Sockets Unlimited

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  #1  
Old 06-28-04, 04:33 AM
Snape
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Sockets Unlimited

In the Uk it is possible to have an unlimited amount of sockets (Recepticles) for a floor area 50m2 if the circuit protection is a 30A or 32A Fuse on a radial circuit and for a ring circuit it is unlimited on a area of 100m2.
Does this apply to Us & Canadian wiring regulations or is there a limited amount.
Also are ring circuits permitted or not.

Thanks
Ian
 
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  #2  
Old 06-28-04, 06:29 AM
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The U.S. rules are different for residential and industrial and commercial. For residential, the U.S. national code puts no limit on the number of receptacles on a circuit. But it does put a limit on the breaker size for general use receptacles. In the U.S., that limit is 20 amps.

I have no information about U.K. codes. Maybe someone else can help.

I've never seen a ring circuit used in the U.S. I'm not sure whether it would be legal or not. I'm not even sure why you'd do it.

P.S. I'm not sure if Hogwarts is considered residential, commercial, or industrial.
 
  #3  
Old 06-28-04, 06:43 AM
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I've heard of Ring circuits, if I'm thinking about the same thing. Basically instead of having a single run of wire where everything is runs from the previous receptacle (panel-a-b-c-d-e-f-g-h) where any break in the wire results in the rest of the receptacles not working. The ring is set up so that (in my example) 'h' feeds back to 'a' again.

The benefit is that any break in the wire has a second path the current can follow. It also cuts your voltage drop some (sometimes by half).
The downside is that if there is a break in a wire, you could have a bare wire somewhere and you wouldn't know it because the circuit is still working.

I have no idea if code permits it, but I don't ever see it used. I have heard it mentioned before when reliability is necessary. I would imagine they are terrible to troubleshoot if you don't know it is a ring.
 
  #4  
Old 06-28-04, 07:15 AM
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In the US a MINIMUM number of "General-purpose" Branch-Circuits is required for dwelling-units.A minimum number of receptacle-outlets is also required, essentialy no "point" more than 6 ft. from a receptacle.

The number of G-P B-C's required is calculated first by determining the load in watts which is calculated on the basis of 3 watts per sq.-ft. of floor-area.If a living-room, a family-room, and X number of bedrooms comprise 4000 sq-ft of area, the load in watts is 12000. This load could be served by X number of 15 or 20 amp circuits. A sound "Design-rule" is allowing 1.5 amps per receptacle or liting outlet.
 
  #5  
Old 06-28-04, 08:11 AM
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In a 'ring' circuit, the conductors feeding the receptacle branch circuit form a loop, going from the breaker panel through all of the receptacles, and then back to the breaker panel. From any receptacle, there are _two_ paths to follow back to the breaker panel.

This is prohibited by several parts of the US NEC.

1) Essentially you have _parallel_ conductors, since there are two paths between panel and load. A ring circuit violates the parallel conductors rules in two ways. A) Parallel conductors are required to be larger than a minimum size. Ring circuit conductors are too small. B) Parallel conductors must also be of the same material and the same length for all parallel paths. In a ring circuit, the lengths of the two paths are almost always different..

2) Ring circuits would violate NEC overcurrent protection rules, since ring circuits are designed with the thought that some current will follow one path and some the other. Net result is that on ring circuits, the OCPD would be at too high a value for the same conductors in the US.

In the US the standard wiring scheme is what would be called 'spurs' in the UK. In the UK you have rings and you are permitted to have spurs with no more than one receptacle. In the US _everything_ is 'spurs', and the ring circuit is prohibited.

-Jon
 
  #6  
Old 06-28-04, 08:13 AM
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By the way, the number of required circuits in the US is greater, but the capacity of these circuits is lower.

In the UK, a 'ring main' will be 240V, 32A. You will have a bunch of receptacles on this ring, and then the power cords plugged into this main are fuse protected.

In the US, a residential receptacle branch circuit will be 120V, 20A (or 120V 15A), delivering less power. Power cords are not fused, but instead protected by the OCPD for the circuit.

-Jon
 
  #7  
Old 06-29-04, 04:15 AM
Snape
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Nice One

This has got quite interesting, in Uk we also have whats called a radial circuit which is basically the wiring method you say you are using in Us & Canada. Basically a single cable from recepticle to recepticle. I think that most applicances in Uk are current hungry and running on 240v so it spreads the current more equally using the ring circuit. Most cookers, showers etc... are run on radial circuits and some socket circuits are also radial. I think it just down to the voltage differences.

Another question is we use 240v 20A Breakers for radial circuits, and you use 15A - 20A for your 110v circuits. According to Ohms Laws if you half the voltage you double the ampage so why are you breakers still the same rating as ours and we are on 240v, maybe im confusing things.

Cheers
Ian
 
  #8  
Old 06-29-04, 06:32 AM
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It is true that a 240-volt 20-amp circuit provides twice the power as a 12-volt 20-amp circuit. Maybe we just put in twice as many circuits as you do. Note that we only use 120 volts for the low power stuff (clocks, radios, TVs). We still use 240 volts for the high power stuff (cooking, hot water, clothes drying, heating).
 
  #9  
Old 06-29-04, 09:12 AM
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What's common in the US is 3-wire "Multi-wire" Branch-Circuits.

If we have such a circuit rated at 20 amps supplying the "Small-Appliance" load in a kitchen, the power capacity is 20 amps X 220 volts =4400 watts.If one "leg" ( wire "1") of the 3-wire B-C "feeds" a 15-amp, 110-volt load, and the other "leg" ( wire "2" ) also "feeds" a 15-amp load, 110-volt load,the current in the "Neutral" (wire "3") is Zero amps. The 2 loads operate in series across 220-volts.

If the circuits were "simplified" by eliminating the "Neutral" and operating with "Small-Appliances" rated at 220-volts, an extermely serious shock-hazard would exist-- 220 volts-to-Ground, shocks-to-Ground being the most common form of electrical shocks.

The maximum voltage-to-Ground, whether the supply system is 3-wire, single-phase, 220/110, or 4-wire, 3-phase, 208/120, is 120 volts.
 
  #10  
Old 06-29-04, 12:18 PM
doingitmyself
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Originally Posted by Snape
According to Ohms Laws if you half the voltage you double the ampage ......
Ian
Wait, wait, wait..... I=E/R

all other things being equal (i.e, resistance), if you halve the voltage, you halve the current, yes?

240-v/8-ohms = 30 A
120-v/8-ohms = 15 A
 
  #11  
Old 06-29-04, 12:45 PM
Glob
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Well...tried to post an observation but I think it got lost!

Some thoughts on an interesting subject "sockets unlimited"

UK 240v domestic supply is of a more lethal nature but as with ALL supplies safety is always a first priority.
240v does not suffer volt drop quite the same as 120 and halves the current. Doubling the current in a 120v system must be watched carefully!

The "ring main" is a more effective way to supply a recepticals as the circuit is supplied in two directions which effectively halves the load on the supplying cables.
In a branch or "daisy chain" circuit the cable leaving the supply point takes all the load.

Overheating of cables can result in some very tragic fires and in the USA with 95% of building material being wood then fuel is readily available. The only approach to electricily is safety first.
 
  #12  
Old 06-29-04, 01:13 PM
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Whether halving the voltage doubles the current or halves the current depends on what you hold constant.
  • If you keep the same appliances and thus hold the resistance constant, you halve the current. However, this is an impractical scenario, since none of your appliances will function any more.
  • If you swap out the appliances for equivalent wattage appliances designed for the other voltage, you double the current. I believe that this is the scenario that Professor Snape was referring to, since it is the only scenario that makes any practical sense (although this scenario is not based on Ohm's law).
The confusion always lies in the unstated assumptions.
 
  #13  
Old 07-02-04, 03:46 AM
Snape
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So it seems to me that the ring final circuit is the best method for wiring recepticles as it balances the load more equally through out the cable. From what i can see with Us & Canadian methods is that it would be very easy to over load circuits as threads in the forum show that most people just run lighting and recepticles on the same circuit. Surely it would be easy to overload if people are always taking feeds from the nearest light or recepticle. It would be like a huge chain. What are the regulations on combining applicances and lighting on the circuits. And what is the max load on your circuits like on a 20A would be 2400watts for insance. For instance take my first question in this thread where in the Uk you can have unlimited sockets on a radial - branch circuit in a 50m2 area.

Thanks
IAn
 
  #14  
Old 07-02-04, 08:39 AM
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It's important to distinguish between "General-purpose" Branch-Circuits, rated at either 15 or 20 amps, and other specific circuits that require a 20-amp rating.

THe NEC reads--- " the small-appliance B-C's ( minimum of 2), the Laundry B-C's, and the Bathroom B-C's required in a dwelling-unit, shall supply only the receptacle-outlets (required)." These are all B-C's rated at 20 amps.

General-purpose B-C's must comply with the 3 watts per sq.ft. requirement. For a single 15 amp B-C with a 1800 watt rating, the maximum area served is 20 ft. X 30 ft.

Art. 210.23 reads----- " In no case shall the connected load exceed the (rating) of the B-C."

A 20 ft. X 15 ft. bedroom with 6 recessed-fixtures with 150 watt lamps would require a single 15 amp B-C for that room only. ( 6 X 150 = 900 watts ) + ( 300 sq.ft X 3 = 900 watts) = 1800 watts.
 
  #15  
Old 07-02-04, 09:56 AM
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The 3va rule is applied over the whole dwelling, not to an individual circuit or room. And it applies to the sum of receptacles and lighting, so you don't need to add the lighting separately. So one 15-amp circuit could legally serve all the lighting and receptacles in six 10x10 bedrooms. Of course, common sense must be used as well as the code. A house wired to the code-minimum 3va per square foot would be a difficult house to live in.
 
  #16  
Old 07-02-04, 11:50 AM
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JN:

A connected load with a wattage-value that exceeds the wattage-rating of the B-C would violate Art. 210.23.

Six bedrooms, per your example, each with 4 fixtures designed for 100-watts lamps, would be a connected liting-load of 2400 watts,and This does not include the required caculated load for the receptacle-outlets in the six rooms.

Cheers, Proud And Thankful-----
 
  #17  
Old 07-02-04, 12:55 PM
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Lightbulb voltages unlimited

Originally Posted by PATTBAA
What's common in the US is 3-wire "Multi-wire" Branch-Circuits.

If we have such a circuit rated at 20 amps supplying the "Small-Appliance" load in a kitchen, the power capacity is 20 amps X 220 volts =4400 watts.If one "leg" ( wire "1") of the 3-wire B-C "feeds" a 15-amp, 110-volt load, and the other "leg" ( wire "2" ) also "feeds" a 15-amp load, 110-volt load,the current in the "Neutral" (wire "3") is Zero amps. The 2 loads operate in series across 220-volts.

If the circuits were "simplified" by eliminating the "Neutral" and operating with "Small-Appliances" rated at 220-volts, an extermely serious shock-hazard would exist-- 220 volts-to-Ground, shocks-to-Ground being the most common form of electrical shocks.

The maximum voltage-to-Ground, whether the supply system is 3-wire, single-phase, 220/110, or 4-wire, 3-phase, 208/120, is 120 volts.
If you were to eliminate the neutral, there are two ways to do it. One would be to have the wiring the way it is done in Europe, where the transformer secondary has 2 wires, and one of them is grounded. You then have that full voltage as your line-to-ground shock hazard.

However, there is another way to do it. Use the same 3-wire center secondary transformer as in the US, and ground the center wire as usual. But just don't use the neutral for appliances. Instead, power all appliances from line-to-line at 240 volts. The shock hazard is the line-to-ground voltage of 120. This is in fact how the NEMA type 6 receptacles (at 15 amps this is the familiar "sleepy face" outlet) are wired. The neutral is not brought up to the load at all, and the shock hazard is still at 120 volts.

There are still problems with using this more in the US. The code discourages loads under 1440 watts from using 240 volts (I suppose the reasoning is if the average person gets an appliance for 240 volts, they might run a very long extension cord to get the power since a typical home does not have very many 240 volt outlets, and that is a hazard, so it is best to avoid 240 volts unless really needed). Also, many locations get only 208 volts line-to-line since they are 2 or 3 phases of a three phase system (at 208/120 volts). High density urban areas of many cities often have this. And when one wire is not grounded, it has to be switched, meaning you have to use double pole switches. Light fixtures would also have to be sure the bulb bases are not exposed (NEC does not allow powering home lights this way).

Had I been the one to design the original power system (but with what I know about it today), I think I probably would go with a system where transformers are grounded for minimum line-to-ground voltage, and the neutral is just not used. Everything would be powered from line-to-line. If I picked 260 volts as the standard for that, then it would be 130 volts line-to-ground on single phase, and 150 volts line-to-ground on three phase. Since few, if any, loads would use line-to-ground in such a world, there would not be a need to have it be the same everywhere; only the line-to-line voltage would be kept the same. That is different than the existing US system where it is the line-to-ground voltage that is kept the same in both 120/240 and 208Y/120 systems.

The European system, while having the disadvantage of the higher shock voltage, does have an advantage of consistency between single phase and three phase. They have fewer appliances for the 400 volts line-to-line (larger electric stoves, kilns, and saunas might be had on this voltage for those who get three phase), but where used, there's basically just that one voltage (within nominal tolerances) to worry about being compatible with (contrasted with two different ones, 208 and 240, in the US). One end result of this voltage compatibility is that it is more feasible to use three phase, and it is also more readily available to homes in much of Europe (though which is the cause and which is the effect, I do not know).
 
  #18  
Old 07-02-04, 02:39 PM
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Can't argue with what you said PATTBAA, but it doesn't change anything I said.

By the way, who puts 400 watts of light in a 10x10 bedroom?
 
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Old 07-02-04, 04:53 PM
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Originally Posted by John Nelson
Can't argue with what you said PATTBAA, but it doesn't change anything I said.

By the way, who puts 400 watts of light in a 10x10 bedroom?
Back in 1969, when I was in junior high school, my parent began a project of building a new custom designed house. My mother did the entire floor plan from scratch. My two brothers and I were given our choice of what kind of light fixture we would have on the ceiling of our bedroom. We had about a dozen catalogs to go through and I finally found one I liked.

But I did things different. Maybe in part it was because I was "different", or maybe just because I had ideas and plans of what I wanted to do (I had many electronic toys and gadgets). The house was being wired with non-grounded outlets (I presume the code didn't require them, yet, but I didn't know much about code in those days), one grounded outlet was being put in for the washer in the laundry room (in addition to a big 30 amp one for the dryer). But I insisted on grounded outlets in my bedroom, and got them (5 of them). And I asked for TWO light fixtures instead of just one (got that), and asked for them to be on separate switches (got that, too), and asked for a duplicate set of switches (now everything would be three way) on the other side of the room where my bed would be (yep, even got that).

These 2 light fixtures were rated for 100 watt bulbs and held 4 each. But I used 75 watt bulbs. That's 8 total 75 watt bulbs. The bedroom was 11.5 x 10. So in a room only slightly larger than 10 x 10, I had 600 watts of light, a 150 watt tube-type stereo, a TV set, 2 shortwave radios, and a reel-to-reel tape deck. I was on the far end of the central heating system, but I didn't seem to have any trouble keeping the room warm.
 
  #20  
Old 07-02-04, 06:07 PM
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To argue against 'ring mains': the OCPD on a ring main is set with the presumption that loads will be balanced and both paths from the supply panel will be essentially equally used. If all of the loads are on one side of the ring, then most of the current will flow through only one of the paths, and that path could be overloaded.

A standard ring main is made with 2.5mm^2 conductors, which are about 13ga. But a standard ring main is protected at 32A. In the US, you need to get to much thicker wire (10 ga, or about 5.26mm^2) before you can use a 30A breaker. By US standards, that ring main is not correctly protected from overcurrent. Of course, there are different requirements for things like how the wire is run (US standards don't distinguish between cable run in an insulated wall and cable run on the surface of the wall, for example), so this is something of an apples to oranges comparison.

With respect to supplying power using two 'hot' feeds balanced about earth potential, this has some significant merit in terms of reducing the voltage available for ground faults. Such 'balanced power' is in fact used in some professional audio applications, and there is an entire article of the NEC dedicated to them (article 647). Note the problems, however. To turn off a simple light, you need a double pole switch, since you have to switch of _both_ hot feeds. In addition, you can't use items such as 'screw shell' lamp holders, because you get an exposed 'hot' terminal.

Finally, there are _many_ loads that will happily operate at either 120 or 240V. Some are resistive, where the load will consume more power at higher voltage, but is designed for this (an example is a hot tub designed to be wired either to a 120V, 20A circuit, or a 240V, 50A circuit.) Other loads are constant power, and adjust their input current to deal with changing voltage (an example is a universal computer power supply, that will operate on anything from 100V to 240V 50 or 60Hz.

-Jon
 
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