Another shop wiring question

Right now my shop is wired for 100 amp service, but it's only 3 wire, I believe 2-2-4 aluminum, through 2 inch conduit. I want to add the fourth wire for a dedicated ground for safety.

There is no separate grounding bar in the breaker box. It looks like I can buy that and add it easily. There are no large grounding lugs left in the meter box, I don't think I could get a stranded ground cable into the smaller lugs, but a solid wire should fit. Would it be kosher to use a solid copper bare wire as a ground back to the meter inside my conduit? Then what gauge copper wire would I use to go to a separate grounding rod outside the shed?

After all this, if I remove the green bonding screw and strap from the neutral bar it should be floating and I'll have a separate ground bar?

Thanks for the help. I've got a copy of the NEC but it's really hard to interpret as I'm still learning!

There will probably be more questions but I'll start with this!

Brandon

I don"t know if this is kosher, but could you skin back the insulation on the existing ground wire and clamp the new wire to it? There are clamps made to double up wires....IDK what they are called, just what they look like....a split bolt. But always, consult local codes.

There is a lug with two smaller tangs that fits into any two smaller holes in the ground bar then steps up for a larger cable to fit in it. You loosen two screw stab it in and then tighten both. Now off to the sdie is a new larger hole with its own screw .Probably made by GE Square D any brand should work as spacing is close. 100 amp service takes number 6 to Gr rod. No need for solid with lug kit.

To answer your first question the only designation between solid and stranded wire in the code is in swimming pools where it has to be solid . Other than that the choice between solid or stranded is up to you or the engineers that drew the plans.

Brandon, as you probably know I'm Mr. Safety and always preaching that and admire you for wanting to make things safer.

THAT BEING SAID

What you have is the way it was done for yearssssssssssssss and yes later versions of the NEC require 4 wires to a sub panel (True it is better, otherwise the NEC experts would have left things as is I'm sure).

Your statement "I want to add the fourth wire for a dedicated ground for safety." bears merit.

HOWEVER the shop branch circuits (assuming they likely have the equipment GroundING Conductor) already have a functioning dedicated ground for safety as it provides a low resistance fault current return path back to the shops panel so the breaker trips and de energizes the circuit and saves your life.

Under the old system when they just ran 3 wires out to a shop, once there the Neutral was again earth grounded PLUS the Neutral and Ground Busses were tied together the same as was done in the homes main service entrance panel. Still if an appliance fed from that panel experienced a short to case frame and if the case frame is properly bonded to the equipment GroundING Conductor (i.e. a 3 wire cord and plug) ITS STILL SAFE AND THE BREAKER TRIPS AND THATS REGARDLESS IF YOU RAN 3 OR 4 WIRES FROM HOUSE TO SHOP.

Alllllll Im trying to do is explain that YES the 4 wire system is better HOWEVER the old 3 wire still already has what you call a "dedicated ground for safety" if its wired correctly.

YES Billy Bob, I prefer and the latest NEC requires 4 wires but I just want to explain to Brandon that he already has a safety ground (if its all wired right) in the old 3 wire system.

What the 4 wire system provides is an isolated fault current return path allllllllllll the way back to the main so fault current doesn't have to flow in the same wire as Neutral return current and so you're not mixin and matching Neutral and Grounds etc.

PS True in a 4 wire sub panel Neutral and Ground Busses must be kept separate and isolated HOWEVER when modifying buss bars don't forget that the panels metal tub, being similar to a non current carrying metallic junction box, NEEDS BONDED TO THE EQUIPMENT GROUND BUSS !!!!!!!!!

Nuff said

John T

John, What happens if you have an "open" in the neutral feed wire? ( on a 3 wire feed) joe

Same thing that happens on a panel with 4 wires when the neutral opens, your line to neutral loads in series across both ungrounded conductors and you burn up electronics and transformers from the imbalance.

Dadgummit John T. that's what I was looking for in the answer to my post 2 pages ago!!

If it is running back to the meter and not to the main service I don't understand why you want to add the 4Th wire. Probably 90 percent of the electrical services in the Us are that way.

Here's the wiring at the moment.

<a href="http://s108.photobucket.com/user/weirddeere/media/IMG_3259_zps35128a2b.jpg.html" target="_blank"> </a>

The only ground is the neutral line to the meter.

I plan to start running circuits in conduit as I get time and supplies. The shed has a few too many leaks and critters for me to be comfortable with just romex. I'm thinking 20 amp 120v circuits with 12 gauge THHN. And a couple 40 amp 240v circuits with 8 gauge for a welder and air compressor. The circuits will be roughly 50 feet long, is that enough to worry about voltage drop?

Thanks for the advice all. I appreciate it and feel better about the 3 wire.

Brandon

For a sub panel under the old 3 wire system or a main panel, yes that Neutral must be earth grounded somewhere (connected to a No. 4 bare copper GroundING Electrode Conductor wired to a GroundING Electrode such as a driven rod or rods etc.), either up near the weatherhead riser or in the meter base or in the main service entrance panel.

The panel in the picture (assuming the Neutral is already earth grounded somewhere like one of the three places above) simply needs the addition of another buss or two busses tied together to be used as a common Neutral/Ground or one Neutral one Ground but bonded together with a cross tie bar.

Without doing the voltage drop calculations that length of run don't sound bad but Id have to know the amps and distance and wire size to plug it into a calculator.

Glad to help, I havent seen you since years ago when we all met at New York Expo as I recall.

John T

Sorry, I thought we had beat that to death a couple days ago but I cant remember what I had for breakfast lol

John T

(quoted from post at 00:57:42 06/06/14) If it is running back to the meter and not to the main service I don't understand why you want to add the 4Th wire. Probably 90 percent of the electrical services in the Us are that way.

Click to expand...

Cheaper, faster and easier. Grandfathered.
If they knew then what they know know.a three wire overhead supply would never have been permitted when electrical distribution was first introduced.
Tingle voltage is real problem on many farms . The owners and operators are struggling with various phantom livestock problems and not knowing why.

Well, this subject has been beat on for 10 or more years here but apparently not yet "to death". LOL
When I installed a 100 Amp sub-panel in my pole building in '96 I used 3 wire 2-0 aluminum buried in conduit which worked fine for years. Only after reading the many discussions on this site over the years did I realize the importance of that separate ground wire and the need for separating the neutral and ground in the sub-panel. Thanks to John T. and others here I was able to get it through my thick skull. A few years ago (just before the price of copper went thru the roof) I ran a solid #4 wire from my barn panel back to the main panel. Probably would never have had a problem but I feel better with that extra margin of safety.

Is cheaper, faster and easier. Not grandfathered in this case as it is new wiring to the shed, done as a quick favor by an electrician friend. He mentioned the 4 wire stuff but basically believed it was not necessary in this case...and the panel wasn't set up for it in any case. However there's absolutely no inspection out here.

Shoot me an email, I have some interesting pictures you might ponder, I'm just not sure if yours is the same. [email protected]

Brandon

The panel seems to have a common ground/neutral bar. The neutral is WELL grounded at the meter.

I'm still considering adding a ground bar kit to the box and separating the neutral and ground