lighting and back feeding a sub-panel
Hi ALL,
I had a recent lightning strike (4th time) and alot of stuff got fried, including stuff in my detached building, which in addition to being grounded with 0-2 into the ground 10′ rods is also grounded to the house main.
The question I have is ……..should I disconnect the ground to the feeder in the detached building? From the house which goes through a sub to the main from the sub in the house which I tapped. i.e. sub in workshop from the main was tapped to to carry power to detached out building.
Breaker and gauge sizing is irrelevant, as everything is overkill.
WSJ
Replies
?? Don't understand your question.
Rephrase it perhaps.
Additional info that could be helpful to all:
Path of electrical power through the sub panels?
What got struck by lightning? House? outbuilding? transformer on pole nearby?
Jim
JTC,
Power pole across the street got hit (I think,.....I was home at the time and heard a loud bang and saw a flash) . I just wondered, given all the selective damage, if the lighting traveled through the ground (earth) vs. though a voltage spike in the lines.
It's just odd how some stuff on the same elec. branch burnt out, but other stuff didn't. And I do tap directly off the pole, as does my neighbor. My computers work fine (all surge protected) but at the same time, other electronic stuff running threw the same are toast.
BTW, I've seen how lighting can travel.........absolutely bazaar.
I do know lighting can travel though the ground, and exit somewhere else.
WSJ
And BTW, I live on top of a hill
Edited 5/25/2009 8:57 am ET by WorkshopJon
Given your track record at this location, I would certainly be installing a whole house surge arrestor in your main SEP. May be inside of the SEP or mounted outside -- not a big box item, need to find a real electrical supply house.
As to grounding / connections / rods / disconnecting any.
SEP should have 2 hots + neutral from pole, then an independent ground wire run to ground rods / UFER. If the house is supplied by underground metallic piping - an additional ground wire should be run to that pipe (inside of foundation and as close to the point of entrance as possible).
In the main SEP - The ground bar and neutral bar are bonded together and to the panel enclosure - generally this is accomplished with a single bonding screw supplied by the panel manufacturer.
Sub-panel (inside of the same structure) should be supplied by a 4 wire cable of appropriate size for the load -- 2 hots, neutral, ground - the neutral bar needs to "float" in the sub-panel. In the sub-panel, there should be a separate ground bar which is bonded (electrically connected, generally by a screw) to the sub-panel enclosure (box). No additional ground rods need to be driven for this sub-panel.
Outbuilding sub-panel - can draw it's power from either the main SEP or from the sub-panel in the main house.
Fed and connected the same way as the sub-panel in the house - fed by appropriate sized 4 wire cable, floating neutral bar, grounded box, etc -----EXCEPT the sub-panel in the outbuilding will need it's own set of ground rods - in this case the ground wire from the rods will connect to the ground bar in the outbuilding sub-panel.
If this description matches the wiring configuration for your main and two sub-panels, it is fine and code compliant ----- do not go disconnecting any ground wires - anywhere.
You mentioned that the cable sizes used are "overkill" which I assume mean they are oversized for the anticipated loads and breakers installed to protect them - that is fine, net effect will be lower voltage drop via decreased resistance.
Not very informed as to lightning protection - you might do well to investigate better informed sources on this topic.
Jim
Never underestimate the value of a sharp pencil or good light.
When you are talking about lightning the more grounding and bonding you have is better. Make sure you have a good ground electrode at each building and put panel protectors in both of them.If you ran a 4 wire feeder isolate the neutral and ground at the second building (4th ground wire bonds the panels and ground electrodes together) but if you only have 3 wires bond the neutral to the sub-panel ground.
GF,
That's exactly as it is. All neutrals isolated, main ground is to a copper pipe from my well that is ~100' deep, out building has two 10' rods tied to 2 gauge wire, again with and isolated neutral bus bar.
Edit: The panel protectors seem like a good idea. I'll have to look into that.
WSJ
Edited 5/25/2009 8:54 am ET by WorkshopJon
Jon,
How has your well pump faired in all this? No one should regard themselve as "God's gift to man." But rather a mere man whos gifts are from God.
"How has your well pump faired in all this?"
Still works, but it's a relatively new pump on a 255V circuit (actual voltage) . The old one was a on a 2 wire 125V breaker, which was toast after a t-storm.
I think most respondents to my post , or should I say I didn't word my question correctly was, can lighting hit something nearby, travel though the earth, enter the grounding system of a residence, then exit via the power connection to the pole.
If this is the case, more interconnected grounding can only make things worse I would think.
WSJ
Actually bonding everything together makes things better in lightning events. You can get "ground shift" where the ground electrode systems in 2 buildings might be 20 or 30 volts different than each other. Bonding them all together shunts that out and keeps everyone at the same voltage. When I did lightning mitigation in computer systems we fixed more with a roll of fat wire than anything else we did.
I'm NO expert by no means & my knowledge is limited, at least I know when to call an expert.
I only ask because we've lost pumps due to lighting hits, one hit was my neighbors tree across the street about 180 ft away from my well.
Our well guy told us that lighting takes out alot of pumps & he gets many calls after a good storm, I asked him about the "lightning protection" on my pump & was told that it only protects the wire to the panel not the motor.
No one should regard themselve as "God's gift to man." But rather a mere man whos gifts are from God.
Dale-electric.com has a pretty good assortment of protectors. Be sure everything coming into the house has protection and that it all gets bonded to the same electrode system. If the telco or cableco drives their own rod, bond it to yours.
>>.....If the telco or cableco drives their own rod, bond it to yours.....<<<<
The telco / cableco in your area has actually been known to do this? They just clamp onto anything they can find around here....usually not very well either.
JimNever underestimate the value of a sharp pencil or good light.
I see cable and satellite companies driving rods more than the telco.
You see it when they decide it is easier to get into the house on the other side from the poco. This ends up being sudden death for TVs and PCs on a cable modem in a thunderstorm.
How many wires run to the detached building?
You do need another rod out there.
You have been hit 4 times my lightning! You should look into "Lightning Protection"! Do not disconnect any ground cables!