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Anonymous asked in Home & GardenMaintenance & Repairs · 1 decade ago

Electricity: If a sub panel was wired just like the main panel (ground and neutral bonded) what is the danger?

In 1990 I back fed a sub panel (located next to the main panel) with a breaker from the main panel, then I bonded both the neutral and ground wires on the (one) bar in the sub panel, then I attached the bar in the sub panel to the bar in the main panel with appropriate sized wire (both bars with green screws attaching the bars to respected breaker cases).

-- The inspector approved it in 1990, but now I read that the new codes require that the sub panel must isolate the ground and neutral wires in the sub panel.

What is the danger of my situation?

Added question: If I unscrew the green screw bonding the one bar in the sub panel, what will ground the the sub panel case? I hope I do not have to pull everything out and float the neutral bar and add a ground bar to the sub panel .

Update:

Dear Going Postal,, Thanks for the moral support.

Update 2:

Dear Dude, Thanks. But, do you see any danger in not isolating the ground and neutral wires in the sub panel?

(I really don't want to call the new inspector and pay the $85 dollar inspection fee. If I call him and ask him for advice, he will insist on looking at again and charging me for the visit. (I know this because I have several rentals and I have called him before and he always says "I cannot give advice over the phone. I guess he is right about that.

But I am open to suggestions. I was licensed in Texas but now live in Arkansas)

Update 3:

Info: When I moved to Arkansas in 1990, Arkansas accepted my Texas Electrician License.

Update 4:

Dear Steve, I know you are right because what you said makes sense.

Dang --- In my case it would happen right at the bus bar in the sub panel.

Why?

because about 20 years ago I thought about that and sent two insulated wires from the sub panel to the main panel.

(not realizing that both insulated wires are stripped bare to connect to the sub panel's (one) bus bar. But I was thinking the sub panel was right next to the main panel and the main panel has the neutral and ground wires both on the same bus. I was figuring that the way I wired the sub panel -- the sub panel would "think" it was inside the main panel.

In the main panel the code allows the ground wire and neutral wire to both connect to the same bus bar. Why? That short distance plus the bus bar has the big neutral wire (cable) connected to it going back to the electric company sub station. -- The push pull effect of the electron flow. Well sort of the "push pull effect" --- I know it is all push but you know

Update 5:

Added:

Main Panel, of course, it is grounded to the grounding rod (via the meter case)

But it is strange the code allows the ground wires and neutral wires to share the same bus bar in the main panel. I wonder why. It seems it would be better if the main panel also had two bus bars; one floating neutral bus and one bonded ground bus (which would be connected to the grounding rods.

BTW: The new codes require two grounding rods for a sub panel in a detached building. (or a 1/4 inch metal plate buried 20 inches deep.) btw: I think that is a good policy for defense against some lightening strikes. Of course we all know, there is no defense against a direct hit against a huge mega strikes.

Update 6:

Dear Talon, Yeah I know what you mean. We are probably about the same age (I am over 50 years old).

Now, they have a fancy way of floating the neutral bar in the sub panels. Plastic insulation and all.

BTW: The new codes want the grounding rods driven 8 feet in the ground.

Here in Arkansas that is just about impossible without a back hoe.

Well Arkansas protested and the NEC added that a 2 square foot 1/4 inch plate could buried in the ground to replace the grounding rod requirement.

Update 7:

Edit:

Dear Grassy,

The inspector at the time said that the sub panel was wired just as if it was a circuit breaker inside the main panel. So what ever is said about a main panel bonding the neutrals and grounds to one bus would apply to the arrangement of the above described sub panel.

I will still take your advice and attach a ground bus to my sub panel and rewire it to current codes.

Specifically, in the sub panel I will float the neutral bus, bond the ground bus -- all white wires to the neutral bus, all bare wires to the ground bus,

Ironically, once I back feed with a main circuit breaker in the sub panel, both the neutrals and the grounds in the sub panel will eventually have a path to the one bus bar in the main panel.

Thanks .

11 Answers

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  • /\
    Lv 7
    1 decade ago
    Favorite Answer

    If you bond the neutral and ground at the sub panel Uncle,

    then stray currents from the neutral return

    could go through the equipment ground on the electrical devices

    fed from the sub panel.

    If you isolate the neutral and ground at the sub panel,

    then any currents would go back to the main panel,

    and go to the service ground.

    The main panel is where the neutral and equipment ground should be bonded..

  • TED
    7 years ago

    There is here a problem in not grounding the neutral in the sub panel next to the main panel. In the main panel the ground is a very robust conductor since it is the neutral from the power company, which is also physically grounded to earth at some point nearby. The size of the ground conductor in Romex cables that connect the main with the sub panel is smaller that the other 3 conductors. For instance, a 6/3 Romex cable typically has a #10 ground wire. If the neutral and ground are coupled only in the main panel, then all the circuits in the sub panel reach ground through that #10 conductor. That does not make sense.

  • Ray
    6 years ago

    You can end up with some very serious problems by not

    wiring a sub panel properly.If you have a twenty and thirty

    ckt there will be a difference of 10 amps.If the sub panel is bonded to the neutral from the main panel, the sub panel

    box can be electrically live and be a very dangerous shock

    hazard, even if the sub is just a 120 volt system and u r

    pulling say 25 amps with the neutral tied to the sub panel

    box then yes the sub box can/will be live to ground. That is why the code says the neutral MUST be insulated/isolated from

    the ground or metal enclosure of the sub panel

    the sub panel box

  • Grassy
    Lv 7
    1 decade ago

    The new codes do not apply to existing construction.

    To be safe do not bond the neutral and the bond in the sub-panel. The ground for the sub-panel is obtained through the neutral back to the grounded-neutral in the main panel.

    In 1990 the inspector made a mistake in allowing the way it was installed.

    The danger lies in having two possible ground reference potential voltages.

    Reference the IEEE Color Series Green book on grounding.

    If you have 3 Pole or 4 Pole Automatic Transfer Switches involved the multiple grounding will get more complicated.

    Industry Standards differ in different parts of the country.

    Bottom Line: Be Safe

    Source(s): An Electrical Engineer for 23 years
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  • Meshuggah Yam-Gazlen
    Lv 7
    1 decade ago

    the danger is that ground fault interrupters will not work correctly if there is any current on the ground line under normal conditions -- either keep them separate, or just drop the ground from the main panel when the feed reaches the sub-panel; and make all the "grounds" out of the sub-panel that same as neutral at the sub-panel -- that will make the GFI's work normally, *BUT* might not meet local code -- double check

  • Stephen
    1 decade ago

    The only risk is that you could have the neutral current flow divided evenly between the insulated neutral wire and the uninsulated (or bare) conductor where they run between the main panel and sub-panel.

    A simple solution: You could purchase a new ground bus that can screw to the sub-panel and attach all of the bare wires to this newly added bus. Then you could remove the sub-panels grounding screw and use if for insulated neutral wiring only. This solution would make it where the bare wire only would carry current if a fault occurred.

    Source(s): I'm a Texas Electrician.
  • Kyle
    6 years ago

    If neutral is bonded to ground in both panels, it also creates a ground loop. Grounding networks should always be connected in a tree topology.

  • ?
    Lv 6
    1 decade ago

    Hey Unc. Don`t pinch a brick. You did it to code in the 90`s Does not matter what the current code is unless you do a major change. White/ bare or single wire can go any friggin` place on the breaker box/bar. Just looks better if everything runs in a line. A ground is a ground ( can`t wait to see the bunch of pissed of electricians tell me the difference between the ground and neutral buss bars). Considering they are both bolted to the metal box they came in,

  • going postal
    Lv 4
    1 decade ago

    I don't know, you lost me at "If a sub panel"... I will star hopefully someone will know

  • chris
    Lv 7
    1 decade ago

    I'm gonna wait for the movie!

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