During a visit to cut down branches that were hanging from the overhead wires the chap from the leccy board commented that we had two supplies into the home and asked if we were on 480 supply.
We are 240 but that got me to wondering.. could there be 2 supplies into the Economy 7 meter? One for NSH and one for the other circuits? Why would anyone want a 480 supply in a domestic property?
Seems like an odd question since in the UK at least the normal 3 phase system pans out as a 415v (now 400V) supply across any phase pair.
Three phase motor in would be the only reason I could think of.
Storage heaters might merit being on a separate phase. Our VH has two phases one for the electric room heaters and one for everything else.
I think it was something to do with local mains cabling capacity.
If it ever had electric full house heating - like storage radiators - it may have needed a second phase.
That's the only reason I can think of. A workshop etc with large motors would need three phase.
When we had a "failure in the road" with our electricity supply last summer, I discovered that we only had 2 phases incoming, I thought it was three. I assume this was done for empirical phase balancing at installation time. There was no evidence of two phases ever being used at the same time.
Think providing two phases was common at one time. When it was thought electricity was going to be the common way to heat a house. My parents one built in the mid '30s had this.
It could be that he was suggesting the supply is what they call split phase, where the transformer secondary is 240-0-240 voltage across the outer tapings will be 480. Don't know how common it is but I have seen it, Al
It's not two phases of a 3 phase supply (which is where you get the 400V from). It's a single phase supply that uses the transformer tappings to supply two 230V phases that are 90 deg out of phase with each other - which is why you end up with 480V.
This would normally supply two separate CUs for houses with a high electrical load where a 3 phase supply is not available.
I have seen this sort of installation about twice in 25 years.
That's often a hang-over from old centre-tapped DC mains. When they converted to AC the street mains cables were replaced for TP&N, but existing domestic services were re-connected to two phases & neutral. That suited the other old practice of having separately metered supplies for lighting and power (with different tariffs).
OTOH the OP's enquiry relates to isolated rural areas where the 11 kV feed is single-phase (bridged across two phases of a distant 3ph circuit). Where more capacity is required than a 240 V supply can provide (the LV mains can also be quite long) a 240-0-240 split-phase is used, the 3-ph option not being available.
Not wishing to sound pedantic, but I presume you mean 180 degrees?
You're how old???
Indeed:-( Thanks for that correction
I was 40 again last October.
Was that why people plugged their electric irons (using BC "plugs") into their pendant light s?
I think he meant 120 degrees!
I've not heard of 2 phase supplies (from a 3 phase system) being common, but they are perfectly possible.
There *was* a 90degree 2 phase system - in London about 70 years + ago.
That was integrated with the 3 phase system by a special conversion transformer (one of 2, a Scott Connection or a Leblanc transformer, eg:
I think Adam is correct, where a single phase transformer on a pole provides 480V split either side of neutral/ground.
It saves on neutral copper as well as a cheaper/lighter transformer on a pole.
Its rather common in the US.
Possibly, although the usual reason was a lack of available sockets. It was common in the inter-war years for houses to be wired for electric lighting only - sometimes on the ground floor only, at that.
480V supplies were used on highland farms and the like, where the expense of carrying 3-phase 11kV for miles for 1 or 2 customers was not worth it. (Yes, I know it's only 1 extra wire). It's a bit like the US system, but twice the voltage.
It started being phased out in the 1950's as more customers wanted to hook up and 3-phase distribution became more viable, but there may be the odd one left, even if there is now an 11kV 3-phase supply just outside.
I beleve Australia did something similar but used a ground return (over much longer distances), so there was just a single HV conductor strung along for miles.
My parents house was a new build in a street on a green field site.
Always been a bit of a black art to me. I have storage heaters, but as far as I am aware they are on the same phase as everything else. I clearly remember when I was young and wandering around in a field in Sussex, that there was a transformer mounted half way up a double pole It was humming quite loudly and although there were two wires overhead that went off into the distance, three wires spurred off the transformer bit and wi ent into a farm building. Seemed odd to me at the time. Brian
On Wednesday, February 11, 2015 at 4:07:36 PM UTC, Dave Plowman (News) wrot e:
Electric heating was a bit unrealistic in the 30s at 5p a unit. That's some where vaguely in the region of £5 a unit in today's money.
NT
If by 5p you mean 0.05 GBP, more like 3 quid now, when that house was built.
But perhaps they had an electric crystal ball and guessed prices would come down?
5 old pence, surely?
So more like £1.19 now allowing for inflation:
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