Ground Wire in My Shop?

jackypaper · March 2017

I'm upgrading to a 2500-watt inverter in my small woodshop. To connect my ground wire, would it be sufficient to sink a 3/8-inch anchor bolt into the concrete floor and connect the ground to that?

Thanks!

WaterWheel · March 2017

No.

jackypaper · March 2017

WaterWheel said:

No.

Okay . . . well, what's another option?

dennis461 · March 2017

Is the woodshop part of the house or a separate building?

jackypaper · April 2017

dennis461 said:

Is the woodshop part of the house or a separate building?

The shop is a separate building. I have two 100-watt panels and a pair of series-connected Trojan 6-volts for the lights and stereo. I'm upgrading my small 450-watt inverter and am wondering if the 2500-watt inverter needs to be grounded and, if so, what's the best way to do that?

westbranch · April 2017

The normal way to ground you system is by using a Ground Rod or Plate found at you local Electrical shop or Lowes or ??

jackypaper · April 2017

westbranch said:

The normal way to ground you system is by using a Ground Rod or Plate found at you local Electrical shop or Lowes or ??

Well, I've built my shop on solid rock (we have only a few inches of top soil here), so putting an 8-foot rod into the ground is not happening.

mike95490 · April 2017

How far is the shop from the main house that has a grounded panel ?

jackypaper · April 2017

mike95490 said:

How far is the shop from the main house that has a grounded panel ?

The shop is 30 yards from the house.

mike95490 · April 2017

Generally, the ground is tied to the main panel box at the house, and that's the only one allowed. After about 100 feet, some say you should use another ground rod at the remote panel. But a bolt into concrete will not do it, you need a 10' Ground Rod with a UL sticker (not a piece of rebar) pounded in and connected to armored wire (so your ground wire can't easily break) and tied to the panel. Your local building department can give you what the local rules they like to see are, Ask about grounding a remote sub panel ____ feet from the main panel.

Horsefly · April 2017

I too am interested in the range of answers to this question. The spot we've chosen to do our ground mount for our PV panels is a very large slab of granite bedrock a few inches below the surface. This makes for an area with good sun exposure (no trees can take root anywhere near there), but it creates other issues. I want to put down a good ground rod next to the PV array, but I'm not sure how I can.

I'd have to believe this isn't an uncommon problem: In search for a good clearing in an off-grid situation, the best may be where no trees would ever grow, e.g. solid bedrock close to the surface.

What to do?

dennis461 · April 2017

NEC 250.32(a) requires a ground at your sub-panel since it is an out-building. The neutrals however are not tied to that ground, a neutral wire runs back to your main Panel.. The main panel should be the only place the neutrals and ground get connected together

As for grounds in rocky soil, that's a separate issue. The slab 'should' have had rebar coming up from inside concrete to provide a ground.

Now, I've used the word ground in places where "bonding' may have been more accurate, the outbuilding metal parts (panel frame, inverter frame, metal receptacle boxes...) are bonded to the ground rod at the shop/outbuilding. The neutrals are 'grounded' to the main panel ground.

http://ecmweb.com/qampa/code-qa-grounding-and-bonding-remote-building

http://iaeimagazine.org/magazine/2004/01/16/grounding-and-bonding-methods-for-outbuildings/

westbranch · April 2017

In the 50's and 60's our old fire lookouts had more 2/0 copper cable than you can imagine on all 4 corners , and along the eve lines, inside and out, that went out 30 feet from the plywood structures, metal roof though, to drilled holes in solid rock on the mountain top, that the grounding rods were placed into... they must have worked to some extent as we never 'lost' a lookout man... those guys had nerves of steel to be inside in a lightning storm!

mcgivor · April 2017

If there is no electrical connection to the house, no sub panel, all loads connected only to the inverter , is there a need to ground the inverter at all, if not secured, it could be deemed portable.? The question in the link deals with portable generators so perhaps the same rules apply, if portable, just food for thought.
http://m.ecmweb.com/qampa/code-qa-78

jackypaper · April 2017

mcgivor said:

If there is no electrical connection to the house, no sub panel, all loads connected only to the inverter , is there a need to ground the inverter at all, if not secured, it could be deemed portable.? The question in the link deals with portable generators so perhaps the same rules apply, if portable, just food for thought.
http://m.ecmweb.com/qampa/code-qa-78

This is exactly my situation. I have a portable 2500-watt generator connected to my two 6-volt batteries to run a few things in my small shop. Does it need to be grounded?

Estragon · April 2017

I have a similar problem of shallow topsoil over bedrock making a ground rod impractical.
For grounding I used grounding plates buried as deep as possible in a bit of a depression where water accululates and which is likely to stay damp.

The plate is made and sold for this purpose in local box/hardware stores. I assume it's allowed by code, but nobody does inpections at my remote location. It's about 1' by 2' with a split bolt welded on to attach ground wire.

There's also a "ufer" ground where the ground wire ties into rebar, but it's something you would normally provide for when doing the concrete work. I doubt it would be practical to retrofit.

If you are in a location subject to code you might want to run it by inspector.

jackypaper · April 2017

Estragon said:

If you are in a location subject to code you might want to run it by inspector.

I'm thankfully well beyond the limits of any city and its pesky inspectors.

dennis461 · April 2017

jackypaper said:
This is exactly my situation. I have a portable 2500-watt generator connected to my two 6-volt batteries to run a few things in my small shop. Does it need to be grounded?

If electricity runs through the shop, then yes you need the system grounded. If a hot wire in your table saw shorts to the metal frame, you want that current going through a green wire, not your leg! Your generator is no longer 'portable' if it powers up a building. Only 'portable' generators with only frame mounted receptacles being used are exempt from grounding..

https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf

Now, lets see some pictures of your system.

jackypaper · April 2017

dennis461 said:

Now, lets see some pictures of your system.

Honestly there's not much to see:

Two 100-watt panels -- SunSaver 20L controller -- two 6-volt Trojan T105s -- 450-watt inverter.

That's it. My power needs are not great.

I was going to swap my inverter for a 2500-watt model, but the instructions say it needs to be grounded. My current inverter doesn't even have a way to connect a ground, so I wanted to ask about that.

Estragon · April 2017

The difference is in how you connect. Small inverters and portable generators are often designed for loads to be connected directly to the power source, and will have a floating ground. Neutral and ground may be bonded internally so internal overcurrent devices trip with faults, but there is no connection to earth ground. Boats and RVs also normally have floating grounds.

The larger inverter is probably designed to feed a panel with circuit breakers sized for branch wiring, and neutral bonded to ground at the panel. Are you running the loads through a panel, and if so, is the neutral-ground bond installed?

BB. · April 2017

There are multiple reasons for grounding.

The first reason is that everything that somebody touches is at "zero volts". We pick the earth at zero volts, and use a ground rod/ground plate/metal water pipe through soils at "zero volts".

The connection to the "earth" is not really a good connection (as far as DC and AC power is concerned)--A "legal" ground rod may have upwards of 25 ohms of resistance. Good for static electricity (your panel frames mounted on the roof can, in theory, get hundreds of volts of static charge on a normal day, and thousands of volts if there is a thunder storm near by. It can also help dissipate lightning strike energy too (earth ground connection).

So--As a practical matter in your shop. First we worry about tools with a metal case (power tools). Use a three wire plug to tie all of the various pieces of equipment (and electrical boxes, etc.) to a common green wire ground. You do not need to tie the green wire to earth ground for it to act as a safety ground. This also allows us to have "hot" and "neutral/return" AC and DC wiring with breakers/fuses/switches only on the "Hot" leads. A true floating supply should have fuses/breakers on both Hot and Return leads (a small AC power system may not even need any fuses/breakers--If the AC power is less than 15 amps @ 120 VAC and you are using 14 AWG or heavier wiring--A fuse will not do anything (the inverter will shut down first before wiring overheats).

If you are worried about getting shocks/electrocution on AC wiring, use a GFI (Ground Fault Interrupt) AC outlet--They do not "care" about grounding--Just if there is more than ~5-10 mAmps of current flow outside the two AC leads). Note that GFI Outlets may have false trips on MSW type AC inverters.

There is secondary uses for ground referencing to a cold water pipe/ground rod... Florescent tube fixtures--They will start easier if the metal case is earth ground referenced. And there are spark based ignition systems--Earth grounding makes the flame detection system work properly (improper grounding causes the spark ignition to be unreliable/constantly sparking).

If you have a radio transmitter (HAM, etc.), the "ground" is the other 1/2 of your antenna system.

If you do not have lightning issues, you do not need any earth bonding for the system to run reliably and safely. You do not even need to run a green wire ground if your loads have 2 prong plugs (equipment is double insulated). If you are worried about being shocked (wet weather, working near water), use a GFI outlet to power your loads.

If you do have lightning in the area--If not a ground rod, then a ground plate (at talked about above), and/or bury some 6 AWG bare copper wiring just outside your building wall (next to the power system) and tie to your solar array frame/mounts, and if you want, to your battery bank negative. If you have an isolated sine wave inverter, you can (if you wish) tie one AC netural (white wire) to the earth ground too (not required).

-Bill

Estragon · April 2017

Maybe a bigger question is what you intend to run with a 2500w inverter off a couple of small 6v batteries. That's a lot of current at 12v from batteries that aren't made for it.

jackypaper · April 2017

Estragon said:

Are you running the loads through a panel, and if so, is the neutral-ground bond installed?

No. I'm just plugging tools into the inverter as needed.

Johann · April 2017

Estragon said:

Maybe a bigger question is what you intend to run with a 2500w inverter off a couple of small 6v batteries. That's a lot of current at 12v from batteries that aren't made for it.

Those high wattage inverters are great to start inductive loads and a necessity in some cases to start motors. The higher amps may only be needed for a few seconds. A high wattage inverter does not indicate that a user will max it out.
Remember, the OP mentioned that it is being used in a workshop so more power may be required for a few seconds at start-up where a smaller inverter may kick out.

Ground Wire in My Shop?

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