Grounded neutral in an old sub-panel

| snipped-for-privacy@ipal.net snipped-for-privacy@ipal.net posted to | sci.electronics.design: | |> In alt.engineering.electrical JosephKK

|> |
|> |> wrote: |> |> |> |>>The existing (old) sub-panel is fed by 2 phases and an |> |>>uninsulated neutral conductor. There is no ground bus, return |> |>>conductor to the service entrance, nor connection to a ground |> |>>rod. The conductors are in conduit when leaving the main panel |> |>>and arriving at the sub-panel, but not in between (they're |> |>>stapled to the flat roof under the roof's insulation & paper). |> |> |> |> You are kidding, right? Run, run away fast... Totally replace the |> |> existing setup, get those wires off the roof! |> |> |> |>> |> |>>I want to replace the sub-panel with a modern one with safe |> |>>breakers and add a ground conductor, which will be run via |> |>>another route (I want to keep the project manageable, so don't |> |>>want to run new conductors). |> |> |> |> The current system is a hazard, and needs full replacement. If |> |> you touch it, do it right. If you don't do it right, and later |> |> there's an accident (and there *will* be) you will be held |> |> responsible. |> |> |> |>> |> |>>Since the neutral conductor is uninsulated, it is in contact with |> |>>the |> |> |> |> No, that is not an neutral conductor. It is a ground conductor. |> | |> | Wrong. |> |> Would you like to try to convince anyone? It fits the description |> of |> a grounding conductor installation. The fact that it is |> (improperly) used as a neutral conductor doesn't change the way it |> is installed. | | It doesn't sound all that difficult. The existing system has no | effective ground. Thus that is a neutral conductor.
If the feeder connects to the main panel (as opposed to some other sub panel) and if that main panel has the neutral and ground bond in the panel, then the wire that is connected to the grounded bus bar in the main panel is the effective ground. If this feed goes to a separate building, adding a grounding electrode or two at the separate building will make it effectively grounded.
It is neither a neutral nor a grounding wire if it is not connected to any circuit or load, when fed from a main panel. A main panel can intermix neutral and ground wires (but no more than one neutral per screw hole in the box) on the bus or busses. A sub panel would have to keep them separate. A circuit from the main panel that includes an uninsulated wire attached to such a mixed bus does not determine that said wire is a neutral or a grounding wire in terms of how it is connected into the main panel. That it is uninsulated would, in terms of today's code, make it a grounding wire. What makes the big difference is how it is connected at the load end and used. If it is used to maintain current balance on a pair of 120 volt L-N loads or circuits, then it is being used as a neutral. But it could just as well be used as a grounding wire as long as all aspects of how it is installed meet the applicable code (which would be today's code if the circuit is upgraded to include another wire).
| One thing is clear, OP is in way over his head and needs to get a | competent contractor to inspect and produce a statement of | requirements and an estimate. Nor will this service be free in most | cases.
Agreed.
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| The existing (old) sub-panel is fed by 2 phases and an uninsulated neutral | conductor. There is no ground bus, return conductor to the service entrance, | nor connection to a ground rod. The conductors are in conduit when leaving | the main panel and arriving at the sub-panel, but not in between (they're | stapled to the flat roof under the roof's insulation & paper). | | I want to replace the sub-panel with a modern one with safe breakers and add | a ground conductor, which will be run via another route (I want to keep the | project manageable, so don't want to run new conductors). | | Since the neutral conductor is uninsulated, it is in contact with the | sub-panel (it is in the conduit bringing the feed conductors into the | sub-panel). In a sub-panel the neutral and ground are not supposed to be | connected.
That neutral conductor is, in today's terms, a grounding conductor (so it seems from your description).
| My question is this: | How do I install this new sub-panel and new ground conductor such that the | neutral and ground are separate?
Add a new insulated neutral conductor that runs with the 2 working phases all the way. If the existing phase wires are separate wires instead of pre-assembled cable, then why can't you run a 3rd wire along with them?
Another alternative: install a 240 to 120/240 volt transformer and derive a new neutral at the subpanel. That new neutral would be bonded to the ground at the transformer itself. Transformers are expensive and waste a bit of power, so this is only an option if the wiring cost would be very high.
Otherwise, you need a new 3+1 wire feeder.
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Incorrect. It is carrying return current and is therefore an uninsulated neutral. He does not have a separate equipment grounding conductor.

Because the National Electrical Code explicitly prohibits that.

That's also a Code violation. Neutral is required to be bonded to ground at the service entrance, and is prohibited from being connected to ground at any other point.

He needs a new feeder regardless. But it doesn't necessarily have to be 3+1. Three insulated circuit conductors inside a properly bonded metal conduit will suffice.
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Doug Miller wrote:

If you read his later reply you will see that the roof top conduit will be exposed to 140 degree heat. That conduit will need one or more expansion couplings in it so a separate equipment grounding conductor is his easiest way out. -- Tom Horne
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wrote:

Or bonding jumpers around the expansion couplings. Better still, he should install it on the interior side of the roof, especially as he has already said he doesn't want to pierce the roof.
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|>| |>| Since the neutral conductor is uninsulated, it is in contact with the |>| sub-panel (it is in the conduit bringing the feed conductors into the |>| sub-panel). In a sub-panel the neutral and ground are not supposed to be |>| connected. |> |>That neutral conductor is, in today's terms, a grounding conductor (so it |>seems from your description). | | Incorrect. It is carrying return current and is therefore an uninsulated | neutral. He does not have a separate equipment grounding conductor.
You misunderstand what I am saying. I'll stand by my statement, but clarify it further for you: As a grounding conductor it is being misused by allowing it to carry current. If he adds an insulated conductor (marked white) and rewires the panel so the neutral current goes over the new conductor (which must be wired along side the phase conductors, of course), then the grounding conductor he already has can be used "as" a grounding conductor (as long as there are no other gotchas in his system that might otherwise disqualify it).
|>Another alternative: install a 240 to 120/240 volt transformer and derive a |>new neutral at the subpanel. That new neutral would be bonded to the ground |>at the transformer itself. | | That's also a Code violation. Neutral is required to be bonded to ground at | the service entrance, and is prohibited from being connected to ground at any | other point.
Wrong. The transformer creates a new derived system. The neutral of that new system BEGINS at the secondary of the transformer. It would be bonded to the ground at that point and that is how a it is done.
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I don't disagree -- but the fact that it *is* carrying current makes it a neutral.

Correct.
Incorrect. Bonding the neutral of the transformer secondary to the grounding conductor on the primary side is a Code violation.
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|>|>| |>|>| Since the neutral conductor is uninsulated, it is in contact with the |>|>| sub-panel (it is in the conduit bringing the feed conductors into the |>|>| sub-panel). In a sub-panel the neutral and ground are not supposed to be |>|>| connected. |>|> |>|>That neutral conductor is, in today's terms, a grounding conductor (so it |>|>seems from your description). |>| |>| Incorrect. It is carrying return current and is therefore an uninsulated |>| neutral. He does not have a separate equipment grounding conductor. |> |>You misunderstand what I am saying. I'll stand by my statement, but clarify |>it further for you: As a grounding conductor it is being misused by allowing |>it to carry current. | | I don't disagree -- but the fact that it *is* carrying current makes it a | neutral.
It makes it used _as_ a neutral. Turn off the power and disconnect it from source and loads, and look only at the feeder and you won't know that it was used as a neutral. It could be the grounding conductor of a 2 wire 240 volt circuit.
My point is by looking at it that way, it may be repurposed (used) as the real grounding conductor (if it fully qualifies in all aspects of how it is installed) and a neutral would be added. Then you only need to add one conductor instead of two.
|> If he adds an insulated conductor (marked white) and |>rewires the panel so the neutral current goes over the new conductor (which |>must be wired along side the phase conductors, of course), then the grounding |>conductor he already has can be used "as" a grounding conductor (as long as |>there are no other gotchas in his system that might otherwise disqualify it). | | Correct. |> |> |>|>Another alternative: install a 240 to 120/240 volt transformer and derive a |>|>new neutral at the subpanel. That new neutral would be bonded to the ground |>|>at the transformer itself. |>| |>| That's also a Code violation. Neutral is required to be bonded to ground at |>| the service entrance, and is prohibited from being connected to ground at any |>| other point. |> |>Wrong. The transformer creates a new derived system. The neutral of that |>new system BEGINS at the secondary of the transformer. It would be bonded |>to the ground at that point and that is how a it is done. |> | Incorrect. Bonding the neutral of the transformer secondary to the grounding | conductor on the primary side is a Code violation.
Please cite code! (I think you will not find any such code unless it has been misinterpreted or misapplied)
Where would YOU bond it? To a separate grounding system not connected to the upstream? The grounding all has to be interconnected. Each neutral must be bonded to ground either at the entrance if it is part of a system entering the building, or at the system origin (the transformer itself or in certain cases the one panel being immediately fed by the transformer).
Think of a building that has 480Y/277 coming in and uses transformers to get either 208Y/120 (or 3 sets of 240/120 via three transformers). This is quite common. How do YOU think it is grounded?
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Of course; but I don't recall anybody suggesting that the OP needed to add two conductors.

Hmmmm. I think you're right. Thanks for educating me.
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On Dec 3, 11:06 am, snipped-for-privacy@ipal.net wrote:

Yes, that is an excellent way to deal with the problem at the subpanel. The wire-buried-in-roof-insulation is, however, ALSO problematic. It scares me.
In rewiring some of my basement sockets, I once found vinyl-sheathed cable sandwiched in paneling, with nails mainly missing the cable (four penetrated) and penetrating nails mainly not hitting more than one conductor (though one nail was melted in half, and made sparks when I pulled the halves...so I couldn't be sure) : -D
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| On Dec 3, 11:06 am, snipped-for-privacy@ipal.net wrote:
|> |> | The existing (old) sub-panel is fed by 2 phases and an uninsulated neutral |> | conductor... stapled to the flat roof under the roof's insulation & paper | |> |> Another alternative: install a 240 to 120/240 volt transformer and derive a |> new neutral at the subpanel. | | Yes, that is an excellent way to deal with the problem at the | subpanel. The wire-buried-in-roof-insulation is, however, | ALSO problematic. It scares me. | | In rewiring some of my basement sockets, I once found | vinyl-sheathed cable sandwiched in paneling, with nails mainly missing | the | cable (four penetrated) and penetrating nails mainly not hitting | more than one conductor (though one nail was melted in half, and | made sparks when I pulled the halves...so I couldn't be sure) : -D
That would be a situation that calls for tear-out and re-wire.
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JoJo wrote:
Where are you? Which code applies?

Lets assume this is in the USA, or at least covered by the NEC.
What sort of loads does this subpanel feed? 120 and 240 or 240V only?
What is the (estimated) age of the original subpanel installation? Look for a permit stapled up somewhere or even a date printed on a panel nameplate or something.
It sounds like you have a subpanel feeding only 240V loads, with no neutrals and what you have is no _neutral_ bus. The bare conductor being a ground. Either that, or this is not in compliance with current code.
But I'm just guessing here.

If you can run a ground conductor via 'another route', the you can certainly run the proper feeder to this new panel.

Correct. But being bare, it sounds more like a ground than a neutral.

You:
1) Run the correct feeder, with ground and neutral.
2) Serve only 2-wire 240V loads with no neutral from the subpanel.

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| It sounds like you have a subpanel feeding only 240V loads, with no | neutrals and what you have is no _neutral_ bus. The bare conductor being | a ground. Either that, or this is not in compliance with current code.
It sure sounded like a 240V only sub to me. But I bet it got used for 120V loads (out of compliance and likely dangerously). That's one reason I offered the transformer suggestion (isolation only, an autotransformer would not meet code there as it could still have ground currents).
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snipped-for-privacy@ipal.net snipped-for-privacy@ipal.net posted to sci.electronics.design:

It may have been compliant when built. Rewiring the feed must be done to current code.
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| snipped-for-privacy@ipal.net snipped-for-privacy@ipal.net posted to | sci.electronics.design: |
|> wrote: |> |> | It sounds like you have a subpanel feeding only 240V loads, with |> | no neutrals and what you have is no _neutral_ bus. The bare |> | conductor being a ground. Either that, or this is not in |> | compliance with current code. |> |> It sure sounded like a 240V only sub to me. But I bet it got used |> for |> 120V loads (out of compliance and likely dangerously). That's one |> reason I offered the transformer suggestion (isolation only, an |> autotransformer would not meet code there as it could still have |> ground currents). |> | | It may have been compliant when built. Rewiring the feed must be done | to current code.
But it may be possible that the existing uninsulated wire is usable as the grounding wire. That depends on other details about the installation work and quality that we cannot see and was not provided in the post. Only a qualified electrician or electrical inspector on site could be sure. But it is a possibility. Still, that wouldn't be useful unless the OP can also install an insulated single wire neutral. And that could be difficult to do in compliant with current code. If the existing wires are a cable, then likely not. But that may be allowed if they singles in a conduit (just add he new neutral into the same conduit, if there is room ... another issue).
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snipped-for-privacy@ipal.net snipped-for-privacy@ipal.net posted to sci.electronics.design:

That is pretty well on target, OP needs to get a qualified person to explain what needs done after on site inspection.
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JoJo snipped-for-privacy@planetslkenv.jo posted to sci.electronics.design:

Well you have walked straight into a very specific and detailed NEC class question. Without knowing much more, i cannot possibly offer a reasonably close to correct answer. It can be especially difficult as it seems to involve grandfathered installations and modifications of them.
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| JoJo snipped-for-privacy@planetslkenv.jo posted to sci.electronics.design: | |> The existing (old) sub-panel is fed by 2 phases and an uninsulated |> neutral conductor. There is no ground bus, return conductor to the |> service entrance, nor connection to a ground rod. The conductors are |> in conduit when leaving the main panel and arriving at the |> sub-panel, but not in between (they're stapled to the flat roof |> under the roof's insulation & paper). |> |> I want to replace the sub-panel with a modern one with safe breakers |> and add a ground conductor, which will be run via another route (I |> want to keep the project manageable, so don't want to run new |> conductors). |> |> Since the neutral conductor is uninsulated, it is in contact with |> the sub-panel (it is in the conduit bringing the feed conductors |> into the sub-panel). In a sub-panel the neutral and ground are not |> supposed to be connected. |> |> My question is this: |> How do I install this new sub-panel and new ground conductor such |> that the neutral and ground are separate? |> |> JJ | | Well you have walked straight into a very specific and detailed NEC | class question. Without knowing much more, i cannot possibly offer a | reasonably close to correct answer. It can be especially difficult | as it seems to involve grandfathered installations and modifications | of them.
The OP apparently wants to treat the feeder as grandfathered. He may be able to. But as soon as the old incorrectly wire sub panel is removed, the feeder has to be considered in the way it is physically wired. If it is sourced from a main panel, then there is no distinction that the uninsulated wire is specifically a neutral or a grounding wire. So the new sub panel going in at the end has to consider what the existing wires are in terms of the way they are installed. That uninsulated wire is thus only a grounding wire in terms of how the new panel is allowed to be wired up. No neutrals may be connected to it in the new panel.
The existing feeder may well be fully in compliance with current code as a feeder for 240-volt-only circuits. This is where more information is needed to be sure all aspects of the circuit allow its _utilization_ in a new installation (the new sub panel is the new installation).
The wiring _may_ or _may_ _not_ be able to have a neutral added to it under the current code. More information is needed.
Apparently a transformer can probably be connected to derive a new system and thus have a neutral as part of the new system. An auto-transformer cannot be used due to the requirement to have a neutral in common in such a connection (can't do that with no neutral coming in).
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When it says "two phases" it probably means Leg 1 and Leg 2 of a single phase 230/115 volt system? Not two phases?????????????
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|> The existing (old) sub-panel is fed by 2 phases and an uninsulated neutral |> conductor. There is no ground bus, return conductor to the service entrance, |> nor connection to a ground rod. The conductors are in conduit when leaving |> the main panel and arriving at the sub-panel, but not in between (they're |> stapled to the flat roof under the roof's insulation & paper). |> |> I want to replace the sub-panel with a modern one with safe breakers and add |> a ground conductor, which will be run via another route (I want to keep the |> project manageable, so don't want to run new conductors). |> |> Since the neutral conductor is uninsulated, it is in contact with the |> sub-panel (it is in the conduit bringing the feed conductors into the |> sub-panel). In a sub-panel the neutral and ground are not supposed to be |> connected. |> |> My question is this: |> How do I install this new sub-panel and new ground conductor such that the |> neutral and ground are separate? |> |> JJ | | When it says "two phases" it probably means Leg 1 and Leg 2 of a | single phase 230/115 volt system? Not two phases?????????????
Most likely it does. But sometimes not. It could be 2 out of 3 of a 3 phase system. That would be 2 phases at 120 degrees instead of 180. A system with 2 phases at 90 degrees is almost unheard of anymore. And the 60 degree ones are also mostly all gone (the railroad industry had them at the 110-120 volt range many decades ago).
Also:
Do not put spaces in the list of newsgroups in your posting. Your newsreader program apparently has a defect (a bug).
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