Neutral and Earth Ground Question

On Fri, 03 Jun 2005 17:21:11 GMT HorneTD wrote: | snipped-for-privacy@ipal.net wrote: |> On Fri, 03 Jun 2005 02:58:31 GMT HorneTD wrote: |> |> | Mount a four hole lug of appropriate size on an insulating stand off, |> | bug the three conductors onto a short pigtail off of the breaker using |> | spit bolts or insulating displacing connectors as appropriate, use an |> | insulated multi tap block to join the four conductors to the jumper from |> | the breaker... There is always a code compliant way to do it. You just |> | have to invest the time or the money in hired expertise to find out what |> | that way is. |> |> If I would approve of things like pigtails and splices, I'd just run some |> 600 kcmil from the main breaker down a raceway and splice off each of the |> 4/0 feeds into the 3 panels they go to. But my intention is to absolutely |> avoid splicing (having seen the mess when they fail). I believe the risk |> is less by just stranding the 4/0 into 2 adjacent holes on the same lug. |> Or can you show me code that says not to split stranded wire into two holes? |> I'm not convinced about the "fracturing" issue since this will involve less |> mechanical stress on the wire than typical wire bending that takes place in |> typical panels, especially if I use the larger box that would be needed to |> put all those pigtails below the breaker. |> | | 110.3 Examination, Identification, Installation, and Use of Equipment. | (B) Installation and Use. Listed or labeled equipment shall be installed | and used in accordance with any instructions included in the listing or | labeling.

So basically, you can't figure out a better way to do it.

At this point I will now ignore all followups that do not have a constructive solution not involving splices, pigtails, or other unsecured connections.

Undoubtedly because they are code compliant and your method is not. Would you mine explaining how an insulated terminal block is an unsecured connection?

On Fri, 03 Jun 2005 19:42:50 GMT HorneTD wrote: | snipped-for-privacy@ipal.net wrote: |> On Fri, 03 Jun 2005 17:21:11 GMT HorneTD wrote: |> | snipped-for-privacy@ipal.net wrote: |> |> On Fri, 03 Jun 2005 02:58:31 GMT HorneTD wrote: |> |> |> |> | Mount a four hole lug of appropriate size on an insulating stand off, |> |> | bug the three conductors onto a short pigtail off of the breaker using |> |> | spit bolts or insulating displacing connectors as appropriate, use an |> |> | insulated multi tap block to join the four conductors to the jumper from |> |> | the breaker... There is always a code compliant way to do it. You just |> |> | have to invest the time or the money in hired expertise to find out what |> |> | that way is. |> |> |> |> If I would approve of things like pigtails and splices, I'd just run some |> |> 600 kcmil from the main breaker down a raceway and splice off each of the |> |> 4/0 feeds into the 3 panels they go to. But my intention is to absolutely |> |> avoid splicing (having seen the mess when they fail). I believe the risk |> |> is less by just stranding the 4/0 into 2 adjacent holes on the same lug. |> |> Or can you show me code that says not to split stranded wire into two holes? |> |> I'm not convinced about the "fracturing" issue since this will involve less |> |> mechanical stress on the wire than typical wire bending that takes place in |> |> typical panels, especially if I use the larger box that would be needed to |> |> put all those pigtails below the breaker. |> |> |> | |> | 110.3 Examination, Identification, Installation, and Use of Equipment. |> | (B) Installation and Use. Listed or labeled equipment shall be installed |> | and used in accordance with any instructions included in the listing or |> | labeling. |> |> So basically, you can't figure out a better way to do it. |> |> At this point I will now ignore all followups that do not have a constructive |> solution not involving splices, pigtails, or other unsecured connections. |> | | Undoubtedly because they are code compliant and your method is not. | Would you mine explaining how an insulated terminal block is an | unsecured connection?

Your description of why not to mix current carrying conductors in the same hole ...

On Wed, 01 Jun 2005 20:04:08 GMT HorneTD wrote:

| It is the thermal cycling of the current carrying grounded conductor | (neutral) that makes having it in the same termination as the Equipment | Grounding (bonding) Conductor (EGC) an unsafe practice electrically. | There has yet to be devised a terminal that can use one pressure | producing part to maintain good electrical contact with two conductors | that are thermally cycling at different rates and times. If you look at | the breakers that are listed to hold two separate conductors you will | see that the conductors are separate from each other and the screw has a | pressure washer under its head. The addition of the pressure washer or | plate allows solid contact between both conductors and the plate into | which the screw is threaded. The pressure washer will flex sufficiently | to permit unequal thermal cycling without the connection failing. | | In thirty years of electric work I have seen many connection failures | caused by improper torquing of connections and by using a single | terminal to terminate multiple conductors. The reason that it is safe | to use a single terminal to terminate multiple EGCs is that they do not | carry current during normal operation and they are not subjected to | repeated thermal cycling.

... would just as readily apply to phase conductors as well as the neutral. If you have 2 or more different loads (hence different thermal cycling characteristics) fed by different conductors in the same hole, the same problem will occur. A pigtail is thus like that. Maybe this is why pigtails have failed. Your earlier post further reinforces my intent to avoid all pigtails with 3 or more conductors (those with 2 will be avoided as well, but your post doesn't really reinforce my intent against those).

But I hardly would consider putting a 600 kcmil and 3x 4/0 together on the same pigtail. Maybe cad-welded ... maybe.

As for a terminal block, how is it any different than a lug on a circuit breaker, other than taking up even more space. How is it that a terminal lug would be safe enough to be listed as a terminal block and not as part of a circuit breaker?

A friend of mine is a metal machinist. Perhaps I'll just have the exact lug needed manufactured for me.

BTW, did you know that a common practice when 2 more more panels are needed in parallel is to put 2 wires in the lugs, one coming from the service entrance metal, and the other going to the 2nd panel? What I wonder is if you would cringe at that? I would. Yet it is common, and has the same issue you explained before. But I will be avoiding such a thing.

On Fri, 03 Jun 2005 19:42:50 GMT HorneTD wrote: | snipped-for-privacy@ipal.net wrote: |> On Fri, 03 Jun 2005 17:21:11 GMT HorneTD wrote: |> | snipped-for-privacy@ipal.net wrote: |> |> On Fri, 03 Jun 2005 02:58:31 GMT HorneTD wrote: |> |> |> |> | Mount a four hole lug of appropriate size on an insulating stand off, |> |> | bug the three conductors onto a short pigtail off of the breaker using |> |> | spit bolts or insulating displacing connectors as appropriate, use an |> |> | insulated multi tap block to join the four conductors to the jumper from |> |> | the breaker... There is always a code compliant way to do it. You just |> |> | have to invest the time or the money in hired expertise to find out what |> |> | that way is. |> |> |> |> If I would approve of things like pigtails and splices, I'd just run some |> |> 600 kcmil from the main breaker down a raceway and splice off each of the |> |> 4/0 feeds into the 3 panels they go to. But my intention is to absolutely |> |> avoid splicing (having seen the mess when they fail). I believe the risk |> |> is less by just stranding the 4/0 into 2 adjacent holes on the same lug. |> |> Or can you show me code that says not to split stranded wire into two holes? |> |> I'm not convinced about the "fracturing" issue since this will involve less |> |> mechanical stress on the wire than typical wire bending that takes place in |> |> typical panels, especially if I use the larger box that would be needed to |> |> put all those pigtails below the breaker. |> |> |> | |> | 110.3 Examination, Identification, Installation, and Use of Equipment. |> | (B) Installation and Use. Listed or labeled equipment shall be installed |> | and used in accordance with any instructions included in the listing or |> | labeling. |> |> So basically, you can't figure out a better way to do it. |> |> At this point I will now ignore all followups that do not have a constructive |> solution not involving splices, pigtails, or other unsecured connections. |> | | Undoubtedly because they are code compliant and your method is not. | Would you mine explaining how an insulated terminal block is an | unsecured connection?

After going through the Square D terminal block catalog, it turns out none are made of the right size. Maybe you know of one they make, or that someone else makes. The need is for 600 kcmil (or maybe even 750) in, and

3x 4/0 (211.6 kcmil) out.

So, back to the 6 hole lug ... because it is the only solution so far.

connections.

Utilco PDB-26-750-1

(2) 250-750 mcm in, (6) #6awg - 250 mcm out, 950 amps

If they do not change out the panel lugs to the multi barrelled variety they are asking for a failure.

-- Tom Horne

On Sat, 04 Jun 2005 22:13:13 GMT HorneTD wrote: | snipped-for-privacy@ipal.net wrote: |> |> Your description of why not to mix current carrying conductors in the |> same hole ... |> |> On Wed, 01 Jun 2005 20:04:08 GMT HorneTD wrote: |> |> | It is the thermal cycling of the current carrying grounded conductor |> | (neutral) that makes having it in the same termination as the Equipment |> | Grounding (bonding) Conductor (EGC) an unsafe practice electrically. |> | There has yet to be devised a terminal that can use one pressure |> | producing part to maintain good electrical contact with two conductors |> | that are thermally cycling at different rates and times. If you look at |> | the breakers that are listed to hold two separate conductors you will |> | see that the conductors are separate from each other and the screw has a |> | pressure washer under its head. The addition of the pressure washer or |> | plate allows solid contact between both conductors and the plate into |> | which the screw is threaded. The pressure washer will flex sufficiently |> | to permit unequal thermal cycling without the connection failing. |> | |> | In thirty years of electric work I have seen many connection failures |> | caused by improper torquing of connections and by using a single |> | terminal to terminate multiple conductors. The reason that it is safe |> | to use a single terminal to terminate multiple EGCs is that they do not |> | carry current during normal operation and they are not subjected to |> | repeated thermal cycling. |> |> ... would just as readily apply to phase conductors as well as the |> neutral. If you have 2 or more different loads (hence different |> thermal cycling characteristics) fed by different conductors in the |> same hole, the same problem will occur. A pigtail is thus like that. |> Maybe this is why pigtails have failed. Your earlier post further |> reinforces my intent to avoid all pigtails with 3 or more conductors |> (those with 2 will be avoided as well, but your post doesn't really |> reinforce my intent against those). |> |> But I hardly would consider putting a 600 kcmil and 3x 4/0 together |> on the same pigtail. Maybe cad-welded ... maybe. |> |> As for a terminal block, how is it any different than a lug on a circuit |> breaker, other than taking up even more space. How is it that a terminal |> lug would be safe enough to be listed as a terminal block and not as part |> of a circuit breaker? |> |> A friend of mine is a metal machinist. Perhaps I'll just have the exact |> lug needed manufactured for me. |> |> BTW, did you know that a common practice when 2 more more panels are |> needed in parallel is to put 2 wires in the lugs, one coming from the |> service entrance metal, and the other going to the 2nd panel? What I |> wonder is if you would cringe at that? I would. Yet it is common, |> and has the same issue you explained before. But I will be avoiding |> such a thing. |> | If they do not change out the panel lugs to the multi barrelled variety | they are asking for a failure.

I think the broader issue is finding the correct lugs. What I have found is that the choices available don't cover all the possible needs. And in some there are no choices at all.

Suppose you are the electrician for a job in a residence where there is

400 amp service, and 2 200 amp panels. The meter has double lugs on the load side and 4/0 feeds each panel separately. More circuits are needed and these 2 panels are full, so the job involves adding a 3rd panel. Load calculations do not call for any more service amperage (before, it was only barely above 200 amps, so now it is maybe around 300 amps). Surely, for 3x 200 panels in parallel, you would put in a 400 amp main instead of letting the panels add up to a theoretical potential of 600 amps on a 400 amp service. But a full 400 amp breaker panel won't fit while a unit breaker panel to serve as a main will for the 3 200 amp panels will. But that's 2 new panels and that uses up all the available space. So how will you wire it?

Phill I know you will say I'm some sort of code extremist but you cannot feed multiple two hundred ampere panels serving the same dwelling with 4/0 Aluminum. If you feed them with 4/0 copper you are wasting the customers money. 4/0 Aluminum can only be used as the service entry conductors for a two hundred amperes panel when the panel is the only main distribution panel for the dwelling. If there are two panels then neither set of conductors is "the main power feeder to a dwelling unit." The code uses the plural in that section only to cover installations in apartment houses and other multiple dwellings. That section cannot be used to size multiple feeders or service entries to a single dwelling unit. When the load for a single dwelling is split between multiple sets of conductors those conductors must be sized in accordance with Table 310.16 or by conductors sized by calculation done under engineering supervision.

To answer your question I would mount an auxiliary gutter above the three panels, run my service entry conductors to the gutter, and tap of the four hundred ampere feeder conductors using insulated taps to connect the 3/0 copper or the 250 MCM aluminum conductors to the individual panels. The four hundred ampere feeder conductor would be "the main power feeder to a dwelling unit" and could be sized from Table

310.15(B)(6). That would mean that they could be 400 MCM copper or 600 MCM Aluminum. I have installed hundreds of taps in my career and I don't know why you find the idea so horrific. An insulated tap block or multi barreled lug is far better practice then jury rigging the wrong size lug.

| Phill | I know you will say I'm some sort of code extremist but you cannot feed | multiple two hundred ampere panels serving the same dwelling with 4/0 | Aluminum. If you feed them with 4/0 copper you are wasting the | customers money. 4/0 Aluminum can only be used as the service entry | conductors for a two hundred amperes panel when the panel is the only | main distribution panel for the dwelling. If there are two panels then | neither set of conductors is "the main power feeder to a dwelling unit." | The code uses the plural in that section only to cover installations | in apartment houses and other multiple dwellings. That section cannot | be used to size multiple feeders or service entries to a single dwelling | unit. When the load for a single dwelling is split between multiple | sets of conductors those conductors must be sized in accordance with | Table 310.16 or by conductors sized by calculation done under | engineering supervision.

There is no customer. This will be my own.

| To answer your question I would mount an auxiliary gutter above the | three panels, run my service entry conductors to the gutter, and tap of | the four hundred ampere feeder conductors using insulated taps to | connect the 3/0 copper or the 250 MCM aluminum conductors to the | individual panels. The four hundred ampere feeder conductor would be | "the main power feeder to a dwelling unit" and could be sized from Table | 310.15(B)(6). That would mean that they could be 400 MCM copper or 600 | MCM Aluminum. I have installed hundreds of taps in my career and I | don't know why you find the idea so horrific. An insulated tap block or | multi barreled lug is far better practice then jury rigging the wrong | size lug.

What kind of taps would you use? How are they fixed in position? I hope you are not thinking of just bolting one wire to another and wrapping it, leaving it free floating.

At this point, though, I think I will have the correct lug manufactured. I'm sure I can get it made in tinned solid copper.

Still, I'm doubtful of any problems with splitting strands between 2 holes. I've handled large copper wire before, and never had strands break. But if there are technical resources that deal with this, I am interested in seeing it.

Your lack of previous problems are what is called anecdotal evidence. That is a very poor substitute for laboratory testing that validates the application as used. What your allergy is to split bolt connectors is of little interest to me as I have used them successfully for decades and they are listed for that application. I do prefer to use insulated multi barreled lugs or insulated tap blocks because I don't then have to install an insulated racking bar in the trough to avoid pressure damage to the taps. Would the taps be free floating? Yes and no. If I rack all the conductors with properly sized tie wraps to an insulated bar or stand offs I don't think that anyone not using cable bending tools will get them in contact with the wall of the trough.

| Your lack of previous problems are what is called anecdotal evidence. | That is a very poor substitute for laboratory testing that validates the | application as used. What your allergy is to split bolt connectors is | of little interest to me as I have used them successfully for decades | and they are listed for that application. I do prefer to use insulated | multi barreled lugs or insulated tap blocks because I don't then have to | install an insulated racking bar in the trough to avoid pressure damage | to the taps. Would the taps be free floating? Yes and no. If I rack | all the conductors with properly sized tie wraps to an insulated bar or | stand offs I don't think that anyone not using cable bending tools will | get them in contact with the wall of the trough.

I suppose I could use your very same argument on split bolt connectors. But I have only seen them fail once (compared to pigtails which is several times). I'm sure it can be argued that anything can be installed wrong and be subject to failure regardless of what it is. All these things I have seen fail were not my installation work.

If the split bolts are actually made of copper, one concern will be gone.

I do remain annoyed at the manufacturer. Two hole lugs are available but three hole lugs are not. But I guess they do that for marketing reasons. I will still investigate having custom lugs manufactured. But I will also investigate alternatives.

I don't want any connections to be located above 1.75 meters. I want to be sure everything can be examined without the need for any climbing.

What is the minimum safe bending radius for single (THWN, etc) copper wire of sizes 4/0, 250, 500, and 600?

Phil I just reread your reply and I'm going to have to ask you when I suggested trying to "pig tail" several large conductors into a single connection? You say you have seen this done. What materials were used to do it because I cannot imagine how that could be done.

-- Tom Horne

| I just reread your reply and I'm going to have to ask you when I | suggested trying to "pig tail" several large conductors into a single | connection? You say you have seen this done. What materials were used | to do it because I cannot imagine how that could be done.

I don't recall that you did. But it is a very common suggestion and I have seen it done on a 200 amp feeder. It was just a very large pigtail covered heavily in black tape. I didn't want to take the tape off to inspect it.

Phill Your kidding right! You didn't ever leave it that way? I cannot imagine any method of connecting multiple large gage conductors together in a single connection that would not be extremely dangerous.

On Thu, 09 Jun 2005 04:02:05 GMT HorneTD wrote: | snipped-for-privacy@ipal.net wrote: |> On Wed, 08 Jun 2005 23:25:18 GMT Takoma Park Volunteer Fire Department Postmaster wrote: |> |> | I just reread your reply and I'm going to have to ask you when I |> | suggested trying to "pig tail" several large conductors into a single |> | connection? You say you have seen this done. What materials were used |> | to do it because I cannot imagine how that could be done. |> |> I don't recall that you did. But it is a very common suggestion and I |> have seen it done on a 200 amp feeder. It was just a very large pigtail |> covered heavily in black tape. I didn't want to take the tape off to |> inspect it. |> | | Phill | Your kidding right! You didn't ever leave it that way? I cannot | imagine any method of connecting multiple large gage conductors together | in a single connection that would not be extremely dangerous.

It was not my responsibility to mess with it. And I certainly did not want to be making something bad possibly worse.

At what wire size would you consider pigtails to be safe?

Not being sure we are talking about the same thing I hesitate to answer. What do you mean when you say "pigtail?"

On Thu, 09 Jun 2005 13:11:11 GMT HorneTD wrote: | snipped-for-privacy@ipal.net wrote: |> On Thu, 09 Jun 2005 04:02:05 GMT HorneTD wrote: |> | snipped-for-privacy@ipal.net wrote: |> |> On Wed, 08 Jun 2005 23:25:18 GMT Takoma Park Volunteer Fire Department Postmaster wrote: |> |> |> |> | I just reread your reply and I'm going to have to ask you when I |> |> | suggested trying to "pig tail" several large conductors into a single |> |> | connection? You say you have seen this done. What materials were used |> |> | to do it because I cannot imagine how that could be done. |> |> |> |> I don't recall that you did. But it is a very common suggestion and I |> |> have seen it done on a 200 amp feeder. It was just a very large pigtail |> |> covered heavily in black tape. I didn't want to take the tape off to |> |> inspect it. |> |> |> | |> | Phill |> | Your kidding right! You didn't ever leave it that way? I cannot |> | imagine any method of connecting multiple large gage conductors together |> | in a single connection that would not be extremely dangerous. |> |> It was not my responsibility to mess with it. And I certainly did not |> want to be making something bad possibly worse. |> |> At what wire size would you consider pigtails to be safe? |> | | Not being sure we are talking about the same thing I hesitate to answer. | What do you mean when you say "pigtail?"

2 or more (often 3) wires connected together, usually by twisting or braiding, under a containment device cap that may be screw on or clamp on, which may be found to be wrapped up by electrical tape in situations where other wires or metal may come in contact or be too close. Some evidently contain some use of magic smoke. The containment devices were not mechanically secured to the enclosing panel (some were not even in a panel, but that's a separate issue) like you might get with a terminal block.

The largest I have seen I cannot say for sure what the size was, but it was definitely larger than 4/0. I'd guess maybe around 500 kcmil with

3 such wires connected together (maybe not all exactly the same size).

The wires were about the same as the ones in this picture (though this shows something entirely different):

Think about what happens if those two wires are removed together. You would disconnect the grounded conductor and the equipment grounding conductor, but the circuit would still be connected to the ungrounded side of the line. This would be extremely dangerous if there was any leakage current or fault.

Ben Miller

And I assume you will have an appropriate listing agency test and label them, so they are code compliant? Why not use the lugs that are commercially available, designed for the purpose, and verified by UL, as Tom Horne has suggested?

Ben Miller