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[Cailen Waddell]

This is not quite a pro audio topic, but I think it is germane for the great number of viewers who have home studio gear, keep instruments or Amos plugged in at home, etc...

We had some bad storms through NC this week.  A colleague of mine had lighting strike near his house.  He said it sounded just like it was outside, but it was the middle of the night...   Regardless, a surge came in on his cable TV line, blew out his cable modem, smoked the Ethernet cable connecting it to his game console and through the HDMI cable to his TV.  A few caps in the power supply for the TV exploded, as did the video card... In talking the next day, he found the cable TV ground wire was not connected to the whole house ground at the service entrance.

Apparently his TV had a grounded plug but neither the game console or cable modem did...

Luckily it was just home gear and not work gear...

Now my question is - if the ground wire had been in place would the gear of been saved - a pretty speculative question, but I am interested in opinions.  Part II of the question is would a surge suppressor with coax connections make a difference and how many people have them?  Part 3 (which I just thought of as I'm typing) while the double insulated gear no doubt protected anyone from touching it and receiving a shock, it appears to have 'passed the buck' on halting the surge and passed it through signal cables - thoughts?  Is double insulated gear a liability in this way?


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[John Roberts {JR}]

Lightning can be difficult to contain.

Modern gear has become a lot better at shrugging off moderate induced voltage spikes, but a direct hit will just melt stuff.

The grounds at the service entrance are most important...there is probably a device (air gap?) to trap dangerous voltage there. The phone company makes their line guys put tags on them (entrance ground wires) to prove they double checked them...



 JR

[Tom Bourke]

Most surge protectors are worse than pointless, they can cause problems or give false hope.  There are some good ones around but they cost 10 times or more as much.

The grounding blocks and air gap type units do help limit the incoming voltage spikes to manageable levels unless the strike is very close or the grounds are not done right.  I think the number is around 3000V.  SurgeX has a white paper on it.

Also being in a town with lots of ground rods close helps.  I have a friend out in the country that would get his phone system fried at least a couple of times a year.  His place was grounded OK but no one else was close so his ground system got over loaded.

Another interesting fact is that lighting is very wide band and has some characteristics of RF.  A sharp bend in the ground wire can render it useless!  The power will jump strait rather than follow a 90 deg bend.

[Stephen Swaffer]

On new homes/services code requires electricians to provide a place to bond CATV/phone lines-usually we install an Interservices Bonding Terminal- this should prevent a lot of the issued.  The problem is if a voltage (doesn't have to be a direct strike-if a bolt is going to jump 1000 feet through air nothing you do is gonna stop it) is induced on a CATV or phone line it will get into the devices and seeking ground will destroy electronics trying to get to the grounded neutral.  An IBT shorts that spike directly to the grounding electrode before it goes through the equipment.

I live in a rural area-nearest other service is a shed about 800' from the house, then a hog building about 1200 feet and a neighbor about 2000 feet then nothing for better than a mile.  We sit on a high spot and take too many strikes for my liking, but rarely have any damage-but I have no landline or CATV to the house and those seem to be the worst culprits for spikes to find their way in.

I have seen CATV/phone lines "grounded" to a clamp attached to the (painted) cover of a breaker panel.  Typically, they use a #10 or #12 solid wire to ground-it would be an inexpensive preventative measure to make sure your phone/CATV goes through a grounding block with a good solid ground to the grounding electrode system in your home.  (This is often ground rods-but anymore concrete encased electrodes or ufer grounds are often preferred.

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