1144Views25Replies

Author Options:

High Voltage Ground Answered

I'm starting to work with high voltages again, but for real this time. I just built an ignition coil driver, using a 555 (and I got an ignition coil), but my 555 broke (the texas instruments ones can only drive 15mA, oppose to the normal 200mA, oops) so I have to go buy one today. My main question is what to use for ground, whether it be for an old screwdriver for arcing sparks or the secondary of a tesla coil. I was originall just going to use the 3rd prong of an outlet, but somewhere on the internet I heard this could destroy all surge protected power strips and destroy all plugged in electronics at your house. I, of course, do not want this cause... well... I'd be screwed. Is this true or not? Can I use the 3rd prong?

Discussions

. I'd drive a metal rod/pipe at least six feet (two meters) into the ground and run a wire from there to the workbench.

. Unless you have a larger-than-very-low-current-output HV source, I can't imagine you overloading a proper house wiring ground. They can handle (some) lightning strikes. But why tempt Fate and Mr. Murphy? A lot of house grounds are not what they should be. :( If you don't have a very low resistance path to ground, HV can cause problems.
. The closer you are to the ground rod (should be one near your meter), the less effect you will have on other equipment (assuming your connection to the ground rod is good).
. I'd still go with a dedicated ground rod. It's not that big of a PITA and well worth the effort. Try to drive it at least 2-3 feet from the meter ground rod.
.
. Or use a metal cold water pipe, preferably where it enters the house. Connect as close as possible to where it comes out of the ground.

well, here's a delema (I totally butchered that spelling) I can't drive a pipe/rod that far into the ground cause of bedrock and where my basement is located The ground around me is pretty... well about half clay, not very conductive My mom doesn't want my connecting HV stuff to water pipes cause you know, water, high voltage what to do!

. Could you find someone your Mother would consider to be an authority to explain to her that using the water pipe is safe? . . BTW, it's dilemma.

I'll ask my dad later, he'd proabably say yes :)

. If it's a metal pipe that goes underground, it should be a good ground. . The equipment to test earth grounds is pretty expensive, even to rent. An ohmmeter will tell you if you have a bad ground - measure between the meter ground rod and your spot on the pipe. You can also measure the voltage between the pipe and your receptacles. If there is any voltage pipe-to-neutral or pipe-to-ground, you have a problem, possibly in the house wiring.

ok, I found a copper pipe that I think is the closest to the ground as possible, it's near my water softener, and it goes into the wall out the house. Near the wall it's wrapped with black insulation and it goes into a PVC pipe...

...near my water softener...goes into a PVC pipe...

Are you on a well? Then the pipe is not ground, wells use plastic pipe. You have to be on city water, with metal pipe going to metal water mains for it to be a good usable ground for house wiring. And many newer homes have plastic somewhere between house and main.

Can't drive down a rod? Then bury a plate. Attach wire to a plate and bury it deep as possible where the ground will stay moist as it gets. Surface area is what counts. NEC would like for a house ground a copper alloy with 5 sq ft exposed, min 0.060" thick (1/16"), at least 30" down. For playing with HV, chunk of sheet metal, maybe only 2 sq ft. Got an old galvanized bucket? Attach wire nice and solid, bare wire is best, bury deep.

Follow the sound careful advice, stay away from the house grounding.

thanks for all the info, my water is city so I think I'm good I've tested it out with a simple ignition coil (my tesla coil isn't done yet) and it works perfectly, my arcs are a bit longer now, and I think that suggests that the water pipe is a ground

yes, and an important component is that it doesn't consider YOU a better ground... :-)

hey, event though this forum is old, i found a good way of finding a good ground. Take some computer speakers, turn up the volume most the way. Put your thump on the end of the 3.5mm jack, you should here a buzz from your speakers now. When you touch something metal with your other hand and it buzzes loudly, then you are touching something grounded.

Isn't the buzz coming from 60Hz signals in the air (showing how good an antenna you are) and not ground noise?

well, I touched a big piece of metal that I knew wasn't grounded and it didn't buzz, then I touched something I did know that was grounded and it buzzed

Maybe you need more iron in your diet ? J / K ;-)

From a website: Properly grounding the secondary is VERY VERY important. Do NOT use the regular ground for your house outlets. The ground must be separate to prevent a high voltage/low current streamer from allowing a low resistance path to house ground for the high current primary. You should consult other web-sites about this (not sure if many talk about it) because it is very important. You need to pound a long metal spike into the ground somewhere and use that for your secondary ground potential. Improperly grounding could lead to health hazards (none of you care or you wouldn't even read this site of course) but also very importantly, anything plugged into your house outlets will be at risk for overvoltage/failure. So kiss your nice fancy CD player and Wagner's mom's 25,000 Watt dildoe charging station goodbye! Darn

I think this is referred to as a ground loop and not a good idea.

Ground loop involves having separate grounds on interconnected systems. Example, ground rod at your photovoltaic panels, inverter is grid-tie and hooked up to your electrical panel and the house ground. Connection is thru the inverter, there's a significant resistance between grounds thus a potential difference, thus ground loop. All grounds should be joined in the main panel, thus you could have a ground clamp on the rod at the PV panels for a ground line to them, then another clamp for a continuous line back to the main panel, and no ground loop.

I wouldn't consider HV stuff as interconnected enough, there are often transformers involved which are isolating, electrostatics are pretty much isolated from supply... Solid state from line voltage might be an issue, but then the difference between grounds would limit whatever surge could possibly show up at the house ground.

Of course, I have often seen the "all grounds connected in the main panel" rule freely violated in industry. A production shop can be a very electrically noisy place, irritates modern electronics. Thus for modern CNC equipment per manufacturer's installation instructions each machine will have its own ground rod, drilled for right thru the concrete floor right at its main electrical cabinet.

Thanks....I have been away from it all for much too long....I need to brush up again on the terminology by rereading my books *sigh*

That reminds me, I better get the 2008 NEC and get studying... Dang they're pricey...

Yeah, my CET study guide is long outdated *sigh*

If a jolt to the Earth prong blows your house electrics, then your house was wired in wrong in the first place. The third prong is designed to take your stuff to Earth.

I use the third prong as an Earth for my VdG, and it doesn't even trip the room's surge-protection, never mind anything else in the school.

There are several factors involved in grounding. Also I suspect your school is wired to heavy-duty commercial / industrial standards thus has superior grounding compared to a house, plus for a load the size I'd expect for a decent-sized school around here the utilities would want (insist on) 3-phase being used which can be more forgiving of surges.

However, you may notice from guyfrom7up's Jul 16 4:11AM post, it mentions a "streamer." In simple terms, high voltage can give you arcing. You do not want arcing in a panel. There are many exposed connectors, also in the main box only grounds and neutrals are connected, a surge on ground is a surge on neutral. Plus house wiring is not rated for high voltage, you could get arcing inside a cable, not good.

Now I can understand how it may be assumed that ground is ground period, any currents going to it will go nowhere else. But then there's reality. What is "ground" for a house may be rather minimal, just a pipsqueak copper wire to a rod in the soil, which is actually very inefficient for a ground. As mentioned, grounds and neutrals are connected in the main panel. What is the acting "ground" for 120/240, the zero point, is the large neutral wire coming in from the transformer. The rod, or water pipe connection etc, acts mainly as a neutral backup, if the connection to the transformer is lost then without the local ground, thru the neutral connections in the panel, your 120V appliances will see 240V, both hot legs. And you may see smoke. Then you will see red.

If you use your house ground, attach right to the rod of water pipe, and it is not the equal of the transformer neutral "ground," then the current may flow back into the panel along the ground wire.

High voltage, fun stuff, can act very strange, and your house wiring is not made for it. Putting in a separate ground is best.

I bow to your higher-voltage knowledge...

...and unplug my VdG from the Earth at home...