Please clarify/settle a portable generator question

PEOPLE DIE FROM INACCURATE INFORMATION.

Back-feed electrocution deaths:
http://www.electricenergyonline.com/?page=show_news&id=38786
http://www.cdc.gov/Niosh/face/In-house/full9005.html
http://incident-prevention.com/ip-a...rticle/115-hidden-traps-of-generator-use.html

C02 Poisoning:
http://www.cpsc.gov/cpscpub/prerel/prhtml04/04141.html

REAL REASON FOR SWITCHING (DISCONNECTING) THE NEUTRAL, has to deal with the "split" grounding conductors (dual grounding rods/neutrals) that are present when a portable generator is operating. [The following does not apply to a permanently installed stand-by generator (the neutrals & grounding conductors are continuous back to the service entrance (floating neutral connections in the transfer switch) AND the generator is grounded with it's own earth ground (at the generator).]

With a portable generator operational - the GFCI breaker protection on the portable generator will not operate correctly, as it will have TWO POSSIBLE neutral paths to return to ground (one at the service entrance & one at the generator). Since the generator's neutral must be bonded & grounded to earth, if the service entrance neutral is not disconnected, there will be TWO neutral paths & earth grounding points.

When a neutral is grounded in two places the voltage will split & the generator's breaker will trip. Then nothing will work.

WHY YOU DON'T WANT TO BACKFEED YOUR HOUSE SYSTEM BY PLUGGING THE PORTABLE GENERATOR INTO THE DRYER OUTLET:
The wiring inside of the wall from the panel to the dryer outlet may not be of sufficient size to handle the output from the portable generator. Overloading this wiring will cause it to overheat (like a toaster element) & posed a fire risk. If you thought you were cold before - imagine standing out in the storm watching your house burn down.

Backfeeding presents danger to utility workers and other homeowners.
Backfeeding your service panel through a dryer receptacle will feed power into the grid unless the main service breaker is opened first. Electricians working on the grid may be electrocuted when they encounter lines that they had assumed were safe (though they are taught to take precautions). You will also be supplying power to other homes on the same secondary distribution transformer that your home is on (aka:" islanding").


The utility company and your portable generator create phases that are not sync'd.
This means that if the utility power is restored while your portable generator is still backfeeding the power grid, your generator will be destroyed in a catastrophic manner. Your generator will burst into flames, igniting it's fuel tank & causing an even bigger fire (maybe your house?).


Reversed cord - energized prongs:
If the generator is on & the cord is unplugged from the dryer wall outlet, then there is a potential for electrocution. Those exposed prongs will have 240 volts!


Hazard at Generator
A lot of older houses do not have a dedicated grounding conductor at their receptacles. Many older homes used water pipes as the grounding rod. As water mains were replaced with plastic, the potential ground decreased. Additionally, few electricians ever test the resistance of the ground (using the fall of resistance method) to determine if a grounding rod is effectively discharging to earth (the resistance of the earth varies around the world). This incomplete discharge to earth results in the neutral conductor being energized, thus back-feeding the secondary side of the utility transformer. This is how a utility worker can be electrocuted.


Hazard at the Utility Transformer
If the utility company feed is not disconnected (main disconnect), your little portable generator will push power backwards to the utility company's step-down transformers. It will work in reverse, increasing this lower electrical voltage to thousands of volts. That will be more than enough juice to kill a lineman miles away!


While these would not occur if you threw your service disconnect - there are just too many "what ifs" and variables possible to guarantee that your system would operate safely.

THESE ARE ALL REASONS TO HAVE A QUALIFIED ELECTRICAL CONTRACTOR INSTALL A SERVICE DISCONNECT. It GUARANTEES that the lines are disconnected & reconnected in the correct order - eliminating the possibility of fire, injury, or death.

It is best to get one installed before you actually need it - during the summer months, when the electricians & parts are readily available.

Back-up generators are not just installed because there is a critical mission occurring inside the structure. Sometimes people want them just to stay comfortable during an outage, keep the wine cellar chilled, take a hot shower, read a book, heat the house, keep the freezer full of food frozen, etc. If you can afford to have and operate one - more power to you! (no pun intended)

P.S. My firm designs & installs permanently installed back-up generators (diesel, natural gas, and propane powered) at fine estate homes across the country. We also install underground diesel & propane tanks to power these generators. This is becoming a popular location as under ground they are not: visible (saving valuable real estate) or susceptible to damage from earthquakes, wildfires, vehicles, storms, etc.). I have a 30 kw natural gas powered (with a buried propane back-up tank). It will run on either fuel by merely the turn of a valve (that happens automatically when it senses a drop in natural gas pressure - like what occurs following a CA earthquake).
 
RCP Phx said:
Very well said!Grounded conductors and grounding conductors serve completely separate functions.

On a similar note,weve had an influx of "Utility-Interactive" photo voltaic installations.We had a big meeting today to discuss issues,some of these are almost 1 Megawatt and the amount were seeing is growing!
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I don't know how it is in AZ but in CA for the inverters in a solar system to convert the DC pannels to AC and feed power into the grid they have to see 120v from the utility side. They do this so there can be no backfeeding of the grid while utility workers are working on things. It is sorta stupid cause if your power goes out your solar pannels are just sitting there doing nothing. You can get around this by installing an isolation switch and a bank of batteries or a small generator to provide the inverters with 120v. For houses not connected to the grid there are some jumpers inside the inverters you can change so it doesn't need the signal voltage.
 
blubullett said:
I don't know how it is in AZ but in CA for the inverters in a solar system to convert the DC pannels to AC and feed power into the grid they have to see 120v from the utility side. They do this so there can be no backfeeding of the grid while utility workers are working on things. It is sorta stupid cause if your power goes out your solar pannels are just sitting there doing nothing. You can get around this by installing an isolation switch and a bank of batteries or a small generator to provide the inverters with 120v. For houses not connected to the grid there are some jumpers inside the inverters you can change so it doesn't need the signal voltage.
Click to expand...
Per UL1741(the Standard for PV equipment)all Utility-interactive inverters must see the presence of utility voltage in order to "turn on".
 
BarFlyFisherman said:

REAL REASON FOR SWITCHING (DISCONNECTING) THE NEUTRAL, has to deal with the "split" grounding conductors (dual grounding rods/neutrals) that are present when a portable generator is operating. [The following does not apply to a permanently installed stand-by generator (the neutrals & grounding conductors are continuous back to the service entrance (floating neutral connections in the transfer switch) AND the generator is grounded with it's own earth ground (at the generator).]

With a portable generator operational - the GFCI breaker protection on the portable generator will not operate correctly, as it will have TWO POSSIBLE neutral paths to return to ground (one at the service entrance & one at the generator). Since the generator's neutral must be bonded & grounded to earth, if the service entrance neutral is not disconnected, there will be TWO neutral paths & earth grounding points.

When a neutral is grounded in two places the voltage will split & the generator's breaker will trip. Then nothing will work.
Some good/some bad info.Your home already has two grounding electrode connections,! is at the utility source.You just dont want a connection to ground downstream of "your" overcurrent devices.
Hazard at Generator
A lot of older houses do not have a dedicated grounding conductor at their receptacles. Many older homes used water pipes as the grounding rod. As water mains were replaced with plastic, the potential ground decreased. Additionally, few electricians ever test the resistance of the ground (using the fall of resistance method) to determine if a grounding rod is effectively discharging to earth (the resistance of the earth varies around the world). This incomplete discharge to earth results in the neutral conductor being energized, thus back-feeding the secondary side of the utility transformer. This is how a utility worker can be electrocuted.
Click to expand...

Some bad info here: your house is already grounded at at least 2 locations,1 being at your house and 1 being at your utility source and of course every other house connected to that particular grid!.You are not supposed to re-ground the neutral downstream of your over-current devices,but upstream is not an issue.

Again not true,the grounding electrode is only there to eliminate any "voltage potential" to ground,The grounding electrode(s) and grounding electrode conductors never carry any current/voltage(with the execption of a "lightning strike")!
 
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RCP Phx said:
Some bad info here: your house is already grounded at at least 2 locations,1 being at your house and 1 being at your utility source and of course every other house connected to that particular grid!.You are not supposed to re-ground the neutral downstream of your over-current devices,but upstream is not an issue.

Again not true,the grounding electrode is only there to eliminate any "voltage potential" to ground,The grounding electrode(s) and grounding electrode conductors never carry any current/voltage(with the exception of a "lightning strike")!
Click to expand...

Alas... they do carry voltage - from the neutral conductor at the service entrance (where the neutral & grounding conductor are bonded together) down to the earth. You don't feel anything when you touch it, if you have the same potential ground.

You can be electrocuted by grabbing a neutral conductor. If a 120V circuit is closed electricity is present on the neutral conductor, as it flow back to the service entrance - where it is discharged into the earth. If you grabbed this conductor prior to the service entrance panel and presented the electricity with a shorter path to earth (ground), then you get zapped. If you turn yourself into a REALLY GOOD source of earth ground (like standing in a puddle of liquid - which reduces the resistance between your feet & the earth) - then you die.

This is the principal why birds on a wire do not get electrocuted. The juice is not flowing THROUGH them. If a large bird happens to touch two wires with their wing tips (hawks & those stupid lead paint eating California Condors), they get fried - the juice flowed through them.

In Condor country, the utilities were required to place triangle bird guards atop the power poles, place insulator sleeves on the wires, or relocate the wires on the poles so that they could not touch 2 wires at the same time.

So, theoretically, if you were standing in a puddle of water at the service entrance and grabbed the grounding conductor, you could receive a shock. I say "in theory", as you would have to be a better source of ground (offer a greater potential) than the grounding rod. If it were broken, corroded, the connection was loose, or the ground offered a lot of resistance, then you could also get shocked.

This is why ufer grounds are so much more effective. Concrete readily absorbs water, releases it slowly, contains sulfides (salts increase conductivity), the grounding conductor is protected from damage, decay, or from coming loose, and the surface area in contact with the earth is so much greater than the copper grounding rod.
 
BarFlyFisherman said:
You can be electrocuted by grabbing a neutral conductor. If a 120V circuit is closed electricity is present on the neutral conductor, as it flow back to the service entrance - where it is discharged into the earth. If you grabbed this conductor prior to the service entrance panel and presented the electricity with a shorter path to earth (ground), then you get zapped. If you turn yourself into a REALLY GOOD source of earth ground (like standing in a puddle of liquid - which reduces the resistance between your feet & the earth) - then you die.
Click to expand...

SPOBI,where are you getting this info from? If your neutral is all connected properly you CANNOT get shocked by it.If your were to open the neutral connection (at lets say at a j-box)and get in the middle of the neutral circuit your definately gonna get shocked.

Any current on the neutral goes back to the utility neutral,None ever "dis-charges"(as you call it) back to earth.

I certainly hope all you do at this company is drive a truck or something similar!
 
BarFlyFisherman said:
You can be electrocuted by grabbing a neutral conductor. If a 120V circuit is closed electricity is present on the neutral conductor, as it flow back to the service entrance - where it is discharged into the earth. If you grabbed this conductor prior to the service entrance panel and presented the electricity with a shorter path to earth (ground), then you get zapped. If you turn yourself into a REALLY GOOD source of earth ground (like standing in a puddle of liquid - which reduces the resistance between your feet & the earth) - then you die.

...

So, theoretically, if you were standing in a puddle of water at the service entrance and grabbed the grounding conductor, you could receive a shock. I say "in theory", as you would have to be a better source of ground (offer a greater potential) than the grounding rod. If it were broken, corroded, the connection was loose, or the ground offered a lot of resistance, then you could also get shocked.
Click to expand...
what? How does a "better source of ground" offer a greater potential? A good ground is at zero potential.

The neutral is bonded to the grounding system at your service panel. It is also bonded to the grounding system on the distribution network (at the pole.) There is no ground wire from the house to the pole, just a bare neutral and two opposing hot wires (not properly termed phases, since residential power is 240V split-phase, not two phase.) If you have a lousy ground all bets are off, yes, but if your ground is properly installed it will be fine. Also, grabbing the neutral won't do shit, unless you cut it in half and touch the neutral from the house. Even then, IF your loads on the hots are perfectly balanced (never happens), you will not get shocked, but someone turning a light on or off on either feed will zap you, so don't try this at home :confused1 The utility co would like every house to have a perfectly balanced load, but in reality as long as the average of all the houses in an area is pretty close to balanced it's OK.

Unless your neutral wiring AND ground wiring are shoddy as hell, you will not get shocked touching either.
 
kastein said:
The utility co would like every house to have a perfectly balanced load, but in reality as long as the average of all the houses in an area is pretty close to balanced it's OK.
Click to expand...

My local electrician told me they could re-route my breaker box to equalize the load better. Is this something that will be helpful to me?
 
If you are near the max load for the panel, and having issues with the main breaker tripping, it can help. It will help the utility company either way, since residential power is split-phase 240V (a single phase, but the center of the transformer coil is grounded instead of one end, so each end shows 120 volts AC with one end going positive and one going negative every half cycle) balancing the load between the hot lines results in the transformer being equally loaded, instead of having half the coil heavily loaded and the other half lightly loaded. As long as the average for your whole neighborhood is pretty close to balanced they won't even notice, but if they got unlucky and everyone has their load unbalanced to the same side it'll help.

I would not bother unless you have problems. If you have a clamp-on AC ammeter you can measure the current through each hot wire into the main breaker with your "average" loads running (lights, fridge, furnace, etc) and then put some thought into balancing the rest of your loads. Fortunately most big loads (water heater, baseboard heat, dryer, stove, AC, etc) are 240V so they don't need to be balanced as they draw equally by definition.
 
No problems with tripping any breakers or anything since we had the faulty main breaker replaced.

I don't remember the exact numbers, but the electrician had the clamp on tester. I want to say it was 60/40-ish. With our 'normal' load, neither of the hot lines was even close to hitting its max load rating (80% of wire rating?).

I would LOVE to have a back up generator for the house - would it be expensive to retrofit the hardware necessary to be able to plug in a generator?
 
60%/40% or 60A/40A? If it's the latter I might look into balancing it (since you have 50% more load on one side than the other) but if you are saying the load was split 60% vs 40% I'd leave it alone.

Expensive depends on your point of reference, figure a few (2-4) hundred spent on the transfer switch, then add in the electrician's labor bill, any new wiring needed, and any necessary inspections.
 
kastein said:
60%/40% or 60A/40A? If it's the latter I might look into balancing it (since you have 50% more load on one side than the other) but if you are saying the load was split 60% vs 40% I'd leave it alone.

Expensive depends on your point of reference, figure a few (2-4) hundred spent on the transfer switch, then add in the electrician's labor bill, any new wiring needed, and any necessary inspections.
Click to expand...

Yeah, sorry - I meant 60%/40%. The electrician indicated that it was well within operating limits and didn't pose a concern at all.

Guess I'm going to do some generator research now. Thanks.
 
I bought a cheap, portable genny last winter, and hopefully, will never need to use it. I don't have it tied into my panel, and unless I'm laid-off and bored, I don't want to bother doing it. I am a qualified electrician, and have dealt with transfer switches. What I was thinking, however, was extension cords, for the fridge and coal stove. Although, if I'm not home when the power goes out, I'm SOL.
A co-worker had a unique approach to the problem of a neutral when feeding a panel with a genny. He routed the service entrance cable through a three pole disconnect, after the meter, but before the panel. It breaks both hots and the neutral, totally breaking contact with the grid. Unfortunately, once again it's not passive, but the price was right-free.
I've taken solar PV installation classes, and am about to take the installer certification test. It's interesting to see the measures built into the systems, to keep them from feeding the grid, in the event of a power outage. The battery option is interesting in a commercial or very rural setting, but not aimed at the typical residential install.
I went into the class as a skeptic, but left a firm believer. Anyone building a house would be well served by looking into PV, as a typical install may be about $40k, but under the right circumstances, using your own energy savings, federal and state tax credits, and the 'clean' credits you earn, can pay for itself in less than five years, and it's all gravy after that!
 
kastein said:
what? How does a "better source of ground" offer a greater potential? A good ground is at zero potential.

The neutral is bonded to the grounding system at your service panel. It is also bonded to the grounding system on the distribution network (at the pole.) There is no ground wire from the house to the pole, just a bare neutral and two opposing hot wires (not properly termed phases, since residential power is 240V split-phase, not two phase.) If you have a lousy ground all bets are off, yes, but if your ground is properly installed it will be fine. Also, grabbing the neutral won't do shit, unless you cut it in half and touch the neutral from the house. Even then, IF your loads on the hots are perfectly balanced (never happens), you will not get shocked, but someone turning a light on or off on either feed will zap you, so don't try this at home :confused1 The utility co would like every house to have a perfectly balanced load, but in reality as long as the average of all the houses in an area is pretty close to balanced it's OK.

Unless your neutral wiring AND ground wiring are shoddy as hell, you will not get shocked touching either.
Click to expand...

I misspoke - if you were standing in water you would have a lower potential (resistance) & therefore be a better source of ground.

The illustration was a response to the mis-statement by PCP-Phx that:
(A) NEUTRALS do not carry electricity
AND
(B) Grounding conductors NEVER carry electricity (except for a lightening strike).

Neutrals do carry electricity - (now read this EXAMPLE carefully)

In a 120 volt circuit the energy flows TO a light bulb on the HOT conductor. The unused electricity (not used by the filament) flows AWAY from the device on the NEUTRAL conductor.

IF the neutral conductor was broken... and you were to touch this broken neutral conductor while it was energized - you'd be shocked! In a closed circuit you can be electrocuted by presenting either the HOT or NEUTRAL conductors with a shorter path to ground. A fine illustration that neutral conductors can kill (when the circuit is closed)!

Grounding conductors DO CARRY ELECTRICITY! - never say never!!

There are a number of situations when a grounding conductor carries electricity - some improperly, some intentionally, some because it's unavoidable.
1) The most common improper reason is the incorrect neutral to case bonds (more on this below - with NEC citations).
2) There are some neutral to case bond that intentionally exist within appliances - electric dryers & ranges immediately come to mind.
3) If the property has a swimming pool - the grounding conductor to the pool equipment from the service entrance panel will be carrying electricity.

REMEMBER: ELECTRICITY ALWAYS SEEKS THE BEST GROUND.
Because the swimming pool shell is the best ground on the property - thousands of feet of reinforcing steel encased in wet concrete - it is a humongous Ufer grid.
Grounding conductors are always continuous and there is no way to force the energy to flow in only 1 direction. THEREFORE, there will be electricity on the grounding conductor to the swimming pool.
It may be minor - it may be huge (if there is a ground fault elsewhere on the property, or if the service entrance grounding rod was a poor connection or the earth high resistance - remember ?: electricity always seeks ground and always the best ground).
There is a whole section of the NEC devoted to the protection of swimming pools & apparatus due to this phenomenon (Section 680 - Section 682 was recently added to provide protection around other bodies of water - lakes, boat docks, fiberglass/vinyl swimming pools, fountains, etc.).

So, if electricity NEVER flow to earth, then how does the swimming pool shell become energized?
Why do pools experience electrolysis of the reinforcing steel?
How do pool lights become energized via inductive electricity (even with the breakers off)*?

Purpose of Neutral
Because electric utilities are not required to install an equipment grounding conductor to service equipment, a grounded (neutral) conductor shall be run from the electric utility transformer to each service disconnecting means and this conductor shall be bonded to the service disconnect enclosure [250.24]. The grounded (neutral) service conductor serves as the required effective ground-fault current path necessary to ensure that dangerous voltage from a ground fault will be quickly removed by opening of the circuit protection device [250.4(A)(3) and 250.4(A)(5)].


Hazard of Open Service Neutral
If the grounded (neutral) service conductor is opened or not provided at all, objectionable neutral current will flow on metal parts of the electrical system and dangerous voltage will be present on the metal parts providing the potential for electric shock. This dangerous electrical shock condition is of particular concern in buildings that contain swimming pools, spas and hot tubs.

In addition, when the grounded (neutral) conductor from the secondary of a transformer is open or not present, the operating voltage for the loads on one line will rise, while the operating voltage for the other line will drop. Another hazard exists from over or under line voltage, and that is a fire from excessive heat.

Equipment Voltage Rating
Manufactures typically rate equipment at 115V +-10-15%, which means that 115V rated equipment should have a continuous operating voltage between 100V and 135V. Because electrical equipment of the inductive type (motors, computers, electronic ballast, etc) can be damaged or destroyed from over voltage, and resistive loads will only be damaged from over voltage, we must be sure that the voltage remains stable within the equipment voltage rating.

Voltage Distribution
The voltage distribution on the circuits and the touch voltage on metal parts from an open service grounded (neutral) conductor are dependent on the impedance of the loads on Line 1, Line 2, and ground resistance as measured by a ground resistance meter.


If the grounded (neutral) service conductor (which serves as the effective ground-fault current path) is opened or not provided at all (this happens when people think that a neutral is not required if there are no line-to-neutral loads), a ground fault cannot be cleared. The result is that metal parts of electrical equipment, as well as metal piping and structure steel will become and remain energized at line voltage. In this case 120V.

The ground resistance must be as low as possible, but a low resistance ground does not reduce dangerous touch voltage to a safe level from a ground fault! Yes, a lower resistive ground will reduce touch voltage if the grounded (neutral) is opened, but not likely to a safe value.

If the grounded (neutral) service conductor is open, neutral current will flow onto the metal parts of the electrical system. When this occurs in a wood frame construction building, neutral current seeking a return path to the power supply will travel into the moist wood members. After many years of this current flow, the wood will be converted into charcoal (wood with no moisture) and ultimately it can result in a fire. This condition is called pyroforic-carbonization.

Service Disconnecting Means [250.24(B)].
Because electric utilities are not required to install an equipment grounding conductor, alternating-current services supplied from a grounded utility transformer shall have a grounded (neutral) conductor run from the electric utility transformer to each service disconnecting means. The grounded (neutral) conductor shall be bonded to each disconnecting means’ enclosure (neutral-to-case connection) by a screw or strap supplied by the equipment manufacturer [250.28].

The grounded (neutral) service conductor shall be sized to safely carry the maximum ground-fault current likely to be imposed on it from where a ground-fault may occur [110.10].

This is accomplished by sizing the grounded (neutral) conductor in accordance with Table 250.66, based on the total area of the largest ungrounded (hot) conductor. In addition, the grounded (neutral) conductors shall have the capacity to carry the maximum unbalanced neutral current in accordance with 220.22.

If a grounded (neutral) service conductor, which serves as the effective ground-fault current path is opened or not provided at all, then a ground fault cannot be cleared and the metal parts of electrical equipment, as well as metal piping and structure steel will become and remain energized providing the potential for electric shock as well as fires.

Transformers or Other Separately Derived Systems [250.30(A)].
To provide the low impedance path necessary to clear a ground-fault from the separately derived system, the metal parts of electrical equipment shall be bonded to the grounded (neutral) terminal (Xo) of the derived system. The neutral-to-case bond can be made at the source of a separately derived system or at the first system disconnecting means (service entrance panel).

The bonding jumper used for this purpose shall be sized in accordance with Table 250.66, based on the area of the largest ungrounded conductor.

Common Improper Neutral-to-Case Connections. The most common improper neutral-to-case bonds occur in panelboards, separate building disconnects, transformers and generators.

Panelboards
Bonding of the neutral terminal to the case of a panelboard, which is not part of service equipment or separately derived systems, creates a parallel path for return neutral current. The result is neutral current (net current) flowing on the metal parts of electrical equipment as well as the grounding and bonding conductors.

Connection at Separate Buildings
Where an equipment grounding conductor is run with the feeder conductors to a separate building [250-32(B)(1)], a common and dangerous mistake is to make a neutral-to-case bond in the separate building disconnect. This ties the neutral and equipment grounding conductors together allowing objectionable neutral current to flow on the feeder equipment grounding conductor.

Separately Derived Systems
The neutral-to-case bond for a separately derived system shall not be made at more than one location because doing so results in a parallel path for neutral return current.

Transformers
If a neutral-to-case bond is made at both the transformer and at the secondary panelboard, then neutral current will flow through metal raceways and grounding and bonding path on its return path to the power supply. Figure 15 Figure 250-06A

Generator
If the grounded (neutral) conductor in a transfer switch is not opened, then the grounded (neutral) from the generator will be solidly connected to the utility’s service grounded (neutral) conductor. Under this condition, the generator is not a separately derived system, and a neutral-to-case bond shall not be made at the generator or at the generator disconnect [250.20(D) FPN 1].

If a neutral-to-case bond is made at both the generator and generator disconnect, then objectionable neutral current will flow through metal raceways and grounding and bonding path to the power supply.

DANGERS ASSOCIATED WITH IMPROPER NEUTRAL-TO-CASE CONNECTIONS:
Improper neutral-to-case connections can create a fire hazard, electric shock and electrocution, improper operation of protection devices, and power quality issues for sensitive electronic equipment. Particularly when the neutral is open or it has a high impedance path.

Fire Hazard.
Fire occurs when the temperature rises to a level sufficient to cause ignition of adjacent combustible material in an area that contains sufficient oxygen. In an electrical system, heat is generated whenever current flows. Improper wiring, resulting in the flow of neutral current on grounding and bonding paths can cause the temperature at loose connections to rise to a level that can cause a fire. In addition, arcing at loose connections is particularly dangerous in areas that contain easily ignitable and explosive gases, vapors, or dust. Figure 22 250-06A 09.cdr

Electrocution.
Death from an electric shock (ventricular fibrillation*) can occur when the touch voltage is above 30V RMS resulting in as little as 30 milliamperes of current flowing though the body. This can occur when improper neutral-to-case connections are made and the neutral is opened.

*Alternating current, particularly 60 Hz disrupts the hearts electrical circuitry, causing it to go into ventricular fibrillation, which prevents the blood from circulating through the brain, resulting in death in a matter of minutes.

Improper Operation of Circuit Protection Devices.
Nuisance tripping of a protection device equipped with ground-fault protection can occur if neutral current returns on the equipment grounding conductor, instead of the neutral conductor because of multiple and illegal neutral-to-case bonds. A circuit breaker with ground fault protection (480Y/277V, 3-phase system over 1,000A) uses the residual current method to detect a ground fault. On a 3-phase, 4-wire system, the trip unit will sum the currents in the 3 phase conductors and in the neutral. When no ground fault is present, the summation of currents flowing on A+B+C+N will equal zero. Any current flow not equal to zero is considered a ground fault. Where multiple neutral-to-case bonds have been made, neutral current will flow on the equipment grounding path. Depending on the impedance of this path versus the neutral conductor path, the ground fault protective relay may see current flow above its pickup point and cause the protective device to open the circuit.

If this condition exits (multiple neutral-to case bonds) and a ground fault occurs, the protection relay might not operate because some of the ground-fault current will not flow on the equipment grounding conductor (some fault current returns on the neutral conductor partially bypassing the ground fault protective device).

Power Quality Issues.
When objectionable neutral current travels on the metal parts of electrical equipment because of improper neutral-to-case connections, the electromagnetic field generated from circuit conductors will not canceled. This uncanceled net current flowing on metal parts of electrical equipment and conductive building parts causes elevated electromagnetic fields in the building. These low frequency electromagnetic fields can negatively impact sensitive electronic devices, particularly video monitors and medical equipment.

Transformers.

If a neutral-to-case bond is made at both the transformer and at the secondary panelboard, neutral current will flow through metal raceways (and on the grounding and bonding path) on its return to the power supply.


Generators.

If the grounded (neutral) conductor in a transfer switch is not opened, the grounded (neutral) from the generator will be solidly connected to the utility’s service grounded (neutral) conductor. Under this condition, the generator isn’t a separately derived system, and a neutral-to-case bond must not be made at the generator or at the generator disconnect [250.20(D) FPN 1].


If a neutral-to-case bond is made at both the generator and generator disconnect, objectionable neutral current will flow through metal raceways-and on the grounding and bonding path-to the power supply. This is what causes the issues with GFCI faults.


* (because the electricity is flowing in on the grounding conductor, through the light bulb & discharging to earth - look there's that "to earth" thing again....)


 
Thanks for explaining that in such detail... I'm not an electrical engineer or anything. Yes, neutrals carry electricity, I'm quite aware of that fact.

Also your description of the "unused" electricity flowing through the neutral is at best misleading and at worst straight up wrong, it's the return line that completes the circuit. Unless there is a ground fault the current in the hot and neutral wires is exactly the same magnitude. Look up Kirchhoff's Current Law for details.

Technically you are also wrong about energy flowing to the load via the hot line, seeing as this is alternating current, current flows in both directions in both wires, on alternating halves of the cycle. That doesn't matter in this case, it's what ground reference is that matters.
 
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