nominally most sensitive to electrical interference kept on running. Only the terminals on cables that ran underground from the building were a problem.

Regards, Martin Brown

Around here we have a company that can pump concrete under such a thing and bring it up to level. Next door neighbor had a driveway panel that had settled ~2" along one joint... they pumped it up to match the adjacent panel. ...Jim Thompson

How much energy is it safe to dump into an HC-series MUX when discharging a cap? It would be convenient to be able to discharge 10 nF from 5V to 0 using a 74VHC4053. I think that is probably safe, but it will certainly exceed the abs max current during the discharge event.

Relevant experience, anybody?

Thanks

Phil Hobbs

It'll be limited by IDSS. Since I have those models from back when I reworked all ON Semi's 'HC parts, I'll check it for you... maybe not until Monday... I have some lengthy simulations in progress ;-) ...Jim Thompson

I can't imagine that would do any harm. Current will be limited by the normal "on" switch resistance, and the energy is tiny.

(Unless you're doing the rail collapse trick, but even that would be safe.)

John

The tower was hit as well, and it was 50 feet higher than the building. It was a TV studio There may have been more than one strike. It isn't unusual to have several thousand ligthnng strikes in a single storm in Central Florida. I was called when the transmitter operator lost the remote satellite feed, and couldn't connect to the remote controls by telephone. It took out the main computer, five terminals, the entire telephone system, the 11 GHz STL, all the LNAs on all the C-band sat dishes and part of the electrical system. The building had UFER grounding along with multiple ground rods thatwere bonded to the UFER. The tower had a complete grounding system that was bonded, as well. Lightning damage to stations is common in Florida. There is a layer of limestone over the Florida Aquifer, and the soil has a lot of sand over most of the southern half of the state. A couple large industrail steel buildings ended up with magnetized beams after strikes, wich caused problems for computer and video monitors. I've seen a few that affeded convegence & purity when you got within six feet of a support column.

Concrete always has some moisture. It won't be visably wet inside, but the olny way to remove the moisture is to bake it in a furnace.

Low grade EMP or ground differential.

They do have smarter regs over there. For example, one house I stayed at last year had lightning protection all along the gables, the top of the roof _and_ the wall perimeter. Guess they forgot to install the latter at your TV station.

And, why was the concrete damp? That's not supposed to happen as it will gradually eat away at the rebar, causing structural issues down the road even if lighnting never hits. Then there's the whole mold issue.

Heat pumps are a no-no for us. PG&E has the monopoly and once you get above baseline (with a heat pump you will) they really sock it to you.

Best lightening protection is to build near a structure (or hill in my case) distinctly taller than yours.

However that does not guarantee against all events. Some years ago a utility distribution yard 2.5 miles from me was struck. The resulting surge traveled thru the _underground_ wiring and hit my house, knocking out several PC's, several TV sets, and numerous light dimmers ;-)

I've since added a whole-house surge block as well as UPS's.

I even have a UPS on the wireless phone system ;-) ...Jim Thompson

Oh, the new health care bill covers this. Well, halfway.

See Subtitle C, sec. 2572, or just search for "restaurants" or "vending".

They thought of everything.

-- Cheers, James Arthur

I can have the same thing done, if I don't eat for the next six months.

Could you jack it up, dig underneath, pour, and then shim? (And then hide what you did with strategically placed bark mulch.) ;)

Cheers

Phil Hobbs

I hadn't thought you were that heavy ...

I'm begining to see why so much stuff goes PFFFT around you. :(

Yes, if they had used a precast concrete pad instead of plastic on loose soil. The plastic pad is hollow with ridges so to get it high enough to pour, it has to be disconnected from the ductwork and electric lines. The simplest way to fix it is rip everything out and do it right. It was installed when I was pretty much confined to bed a few years ago. When I did ask what they were doing, I got the same, 'You don't know s*it' response I get from a couple people on this newsgroup. They cut every corner possible on the job, and the results show it. I have the low side lifted with a 12' 2"*10" and piece of 6"*6" landscape timber for a fulcrum, but the plastic has bowed so bad that it's going to snap if I don't start over from scratch. I may 'cheat' and ask for help from a local 'Young Marines' group to do the digging and to mix the concrete. I've done enough volunteer work for them already. :)

Yep, my tests are kind of rigorous. I remember the first time I saw a power supply manufacturer have their comeuppance at TUEV in Cologne. Both submitted units blew up. Not just smoke, but also flames.

Oh, THAT :-) ...Jim Thompson

Except how to pay the debt.

Beats the alternative.

I'm not so fond of it because of the maintenance expense. The "efficiency" is real, for small values of efficiency. A heat pump with a SEER (like my two) is about 250% better than resistive heat. That goes down close to freezing but never below 100% (or the heaters kick in ;-). Interestingly these units are significantly better at heating than cooling. The temperature differential in the winter is much larger than the operating cost difference.

Yes, Barak.