Three Phase Power

[LA3222]

Evening, 

 

I am looking at potentially installing three phase power as opposed to the norm which tends to be single phase for domestic installations.

 

Having trawled this forum and numerous other areas there doesn't appear to be a great detail of information on the pros and cons of three phase in a domestic setting (other than the usual - if you are using 3 phase machinery, can spread the load, careful with mixing phases in same room etc.).  I think there are maybe three or four threads on this forum which touch on the subject.

 

It would be great if those of you whom have three phase could give some sort of insight into their own experience in practical terms of this route.  Pros, cons, if you could do the build again would you still install three phase? If not, then why not?

 

A bit of insight from those in the know would be beneficial not just to myself, but likely others in the future whom may be pondering the same thing.

 

TIA

 

Jamie 

Edited May 21, 2018 by LA3222
Spelling

[Mr Punter]

If it is for a building site and you are using a self erecting / mantis type crane they often need 3 phase where you would otherwise need a 3 phase generator.  Also a cheap way of getting power to more than 1 unit if doing flats etc.

[ProDave]

If you are into machine tools you can often get 3 phase machines cheaper .

 

You may pay a higher standing charge for a 3 phase supply and it may limit some of your options like economy 7

 

Of you install solar PV, self usage may be less effective if your domestic load is split.

 

Installation cost will be more, possibly a lot more, depending on what infrastructure is near you (e.g. we are on the end of a mile long single phase 11KV overhead line, imagine the cost if I wanted 3 phase)

[le-cerveau]

Getting the supply (DNO):

Ours was easy, the pole that fed the original house had 3-phase power on it (4 open conductors) and was fed from underground just in front of our house so our new underground supply was simply spliced from the underground cable and fed to the site box (initially).

Replacing the meter(Supplier):

More difficult because as soon as you mention 3-phase to suppliers they look at you blankly (on the phone), I ended up with one of the big six, however I will be changing in the near future so I will see how the other suppliers cope now I have a meter.

PV:

You can fit more before exceeding the G83 limits 3.68kW per phase, I have nearly 10kW of PV all within the G83 limits.  G59 has more stringent rules and is not as widely available, however you can get up to 17kW per phase with approved G83 type equipment but that will depend on your DNO and the current loading in your area.

PV(Cons):

Battery technology is geared, currently, to single phase domestic situations, you can put batteries on your 3-phase system, and they will supply each phase individually however they will not supply 3-phase equipment as each battery-inverter needs to be phase locked with the others, this is not generally available in the domestic market yet, under development.  The Tesla Powerwall 3 may be 3-phase, due out this year sometime.

Appliances:

We have only 2 3phase appliances and a spare feed.  The ASHP is 3-phase, allows soft start, if you have ever been to a US home when the AC starts up and everything dims for a second that is what soft start avoids.  Also, the bigger ASHP’s are only 3-phase though ours 9kW was available in either.  Our lift is also 3-phase, also it is a lot larger than a standard domestic, more resilience than one designed for just a wheelchair.  Also rotating machinery (Lift and ASHP) benefit from 3 phase power as bigger motors tend to be designed 3-phase (make sure they are wired up correctly!).  I also have a 3-phase supply to the garage with a 32A breaker on it for car charging, terminated at a switch in the garage.  This will allow a 22kW charger if required (tesla supercharger not that I can afford one).

Electricians:

My electrician had no problem with 3-phase as he also does commercial work, however not all domestic electricians will be happy with it.  If you put two normal (single phase) lives together normally nothing happens, however if you put two 3-phase lives together you could blow the system if they are from different phases (200V potential between them) so everything has to be labeled and you can’t just poke around in things.

Why:

The biggest reason was potential power consumption we have 2 x 7kW induction hobs (one at normal height and one at wheelchair height) 3 ovens (up to 4kW each) so if someone (highly unlikely) put the kitchen into full power mode it would kill a normal single phase domestic supply!  Ordinarily we don’t draw anywhere near the power to do that but plan for the worst.

Living with it:

In reality those in the house don’t notice or care about the 3-phase supply, they get 230v out of a socket.

[ProDave]

My single phase ASHP has soft start variable speed inverter drive, that is not a feature limited to 3 phase models.

[le-cerveau]

Just now, ProDave said:

My single phase ASHP has soft start variable speed inverter drive, that is not a feature limited to 3 phase models.

 

Yes, but not all single phase ASHP have this, particularly older models, and some imports. 

[dpmiller]

and just to confuse further,  "inverter" HPs are internally 3PH but at variable frequency.