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[Frank DeWitt]

Apparently people have been making there own Distros for a long long time

http://www.ebay.com/itm/Vintage-Stage-Lighting-Panel-Antique-Early-Electrical-Fuse-Panel-1920s-/112399785429?hash=item1a2b8c9dd5:g:2uoAAOSwcgNZD7ls

[Mike Sokol]

Apparently people have been making there own Distros for a long long time

http://www.ebay.com/itm/Vintage-Stage-Lighting-Panel-Antique-Early-Electrical-Fuse-Panel-1920s-/112399785429?hash=item1a2b8c9dd5:g:2uoAAOSwcgNZD7ls

That's scary. NOBODY BUY THIS!!!!

[Tim McCulloch]

That's scary. NOBODY BUY THIS!!!!

Right.  Because Mike just put in a bid and he's already on his way from Hagersbush, MD to CT to pick it up  .  At the $49 starting bid it's worth it for the brass cover plates alone.

This looks like it's being removed from an old theatre or vaudeville house and there is probably more copper and brass work from the Olde Dayz.

[Jonathan Johnson]

This looks like it's being removed from an old theatre or vaudeville house and there is probably more copper and brass work from the Olde Dayz.

The seller does have some other things that could be of interest to folks around here

http://www.ebay.com/usr/gaselectric17?_trksid=p2047675.l2559

[Frank DeWitt]

Right.  Because Mike just put in a bid and he's already on his way from Hagersbush, MD to CT to pick it up  .  At the $49 starting bid it's worth it for the brass cover plates alone.

This looks like it's being removed from an old theatre or vaudeville house and there is probably more copper and brass work from the Olde Dayz.

There is plenty of room in the panel. The wiring is neat.  Each outlet has it's own fuse(s) and switch.  What is not to like.   Joking.  Not a good idea unless you are a collector.  I am but I already have all of the components in there.  I also have a panel about that size but it is made of wood with a wood door (A "Fuse Box")

[Mike Sokol]

There is plenty of room in the panel. The wiring is neat.  Each outlet has it's own fuse(s) and switch.  What is not to like.   Joking.  Not a good idea unless you are a collector.  I am but I already have all of the components in there.  I also have a panel about that size but it is made of wood with a wood door (A "Fuse Box")

We've come a long way with power distro since the early 1900's. In one of the theaters I worked in during the 80's, they still had fuses on the neutral lines feeding the stage power and lighting. Of course, that's no longer to code.

[Jonathan Johnson]

We've come a long way with power distro since the early 1900's. In one of the theaters I worked in during the 80's, they still had fuses on the neutral lines feeding the stage power and lighting. Of course, that's no longer to code.

Speaking of fuses on the neutral...

Having a fuse on the neutral was realized to be a Bad Thing, since a fuse opening on a neutral could leave the system energized. There were no "common trip" in the days of fuses. Besides, back then, it was highly unlikely that a neutral in a properly wired system would be overloaded, so it was decided to dispense with the fuse in the neutral and require common switching if the neutral was to be switched. (Now, if my grandpa had wired it, it's a possibility. But he wasn't an electrician; he was a farmer.)

Then we transitioned to circuit breakers, but we didn't bother protecting the neutral, because it wasn't our habit to fuse the neutral anymore.

Nowadays, we have a new problem: overloaded neutrals due to the presence of triplen harmonics generated by switching power supplies and power supplies that aren't power factor corrected. But our neutrals aren't protected from overcurrent. This was initially a problem in specific commercial environments, but with the intrusion of LED lighting and mobile devices in both commercial and residential environments, these problems are becoming more widespread.

Seems to me that it's time for the industry insiders to revisit this issue, and possibly start requiring overcurrent protection on neutral lines with common-trip breakers that open both the line and neutral in the presence of an overload on any conductor including the neutral.

Since some three phase and 120/240V single phase installations were allowed to have downsized neutral conductors (in the past), this may require the introduction of a common trip breaker that features one breaker rated lower than the others. For example, a 200A three-phase service may be wired with 4/0 AWG line conductors and a 3/0 neutral conductor (aluminum THHN), and a 200A triple-pole common-trip breaker. Under the new scheme, the breaker might have to be a quad-pole breaker rated at 200-200-200-175A (or something like that) with the 175A pole protecting the neutral.

This also presents an interesting issue with maintaining equipment ground in a service entrance, as typically the neutral is bonded to ground at that point. If the service entrance has a protected neutral, where does the bond point go? Before or after the breaker? (I'd say on the downstream side of the breaker.)

[Jean-Pierre Coetzee]

Solved easily here. GFCI reference live to neutral at the main incoming line, so triplen harmonics can cause nuisance trips.

For the bonding it happens at the poco so no problems there.

Undersized neutrals are still a problem but honestly if your building burns down because of that you deserve it, that's a little harsh but its in the owners best interest to get a properly qualified electrician to do his wireing specifically when 3phase power is involved.

I honestly believe that neutrals should be oversized in modern 3-phase systems.

[Frank DeWitt]

In th every early days there were fierce discussions about grounding the neutral.  In New York it was not allowed at one time.  Industries were required to have a light bulb between the neutral and ground and another between the hot and ground so that if the light was ever on the problem could be found.  Another hot topic was should buildings be wired to protect the building from fire or to prevent people from being electrocuted.  Buildings have no sense, but people do so people don't need protection. More important buildings were insured.  The early codes were the work of the fire insurance companies.  Fun reading.

[Stephen Swaffer]

Solved easily here. GFCI reference live to neutral at the main incoming line, so triplen harmonics can cause nuisance trips.

For the bonding it happens at the poco so no problems there.

Undersized neutrals are still a problem but honestly if your building burns down because of that you deserve it, that's a little harsh but its in the owners best interest to get a properly qualified electrician to do his wireing specifically when 3phase power is involved.

I honestly believe that neutrals should be oversized in modern 3-phase systems.

Not to be picky, but you're last sentence illustrates the importance of an electrician having an understanding of the loads involved in the system he is designing.  If the majority of the load is lighting or single phase non-linear loads, then sure, oversizing makes sense.  OTOH, if the majority of the load is either resistance heating, using a linear control method, or 3 phase motor loads, then a neutral sized the same as phase conductors may actually be effectively " oversized.".

The plant I work in has a 3000 amp service that is heavily loaded- but only one lightly loaded 200 amp lighting panel.  Why would I oversize the incoming neutral?  Most of the loads have no neutral connection.

I would argue that a better method for protecting a neutral would be a CT on the neutral using a current monitoring relay to a shunt trip breaker.  This would remove power when an overload occurs while retaining the bonding safety- and could be done in compliance with current codes.

[Jean-Pierre Coetzee]

Reason I said it is because more and more buildings are using led lighting and not always PF corrected ones and a lot of switch mode power supplies.

Sure there are use cases where there is very little current running in the neutral(in relation to the lines) but IMHO that is becoming the exception and not the norm.

I'm not talking about manufacturing plants because I doubt anyone on this forum is going to be building a manufacturing plant that will be using purely 3phase motors and heaters, most people that come to this forum will provably be setting up an AV rig or running a venue where AV is a large chunk of business. Modern trends show lighting loads being significantly greater than sound or video and all 3 use switch mode power supplies that might not be PF corrected.

[Tim McCulloch]

Reason I said it is because more and more buildings are using led lighting and not always PF corrected ones and a lot of switch mode power supplies.

Sure there are use cases where there is very little current running in the neutral(in relation to the lines) but IMHO that is becoming the exception and not the norm.

I'm not talking about manufacturing plants because I doubt anyone on this forum is going to be building a manufacturing plant that will be using purely 3phase motors and heaters, most people that come to this forum will provably be setting up an AV rig or running a venue where AV is a large chunk of business. Modern trends show lighting loads being significantly greater than sound or video and all 3 use switch mode power supplies that might not be PF corrected.

One of my non-audio gigs is arena entertainment electrician.  Overall show power requirements have dropped somewhat even as lighting has expanded - the most recent stuff puts out a lot of light for the amount of power used.

The big power hog in arena entertainment is LED video walls.  I'm typically giving the VDO dept a 400A 3phase 120/208 service as a base line (until about 3 years ago it was 2x 400A services), often with another 200A service for projection and engineering.  These days PA gets one 200A 3p 120/208 or two 200A services or a single 400A service depending on how the production company wants it.  Lighting has gone from 2400A to half that on shows like Trans Siberian Orchestra (they've cut their lighting power use by 50% over 10 years).  Automation typically gets a 200A 3p 120/208 wye service and they use a transformer to get the 277/480 3p delta service for their motors, pumps and actuators.  Rigging, especially on shows with moving truss choreography gets their own 200A (typically) 120/208 3p service.

Another item that uses a fair bit of power that the crowd doesn't really see: HVAC for performers onstage and in back stage areas.  One band with a very tall drummer had quick change booths at opposite sides of the stage, one was heated, the other refrigerated.  100A of 200A of "backstage utility" power.  Another band that is breaking has AC for the front man from both front and back.

Now that we've had the tour... I routinely check neutral currents with my Amprobe clamp meter and for the most part have seen maybe a 15% increase in neutral current, above the phase leg load imbalances... except for one time when I swear I saw a current reading that look abnormally high (almost 200 Amperes on a 400 Ampere service).  I used an infrared thermometer but none of the neutral conductor stuff was warmer than the phase legs.  I never saw it get that high again, though and the show's electrician had no explanation for it so I chalked it up to either hallucinations or bad eyesight.

[Kevin Graf]

Triplen harmonics are only a problem in 3 phase system. Because these harmonics are all in phase from each of the legs, they add together.
It's not a problem is single phase (or center tapped) systems.

[Stephen Swaffer]

Tim,

Is most of what you are seeing PF corrected?  On the commercial lighting side, most of what I see is because it is mandated by building codes.

[Jonathan Johnson]

Triplen harmonics are only a problem in 3 phase system. Because these harmonics are all in phase from each of the legs, they add together.
It's not a problem is single phase (or center tapped) systems.

That's my understanding as well. But power factor issues can cause imbalances on single-phase center-tapped systems.

Say one pole has all equipment with a normal power factor of 1 (it's all resistive loads, for example). The other pole has all equipment with a significant power factor (inductive or switched-mode loads). Both poles have equipment drawing the same current load.

If the loads on both poles had the same power factor, the current on the neutral should be zero. But, because the current load is not in phase between the poles, there will be current on the neutral.

Even if both poles were fully loaded, and the power factor on on pole was 1 and the other pole was 0 (or near 0), the load on the neutral shouldn't exceed the maximum load on either pole. The neutral conductor may need to be the same size as the pole conductors, but it shouldn't need to be larger.

The above is for single-phase circuits. For three-phase, I'm not sure how it would be affected. Maybe under the right circumstances you could overload a same-sized neutral with power factor imbalances.

I am not an electrical engineer. I can't prove the above with math.

[Mark Cadwallader]

IIRC, Indu-Electric offers some of their 3 phase entertainment distros with a second neutral cam. One ground, two neutrals, and 3 phases hot. I didn't know why that might be needed; I've only seen 5 cam distros in the wild.  Now I think I might understand.

[Tim McCulloch]

IIRC, Indu-Electric offers some of their 3 phase entertainment distros with a second neutral cam. One ground, two neutrals, and 3 phases hot. I didn't know why that might be needed; I've only seen 5 cam distros in the wild.  Now I think I might understand.

NEC has required double-neutrals for high-harmonic loads like electronic dimming for at least 20 years.  All of the company switches at out downtown arena have 2x white (neutral) camlocs.  See NEC 520.

[Brian Jojade]

IIRC, Indu-Electric offers some of their 3 phase entertainment distros with a second neutral cam. One ground, two neutrals, and 3 phases hot. I didn't know why that might be needed; I've only seen 5 cam distros in the wild.  Now I think I might understand.

Another side advantage to double neutrals is that it reduces the risk of a loose neutral connection situation.  You would now need 2 bad connections before you would see a problem.  Added redundancy!

[Brian Jojade]

We've come a long way with power distro since the early 1900's. In one of the theaters I worked in during the 80's, they still had fuses on the neutral lines feeding the stage power and lighting. Of course, that's no longer to code.

Sadly, sometimes you can still see that today. 

The Gemini PL-8 power power conditioner I had was wired so that the voltage meter was after the power switch.  I thought this was stupid, so I opened it to re-tap the voltage meter before the switch.  What I found inside was that the breaker was wired to the neutral line, NOT the hot line.  No, not a dual channel breaker, just a simple breaker on the neutral, and that's it!!  It wasn't a fluke, as I had a half dozen of the units that needed to be reworked.  Scary indeed!

http://www.guitarcenter.com/Used/Gemini/PL8-Power-Conditioner.gc

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