Hi
I have a normal domestic supply to a house in the UK. I have seen a printing press that needs 415v. I assume my house is fed with 240v, and not transformed within the house down from something else.
Question: if I need to supply 415v to this press, how would I do it? Would I need a massive transformer (any guess at cost?); or would new lines have to be laid by my electicity distributor? Has anyone any experience of getting 415v at home?
Thanks
Ben
If it needs 415V, it probably needs 3-phase too. What power rating is it? It would be useful to know everything on the rating plate.
You could ask for a 3-phase supply. If 3-phase runs down the street (very likely unless you are in a sparse rural area), this should be possible, but I've no idea what the costs might be now the supply industry is all split into separate companies. If you will need a supply > 24kW when adding the press to your household load, you will be required to have a 3-phase supply anyway (100A is max allowed for a 1-phase supply).
Other options would be a motor-generator to generate 3-phase, or to change the motor in the press to a single phase one. Depends what power consumption we're talking about, and what rating supply feed you currently have.
Question from a Yank about service in the UK.
If 100A is max allowed, what happens if you have a super large home (or castle) with all electric appliances? Do you need to install extra panels? 3-phase service? Are there restrictions on this?
Also, are the British unique among the EU community for having ring wiring in house distribution services?
Beachcomber
You can have as much power as you want (and can afford), but the maximum single phase supply provided is 100A which probably covers 99% of homes. Above that, a 3-phase supply is provided. There's no 100A limit on a 3-phase supply. Sometimes you'll also see 2 phases from a 3-phase supply provided, but I don't think that's been an install option for some years now.
I think this is pretty similar across all the EU, except the single phase supply limit varies by country. In some countries, it's as low as 20A, so almost everyone has a 3-phase supply.
For a 3-phase supply, you can use multiple single phase Consumer Units (panels) and/or a 3-phase Consumer Unit. If you have any internal 3-phase circuits/appliances, you will have to have a 3-phase Consumer Unit.
No, I think Malta does too. We use ring circuits in the house only for supplying socket outlets, where you might want high power loads almost anywhere in the house on a portable basis, but not everywhere at once. It's not actually a requirement that a house be wired with ring circuits, but it is always done.
Some countries outside the EU also use them (such as current/former British Commonwealth countries and colonies), due to having adopted the british wiring regulations for their own use at some time in the past, or having used the british wiring regs as the basis for their own (as was the case with Malta too). Whilst lots of countries use the british 13A socket outlet, but I doubt that they all also use ring circuits, although a number do.
Thanks Gabriel
You said you've no idea of the costs now, but are we talking about it being a set fee, or would they pass costs directly on to me for digging up roads etc.
At a guess is it hundreds of pounds or thousands if it doesn't run up the street?
Cheers
Ben
You need to discuss this with your local distribution company. The local manager has considerable discretion as to the cost passed on to you - which can be anything from nothing to the full cost, which /could/ be thousands of pounds. Crossing a road, particularly a trunk road, costs lots and lots.
Offering to do part of the job yourself can help. I got mine fitted for free, in return for digging the trench to the property line, putting in the new hockey stick and plastic cableway tubing (both of which they supplied) and making good after they had pulled the new cable through and connected up. They joined it to the lv cable, about 1m from my property line.
Know of any internet info on British/European voltages, frequencies, common supply currents? Would also be interesting why different areas have different voltage/frequency.
Know of any internet info on ring circuits? Like: What are typical "high power loads"? Are there just 1 or 2 rings in a large house? Are they just used because of lower copper costs? Other advantages? How much is the ring conductor reduced in size? In a large house (ring to far end) are rings still an advantage? Are there problems with long rings with an outlet near one end (long side too long to keep short side at acceptable current? Permitted only in dwelling?
Bud--
One resource is:
Normally more than one, but it depends. You should size a ring circuit so the total load is unlikely to be exceeded. There is a recommendation that a ring circuit should not supply power for more than 100m² of floor area, but if it is known some area is going to have a non-typical loading, the designer should adjust the area covered by the ring circuits and the number of them appropriately. For example, it's not uncommon for a kitchen to have a dedicated ring circuit. In practice, most ring circuits are hardly ever run anywhere near their full capacity. The main building heating (if electric) and main water heating (if electric) require dedicated circuits to themselves, and would not be on a ring circuit.
They were the result of a post WWII redesign of building wiring, and usage of copper was one factor, but not the only one. The pre-WWII wiring consisted of 15A socket outlets each on a dedicated wire back to the fuseboard. This wasn't a problem when each room typically had only one socket, but increasing use of electrical appliances was already showing one socket per room was inadiquate, and leading to heavy use of multi-way adaptors. The existing scheme didn't scale -- multiple 15A outlets would have required vastly more copper, but actually the copper was all under used -- the 15A sockets were rarely supplying anything like 15A. There were also
2A and 5A sockets connected to lighting circuits, but having more than one socket type had become a major inconvenience.The new design therefore sought to provide multiple socket outlets for choice and convenience, but didn't need to provide any more total power. 13A was chosen to enable a max appliance power of 3kW. This was probably the same design power which led to the earlier choice of 15A, as the mains voltage had risen in most areas since then. (In contrast, some European countries had designed for 3.5kW socket outlets between WWI and WWII.) The ring circuit enabled any number of socket outlets with less copper required. The ring circuit wire was the same as had been used for the 15A socket outlets, which avoided the need to generate any new cable size. It also meant it was quite easy to convert a 15A radial installation to a 30A ring circuit, but in practice I don't think much such conversion was done.
By 1/3rd. A reevaluation of the current carrying capacity of the
2.5mm² cable used a few years ago revealed it actually had a higher current rating than previously thought, so in most cases, the size reduction is effectively less than 1/3rd, and in some cases, almost no reduction at all.They are always used. The other options require thicker wire which is harder to handle, or a circuit which covers much less floor area, so many more circuits would be required. Other factors such as the requirement for multiple earthing paths where use of IT equipment with expected earth leakage is likely is also harder to meet when not using a ring circuit.
In theory, yes. It is recommended that a ring should not be designed with a large proportion of its load within 10% of the ring ends. In practice, this never seems to be a problem -- it is a recent recommendation based on theoretical analysis, not on any problems observed in reality AFAIK.
No, it is used in most commercial premises too.
It's also been used for the street distribution of electricity in the form of Ring Mains for many years before Ring Circuits for socket outlets became common. (Ring Circuits are very often incorrectly called Ring Mains.)
Use of ring circuits has never been mandatory in the UK. It is a permitted option which most people find the most convenient, hence its use.
Standardization - what a radical idea. Almost shocking.
Seems like 13A connectors and line cords on a 32A circuit could invite problems. Although, if I remember other posts, UK circuit breakers dont have a time delay (US small breakers would be hard to find without a thermal delay element).
My understanding from your post is that ring circuits are for all general purpose loads - like US 15 & 20A branch circuits (although they usually also usually contain lighting) and 20A kitchen and laundry circuits.
Great description.
Thanks for the info. It would be nice if there were Wiring Practice FAQs for the UK, US, ....
Bud--
I read your suggested web reference on world power and discovered fused plugs - kind of like RTFM.
Bud--
The 13A plugs all have fuses in them, anything from 2A to 13A depending on the appliance and flex size/length.
Need to introduce some terminology here before continuing... An overload current happens when an otherwise non-faulty circuit is simply carrying more than its maximum design current, e.g. too much load. A fault current happens when a circuit is carrying a current limited only by the supply and circuit impedance, e.g. some type of short circuit.
In the UK (and now all the EU too) breakers have two tripping components in them -- overload protection (thermal) and fault protection (magnetic).
The current rating marked on the breaker is the max continuous non-trip rating of the overload protection component. Typically, a breaker would allow twice the marked current rating for a minute without tripping, just as any cable is going to handle twice its current rating for a minute without coming to any harm. At progressively higher currents, the overload trip will operate faster.
The fault current component's trip rating is a multiple of the overload trip rating. The multiple is specified by a letter: B is 3-5 times, C is 5-10 times, and D is 10-50 times. The magnetic trip is pretty instant, disconnecting the supply within a mains cycle (20ms), although most makes of breaker actually manage to do it within less than half this time.
A ring circuit would normally be protected by a B32 breaker in the home (C32 is possible too, but more likely in commercial premises). This means the circuit will run continuously at 32A. At 64A, it would probably trip after a minute, and at 100A probably within 20 seconds. This behaviour allows things like startup surges through, without compromising the circuit cable. At much over 100A, the fault current protection would kick in and disconnect within 20ms. This is intended to very quickly disconnect in the event of a short circuit. The circuit designer is required to check that the supply impedance and earth fault loop impedance are low enough that in the event of a fault current, enough current will flow to trip the fault current protection and give an instant disconnect. (This is a gross simplification, but you get the idea.)
Yes, that's right. Lighting can go on a ring circuit -- it's never done when a building is initially wired up, but it is sometimes done when modifying an installation if it's easier to pickup from the ring circuit in a given situation. Such lighting will require an additional fuse in the circuit (5A normally used). Other fixed low power or fixed occasional use high power loads (3kW max) can be fed from the ring circuit through a permanent connection with a switch and fuse (same fuse type as used in 13A plugs).
A pleasure to see an acurate post from a fellow uk engineer.
On 20 Jul 2005 20:10:03 GMT Andrew Gabriel wrote: | In article , | Bud writes: |> Andrew Gabriel wrote: |>> |>> 13A/3kW is the max single item load on a ring circuit, and |>> 32A/7.5kW is the max total load on a ring circuit. |> |> Seems like 13A connectors and line cords on a 32A circuit could invite | | The 13A plugs all have fuses in them, anything from 2A to 13A | depending on the appliance and flex size/length.
Can a 32A receptacle also be put on the circuit? Or are such circuits limited to receptacles of 13A?
What size of wire is required for that circuit?
| In the UK (and now all the EU too) breakers have two tripping components | in them -- overload protection (thermal) and fault protection (magnetic).
They do in the US, too. You can get them for special applications just one way or the other. But most homes would never have any use for such.
| A ring circuit would normally be protected by a B32 breaker in the | home (C32 is possible too, but more likely in commercial premises). | This means the circuit will run continuously at 32A. At 64A, it would | probably trip after a minute, and at 100A probably within 20 seconds. | This behaviour allows things like startup surges through, without | compromising the circuit cable. | At much over 100A, the fault current protection would kick in and | disconnect within 20ms. This is intended to very quickly disconnect | in the event of a short circuit. The circuit designer is required to | check that the supply impedance and earth fault loop impedance are | low enough that in the event of a fault current, enough current will | flow to trip the fault current protection and give an instant | disconnect. (This is a gross simplification, but you get the idea.)
If the fault drew fewer amps because of significant impedance, then shouldn't there be less risk? If it drew 100 amps, the wire should be OK for 20 seconds and then the breaker trips.
Of course, there is an answer to this. Faults have harms above and beyond the current drawn. They are typically arcing faults. The arc of 100 amps can start a fire in a second, long before the thermal trip kicks in. Since most faults will (if the impedance is low) draw well over 100 amps, we get to use the magnetic trip to protect in most of these cases. Now we have arc-fault detection to cover the rest of them. Are such being used in UK?
|> My understanding from your post is that ring circuits are for all |> general purpose loads - like US 15 & 20A branch circuits (although they |> usually also usually contain lighting) and 20A kitchen and laundry circuits. | | Yes, that's right. Lighting can go on a ring circuit -- it's never | done when a building is initially wired up, but it is sometimes done | when modifying an installation if it's easier to pickup from the ring | circuit in a given situation. Such lighting will require an additional | fuse in the circuit (5A normally used). Other fixed low power or | fixed occasional use high power loads (3kW max) can be fed from the | ring circuit through a permanent connection with a switch and fuse | (same fuse type as used in 13A plugs).
When I was in my teens, I thought up the idea of a ring circuit as a way to cut wire size and/or increase circuit capacity. At the time, my family was building a new house and I got to talk with the electrician doing the work on the house. I told him of the idea. He didn't tell me about it being used anywhere, but he reacted like he understood just what I was talking about. He told me it would be unsafe because one span could break and not carry any current, forcing the other span to carry all of it. Then I suggested that each span be connected to it's own 15A breaker, instead of both connected to the same 30A breaker. He said that might work, but they'd never change the way things are done now. I never thought about it again until I heard about ring circuits in the UK. I didn't call it a "ring", nor did the electrician I talked to. I didn't have any name for it.
No, 13A is the max single load allowed either by socket or by some appliance being permanently connected.
The regs require that the wire be rated for 2/3rds of the circuit capacity. The size of wire for this rating depends on the type of wire, where it's fitted (e.g. on a cable tray, inside thermal insulation, etc), and how many other wires are in close proximity (we call this Grouping Factor). Most commonly, 2.5mm² cross-section area conductors are used, which when embedded in a wall as is most commonly done in the home, is rated at 27A. The thinnest allowed is 1.5mm² MICC cable (Mineral Insulated Copper Covered -- not sure if that exists in the US or what you would call it). Also, remember that voltage drop isn't an issue for us to anything like the same extent it is for you.
We have other requirements in our regs though. A circuit breaker must trip within 5 seconds in the case of a short to earth, and for circuits supplying sockets, this is reduced to just 0.4 seconds.
No. That particular type of fault seems to be much more of a problem in the US than elsewhere. Our approach over the last
50 or so years was to engineer out the situations which give rise to arcing in the first place.This is the often quoted concern, but it just isn't a problem in practice. OTOH, if you get a bad connection in a ring, then it's much less likely to overheat as there's another path.
Problem there is that the current isn't balanced in a ring, so you could legitimately and safely have more than 15A in one leg. Maybe you could argue for a 21A or 27A breaker in each leg, ganged, feeding from a common 32A breaker, but that's a lot of extra complexity to solve a problem that just doesn't exist in practice.
A #14 AWG with a cross section of 2.1 square millimetres is rated 20 amperes in free air and 15 in cable (CSA and NEC, 60 C insulation). A #12 with an area of 3.3 square millimetres is rated 25 amperes in free air ( at 60 C insulation in a 30 C ambient) and 20 A in cable. We don't embed single wires in walls, it's always cable.
A No. 16 AWG has a cross section of 1.48 square millimetres and is not permitted as a size for fixed building wiring (though it's common in flexible cords).
It's called Mineral Insulated Cable here, too - it's faboulously expensive to install, though, and never used for residential or commercial work in my admittedly limited experience. I did see a great deal of it at an irrigation dam, though.
Oh, yeah, we're constantly fumbling around in the dim light due to the massive voltage drops running a 100 watt bulb at 120 V instead of 240. It's a wonder that the State of Califonia alone manages to use more residential electric energy than the entire UK, given this drawback. Really, it's less of an issue than you think. Don't forget that with the split 120-240 system we have all the advantages of 240 and light bulbs that last longer, too.
Bill
Actually, I was referring to cable in all cases too. Wasn't sure what term to use which would make sense in the US so I just stuck with that of the poster's.
Our Twin and Earth cable comes in 70C and 90C types. The figures I gave were for 70C type, which is what's normally used in a house.
Same here.
We use 1mm² and 1.5mm² for lighting, normally protected at
6A (10A commercially). The cable rating is significantly higher than this -- the 6A and 10A protection is imposed by the use of certain types of lampholders. As a side effect, it also means the cable can be safely embedded in attic insulation material without having to be concerned. 2.5mm² is used for ring circuits at 32A and for radial circuits protected at 20A. For higher currents, 4mm², 6mm² and 10mm² are used. A 100A supply is usually on 25mm² for the parts owned by the householder (different rules apply to the supply company's wiring).It was common in UK in commercial premises perhaps 40 years ago. Not common now -- too expensive in both parts and labor -- unless you really need cable that continues working in a fire or cable that is impact-proof. I've also seen it used when rewiring old buildings of historic architecturual value, where the thin cable can be better hidden.
Well, life of filaments lamps is a question of what efficiency tradeoff is made. I thought your A-line lamps were normally rated
750 hours, whereas our GLS lamps are normally rated 1000 hours (longer life ones are also available with a lower efficiency). For the same life, a 120V filament lamp is more efficient than a 240V filament lamp. I'm not sure this matters any more though; there have been almost no 240V filament lamps in my house for the last 10 years.One thing most UK people notice when visiting the US is the way your lights get brighter and dimmer when other loads in the house switch on and off. That's very rare here in UK and when it does happen, it will normally trigger a search for a fault, which is probably why it initially alarms visitors to the US.
You may not have the dimming lights phenomenon in the UK, but it is not something that is confined to US. In fact, it rarely, if ever occurs in modern wiring or new construction if the codes are followed and the installation was done properly. Sometimes if you are unlucky enough to live at the end of the line in the most distant house of a rural area, you may be subject to fluctuating voltage levels. It also depends on what other loads (the aluminum factory?) are connected to your system on the primary side.
I recall seeing dimming lights when I lived in France. In some cases, an entire small village would be served by one 240 volt transformer and there were thick cables (apparently not thick enough though) that would string all of the houses together. The incandescent lights would be subject to all sorts of flickering variations as neighbors switched loads in and out of the system.
Beachcomber
| No. That particular type of fault seems to be much more of a | problem in the US than elsewhere. Our approach over the last | 50 or so years was to engineer out the situations which give | rise to arcing in the first place.
How has this been done?
A series arc is one example. Twice the voltage and half the current does change the character of the arc. But over twice the distance it can still dissipate the same energy with half the current. That would be an arc that would drop out at a lower voltage.
Are the cords leading to appliances mechanically protected to avoid stepping on them causing damage? That would be something I'd like to see here.
|> When I was in my teens, I thought up the idea of a ring circuit as a |> way to cut wire size and/or increase circuit capacity. At the time, |> my family was building a new house and I got to talk with the electrician |> doing the work on the house. I told him of the idea. He didn't tell me |> about it being used anywhere, but he reacted like he understood just |> what I was talking about. He told me it would be unsafe because one |> span could break and not carry any current, forcing the other span to | | This is the often quoted concern, but it just isn't a problem | in practice. OTOH, if you get a bad connection in a ring, then | it's much less likely to overheat as there's another path.
OTOH, you wouldn't know something is going wrong. The lights won't be blinking.
|> carry all of it. Then I suggested that each span be connected to it's |> own 15A breaker, instead of both connected to the same 30A breaker. | | Problem there is that the current isn't balanced in a ring, so | you could legitimately and safely have more than 15A in one leg. | Maybe you could argue for a 21A or 27A breaker in each leg, ganged, | feeding from a common 32A breaker, but that's a lot of extra | complexity to solve a problem that just doesn't exist in practice.
I've given up on the ring circuit idea for over here, anyway. Perhaps the biggest problem bringing it in here would be educating people about how it works. But I'll just stick with radial and bus.
|> Oh, yeah, we're constantly fumbling around in the dim light due to the |> massive voltage drops running a 100 watt bulb at 120 V instead of 240. |> It's a wonder that the State of Califonia alone manages to use more |> residential electric energy than the entire UK, given this drawback. |> Really, it's less of an issue than you think. Don't forget that with |> the split 120-240 system we have all the advantages of 240 and light |> bulbs that last longer, too. | | Well, life of filaments lamps is a question of what efficiency | tradeoff is made. I thought your A-line lamps were normally rated | 750 hours, whereas our GLS lamps are normally rated 1000 hours | (longer life ones are also available with a lower efficiency). | For the same life, a 120V filament lamp is more efficient than | a 240V filament lamp. I'm not sure this matters any more though; | there have been almost no 240V filament lamps in my house for | the last 10 years. | | One thing most UK people notice when visiting the US is the way | your lights get brighter and dimmer when other loads in the house | switch on and off. That's very rare here in UK and when it does | happen, it will normally trigger a search for a fault, which is | probably why it initially alarms visitors to the US.
We can both have low voltage (e.g. 12V) lighting and have all the same bulb advantages. Maybe if I run my 12V transformers from 240V instead of from 120V, I would avoid much of the dimming effect as well. If I could get 480V, I'd use that (not to the bulb, of course).
I don't notice any such dimming at all except when the garbage disposal is turned on. I suspect that thing is pulling over 100 amps to start up. It lasts about 1-2 cycles.
I don't claim to know all the areas, but some of the better known areas where problems of this sort had been observed... Wirenuts ceased to be used (actually, that's over 60 years ago, but their use was never very widespread for mains wiring even before then). Wrap-around screw terminals have been gradually phased out. Plugs and sockets have much larger contact areas, higher contact pressure, and firmer grip -- no wobbling around (this is also well over 60 years ago, as it was started with the design of our previous round pin plugs). We didn't use Alumin{i}um wiring in houses.
Arcs are sustained by current. The higher the current they pass, the lower voltage they need to sustain them. They aren't ohmic.
Yes. All appliance cords are sheathed, since 1960's I think. All except low current ones were sheathed long before that. They probably get stepped on quite often, but I don't ever recall any damage due to stepping on one. Unsheathed cords are limited to 50V max, so they can be used for LV side of LV lighting.
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