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View Full Version : Sub-Panel Neutral and Ground Bonded



TJanak
12-10-2009, 07:29 PM
The sub panel in my 40 year old house has all of the neutral and grounds on the same bus. I know this is incorrect but would like to figure out the best way to fix it. The current wire feeding the panel from the main is a 2 wire plus ground "romex" type insulated cable. It feeds the whole house other than the A/C compressor so this feed is probably 4-6 gauge (EDIT: actually looked at it today and it's #2) because it makes a 55' run from the main panel. The ground on this cable is non insulated like in a romex type cable.

To separate the neutrals and grounds I would assume I need to add another bus bar and then run another wire from the main panel to the sub. Would this new wire need to be the neutral since my current ground is non insulated? If so, I assume it would need to be the same gauge as my current hot feed?

Lastly, how important is it that I fix this? I also need to add GFCI's in bathrooms and the kitchen (maybe a GFCI breaker in the sub panel) and wasn't quite sure if this neutral ground bond issue at the sub panel would affect GFCI operation.

Thanks!

jar546
12-10-2009, 09:14 PM
If it has been like that for 40 years leave it alone unless you are willing to run a new 4 wire cable.

GabeS
12-11-2009, 01:01 PM
If the neutrals and ground are joined then you could get current on the ground wires. The ground should not carry current. Do you mean that you have a three wire plus ground coming into the panel? Two wire and ground would only be 110 volts.

Jar, why do you recommend to leave it alone? Isn't it a potentially dangerous situation?

Scuba_Dave
12-11-2009, 01:52 PM
2 hots+neutral=240v, used to be the way things were run-not sure how long ago
How many wires from your POCO ? - never seen 4

Plenty of places still hooked up this way

220/221
12-11-2009, 02:18 PM
That's the way it was done in the olden days.

Don't mess with it unles you are doing some major work or replacing the panel.

hj
12-11-2009, 04:45 PM
HOW olden days was it. That type of cable is often aluminum. Connect the grounds to a new bus bar, and connect THAT to a ground rod. Leave the current third wire as the neutral. BUt as it is now, the grounds are NOT carrying current, unless they are attached to an active circuit at their origination point.

TJanak
12-11-2009, 07:28 PM
Looks to be copper but I'm not 100% sure. Didn't scratch it because it was hot.

The current third wire comes into the box with no insulation, just like the ground in romex. It touches the sides of the box as it makes its way down to the lug at the bottom. I don't really care for this because of the neutrals and grounds connected to this third wire, specifically the neutrals. It doesn't seem to me to be a suitable neutral due to the lack of correct insulation.

Also, by the time I get to a suitable location to put in a ground rod I might as well run the extra 10-15 ft. to the main panel. EDIT: frenchie: Don't know why I would do the ground rod though, both main and sub panel are on the house, just opposite sides.

frenchie
12-11-2009, 08:04 PM
If you want to do it right, it need a ground rod because it's in a separate building, and it needs 4-wire to the main panel.

codeone
12-13-2009, 06:55 AM
HOW olden days was it. That type of cable is often aluminum. Connect the grounds to a new bus bar, and connect THAT to a ground rod. Leave the current third wire as the neutral. BUt as it is now, the grounds are NOT carrying current, unless they are attached to an active circuit at their origination point.

If you take this advice be sure you rewire with a four wire conductor. Otherwise your grounds will be doing nothing. Contrary to popular belief current is not trying to find ground its trying to find its source. You have to have a complete circle. The earth is not a low impediance path for current to follow. Thats why you need the fourth wire. It is true today this situation would not be allowed. However it is permitted to leave the way it is. As long as a dryer or range does not originate out of the sub panel.

Speedy Petey
12-13-2009, 07:03 AM
If you take this advice be sure you rewire with a four wire conductor. Otherwise your grounds will be doing nothing. Contrary to popular belief current is not trying to find ground its trying to find its source. You have to have a complete circle. The earth is not a low impediance path for current to follow. Thats why you need the fourth wire. It is true today this situation would not be allowed. However it is permitted to leave the way it is. As long as a dryer or range does not originate out of the sub panel.
Absolutely agree!

Simply connecting a ground wire to a ground rod will do absolutely nothing.

rmelo99
12-13-2009, 09:25 AM
If you want to do it right, it need a ground rod because it's in a separate building, and it needs 4-wire to the main panel.

Am I missing somewhere in the post where he said the 2 panels were in sep buildings?

TJanak
12-13-2009, 10:00 AM
Well I figured I would just leave it alone since it is permitted, but you mentioned the dryer and range coming off of this panel. They both do as well as my well sub pump (3 wire) and water heater. Are the range and dryer a concern because they are 110/220 appliances?

For what it's worth, yesterday I looked at my parents house which was built in 1988 or so. It is set up exactly like my house except my meter and main panel are on the house. They have one main panel on the meter pole and the sub in the house is wired the exact same way mine is, even including the dryer.

frenchie
12-13-2009, 11:15 AM
Am I missing somewhere in the post where he said the 2 panels were in sep buildings?

...My bad. Not too sure where I got that from.

jar546
12-13-2009, 11:47 AM
Jar, why do you recommend to leave it alone? Isn't it a potentially dangerous situation?

If you read what I said again, my intention was to basically say that anything short of running a new 4 wire cable is a waste. If you are not going to do it right then don't do it at all.

codeone
12-14-2009, 05:21 PM
Well I figured I would just leave it alone since it is permitted, but you mentioned the dryer and range coming off of this panel. They both do as well as my well sub pump (3 wire) and water heater. Are the range and dryer a concern because they are 110/220 appliances?



The deal with the range and dryer using the ground and the neutral on the same conductor is that it carries current normally. As you know electricity takes all paths available to it. We try to have a low impedance(resistance)path as possible by seperating the grounds and neutrals in the sub panel. This is so if you have a bad connection some where you do not have current where it shouldnt be.

Both the 2005 and the 2008 NEC's read essentially the same
Article 250.140
Frames of Ranges and Clothes Dryers.
Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units,clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units,clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met.

(1) The supply circuit is 120/240-volt, single-phase,3-wire: or 208y/120-volt derived from a 3-phase,4-wire, wye-connected system.

(2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.

(3) The grounded conductor is insulated, or the grounded conductor is uninsulated and part or a Type SE service-entrance cable and the branch circuit originates at the service equipment.

(4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment

TJanak
12-14-2009, 08:10 PM
codeone,

Help me understand the principles behind this:

This means that the branch circuits to the range and dryer will carry current in the neutral (they are 3 wire) and then you are guaranteed to have current in the third uninsulated wire from the sub panel to the main box?

If this is the case, don't you have current in this third wire most of the time anyways from the 110 branch circuits out of the sub panel?

This third wire from the sub to the main panel is not insulated like the other two conductors are. It is bare and just enclosed in the woven fiber looking sheath of this "romex" type cable between the other two conductors. How dangerous is this since this wire is normally carrying current?

Thanks!

codeone
12-15-2009, 05:49 PM
Lets say you have copper piping for your water supply and your piping is used as a grounding electrode from your service. Your bare neutral corodes and causes a bad connection back to your service. You touch the frame of your dryer or range and the water pipe at the same time. you then could become a low impedance path back to the main service. Your 120v items do not usually have accessable parts for you to ground yourself out to become that path. At least the ones made today. Hopefully this basic explanation helps.

TJanak
12-15-2009, 07:15 PM
Got it. Thanks! It all makes sense now.