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3 phase electricity, split from housebuilding
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BritDownUnder



Joined: 21 Sep 2011
Posts: 242
Location: Hunter Valley, NSW, Australia

PostPosted: Wed Nov 29, 2017 8:33 am    Post subject: 3 phase electricity, split from housebuilding Reply with quote

Quote:

They are 270W panels for a total of 6.5kW.


Do you need a 3 phase connection for that size? In Australia you must get 3 phase if you get greater than 5kW of PV.

Edit by admin, this post and those following have been split from a topic regarding the new house being built by a respected member.
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fuzzy



Joined: 29 Nov 2013
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Location: The Marches, UK

PostPosted: Wed Nov 29, 2017 8:59 am    Post subject: Reply with quote

No 3 phase in UK homes. AFAIK it's not allowed.
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adam2
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PostPosted: Wed Nov 29, 2017 11:23 am    Post subject: Reply with quote

fuzzy wrote:
No 3 phase in UK homes. AFAIK it's not allowed.


Nothing prohibits 3 phase in UK homes, it is however unusual.
Most UK homes have a single phase supply of 60 amps, 80 amps, or 100 amps.
There are a few 40 amp services, and a very few 25 amp services, and in some circumstances a single phase 125 amp service MIGHT be allowed.

If a single phase service of 100 amps is not considered sufficient, then a 3 phase supply of 80 or 100 amps would be the norm. Few homes need more than 100 amps single phase.

A few homes have 3 phase because a previous occupier paid extra for this because they needed 3 phase for workshop machinery, despite the total load being modest.

3 phase is available if needed, almost anywhere in the UK, though there are exceptions, even in urban areas !
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vtsnowedin



Joined: 07 Jan 2011
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PostPosted: Wed Nov 29, 2017 12:51 pm    Post subject: Reply with quote

I can't imagine why anyone would restrict three phase. It has to be installed properly but that is true of single phase arrangements.
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adam2
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PostPosted: Wed Nov 29, 2017 1:22 pm    Post subject: Reply with quote

vtsnowedin wrote:
I can't imagine why anyone would restrict three phase. It has to be installed properly but that is true of single phase arrangements.


Three phase in the UK is virtually certain to be at the standard voltage of 240/415
This is twice the domestic 3 phase voltage used in America which is 120/208. (for larger businesses etc in the USA 3 phase at 277/480 volts is widely used, but is prohibited domestically)

Historically there has been rather a fear of 3 phase in the UK. Regulations used to require that all lamps and outlets in the same room be on the same phase (or the same pole of a DC supply), with an exception for large rooms in which outlets on different phases (or different poles of a DC supply) were allowed if at least 6 feet, later 2 meters apart.

This regulation was removed decades ago, but is still widely followed ! A favourite question asked of trainee electricians is what is "the most widely followed regulation that does not in fact exist" The accepted answer is 2 meters between phases.

In parts of mainland Europe they use 3 phase domestically without problems, usually 3 phase, 4 wire, 230/400 volts. A few legacy systems still exist including 3 phase, 4 wire, at 127/220 volts and 3 phase 3 wire at 220 volt, and single phase 3 wire at 220/440 volt.
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fuzzy



Joined: 29 Nov 2013
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PostPosted: Wed Nov 29, 2017 3:40 pm    Post subject: Reply with quote

adam2 wrote:
fuzzy wrote:
No 3 phase in UK homes. AFAIK it's not allowed.


Nothing prohibits 3 phase in UK homes, it is however unusual.
Most UK homes have a single phase supply of 60 amps, 80 amps, or 100 amps.
There are a few 40 amp services, and a very few 25 amp services, and in some circumstances a single phase 125 amp service MIGHT be allowed.

If a single phase service of 100 amps is not considered sufficient, then a 3 phase supply of 80 or 100 amps would be the norm. Few homes need more than 100 amps single phase.

A few homes have 3 phase because a previous occupier paid extra for this because they needed 3 phase for workshop machinery, despite the total load being modest.

3 phase is available if needed, almost anywhere in the UK, though there are exceptions, even in urban areas !


You are correct, but I assume it is only allowed at a specific point eg a commando socket, for running a heavy appliance. Surely you are not allowed to have different phases for various ring and and lighting circuits?
In factories, separate phases always appear to be easily identified.

We do have bizzare wiring regs run by the high priests. IIRC there is no minimum distance for a socket from a sink in a food preparation area.
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adam2
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PostPosted: Wed Nov 29, 2017 4:33 pm    Post subject: Reply with quote

Nothing under current UK regulations prohibits the use of 3 phase supplies for general domestic purposes including general purpose lighting and power circuits.
As an example, nothing prohibits the cooker on one phase, the 13 amp sockets in the same room being on another phase, and the lights on the third phase.

The requirement for lamps and single phase outlets to be on the same phase if within 2meters went out many years ago, in the 1960s I think, but many still believe this to be a requirement.

The requirements for lamps in the same room or area to be on the same phase (or the same pole of a DC system) was arguably sensible back in the days of un-earthed lighting circuits, brass lamp holders and light switches, and perished twin twisted rubber insulated lamp flex.
I would not have fancied 415 or 480 volts between two un-earthed brass light switches.
For many years now, lighting circuits have had to be earthed, indeed the requirement to earth lighting circuits MAY have come in at the same time that the regulation requiring separation between phases/poles was abolished.
Also the introduction of fluorescent lighting in the 1950s meant that splitting factory lighting over 3 phases was recommended to avoid stroboscopic effects with moving machinery. Try getting light from fluorescent lamps on each phase to each part of a factory, AND keeping the lamps on different phases 2 meters apart !
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fuzzy



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PostPosted: Wed Nov 29, 2017 5:23 pm    Post subject: Reply with quote

Thanks for the info, you have a lot of knowledge! In this age of comms and many low powered appliances, different phases seems a recipe for hums and noise. I think I read that about 30% of houses still have lighting without earth [mine included]. A recent bathroom move required a very laid back electrician.
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BritDownUnder



Joined: 21 Sep 2011
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Location: Hunter Valley, NSW, Australia

PostPosted: Wed Nov 29, 2017 5:37 pm    Post subject: Reply with quote

The excuse given in Australia by power companies to insist on 3 phase inverters for solar PV installations above 5 kW is otherwise one of the 3 phases of the local distribution electricity supply will get unbalanced if the inverter outputs only a single phase. Having one phase feeding in at peak solar generation and minimal usage around midday when few people are at home and the other two non PV phases supplying current would probably screw things up for the local transformer.

I suppose the power grid is much more spread out in Australia than the UK.

I have three phases sent to my house but I only use one phase as you pay more standing charge for three phases and I have no large motor loads that need three phase at my current address.

I have a colleague with three phase in his house and has lights on one and ring mains on another and the stove on the third phase. In a typical Australian house the only device using all three phases would be a large ducted air conditioning unit. Another colleague was forced to get three phase by virtue of his 6kW grid tied solar PV array and uses only one of his three phases for everything.
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vtsnowedin



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PostPosted: Wed Nov 29, 2017 6:29 pm    Post subject: Reply with quote

fuzzy wrote:
Thanks for the info, you have a lot of knowledge! In this age of comms and many low powered appliances, different phases seems a recipe for hums and noise. I think I read that about 30% of houses still have lighting without earth [mine included]. A recent bathroom move required a very laid back electrician.
Laid back? Shocked
I wouldn't install anything in a bath or food preparation area that didn't employ ground wire and Ground fault interrupters at either the breaker box or the individual outlets.
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adam2
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PostPosted: Wed Nov 29, 2017 7:53 pm    Post subject: Reply with quote

If the light(s) in a bathroom are of "all insulated" construction, and the switch is plastic and either outside the bathroom or is operated by a pull cord, then an earth wire serves no purpose, but is a regulatory requirement.

It is IMHO a reasonable requirement to allow for the future installation of a metal light fitting that probably DOES need earthing.

Standard mains voltage outlets were for many years strictly prohibited in UK bathrooms. They are now allowed under certain conditions, but must firstly be earthed, and secondly must be protected by an RCD (UK term for what in America is called a GFCI)

All general purpose mains voltage outlets in the UK MUST be earthed, non earthed , 2 pin outlets "went out with the war"
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Mr. Fox



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PostPosted: Wed Nov 29, 2017 10:46 pm    Post subject: Reply with quote

Older installations with no CPC (earth wire) on the lighting circuits can be brought to a level of conformity with current regs by ensuring all fixtures and fittings are class II (double insulated)...

When I've come across them (and rewiring wasn't an option), we've used bayonet pendants with the pins that disconnect when no lamp is inserted, 'Nexus' range switches (that have plastic covers for the screws), etc.

Not ideal, but the regs aren't retrospective, so sometimes you've just got to do what you can... what is 'practicable', in regs-speak. Wink
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clv101
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PostPosted: Wed Nov 29, 2017 11:26 pm    Post subject: Re: 3 phase electricity, split from housebuilding Reply with quote

BritDownUnder wrote:
Quote:

They are 270W panels for a total of 6.5kW.


Do you need a 3 phase connection for that size? In Australia you must get 3 phase if you get greater than 5kW of PV.

Edit by admin, this post and those following have been split from a topic regarding the new house being built by a respected member.


We're off grid so it's not an issue. I don't think I'd need a 3 phase connection though even if we did inject to the grid.
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vtsnowedin



Joined: 07 Jan 2011
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Location: New England ,Chelsea Vermont

PostPosted: Thu Nov 30, 2017 1:35 am    Post subject: Reply with quote

Mr. Fox wrote:
Older installations with no CPC (earth wire) on the lighting circuits can be brought to a level of conformity with current regs by ensuring all fixtures and fittings are class II (double insulated)...

When I've come across them (and rewiring wasn't an option), we've used bayonet pendants with the pins that disconnect when no lamp is inserted, 'Nexus' range switches (that have plastic covers for the screws), etc.

Not ideal, but the regs aren't retrospective, so sometimes you've just got to do what you can... what is 'practicable', in regs-speak. Wink
It is good to see that your regulators have a bit of common sense and can let a arraignment that has worked for decades to continue on.
Often in the USA the regulator insists on full compliance with the latest regs.so that their cousin Vinny gets lots of work from people that can't negotiate prices.
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fuzzy



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PostPosted: Thu Nov 30, 2017 8:29 am    Post subject: Reply with quote

vtsnowedin wrote:
fuzzy wrote:
Thanks for the info, you have a lot of knowledge! In this age of comms and many low powered appliances, different phases seems a recipe for hums and noise. I think I read that about 30% of houses still have lighting without earth [mine included]. A recent bathroom move required a very laid back electrician.
Laid back? Shocked
I wouldn't install anything in a bath or food preparation area that didn't employ ground wire and Ground fault interrupters at either the breaker box or the individual outlets.


Yes, there are ways of making bubbles of modern safety on the back of 2 wire lighting installs by fitting a 'Ground fault interrupter' [residual-current circuit breaker is the UK jargon]. As noted, we aren't allowed any sockets in bathrooms. Our wearedodgy is not as old as the main house wiring, it's '16th edition' standard [1990s] in UK jargon. I once did a course on the US NEC wiring regs, and they seemed a lot more logical than our IEE version.
As a comparison, our brick and block housing is often very disruptive to rewiring. Modern houses UK are made with flimsy floor joists but at least with preformed holes on centre, for services.
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