3-phase split load design

[ajdelange]

For geothermal heat pumps, the motor is either to be wired as 3-phase or 1-phase connected via a safety switch. A safety switch is a switch that shuts off power if it notices the wire heating up i.e. the motor is not spinning for some reason.

I assume that you mean it can be either a 3ø motor or a single phase motor but not a 3ø motor wired single phase. This does work if you can get it started but is certainly hard on the motor and clearly presents an asymmetric load to the system.

Both single phase and 3ø motors will be equipped with some sort of protection against the locked rotor condition. This can be an overcurrent sensor (fuse, magnetic or thermal or combination circuit breaker) or sometimes just a thermally operated switch on the motor which opens if the motor gets too hot and can be reset manually ((typical for garbage disposal units) or automatically when it cools. 3ø motors are often equipped with single phasing detectors (one phase fails) as well.

The motor that circulates hot water in my house for heating and showers is wired with a safety switch. And it's a real ***** because every time I shut off power to the house, that motor refuses to restart on it's own. I need to unmount it, stand it on a shelf and hit the fins with my finger to kick start them. Then I need to let it run like that for about 15 minutes before it will restart on it's own with the safety switch before I can remount it.

Of course I have no idea what you actually have there but if it is a single phase motor with a starting or starting/running capacitor I'd check that. Also see if you can clean/lubricate the bearings. Circulating pumps in heating systems are usually pretty puny and often don't have the starting circuitry (they are shaded pole construction) in which case it may just be the bearings are binding.

 

[ajdelange]

Yes, well for example in Finland you can't get more than 3 x 63 amp service to a residence.

Unbelievable. That's less than 50 KVA. I guess pottery isn't a common hobby over there. In the US they'll install as much as you are willing to pay for - even three phase if you want it (you don't when you see the price tag). I have, for example, three 200 Amp bi-phase panels for a total of 144 KVA installed. No, I'm not Al Gore. My average load over the last year has been 3.75 KW. The house is relatively small but it has been added on to twice and each time they installed another 200 amp panel (total of 3). When the utility saw that they just put a bigger transformer on the pole (and sent me a bill).

 

[The10mmKid]

Podz,
I've noticed your pics show 'surface mounted' cabling. Are any wires concealed in the walls, attics, sub flooring?

'da Kid

 

[podz]

Unbelievable. That's less than 50 KVA. I guess pottery isn't a common hobby over there.

Not many home potters, no.

Additionally, the maximum allowable size for a single phase circuit is 16 amps and that has to run on 2,5mm2 wire, which would be the equivalent of 13 AWG if such a size existed. In other words, no 240v sockets are sold here with a rating of greater than 16 amps and bypassing this will void your home insurance.

You have to remember, though, that we are running 240v single phase and 400v 3-phase, so the amperage requirements are much lower. I haven't yet seen a 3-phase MIG welder that won't run on a 16 amp circuit at 400v.

I believe, but have no proof, that the 63 amp restriction is political. 3-phase power comes in 16, 32, 64 amp and so on. Businesses that pay business-rate electricity prices don't want people to get away with running 64 amp 3-phase on residential rates (creates competition, and the european way is all about locking new competition out).

 

[ajdelange]

QUOTE=podz;6813858]

You have to remember, though, that we are running 240v single phase and 400v 3-phase, so the amperage requirements are much lower. I haven't yet seen a 3-phase MIG welder that won't run on a 16 amp circuit at 400v.[/QUOTE] If you delta connect you can get 3*63*240*sqrt(3) = 78.6 kVA which is certainly better but still not a lot by comparison to what one finds in the American McMansion. Again, though, we note that the average load drawn is usually only a few percent of the installed capacity.

I believe, but have no proof, that the 63 amp restriction is political.

I figured as much but wanted to step delicately around that and though I am tempted to add some further comments will refrain from doing so.

 

[podz]

Podz,
I've noticed your pics show 'surface mounted' cabling. Are any wires concealed in the walls, attics, sub flooring?

'da Kid

Not in this house, except for the cable that runs between the feed fuses and the main circuit panel. And that will be replaced with surface mount soon. My walls are full of sawdust as insulation and soundproofing and I don't really want cables in there. The new way is to pull flexible plastic pipes and then pull individual cables inside of those, not the PVC coated cables like I have.

This is an old house built after the war when the government had to build 300 thousand new houses FAST for displaced citizens and returning war heroes. You can imagine the quality with which they built them at that speed. The oldest wires in my house are wrapped with woven cloth and coated with tar. Thank god they aren't feeding more than LED lamps at this time and will be replaced ASAP. I took apart one of the old light switches the other day and the coating on the wires had melted together.

 

[podz]

I figured as much but wanted to step delicately around that and though I am tempted to add some further comments will refrain from doing so.

Be as it may, I am still able to run an 8.5kW heating element on my puny service whereas most of you are not able to do it even on your huge ass services. ;-)

 

[ajdelange]

Be as it may, I am still able to run an 8.5kW heating element on my puny service whereas most of you are not able to do it even on your huge ass services.

I have a 14 KW auxiliary heater in one of my air handlers. It's on a 60 amp breaker in a 200 amp panel. Thank heaven it rarely runs. Even this last winter which was unusually cold.

 

[podz]

point being that we don't really hit limitations til we try to do industrial things at home. which is how it is designed.

 

[Facinerous]

Please educate me. Why are you calculating your current with a power factor of .8? Your element should be pretty much purely resistive, no inductance or very very little.

Am I wrong in thinking this way. You should he able to calculate ampacity at 100% power factor. Either way that would correct your ampacity to a lower value .

[edit]
I was at work when I first posted this so I only gave it a little attention. Here is a touch more.

So I went ahead and did a little math for you. This is my math from using Python on my computer.

Python 3.4.2 (v3.4.2:ab2c023a9432, Oct 6 2014, 22:15:05) [MSC v.1600 32 bit (In
tel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> rt3 = math.sqrt (3)
>>> lineVoltage = 400/rt3
>>> lineVoltage
230.94010767585033
>>> lineAmps = (8500/3.0)/lineVoltage
>>> lineAmps
12.268693220279546
>>>

Here in the states it would be (8500/2)/120 = 35.5 amps. Which would require 2 X 8awg or (I think for metric) 3.5mm wire. Thats a pretty big difference between that and 3 X 14awg or 1.5mm wire if I had your electric system.

 

[podz]

Please educate me. Why are you calculating your current with a power factor of .8? Your element should be pretty much purely resistive, no inductance or very very little.

Here in the states it would be (8500/2)/120 = 35.5 amps. Which would require 2 X 8awg or (I think for metric) 3.5mm wire. Thats a pretty big difference between that and 3 X 14awg or 1.5mm wire if I had your electric system.

I just use .8 for safe measure as a general rule, but you're right - I could run an even bigger element on my 16 amp circuit.

The law here regarding fixed wiring: 1.5mm for 10 amp breakers, 2.5mm for 16 amp breakers, 4mm for 20 amp breakers (although I'm running 6mm to my sub panels that are connected with 20 amp breakers). So, my 3-phase socket is wired to the panel with 5x2.5mm.

For extension cords and underground cable, you can run 16 amps on 1.5mm wires but I buy 2.5mm extension cords anyway. Skinny wires start fires.

 

[lschiavo]

hot water heater

I only bother to heat cold water I thought this was a regional misnomer. Makes me feel better that it is a global phenomenon.

For geothermal heat pumps, the motor is either to be wired as 3-phase or 1-phase connected via a safety switch. A safety switch is a switch that shuts off power if it notices the wire heating up i.e. the motor is not spinning for some reason.

The motor that circulates hot water in my house for heating and showers is wired with a safety switch. And it's a real ***** because every time I shut off power to the house, that motor refuses to restart on it's own. I need to unmount it, stand it on a shelf and hit the fins with my finger to kick start them. Then I need to let it run like that for about 15 minutes before it will restart on it's own with the safety switch before I can remount it.

That does sound like a motor issue. Thermal protection should not affect the motor especially if it is external.

Not sure if the calculation is correct, but with 400v, 3-phase, power factor 0.8, an 8500 watt element should pull about 15.5 amps. So, that will clearly fit within my 16 amp circuit. I don't know if that power factor is correct or not, I just guessed it.

Assuming I heat 25 litres of water from 20c to 100c with an 8500 watt element, it should take 16.5 minutes. Not bad.

http://processheatingservices.com/water-heating-time-calculator/

I finally get it after reading the previous posts. You have a 400V wye system with 230V to neutral. Derp. Well now I know.

Be as it may, I am still able to run an 8.5kW heating element on my puny service whereas most of you are not able to do it even on your huge ass services. ;-)

A watt is a watt my friend. I have plans to build a 22kW 1 bbl brewery on my 100A 120/240V service. The family may have to sit in the house in the dark until the brew day is over Actually my brew buddy seems to have lost interest so I may just get my 50A 10 gal system going again.

Unbelievable. That's less than 50 KVA. I guess pottery isn't a common hobby over there. In the US they'll install as much as you are willing to pay for - even three phase if you want it (you don't when you see the price tag).

It is not far from a 200A 120/240V which is way oversized for just about any residence except for the one with a guy with 3 kilns trying to run a business from his garage. I wired that guy's garage BTW

Podz,
I've noticed your pics show 'surface mounted' cabling. Are any wires concealed in the walls, attics, sub flooring?

'da Kid

It seems my finely tuned wire fishing skills would be worthless in Europe. I never fished through sawdust insulation though. We are not that far removed from Finland around here but I have yet to find a wall insulated with sawdust

 

[podz]

I only bother to heat cold water I thought this was a regional misnomer. Makes me feel better that it is a global phenomenon.

Yeah, it's a funny one!

I finally get it after reading the previous posts. You have a 400V wye system with 230V to neutral. Derp. Well now I know.

Yes, I get 400 volts between phases and 230 volts between phase and neutral.

It seems my finely tuned wire fishing skills would be worthless in Europe. I never fished through sawdust insulation though. We are not that far removed from Finland around here but I have yet to find a wall insulated with sawdust

It sucks quite badly. It's not even sawdust, it's more like wood shavings from the sawmill planers. Even when using a 40cm long 30mm wood boring bit, the holes get clogged when trying to pull anything through them. I did have to pull a 5x6mm2 cable above the ceiling from the foyer to the kitchen because the room between them had a lowered ceiling and this was the only route.

Fact is, though, that most walls in european dwellings are solid concrete. Drywall is not an incredibly popular thing here and almost everybody owns a hammer drill even for the purpose of mounting pictures on the wall. And in the houses that do use drywall, they lay flexible piping first and then pull a bunch of phase / neutral / ground wires through it - always leaving the pulling string in place for future work. So, yeah, drywall fishing skills are not of much use here.

 

[podz]

I have 3-phase 400v in my garage now, with it's own 4-pole GFCI.

 

[lschiavo]

Progress! I was wondering what happened to you. Sexy looking connectors. So you can run that cable straight through concrete without a sleeve? I wanna see some brewery pics soon

 

[podz]

Progress! I was wondering what happened to you. Sexy looking connectors. So you can run that cable straight through concrete without a sleeve? I wanna see some brewery pics soon

It's not illegal, where the f... is the concrete going to go?

Brewery will be completed when 1) I win the lottery and 2) swmbo loses her attitude about helping me organise the garage! Or maybe sooner...

 

[lschiavo]

It's not illegal, where the f... is the concrete going to go?

I agree. I guess it is more the issue of exposed cable on concrete. I suppose some ******* crushed a cable against concrete and got dead somehow. Now its a rule around here

Brewery will be completed when 1) I win the lottery and 2) swmbo loses her attitude about helping me organise the garage! Or maybe sooner...

I would start buying tickets. Much better odds than a SWMBO loosing her attitude. I just got reamed a few minutes ago for no reason I can imagine. I even had dinner ready when she got home from work. Hopefully..."maybe sooner"

 

[podz]

I agree. I guess it is more the issue of exposed cable on concrete. I suppose some ******* crushed a cable against concrete and got dead somehow. Now its a rule around here

Tort does not exist in Finnish law; you can not sue an electrician or cable manufacturer because you chop a cable in half with a full-metal axe and get a shock. GFCI would trip in 30 milliseconds, anyway.

I would start buying tickets. Much better odds than a SWMBO loosing her attitude. I just got reamed a few minutes ago for no reason I can imagine. I even had dinner ready when she got home from work. Hopefully..."maybe sooner"

TIP: not a good idea to start drinking before SWMBO is able to start drinking. Jealousy of the situation and all that.