>>If the line voltage stays sinusoidal, there is no true power in the
>>current harmonics. But lots of wire losses, which will annoy the power
>>company.

>The problem with harmonics is that the AC power meters are not very
>good at measuring the power in the harmonics.  In the power biz,
>failure to pay for power is a serious problem.  If PG&E were to
>deliver square wave instead of sine wave power, 1/3 of the power would
>be in the harmonics.

>>There have been office fires from all those old non-PFC PCs frying the
>>neutral wires in partition wiring. The wiring was sized assuming that
>>phase currents in neutral would mostly balance, but they don't for the
>>spikes from switching power supplies.

>That's usually the official excuse when the insurance company wants to
>pass the blame for a fire to the building owner or electrical
>contractor and thus avoid paying for the fire damage.  The thermal
>circuit breaks should|would have tripped long before any danger of
>fire.

>In the US, the neutral wire is sized to carry the maximum current of
>ONE of the two phases.  This way, if one phase is loaded to maximum,
>and the other has no load, the system would still be safe.  With such
>a neutral, I don't see how PF changes can create exessive current in
>the neutral wire in a 2 phase residential system.  

>Things are not so convenient with 3 phase power, where the maximum
>neutral current is 1.73 times the current in each phase.  That can
>cause problems, but certainly will not burn down the building.  The
>article below suggests that for 3 phase power, the neutral is sized at
>125% of the current in each phase, but lacking the time to dig through
>the NEC code book, I'm not certain that's the correct number.

>>On Fri, 09 Nov 2012 12:09:57 -0800, John Larkin
>><jlar...@highlandtechnology.com> wrote:

>>>If the line voltage stays sinusoidal, there is no true power in the
>>>current harmonics. But lots of wire losses, which will annoy the power
>>>company.

>>The problem with harmonics is that the AC power meters are not very
>>good at measuring the power in the harmonics.  In the power biz,
>>failure to pay for power is a serious problem.  If PG&E were to
>>deliver square wave instead of sine wave power, 1/3 of the power would
>>be in the harmonics.

>But there's no power in the current harmonics.

>>>There have been office fires from all those old non-PFC PCs frying the
>>>neutral wires in partition wiring. The wiring was sized assuming that
>>>phase currents in neutral would mostly balance, but they don't for the
>>>spikes from switching power supplies.

>>That's usually the official excuse when the insurance company wants to
>>pass the blame for a fire to the building owner or electrical
>>contractor and thus avoid paying for the fire damage.  The thermal
>>circuit breaks should|would have tripped long before any danger of
>>fire.

>Not many people put breakers in the neutral wires.

>>In the US, the neutral wire is sized to carry the maximum current of
>>ONE of the two phases.  This way, if one phase is loaded to maximum,
>>and the other has no load, the system would still be safe.  With such
>>a neutral, I don't see how PF changes can create exessive current in
>>the neutral wire in a 2 phase residential system.  

>>Things are not so convenient with 3 phase power, where the maximum
>>neutral current is 1.73 times the current in each phase.  That can
>>cause problems, but certainly will not burn down the building.  The
>>article below suggests that for 3 phase power, the neutral is sized at
>>125% of the current in each phase, but lacking the time to dig through
>>the NEC code book, I'm not certain that's the correct number.

>The classic wire sizing assumes that current from the three phases
>will cancel into the neutral. When the current is dominated by higher
>harmonics, namely big current spikes at the peak of each sine wave,
>they add up; they don't cancel because they are not simultaneous in
>time.

>>> So then you are agreeing that power can be negative.  The fact that your
>>> meters are incapable of representing this as a negative value is of no
>>> consequence to the concept of power.

>> All the meters that I've done can measure positive and negative power;
>> it's actually harder not to. Some, like apartment submeters, can only
>> accumulate positive KWHs. To my knowledge, no apartments at Battery
>> Park City sell power back to the utility.

>Your power meters are only useful in one city in the *world*?

>>> On 11/7/2012 9:29 PM, josephkk wrote:
>>>> On Sat, 03 Nov 2012 21:50:43 -0400, rickman<gnu...@gmail.com>   wrote:

>>>>> So why do they want to replace the disk meters with digital ones?  You
>>>>> could add a VERY simple optical monitor to the disk meter to read the
>>>>> number of revolutions and provide all the other benefits of digital
>>>>> without the mess of the ADCs, etc.  I suppose the old meters can be a
>>>>> bit more expensive than the fancy, dancy digital ones?

>>>>> Rick

>>>> Two things:

>>>> The way the certification process works.

>>> How does it work that precludes modification of existing meters?

>>>> They want new features that are not possible by just instrumenting
>>>> rotating disk types.

>>>> ?-)

>>> Such as???

>>> Rick

>> Remote turn-on / turn-off.  Time of usage rate billing.  Undoubtedly more.

>> ?-)

>I don't follow.  If you add a digital back end to a rotating disk meter
>you can add any of these features.  So what features can't you add to a
>rotating disk meter with a digital back end?  Is the advantage that the
>digital meters are less expensive?

>In the US, the neutral wire is sized to carry the maximum current of
>ONE of the two phases.  

>>The problem with harmonics is that the AC power meters are not very
>>good at measuring the power in the harmonics.  In the power biz,
>>failure to pay for power is a serious problem.  If PG&E were to
>>deliver square wave instead of sine wave power, 1/3 of the power would
>>be in the harmonics.

>But there's no power in the current harmonics.

>>That's usually the official excuse when the insurance company wants to
>>pass the blame for a fire to the building owner or electrical
>>contractor and thus avoid paying for the fire damage.  The thermal
>>circuit breaks should|would have tripped long before any danger of
>>fire.

>Not many people put breakers in the neutral wires.

>>> On 11/7/2012 9:29 PM, josephkk wrote:
>>>> On Sat, 03 Nov 2012 21:50:43 -0400, rickman<gnu...@gmail.com>   wrote:

>>>>> So why do they want to replace the disk meters with digital ones?  You
>>>>> could add a VERY simple optical monitor to the disk meter to read the
>>>>> number of revolutions and provide all the other benefits of digital
>>>>> without the mess of the ADCs, etc.  I suppose the old meters can be a
>>>>> bit more expensive than the fancy, dancy digital ones?

>>>>> Rick

>>>> Two things:

>>>> The way the certification process works.

>>> How does it work that precludes modification of existing meters?

>>>> They want new features that are not possible by just instrumenting
>>>> rotating disk types.

>>>> ?-)

>>> Such as???

>>> Rick

>> Remote turn-on / turn-off.  Time of usage rate billing.  Undoubtedly more.

>> ?-)

>I don't follow.  If you add a digital back end to a rotating disk meter
>you can add any of these features.  So what features can't you add to a
>rotating disk meter with a digital back end?  Is the advantage that the
>digital meters are less expensive?

>Rick

>> The utility can claim that they are bound by their charter to meter the
>> electricity, and metering as well as bill-printing/mailing are business
>> expenses, not profit.  They might be vulnerable, though, to the
>> claim that motor-type meters are more energy efficient than the
>> electronic ones (about 3W quiescent).

>Three watts seems pretty extreme to me.  This is something that should
>be doable for well under a quarter of a watt before power supply
>inefficiencies are considered.  I have no idea how they deal with that
>however.  In fact, the more efficient, switched power supplies will have
>poor PF, lol!  I believe I've read that there will be a requirement to
>manage PF even on low wattage power supplies.

>Rick

>> In the US, the neutral wire is sized to carry the maximum current of
>> ONE of the two phases.

> Arrgh.  It is the same phase in 120/240 V systems, NOT phases.  Just
> opposite ends of a single center tapped winding.  Opposite polarity is
> correct, and other hot ( / leg) is acceptable.  I get twitchy on this
> because i have to correct sparkies and dumball "engineers" on this all the
> time.

>> This way, if one phase is loaded to maximum,
>> and the other has no load, the system would still be safe.  With such
>> a neutral, I don't see how PF changes can create exessive current in
>> the neutral wire in a 2 phase residential system.

>>On Fri, 09 Nov 2012 12:09:57 -0800, John Larkin
>><jlar...@highlandtechnology.com> wrote:

>>>If the line voltage stays sinusoidal, there is no true power in the
>>>current harmonics. But lots of wire losses, which will annoy the power
>>>company.

>>The problem with harmonics is that the AC power meters are not very
>>good at measuring the power in the harmonics.  In the power biz,
>>failure to pay for power is a serious problem.
>>  If PG&E were to
>>deliver square wave instead of sine wave power, 1/3 of the power would
>>be in the harmonics.

>But there's no power in the current harmonics.

>>>There have been office fires from all those old non-PFC PCs frying the
>>>neutral wires in partition wiring. The wiring was sized assuming that
>>>phase currents in neutral would mostly balance, but they don't for the
>>>spikes from switching power supplies.

>>That's usually the official excuse when the insurance company wants to
>>pass the blame for a fire to the building owner or electrical
>>contractor and thus avoid paying for the fire damage.  The thermal
>>circuit breaks should|would have tripped long before any danger of
>>fire.

>Not many people put breakers in the neutral wires.

>>In the US, the neutral wire is sized to carry the maximum current of
>>ONE of the two phases.  This way, if one phase is loaded to maximum,
>>and the other has no load, the system would still be safe.  With such
>>a neutral, I don't see how PF changes can create exessive current in
>>the neutral wire in a 2 phase residential system.  

>>Things are not so convenient with 3 phase power, where the maximum
>>neutral current is 1.73 times the current in each phase.  That can
>>cause problems, but certainly will not burn down the building.  The
>>article below suggests that for 3 phase power, the neutral is sized at
>>125% of the current in each phase, but lacking the time to dig through
>>the NEC code book, I'm not certain that's the correct number.

>The classic wire sizing assumes that current from the three phases
>will cancel into the neutral. When the current is dominated by higher
>harmonics, namely big current spikes at the peak of each sine wave,
>they add up; they don't cancel because they are not simultaneous in
>time.

>>On Tue, 13 Nov 2012 13:07:59 -0800, Jeff Liebermann <je...@cruzio.com>
>>wrote:

>>>On Fri, 09 Nov 2012 12:09:57 -0800, John Larkin
>>><jlar...@highlandtechnology.com> wrote:

>>>>If the line voltage stays sinusoidal, there is no true power in the
>>>>current harmonics. But lots of wire losses, which will annoy the power
>>>>company.

>>>The problem with harmonics is that the AC power meters are not very
>>>good at measuring the power in the harmonics.  In the power biz,
>>>failure to pay for power is a serious problem.

>>>  If PG&E were to
>>>deliver square wave instead of sine wave power, 1/3 of the power would
>>>be in the harmonics.

>>But there's no power in the current harmonics.

>What if the users' equipment was a resistive heater load ?  The square
>wave wouldn't power that with all its might and use all the energy
>to make heat ?

>   (assume a low-inductance resistor)

>boB

>>> In the US, the neutral wire is sized to carry the maximum current of
>>> ONE of the two phases.

>> Arrgh.  It is the same phase in 120/240 V systems, NOT phases.  Just
>> opposite ends of a single center tapped winding.  Opposite polarity is
>> correct, and other hot ( / leg) is acceptable.  I get twitchy on this
>> because i have to correct sparkies and dumball "engineers" on this all the
>> time.

>If we're considering sine waves with odd harmonics, why would it matter
>if one talks of opposite polarity or 180 degrees phase difference?

>> 120/208 V "single phase systems" are different.  Other leg still applies.

>>> This way, if one phase is loaded to maximum,
>>> and the other has no load, the system would still be safe.  With such
>>> a neutral, I don't see how PF changes can create exessive current in
>>> the neutral wire in a 2 phase residential system.

>As John pointed out, if the load consists of rectifiers without
>PF correction, the currents do not cancel in the neutral wire.
>In fact, the current may end up to be the *sum* of the currents
>in both hot wires.

>Jeroen Belleman

>The classic wire sizing assumes that current from the three phases
>will cancel into the neutral. When the current is dominated by higher
>harmonics, namely big current spikes at the peak of each sine wave,
>they add up; they don't cancel because they are not simultaneous in
>time.

>>On Tue, 13 Nov 2012 13:07:59 -0800, Jeff Liebermann <je...@cruzio.com>
>>wrote:

>>>Things are not so convenient with 3 phase power, where the maximum
>>>neutral current is 1.73 times the current in each phase.  That can
>>>cause problems, but certainly will not burn down the building.  The
>>>article below suggests that for 3 phase power, the neutral is sized at
>>>125% of the current in each phase, but lacking the time to dig through
>>>the NEC code book, I'm not certain that's the correct number.

>>The classic wire sizing assumes that current from the three phases
>>will cancel into the neutral. When the current is dominated by higher
>>harmonics, namely big current spikes at the peak of each sine wave,
>>they add up; they don't cancel because they are not simultaneous in
>>time.

>While I very much doubt that the harmonics will actually burn down the
>house, the (possibly urban legends) that the harmonics have burned the
>neutral conductor in a cable, causing hazardous voltages appears to be
>believable.

>> I don't follow.  If you add a digital back end to a rotating disk meter
>> you can add any of these features.  So what features can't you add to a
>> rotating disk meter with a digital back end?  Is the advantage that the
>> digital meters are less expensive?

>> Rick

> Certainly both of these and providing for co-generation (e.g. solar) is
> much easier by just going all digital direct in the first place (also
> cheaper which the utilities DO care about).

>>> The utility can claim that they are bound by their charter to meter the
>>> electricity, and metering as well as bill-printing/mailing are business
>>> expenses, not profit.  They might be vulnerable, though, to the
>>> claim that motor-type meters are more energy efficient than the
>>> electronic ones (about 3W quiescent).

>> Three watts seems pretty extreme to me.  This is something that should
>> be doable for well under a quarter of a watt before power supply
>> inefficiencies are considered.  I have no idea how they deal with that
>> however.  In fact, the more efficient, switched power supplies will have
>> poor PF, lol!  I believe I've read that there will be a requirement to
>> manage PF even on low wattage power supplies.

>> Rick

> Actually low watt PF corrected power supplies can be efficient, it is just
> a different design.  What is really difficult is near zero idle power and
> short pulses of a fractional to a few watts.  MPS430 based designs are
> famous for this.  Many sleepable uCs and uPs have this issue.

> ?-)

>>On Tue, 13 Nov 2012 13:07:59 -0800, Jeff Liebermann <je...@cruzio.com>
>>wrote:

>>>Things are not so convenient with 3 phase power, where the maximum
>>>neutral current is 1.73 times the current in each phase.  That can
>>>cause problems, but certainly will not burn down the building.  The
>>>article below suggests that for 3 phase power, the neutral is sized at
>>>125% of the current in each phase, but lacking the time to dig through
>>>the NEC code book, I'm not certain that's the correct number.

>>The classic wire sizing assumes that current from the three phases
>>will cancel into the neutral. When the current is dominated by higher
>>harmonics, namely big current spikes at the peak of each sine wave,
>>they add up; they don't cancel because they are not simultaneous in
>>time.

>While I very much doubt that the harmonics will actually burn down the
>house, the (possibly urban legends) that the harmonics have burned the
>neutral conductor in a cable, causing hazardous voltages appears to be
>believable.

>At higher distribution levels, it is assumed that the neutral current
>will cancel out in a three phase system and thus, the neutral
>connector might quite a lot weaker than the phase connector. In a
>ground cable, the armoring around the phase conductors might act as
>the neutral conductor. In a pole mounted cable system, three aluminum
>phase connectors plus a steel cable servicing as the mechanical
>strength as well as the neutral condition (assuming neutral conductor
>canceling out).

>However, if this canceling assumption is not true with electronics
>load, the third harmonic current is far larger than initially assumed,
>causing burn through of weak neutral conductors.

>>>> The utility can claim that they are bound by their charter to meter the
>>>> electricity, and metering as well as bill-printing/mailing are business
>>>> expenses, not profit.  They might be vulnerable, though, to the
>>>> claim that motor-type meters are more energy efficient than the
>>>> electronic ones (about 3W quiescent).

>>> Three watts seems pretty extreme to me.  This is something that should
>>> be doable for well under a quarter of a watt before power supply
>>> inefficiencies are considered.  I have no idea how they deal with that
>>> however.  In fact, the more efficient, switched power supplies will have
>>> poor PF, lol!  I believe I've read that there will be a requirement to
>>> manage PF even on low wattage power supplies.

>>> Rick

>> Actually low watt PF corrected power supplies can be efficient, it is
>> just
>> a different design.  What is really difficult is near zero idle power and
>> short pulses of a fractional to a few watts.  MPS430 based designs are
>> famous for this.  Many sleepable uCs and uPs have this issue.

>> ?-)

> How does that work exactly?

> Rick

> Rick

>                                          ...Jim Thompson

>> They had a temporary (above-ground) neutral installed within the
>> hour... a cable about as thick as my wrist ;-)

>>                                          ...Jim Thompson

> I do hope you are writing "a cable about as thick as my wrist" as an
> embellishment. If so, I can deal with that.

>>> In the US, the neutral wire is sized to carry the maximum current of
>>> ONE of the two phases.

>> Arrgh.  It is the same phase in 120/240 V systems, NOT phases.  Just
>> opposite ends of a single center tapped winding.  Opposite polarity is
>> correct, and other hot ( / leg) is acceptable.  I get twitchy on this
>> because i have to correct sparkies and dumball "engineers" on this all the
>> time.

>If we're considering sine waves with odd harmonics, why would it matter
>if one talks of opposite polarity or 180 degrees phase difference?

>> 120/208 V "single phase systems" are different.  Other leg still applies.

>>> This way, if one phase is loaded to maximum,
>>> and the other has no load, the system would still be safe.  With such
>>> a neutral, I don't see how PF changes can create exessive current in
>>> the neutral wire in a 2 phase residential system.

>As John pointed out, if the load consists of rectifiers without
>PF correction, the currents do not cancel in the neutral wire.
>In fact, the current may end up to be the *sum* of the currents
>in both hot wires.

>Jeroen Belleman

>>>> This way, if one phase is loaded to maximum,
>>>> and the other has no load, the system would still be safe.  With such
>>>> a neutral, I don't see how PF changes can create exessive current in
>>>> the neutral wire in a 2 phase residential system.

>>As John pointed out, if the load consists of rectifiers without
>>PF correction, the currents do not cancel in the neutral wire.
>>In fact, the current may end up to be the *sum* of the currents
>>in both hot wires.

>>Jeroen Belleman

>That even applies to 120/240 center-tapped systems where the 120 volt
>loads are 0 and 180 degrees. If the loads were half-wave diode
>rectified, and each line was running at its rated max RMS current, the
>neutral could be overloaded. Again, if the line currents don't overlap
>in time they  add into the neutral, not balance as would happen with
>sinewave loads.

>You could get the same effect with a resistive load on one side and a
>capacitive load on the other. The orthogonal neutral currents wouldn't
>cancel.