3 Wire Electrical Subpanel Question

pburchett

Member
I have a barn with a preexisting electrical subpanel which is ran from my home breaker box with 3 wires (two hot/1 neutral/no ground 240 volts). I know this is not to code today but it was appropriate when it was built.

I have currently built onto the barn, poured concrete floors, installed garage doors and in the process of covering the outside with metal siding and then upgrading the electrical to a 4 wire feeder. I work slow and only have an hour or so after I get home from my day job till it is dark so it may take a while to get the 4 wire feeder installed.

My question is if the subpanel is wired correctly concerning the ground. Here is how it is wired from the house out to the barn. House is up to code with breaker panel consisting of ground and neutral bar bonded to each other. A double pole 30 amp breaker feeds 2 hot and a neutral wire to the barn subpanel by underground wire not in conduit (no other water lines or phone lines are connected to the barn) Subpanel has the neutral from the house tied to all the neutrals in the barn along with the receptacle grounds. From what I can tell from the NEC this is correct for that time period, BUT should there be a ground rod connected to the barn subpanel?
 
Hi, mine has a galvanized plate about 1/2"thick
fastened to copper bare braided 1/4" thick wire
buried 3ft deep for grounding panel. Ed Will Oliver
BC
 
As per my local Inspector, if it is a 3 wire
feed then yes it needs a ground rod or even
2 depending on how well they ground. If it
is a 4 wire then no ground rod.
 
The ground should be bonded to the nuetral
at one point only and that would be at your
house panel. You should seperate the grounds
from the nuetral at your sub panel. Then
check to see that the nuetral buss is not
bonded to the panel, then install a ground
buss in the panel and connect it to a ground
rod. Prim and proper installation when you
get the 4 wire feed installed would require
connecting the fourth wire to that ground
buss thus carrying the ground all the way
back to your house box. To leave it also
connected to a ground rod driven at the sub
panel is debatable. Guy who helped me at my
place said that it was not needed but not
dangerous.
 
Your dedication is admirable. I have multiple sub panels, all old enough they're all three wire, and will stay that way. As long as you're going to run new wire, are you going to upgrade to a higher amperage? I hope so. My main panel is at the grain bins, close to the road. The underground feed to my house is probably 200'. It's 100 amp. I don't remember the size of the wire, but it's very big. The electrical supply house sized it, and it works fine.
 
On a sub-panel all the neutral and ground wires should be kept separate. Is there some way you can run an additional wire to the main box for the ground? It should also have at least one earth ground rod installed at the barn. The neutral is considered a current carrying line and if for some reason the line going to the main box was interrupted it would make everything you have grounded live. If it was kept separate your lights and everything on 110v would just stop working. It would be safe.
 
(quoted from post at 16:25:48 01/12/17) Your dedication is admirable. I have multiple sub panels, all old enough they're all three wire, and will stay that way. As long as you're going to run new wire, are you going to upgrade to a higher amperage? I hope so. My main panel is at the grain bins, close to the road. The underground feed to my house is probably 200'. It's 100 amp. I don't remember the size of the wire, but it's very big. The electrical supply house sized it, and it works fine.
Dedication??? Might be a combination of it gets me outside in the fresh air, teaches the son some life skills and saves a little money doing it myself as I have a young'in in college and another that will soon be there. Since the wife and myself work our children get no financial aid. I do plan on upgrading the new feed wire for more amps. This one will do for a while and thanks for the suggestion.
 
Good detail and serious thoughtful questions, you're no Billy Bob lol

You ask "BUT should there be a ground rod connected to the barn subpanel?" My short answer/opinion is YES

Unless the NEC has changed (which I seriously doubt) as I best recall (NO Warranty) EVERY BUILDINGS ELECTRICAL SERVICE REQUIRES GROUNDING and Id say your barn is a building and it has an electrical service SO YES YOUR BARNS ELECTRICAL SERVICE REQUIRES GROUNDING IN MY OPINION but no warranty I'm too long retired and not up on latest codes and this may be wrong as rain, do as you please

That being said, and speaking of "ground rods" when I practiced power distribution design we (per NEC and local jurisdiction) were required to bond to all "readily available" Grounding Electrodes and such may consist of structural building steel, earth ground grids, metallic buried utility pipes, and "made electrodes" such as copper rods driven into earth. Since you may not have structural steel and no water lines or buried grids, I would use at least one better two driven into earth copper ground rods subject to local authority (if any) and local codes (if any). In our jurisdiction at the time we were required to drive the first rod then test it and if it failed drive another rod HOWEVER YOUR JURISDICTION MAY REQUIRE TWO RODS SO CHECK WITH THEM IF ANY SUCH EXIST AND IF IN DOUBT ID JUST DRIVE TWO AND BE DONE WITH IT is my best rusty professional advice

So its my best professional (albeit old n rusty lol) opinion YES use one or two driven into earth "made grounding electrodes" of copper rods at the "buildings electrical service"

PS the old codes only required three wires (2 Hots and Neutral) be ran to a barn sub panel but later codes recognized it was safer to run 4 wires (2 Hots, Neutral, Equipment Ground) out to sub panels and at the sub the Neutral Buss and Equipment Ground Buss were electrically separated and isolated from each other unlike at the main where they are bonded. This allows for the concept of SINGLE POINT GROUNDING which is safer for several reasons. There should be ONLY ONE Neutral Ground Bond for safety purposes..........

Check with local authority and trained competent professional electricians and engineers and if they say do it different then anything posted here (me included) you may want to give that serious thought....

John T Too long retired electrical power distribution design engineer so no warranty, consult professionals
 
relying on a ground far away can cause some problems.. In a very rocky area, a local mall had a problem where the telephone and power came in for opposites sides and everytime you touch between the different equipment you would get shocked. Power company had to come in and place additional grounds in this long building to lower the potential. and bring its grounding system down to a safe level. With enough grounds, and bonding all the steel structure, the 30 to 60 volts was brought down to a safe level. Due to the rock, a lot of grounding by the building owner had to be done as well.

SO.. in your 3 wire system,, absolutely add a very good ground.. If metal building also ground the build well at multiple locations and tie to box ground. If 4 wire system, and long run, a major fault could see a ground rise potential..(like the case of North Star Mall) and may be enough to be deadly.. so a grounding system there is very important as well. wet working conditions, very good grounds and connections on all runs is important. The power company grounds the neutral at EVERY pole now to keep the neutral safe and always NEAR ground. or as near ground as possible in a fault or lightning hit situation. This is mandatory for the other utilities sharing the pole run as well, as their messenger strand must be tie to.. and at the same potential as the neutral.

all the same disclaimers, from a retired utility company engineer.
 

Depending on the type of soil and moisture. A pair of 10ft ground rods , spaced at least 10ft apart should be sufficient grounding at the remote breaker panel.
As previously stated the grounds and neutrals need to be separated at the remote panel or neutral current will flow in the ground system.
 
While not as exhaustive as the full NEC article 250, here is a pretty good overview on grounding. Not that the picture of the wad of wires at the single ground lug mounted with a screw and washer in the panel is NOT acceptable. Should have had a caption: "Bubba wuz heer".

http://fyi.uwex.edu/mrec/files/2011/04/W4.-Biesterveld-NEC-grounding-MREC2010.pdf
 
Sorry to have to ask again...but I want to make this three wire system is as safe as possible till I can get a larger 4 wire feed installed.

I am starting to get confused by some of the replies about the grounds and neutrals being bonded or separate in my three wire sub panel.

The system I have looks identical to the below diagram except for the ground rod in the subpanel which I do not currently have but plan on installing. It will be connected to the bonded neutrals and grounds in the current subpanel. Is this correct? Thanks in advance.

75836d1404882959-square-d-sub-panel-3-wire-feeder-detached-building.jpg
 
Sorry for the delay in getting back to this, but in most localities yes, as per the diagram it is both "safe" and "approved". Your local "Authority Having Jurisdiction" (building code enforcement officer) would be the one to check with for the final word for where you are at. Some places would require 2 ground rods on a loop of wire, not just one as per the diagram. Any other metal piping (water, gas, air) would need to be bonded to that ground connection, as would the steel frame of a building.

Hope that helps.
 

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