| reply to harald
Re: Myth of the Neutral Wire said by harald:Computers may not care, but other kinds of equipment may. Try reversing the hot and neutral on a modern gas furnace. It won't run. The same applies to neon sign transformers, if hot and neutral are reversed the transformer will not power up. |
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 fcislerPremium
join:2004-06-14
Riverhead, NY | reply to sk1939
Interesting fact: A switching mode PC power supply, in the 208/240v range can be run off of approx 330VDC without any modification.
Source: »en.wikipedia.org/wiki/Switched-m···er_stage |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
 ·TekSavvy DSL
| reply to MatrixHDV
said by MatrixHDV:said by harald:Try reversing the hot and neutral on a modern gas furnace. It won't run. The same applies to neon sign transformers, if hot and neutral are reversed the transformer will not power up. The few exceptions where hot/neutral can't be reversed "technically" even if you tried hard ... were actually designed by electrical engineers with electrician/technician/DIY folk's safety in mind. 
If you are curious about why modern UL-2161 compliant neon "transformers" won't power up with hot/neutral reversed, read this: »signweb.com/content/ul-2161-faq
Same safety concern with the high voltage AC created for flame rectification board in some gas furnaces. |
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| reply to sk1939
said by sk1939:Interesting read, but not new information to well-versed tradesmen in all likelihood. It also contains some incorrect assumptions, such as.
The 3-wire system that the user sees is actually derived from three phase distribution, which uses a 5-wire system. In the 5-wire system, there are 3 hot wires, 1 neutral wire, and 1 grounding wire. The common 3-wire receptacle uses only one of the 3 hot wires.
Here one can see there are a total of 2 drops consisting of 8 conductors serving two 3 phase customers.
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| reply to lutful
said by lutful:The few exceptions where hot/neutral can't be reversed "technically" even if you tried hard ... were actually designed by electrical engineers with electrician/technician/DIY folk's safety in mind. And they ain't worth a crap, take a new neon sign transformer and strobe it and it WILL SHUTDOWN, rendering it for my use, useless…
If you are curious about why modern UL-2161 compliant neon "transformers" won't power up with hot/neutral reversed, read this: |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| said by MatrixHDV:No thanks I’ll just stick to the old gold Francefromer’s, They have "For Export Only" models with even more convenience for you: »www.franceformer.com/neon_data.h···ninstall |
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robbinPremium,MVM
join:2000-09-21
Leander, TX
kudos:1 | reply to MatrixHDV
said by MatrixHDV:It also contains some incorrect assumptions, such as...In multi-grounded neutral 3 phase distribution, there is no such thing as a “grounding wire” as can be seen in this photograph of a 3 phase distribution switch, note there are 4 conductors, 3 hots and a neutral, likewise the same applies to a drop. Isn't this a grounding wire?
Grounding Wire ?
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 John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:5 | reply to sk1939
Don't forget there is a difference between the NESC and the NEC... |
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sk1939Premium
join:2010-10-23
Washington, DC
kudos:9 Reviews:
 ·T-Mobile US
| said by John Galt:Don't forget there is a difference between the NESC and the NEC...
Indeed.
The National Electrical Safety Code (NESC) is a code published by the Institute of Electrical and Electronics Engineers (IEEE). It has defined safe practices for installing, operating, and maintaining electric supply and communications lines, and associated equipment, for more than 90 years. Every 5 years, the NESC is updated with critical revisions concerning new techniques and technologies. Utilities workers use the NESC to safeguard themselves and the public while working under specified conditions.
The National Electrical Code (NEC), or NFPA 70, code is published every 3 years by the National Fire Prevention Association (NFPA). The NEC defines the requirements for safe electrical installations. State and local laws commonly require electricians to comply with the NEC. |
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 alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | reply to robbin
said by robbin:said by MatrixHDV:It also contains some incorrect assumptions, such as...In multi-grounded neutral 3 phase distribution, there is no such thing as a “grounding wire” as can be seen in this photograph of a 3 phase distribution switch, note there are 4 conductors, 3 hots and a neutral, likewise the same applies to a drop. Isn't this a grounding wire? Actually, I wonder that too.
I drive by some neighborhood where they have 4 wires running along the poles and one of them is bare. My neighborhood only has 3 wires, all insulated (except for the drop to the residences, where the neutral is bare).
I know about the high voltage lines running at the very top of the poles, so I don't confuse the 4th wire to it.
Point is: I know those neighborhoods are split phase, not 3 phase. So I wonder what that bare wire is.
edit - Though the picture shown above does look like 3 phase. |
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| reply to robbin
said by robbin:Isn't this a grounding wire? That is the MGN ground, it provides a ground for the neutral and the transformers primary surge protectors, however it is not a distribution conductor as it isn’t run from pole to pole nor is it extended to the premises, hence the 4 wire 3 phase drops. |
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robbinPremium,MVM
join:2000-09-21
Leander, TX
kudos:1 | Where in your previous quote does it say "distribution conductor"?
said by MatrixHDV:In the 5-wire system, there are 3 hot wires, 1 neutral wire, and 1 grounding wire. I believe that wire qualifies as a "grounding wire" and it is necessary part of the distribution system. And yes, the premises also have a grounding wire going to the ground rod(s). |
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 tschmidtPremium,MVM
join:2000-11-12
Milford, NH
kudos:8
·G4 Communications
·Fairpoint Commun..
 ·Hollis Hosting
| reply to robbin
NEC Service Entrance wiring | 
Safety Ground |
As sk1939  pointed out there are two different groups responsible for setting electrical safety standards. The National Electrical Safety Code (NESC) controls what the utilities do and ends with the meter socket. The National Electrical Code (NEC) controls building wiring.
In most parts of the country the electrical system uses multi grounded neutral (MGN). The neutral conductor is connected to Earth at the utility pole. This occurs multiple times, typically at each pole. Per ohms law neutral current divides between the neutral conductor and Earth.
Because the neutral conductor is connected to Earth it is at nearly the same potential as local Earth. If there are other conductors on the utility pole (telephone or Cable) the shields for these services are also grounded and bonded to each other, minimizing the potential difference between the various services. Distribution network is typically 3 phase wye. In a wye configuration the center of the wye is the neutral conductor and is connected to Earth.
The purpose of Earth grounding:
1) Provide lightning protection, nearby lightning discharges are absorbed by the Earth.
2) Insure neutral conductor is at nearly 0 volts relative to Earth. In that case someone in contact with Earth and touching the neutral conductor will not be shocked.
Once within the residence we enter the realm of the NEC. The neutral conductor is once again connected to Earth. A new conductor is created called the Equipment Grounding Conductor (EGC). The EGC is connected to neutral at one place and only one place at the service disconnect. Under normal circumstances no current flows in the EGC. EGC is used to create a low impedance path back the neutral so fault current is large enough to trip the over current device. Let’s use an electric drill as an example. Without EGC a fault will energize the drill’s metallic housing. When our hapless user touches the drill they complete the circuit to Earth through their body. Unfortunately skin resistance is fairly high so current is too low to trip the over current device, but more than enough to electrocute our hapless user.
The purpose of EGC:
1) EGC provides a low impedance path back to neutral so equipment faults will create enough current to open the circuit rather than creating an electrocution hazard.
The purpose of bonding:
1) Bonding creates a low impedance connection between metallic objects. This insures they are at nearly the same potential, and because the system is also connected to Earth it will be at nearly the same potential as Earth.
A fault to the bonded object will create enough current flow to trip the over current device. In the event of nearby lightning strikes bonding insures everything moves up and down in unison. This prevents damage to equipment and electrocution hazard. Think of a bird sitting on a power line verses a squirrel coming into contact with power and neutral.
/tom |
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| reply to robbin
said by robbin:I believe that wire qualifies as a "grounding wire" and it is necessary part of the distribution system. And yes, the premises also have a grounding wire going to the ground rod(s). It would only be considered a grounding wire if it was continuous from the distribution to the premises, as per the diagram in the article and as depicted below, which of course would require a 5 wire drop. |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| reply to lutful
I think MatrixHDV did not get the joke. Buy UL/CSA listed neon transformers and install according to instructions ... or risk someone's life in pursuit of faster strobing.  |
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| said by lutful:I think MatrixHDV did not get the joke. Buy UL/CSA listed neon transformers and install according to instructions ... or risk someone's life in pursuit of faster strobing.
There's no joke to get and you're trying to make a mountain out of a molehill as the older non-protected transfromers have been in use for decades without risking anyones life when installed and maintained properly. |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| reply to MatrixHDV
said by MatrixHDV:said by robbin:I believe that wire qualifies as a "grounding wire" and it is necessary part of the distribution system. And yes, the premises also have a grounding wire going to the ground rod(s). It would only be considered a grounding wire if it was continuous from the distribution to the premises, as per the diagram in the article and as depicted below, which of course would require a 5 wire drop. Original app note was from APC and it is clear they meant distribution within the premises like an office building. That diagram clearly shows neutral is grounded at the "premises" using a bond to real ground.
That is exactly what the utility is doing at the poles. Electrical engineers would not even "imagine" a grounding conductor running all the way back to the pole from every home or from every pole back to the substation. |
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| said by lutful:Electrical engineers would not even "imagine" a grounding conductor running all the way back to the pole from every home or from every pole back to the substation. That's not true, while it is not common there are parts of California where the utilities run the 5th conductor (3 phases 1 neutral and 1 ground) all the way from the substation to the customer.
And while MGN is the predominant distribution scheme in the U.S. and has been proven to be relatively safe, there is a growing chorus of transmission/distribution EE's who are pushing for the 5th wire even on MGN systems. |
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lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| said by MatrixHDV:there is a growing chorus of transmission/distribution EE's who are pushing for the 5th wire Post a reference and we will see who sings in that chorus and why.
The grounding conductor of either a home or an utility pole goes to real ground as close as practically possible ... for your safety. |
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| said by lutful:Post a reference and we will see who sings in that chorus and why. Do an IEEE search for uni-grounded versus MGN distrbution systems.
As for the reason it is quite simple an MGN system can present dangerous stray voltages and hazardous step voltages due to the nature of the way the MGN's operate.
You can also find quite a bit of information on the subject on Mike Holts web page.
The botton line is 5 wire is safer than MGN, but requires a 5 wire distribution network and the utilities oppose the deployment of such a system for what they perceive as only a minor gain in safety for a lot of cost on their part and with 80% or so distribution in the U.S. being MGN that would be one heck of a cost to upgrade.
Then there is rule 33.2. which is why in California 5 wire distribution is used.
California’s Public Utilities Commission’s General Orders –
95 On January 19, 1994 the California’s Public Utilities Commission in their General Orders – 95 generated a resolution SU-25 resulting in Rule 33.2.
Ground or earth shall not be used as a normal return or circuit conductor. In direct current supply systems or in single phase or polyphase supply systems, a neutral or any other conductor shall be used under normal use as a return or circuit conductor; however, the grounding of the neutral or any other conductor is not permitted as a normal return or circuit conductor. The neutral or any other conductor is permitted to be grounded only for the purposes of stabilization and protection. |
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