The US electrical system

[cliffyk]

I think the wattage of the dryer is a rather useless metric though, what matters is the kWh required to dry a load of clothes. A lower powered dryer will consume less instantaneous power but all else being equal it will run longer. Seems like mine takes 30-40 minutes to dry a full load out of the washer, and it handles 2-3 times the load of a typical UK dryer. Bigger capacity machines are run less frequently, I doubt there is that much difference in consumption per item of clothing.

A heat pump makes a big difference there. Or even a heat recovery exchanger, for that matter.

Do heat pump based clothes dryers exist? Interesting concept--our "new" (2 years old) R-410a based central HVAC system with heat pump (common here in Florida) can, in heat pump mode, produce a good flow (1600+ cfm) of 85° F air with an outdoor ambient of 40° F--below that 13.2 kW of coiled nichrome kicks in for "emergency" heat. We see the latter for usually < 100 hours/year...

The neat thing about the heat pump is of course that the heat is, like fossil fuels¹, free, I just pay to "pump" it in the direction I want it to go. I wish there were a market for that I pimp out this time of year. A practical, economical heat capture/distribution technology would be a winner--

---------------------------------
¹ - Leaving landowner subterranean mineral rights issues aside, oil, natural gas, coal, etc, are free, we pay for them to be extracted, refined, and distributed.

[Monkeh]

Maybe I missed it, but it did seem that he glossed over or did not emphasize that the so-caled "neutral" wire in our silly earth return split phase system is anything but neutral. It carries the full difference of the loads applied to each phase. If you draw 200 A from 120 V phase "A", and 100 A from phase "B", the "neutral" wire will be carrying 100 A--enough to be a BIG surprise for anyone believing it to be "neutral", and mucking about with it while the full phase load is unbalanced.

That the neutral can carry current is absolutely normal, not unique to your split-phase (which is not earth return, because you have a wire, not the earth) system. It is not neutral because it does nothing, but neutral because it is nominally at 0V.

[bdunham7]

If you draw 200 A from 120 V phase "A", and 100 A from phase "B", the "neutral" wire will be carrying 100 A--enough to be a BIG surprise for anyone believing it to be "neutral", and mucking about with it while the full phase load is unbalanced.

That is exactly what a neutral is supposed to do.  What big surprise would the neutral have?  3 volts?

[tooki]

7kw to dry yer clothes, aint you guys heard of washing lines

   Seriously, not since the 1960s. Besides with the now popular zero lot line subdivisions, there's NO room for one. I literally haven't seen a clothes line since probably 1968.

We still had one until 1992 (when we moved from USA to Switzerland), at a house built in the late 70s. My grandma (living in Florida) used one until she passed away in 2013.

Do heat pump based clothes dryers exist? Interesting concept--our "new" (2 years old) R-410a based central HVAC system with heat pump (common here in Florida) can, in heat pump mode, produce a good flow (1600+ cfm) of 85° F air with an outdoor ambient of 40° F--below that 13.2 kW of coiled nichrome kicks in for "emergency" heat. We see the latter for usually < 100 hours/year...

Yes. They’re exceedingly rare in USA (where just a handful of models exist, e.g. Miele), but in Europe, they’ve been the only type sold for several years AFAIK, in order to comply with energy efficiency regulation. Just as window air conditioners are cheap in USA due to economies of scale, heat pump dryers are available cheaply in Europe.

My apartment came with one from Bosch-Siemens, and it’s great. It doesn’t get as hot as a traditional dryer, making it gentler on the clothes, but the dehumidifying effect of the heat pump system makes it work just as fast. It uses less than 1KW.

[free_electron]

do you have any idea of the load of a 5 ton airco unit ? that thing pulls 30 to 32 ampere on a hot day ... throw in an electric water boiler, a 5 kilowatt oven (or a double one)  , a 3 kilowatt cooktop , a  2 kilowatt microwave, a 2 horsepower food disposal unit , a dishwasher, washing machine and electric clothes dryer,  a well pump , a 2 hp pool pump , 1kw saltwater chlorine generator,  ... yup you need that 200 ampere !

The demand can be way reduced with smart engineering, even if 5 tons of A/C really is needed. (Hint: if your insulation is decent, it's unlikely unless you truly have a huge house.) The water heater isn't going to need to run at full capacity when the A/C is needed at all, plus one based on a heat pump reduces the power usage down to a few hundred watts. The oven is only going to draw full power during preheating, same with the cooktop. The microwave is only used for short bursts and the disposal for even shorter. Heat pump dryers also use much less power. The pool equipment doesn't need to run full time so a smart controller can run it when demand is low and/or energy is cheap.

My warm water boiler runs at night for now. The airco runs pretty much full time.. Central valley gets hot in summer. I bake bread twice a week. cooking : three times a day. The problem is that there are moments , even if only for 5 minutes where peak power is very large. if your main breakers can't handle such a load it is going to get annoying very quickly. I have a heatpump airco system , but still the load is big. And then there's two electric cars that pull 30 ampere each. The pool pump and chlorine generator run 9 to 10 hours a day. You have to, otherwise the pool turns to soup. This is a saltwater pool , so it needs circulation to do the electrolytic conversion of the salt into chlorine and sodium. Pool is solar heated so that array needs circulation as well.

Cooking indian food is very involved. they don't do simple meals and run everything  on hot hot hot ( my wife is from india ) a 5 zone induction cooker pulls quite a load ...

Even the smallest homes in the us have 100 amp main breakers.

That's why i am going solar The system will give me more than 100 ampere off the panels on a bad day. Whatever is possible : dump it in the packs. Run the house at night off the packs and dump the rest in the cars. Everything else is going on smart controllers. if peak power is available on the array : use it. Run the 100 gallon water heater for the shower. run anything that can 'store energy' : water heater , pool heater , battery packs, cars. When the array becomes less productive : divert energy to large loads that are temporary : washing and drying.
As the array becomes less productive during the day : spin down the large loads and keep topping off the batteries ( if they are already full no problem. once it gets dark : shed the large loads. no running dryers ovens etc. cooking ok. Use the packs to run airco and the necessities : refrigerators and the stuff that needs to be on. keep dumping power into the cars if they require it.

the controller is self-learning and will adapt the load shift.

[tom66]

Do heat pump based clothes dryers exist? Interesting concept--our "new" (2 years old) R-410a based central HVAC system with heat pump (common here in Florida) can, in heat pump mode, produce a good flow (1600+ cfm) of 85° F air with an outdoor ambient of 40° F--below that 13.2 kW of coiled nichrome kicks in for "emergency" heat. We see the latter for usually < 100 hours/year...

Yes, we have those in Europe. They are relatively expensive because you need the equivalent of a 9000 BTU/hr A/C unit (~800W input power, 2600W output power) in the bottom of your dryer, plus all the associated complexities of a heatpump system, but they are considerably more energy efficient provided they are operating in a warm room.  And no, they aren't the only models available.  We have heat pump, condenser and vented dryers all available for sale.

The dryer we have is a condenser dryer, which is slightly more efficient than a straight vented arrangement as heat is recycled through the system and no heat is deliberately exhausted to atmosphere.  Cold metal coils (by shear thermal mass) condense the water in the hot humid air, which is then recycled through the machine.  A small pump moves that water into a disposal tank.  Humidity sensors detect when the humid air has become dry enough for the clothes to be considered "done".

Since my dryer is often operating in a cold garage (in summer clothes are hang-dried) I don't know if a heat pump would be much better.  It would depend on how efficient it is at extracting heat from a 5C room.

[tooki]

Relatively expensive? I’ve seen no-name heat pump dryers on sale here for $300.

(And it’s not like 9000BTU AC is that big. Those are routinely used as window AC units in USA, and don’t cost very much.)

Non-heat-pump condenser dryers use more energy than vented, not less: https://www.cda.eu/laundry/condenser-vs-vented/

They only made sense when you couldn’t have a vent. With the advent of heat pump dryers, are plain condenser dryers don’t make sense at all.

[tom66]

Are you sure?  The EU standards (Annex IV):
https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32012R0932

state that the 'standard' of each dryer should consume (@8kg capacity):
Vented - 4.1 kWh/cycle
Condenser - 2.30 kWh/cycle

The ratings get better at lower capacities, with the energy consumption of a 5kg vented dryer and 5kg condenser dryer only differing by about 20% or so, although the condenser still wins.  I'd be curious why there isn't a linear relationship, it might relate to the extra energy required by the condenser system, pushing the hot air through the internal condensation system might consume extra energy and give more opportunity for heat loss inside the machine perhaps.  The energy consumption of the tumble motor shouldn't be that high (100W or so.)

I have not seen a heatpump dryer for under £400 (~$500USD) here but then again, my current tumble dryer was a  road-side find (it had a blown fuse...)  I suspect that it may be more expensive to buy these types of dryers here as regulations for refrigerants may be more strict.  I would be surprised if propane is an acceptable refrigerant in such a device, which is common in cheap A/C units and refrigerators here.

There's probably the other factor that as you mention, condenser dryers are preferred as there is limited ventilation requirement, with no exhaust to atmosphere, especially important for flat dwellers.

[NiHaoMike]

Non-heat-pump condenser dryers use more energy than vented, not less: https://www.cda.eu/laundry/condenser-vs-vented/

In cold climates, vented dryers are the least efficient after accounting for heat lost from the building.

[duak]

I set up a little drying cabinet for delicates in the furnace closet.  The excess heat from the house's original furnace and hot water heater would dry laundry and remove the humid air by combusting it and firing it up the B-vent.  After replacing both units with closed combustion units, the furnace closet was cooler and had no natural venting.  I now had room for a dehumidifier that keeps the closet and most of the lower floor less humid than before, especially in the summer.  The dehumidifier doesn't run all the time even when drying laundry.  Three or four pairs of jeans or a few terry cloth towels will dry overnight as long as the circulating fan moves air around in the closet.

[AlbertL]

If you draw 200 A from 120 V phase "A", and 100 A from phase "B", the "neutral" wire will be carrying 100 A--enough to be a BIG surprise for anyone believing it to be "neutral", and mucking about with it while the full phase load is unbalanced.

That is exactly what a neutral is supposed to do.  What big surprise would the neutral have?  3 volts?

It depends on the nature of the mucking.  In a properly installed, intact system, touching the neutral and ground (earth) shouldn't yield any great surprise.  But getting in series with a neutral, or between an open neutral and ground, could expose one to essentially the full line voltage.  And opening a current-carrying neutral could produce a significant arc.

This leads into another interesting aspect of US distribution: the multi-grounded neutral.  The utility substation typically supplies three-phase distribution feeders from the wye-connected secondary of a step-down transformer.  The neutral of the wye is grounded at the substation, travels along with phase conductors, and is grounded at intervals along the line.  Transformers along the feeder make the final step down to customer delivery voltage, which is typically 120/240V single-phase (i.e. a center-tapped 240 volt secondary) or three-phase 120/208V or 277/480V wye.  The secondary neutrals of these transformers are connected to the feeder neutral, and grounded at the transformer location.  Finally, the neutral is carried to the customer's main service equipment, where it is again grounded, often at more than one location on the premises.

The two key points are (1) the neutral is common to both sides of the distribution transformers, and (2) the neutral is grounded (earthed) at multiple locations, some of them widely separated.

[Monkeh]

The two key points are (1) the neutral is common to both sides of the distribution transformers

This seems unwise. Also unlikely. HV and LV earths are normally kept separate for good reason.

(2) the neutral is grounded (earthed) at multiple locations, some of them widely separated.

And this is nothing unusual.

[AlbertL]

The two key points are (1) the neutral is common to both sides of the distribution transformers

This seems unwise. Also unlikely. HV and LV earths are normally kept separate for good reason.

(2) the neutral is grounded (earthed) at multiple locations, some of them widely separated.

And this is nothing unusual.

Using the same wire as the common grounded neutral for both sides of the transformer is standard US practice.  This brochure shows typical pole-mounted distribution transformers: https://www.eaton.com/content/dam/eaton/products/medium-voltage-power-distribution-control-systems/cooper-power-series-transformers/single-phase-overhead-transformers-catalog-ca201001en.pdf.  Note the ground strap connecting the center tap of the secondary to  the transformer tank.  And note that some of the transformers have just one primary terminal - in these models, the other end of the primary winding is internally connected to the tank, which has an external lug for connection of the ground wire.  The models with two primary terminals are intended for delta connections, but can be used in wye by grounding one of the terminals.  My neighborhood in fact has a mix of both types on its wye-connected feeder.  I think one reason for the common neutral is to limit the voltage rise on the secondary side if the primary and secondary circuits accidentally become connected; for example by a fallen wire.

The multiple ground points have the benefit of redundancy and lowered resistance, but can also hide the failure of one or more grounds, and cause undesirable "stray" ground-current paths.
 

[Monkeh]

Using the same wire as the common grounded neutral for both sides of the transformer is standard US practice.

Well, that's.. nice. We don't like bringing the primary into people's houses in the event of an earthing fault, so.. we don't do that.

To quote one technical spec on the subject:

i. All pole-mounted substations shall be designed with separate HV and LV Earthing Systems and shall be separated by at least 20 m.

ii. The HV Earth Electrode earth resistance shall not exceed 20 Ω in order to provide reliable protection operation. (Where surge arresters are installed, the HV Earth Electrode earth resistance shall not exceed 10 Ω).

iii. The LV Earth Electrode earth resistance shall not exceed 20 Ω to comply with ENA Engineering Recommendation EART-01-002.

iv. The HV Earth Electrode and Earthing Conductors shall be of sufficient size and surface area to safely carry fault current at that site (see sections 14.1 and 14.4).

v. EPR on pole-mounted steelwork can approach system phase-to-earth voltage, which in some situations might be close to 6.33kV. All LV equipment shall be suitably insulated and separated from HV equipment to prevent flashover during HV fault conditions.

That said, subject to certain conditions, ground-mounted substations may have an HV earth only (which is then shared). They're a little less damage prone, for a start..

[tooki]

Are you sure?  The EU standards (Annex IV):
https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32012R0932

state that the 'standard' of each dryer should consume (@8kg capacity):
Vented - 4.1 kWh/cycle
Condenser - 2.30 kWh/cycle

The ratings get better at lower capacities, with the energy consumption of a 5kg vented dryer and 5kg condenser dryer only differing by about 20% or so, although the condenser still wins.  I'd be curious why there isn't a linear relationship, it might relate to the extra energy required by the condenser system, pushing the hot air through the internal condensation system might consume extra energy and give more opportunity for heat loss inside the machine perhaps.  The energy consumption of the tumble motor shouldn't be that high (100W or so.)

I have not seen a heatpump dryer for under £400 (~$500USD) here but then again, my current tumble dryer was a  road-side find (it had a blown fuse...)  I suspect that it may be more expensive to buy these types of dryers here as regulations for refrigerants may be more strict.  I would be surprised if propane is an acceptable refrigerant in such a device, which is common in cheap A/C units and refrigerators here.

There's probably the other factor that as you mention, condenser dryers are preferred as there is limited ventilation requirement, with no exhaust to atmosphere, especially important for flat dwellers.

Well, I was sure, since until this thread, I’d never heard any claims of non-heat-pump condenser dryers being more efficient than vented. When I googled just now, the first result that had any statements about energy consumption agreed with me, hence why I posted it.

As for refrigerants, Switzerland is at least as strict as the EU, if not more. (Switzerland has arranged for itself the cushy position of enjoying most EU benefits while being subject to comparatively few of the responsibilities.) I know Switzerland follows EU appliance energy efficiency rules 1:1.

I have no idea what’s in mine, but you have me curious now. I’ll see if I can find out.

(Surprisingly to many outsiders, the US is also really strict on a lot of air quality stuff. In some areas, stricter than the EU, like vehicle exhaust. Unless the guy squatting in the White House gets his way, in which case we can soon expect 70s era smog there again.)

[GlennSprigg]

If you draw 200 A from 120 V phase "A", and 100 A from phase "B", the "neutral" wire will be carrying 100 A--enough to be a BIG surprise for anyone believing it to be "neutral", and mucking about with it while the full phase load is unbalanced.

That is exactly what a neutral is supposed to do.  What big surprise would the neutral have?  3 volts?

Nope!!  "Funny" things used to happen, (here in AussieLand) with say 3-Phase 'Star' (neutral) connected
supply authority transformers, (like the/our  11-kv ones). The Public never saw this, but 'Un-Loaded', you
would see very strange voltages, and often MANY hundreds of volts on the Neutral Star-Point!!   
Was lethal, until loaded/grounded.  Thinking back, it was never explained to us WHY, though...   

[cliffyk]

If you draw 200 A from 120 V phase "A", and 100 A from phase "B", the "neutral" wire will be carrying 100 A--enough to be a BIG surprise for anyone believing it to be "neutral", and mucking about with it while the full phase load is unbalanced.

That is exactly what a neutral is supposed to do.  What big surprise would the neutral have?  3 volts?

It depends on the nature of the mucking.  In a properly installed, intact system, touching the neutral and ground (earth) shouldn't yield any great surprise.  But getting in series with a neutral, or between an open neutral and ground, could expose one to essentially the full line voltage.  And opening a current-carrying neutral could produce a significant arc.

This leads into another interesting aspect of US distribution: the multi-grounded neutral.  The utility substation typically supplies three-phase distribution feeders from the wye-connected secondary of a step-down transformer.  The neutral of the wye is grounded at the substation, travels along with phase conductors, and is grounded at intervals along the line.  Transformers along the feeder make the final step down to customer delivery voltage, which is typically 120/240V single-phase (i.e. a center-tapped 240 volt secondary) or three-phase 120/208V or 277/480V wye.  The secondary neutrals of these transformers are connected to the feeder neutral, and grounded at the transformer location.  Finally, the neutral is carried to the customer's main service equipment, where it is again grounded, often at more than one location on the premises.

The two key points are (1) the neutral is common to both sides of the distribution transformers, and (2) the neutral is grounded (earthed) at multiple locations, some of them widely separated.

Yes, that was my point--disconnecting it, thinking it's harmless would cause a surprise...

[tom66]

A very dangerous condition can occur on TN-C-S electrical systems, which are very common in the UK.  A PEN connection, combined earth/neutral, is passed along with live in the supply cable.  PEN is split into neutral and earth at the main entry fuse.  Most UK homes do not have additional earthing (PME)

The risk is that if PEN fails due to cable damage, corrosion, poor maintenance etc then, although power to the building will be lost, the PEN can effectively float towards Live as any appliance that conducts current in the "off state" (think fridge compressors, heating elements, even some SMPSes) will pull that PEN node up via a low impedance node.  This will then mean if someone touches one of their now-floating appliances and an earthed device (such as water piping, or walks on wet ground outside while touching their PEN-earthed electric car) then they could receive a fatal electric shock.

This is a particular pain for EV charging installations, as far as I am aware there are only two ways to solve the problem:
- Earth rods until the impedance is below some nominal figure, which can often require 5+ earth rods to be drilled in to the driveway and fitted (expensive, time consuming)
- An EV charging station that isolates PE as well as L/N when power fails and only connects PE when the vehicle has been detected

It's for this reason PME is now standard at newer builds ... but again, one of those cost saving decisions made 50 years ago that bites us in the ass now.

[Monkeh]

A very dangerous condition can occur on TN-C-S electrical systems, which are very common in the UK.  A PEN connection, combined earth/neutral, is passed along with live in the supply cable.  PEN is split into neutral and earth at the main entry fuse.  Most UK homes do not have additional earthing (PME)

The majority of TN-C-S systems are PME. PME is distribution side, not customer.

This will then mean if someone touches one of their now-floating appliances and an earthed device (such as water piping

This is what bonding is for, see: equipotential zone.

or walks on wet ground outside while touching their PEN-earthed electric car

And this is a rather overblown concern IMO, but it is in fact proving to be a pain.

[richard.cs]

And this is a rather overblown concern IMO, but it is in fact proving to be a pain.

Well yes, it's not introducing a genuinely new risk, the general public was already hopelessly unaware of the risk of outdoor class I appliances with TNC-S earthing and happily bought all manner of earthed metalwork outdoors (outside of the equipotential zone), in addition to the various light fittings, outdoor taps and gas pipes (which now seem to default to running along outside walls) that form part of the installation more generally. The only difference with electric cars is that it's a new kind of class I appliance intended for use outdoors (rather than incidentally used as such), and lots of people have got in a bit of a panic about it. Class II cars would be possible, but it's now rather too late for that.

Generally the safety case for TNC-S in the UK has been looking progressively poorer for decades as the metallic water and gas pipes that used to provide free sub-Ohm backup earthing have disappeared, and the promised reliability of double-crimped neutral connections has not really been achieved.

[Gyro]

John Ward has a useful video on the subject (EV charger earthing)...  https://youtu.be/gZVx7GbAwlg

There are also an increasing number of chargers with earth fault detection, which do not require separate earthing... https://youtu.be/3-HEKqeSrwk

[helius]

The risk is that if PEN fails due to cable damage, corrosion, poor maintenance etc then, although power to the building will be lost, the PEN can effectively float towards Live as any appliance that conducts current in the "off state" (think fridge compressors, heating elements, even some SMPSes) will pull that PEN node up via a low impedance node.

The same situation in North America is called a broken neutral, and because of the split pole arrangement, does not cause power to the building to be lost! The tell-tale sign is when some of the lights dim or grow brighter in concert with a refrigerator or heater cycling on and off. Incandescents show the effect most because they run unregulated.

- Earth rods until the impedance is below some nominal figure, which can often require 5+ earth rods to be drilled in to the driveway and fitted (expensive, time consuming)

Measuring earth bonding also requires the installation of temporary grounding rods at some distance (100') to null the effect of local potential variations in the earth (caused by earth leakage). This is obviously complicated in a neighborhood with small subdivisions. And driving 10' grounding rods is no fun...

[Monkeh]

And this is a rather overblown concern IMO, but it is in fact proving to be a pain.

Well yes, it's not introducing a genuinely new risk, the general public was already hopelessly unaware of the risk of outdoor class I appliances with TNC-S earthing and happily bought all manner of earthed metalwork outdoors (outside of the equipotential zone), in addition to the various light fittings, outdoor taps and gas pipes (which now seem to default to running along outside walls) that form part of the installation more generally. The only difference with electric cars is that it's a new kind of class I appliance intended for use outdoors (rather than incidentally used as such), and lots of people have got in a bit of a panic about it. Class II cars would be possible, but it's now rather too late for that.

Generally the safety case for TNC-S in the UK has been looking progressively poorer for decades as the metallic water and gas pipes that used to provide free sub-Ohm backup earthing have disappeared, and the promised reliability of double-crimped neutral connections has not really been achieved.

Now, I could be wrong, but as far as I'm aware most electric cars do not connect the charging CPC to the chassis. That coupled with plastic handles and extremely high quality paint finishes leaves me entirely unconcerned about taking a belt off a car. Oh, that and like most people I walk around on a big sheet of rubber, not my bare feet.

I do, however, think we should never have used TN-C-S as an excuse not to properly control potential at the installation. It's a perfectly good system for ensuring a nice low impedance fault path for currents in normal operation without using lots of extra copper (or lead, or alu), but a poor excuse for not having good earthing at the property (and the American method of whacking a rod in quickly doesn't cut it).

[tom66]

Now, I could be wrong, but as far as I'm aware most electric cars do not connect the charging CPC to the chassis. That coupled with plastic handles and extremely high quality paint finishes leaves me entirely unconcerned about taking a belt off a car. Oh, that and like most people I walk around on a big sheet of rubber, not my bare feet.

You would unfortunately be incorrect.  The chassis of my PHEV VW Golf GTE is connected to the earth pin on the type 2 connector.  This means 12V battery earth and the Type 2 connector earth are the same.

While the paint on the vehicle provides some level of insulation (I was unable to measure a direct connection, although I of course did not press into the paint) parts of the car like the door locks and frame were found to be conductive in my tests.  It's possible to imagine someone stepping into their car and getting a shock that way. Also, the trailer connection if fitted would expose this, as would cigarette lighter/USB convenience socket or parts under the engine compartment.

I actually measured a direct connection from the alloy wheels to the protective earth if you want to talk about an interesting way to get a shock. I guess there are some bearings somewhere that are chassis connected.

[Monkeh]

Well, that's a shame. Roll out the earth mats (not that anyone wants to spend money on infrastructure).