Lightening Strike Question
Hi guys
I have a quick question.
We suspect that lightening has hit one of our remote sites and multiple devices have fried. The only thing common between the devices is electrical power. There is no other common physical connections that connect all the devices.
There are surge protectors, but they are still intact and working as normal.
Any ideas guys?
Depends where the surge protectors are. If they are on each power plug, then I'd suspect the quality of the protectors. If they are on a common bus, like at the UPS, distribution board or power distribution unit (multiplug), then a strike on one of the devices will easily hit everything on the common bus by going down the cable and spreading out across the "protected" space.
Additionally, not all the devices have to be connected, if you have three or four clusters that are connected, and the clusters share a single common connection, then the lightning might hop cluster to cluster. A doesn't have to be connected to D, as long as A->B->C->D is there. If that makes sense
Ok, I'm following you and it makes sense.Originally Posted by bruce_the_loon
Depends where the surge protectors are. If they are on each power plug, then I'd suspect the quality of the protectors. If they are on a common bus, like at the UPS, distribution board or power distribution unit (multiplug), then a strike on one of the devices will easily hit everything on the common bus by going down the cable and spreading out across the "protected" space.
Additionally, not all the devices have to be connected, if you have three or four clusters that are connected, and the clusters share a single common connection, then the lightning might hop cluster to cluster. A doesn't have to be connected to D, as long as A->B->C->D is there. If that makes sense
Simple question, is it possible to have a lightening strike that fries electronic devices, but the surge protectors are still working 100% (the surge protectors have not been fried)?
There's an old joke about a transitor being a $5 device in a circuit that blows to protect the 10c fuse.
Surge protectors are like burgler bars, they are supposed to keep the bad stuff off the protected power bus. Some are designed to blow with the surge and be replaced, others merely remove the surge and carry on working. A simple spark gap/MOV device will happily survive a surge if it wasn't beyond the breakdown voltage of the device, and if the source was inside the protection ring, you'll still lose devices.
It is also possible for the surge protectors to survive if the surge propogated by other means, like network, signal, antenna or other cables, then the power bus wouldn't be surged to damage them.
Some surge protectors are structured linearly as well, with spark gaps, MOVs, inductors and other bits in an order to kill massive overvoltage first, then high frequency AC and noise after that. A surge on the inside of the protected space might then blow only the HF circuits and the protector might appear to be fine and working.
Poor earthing can help propogate lightning strikes as well, if the earth line has a bad connection to ground, it won't conduct all (or any) of the strike power away from the devices. It's worth getting that checked out as well.
In addition, if the surge is carried by the mains, you should have type 2 suppression fitted to your DB.
Type 3 suppression [plugs etc] - on its own - is not particularly successful.
I've got a very simple definition to your problem...
No matter how positive you are.If a lightning bolt thinks your negative you're gone kack
We cant even measure the manitude of the largest electrical storms.How are we gona build surge protectors to negate the surge?
If it works you're lucky.If not better luck next time.
Consider that ESCOM supplies power at 50% higher voltage. Some stupid technician switches to the wrong wire of the power transformer on the pole. Few minutes later he realises mistake, replaces fuses....
It happenned to us in the past. Lightning protection. MOVs, etc... work still below triggering level. No protection against such scenario. However there are overvoltage protection devices, cutting off circuit, similiar to household overcurrent circuit breakers and leakage protectors.
A surge is an electrical current from cloud to earth. And through earth to distant earthborne charges. That current is everywhere in that path - simultaneously. Much later, only something in that path is destroyed.
You had damage because that path was via electronics. Again, a current was incoming on a protector at the same times that current was outgoing on the other side. What in that path failed? The weakest link was probably inside electronics.
What does an adjacent protector do? Connect that current to earth. Being too close to electronics, sometimes the best path to earth is via adjacent electronics. Do you really think a protector might work by disconnecting? Three kilometers of sky could not stop it. Why would millimeters in a disconnecting device do better? Nothing stops or blocks a surge. Nothing.
Lightnnig striking AC wires far down the street is incoming to every appliance in the building. Is everything damaged? Of course not. Which appliance (or electronics) is the best connection to earth? Only damaged is anything with both the incoming and 'outgoing to earth' paths. Damage is often on the outgoing side. Adjacent protector do nothing to avert that threat.
Protector that actually does protection is connected low impedance (ie 'less than 3 meters') to the single point earth ground. Other protectors - especially those adjacent to electronics - can even make damage easier as described above. Protection means that current need not connect to distant charges via the building. Protection means earthing that current so that it is never inside hunting for earth destructively via appliances. Then superior protection, already inside all electronics, is not overwhelmed.
Worry much less about protectors. Worry much more about the single point earth ground. And how a protector connects to earth. Because protectors do not absorb those hundreds of thousands of joules. Only earth ground does that protection.
Last edited by westom; 02-08-2012 at 03:45 PM.
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