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Electrics in the US?

Discussion in 'Electrics Outside of the UK' started by eveares, 6 Jan 2016.

  1. eveares

    eveares

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    Maybe PBC_1966 could eighteen me on a few questions I have about electrics in the US:

    1) Do you have rewire-able plugs and are they common?

    2) Do modern plugs have the insulated ends to stop one from getting a shock when plugging them in?

    3) Do all modern circuits from the DB have RCD's/GFCI's?

    4) How common is each earthing system in the states? (i.e. TT, TN-S, TN-C-S)

    5) What are some of the major differences from the UK other than the obvious such as the mains voltage (120v), mains frequency (60hz), wiring colours (Line = black, Neutral = White), Terminology (RCD vs GFCI), etc...

    6) Is it true that the Neutrals and CPC's are often connected together at the DB?

    7) How do you rate the electrical standards in the US compared to the UK?

    Regards: Elliott
     
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  3. PBC_1966

    PBC_1966

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    I'll try! (I might even try for nineteen..... ;) )

    Yes, we have them, and they're widely available and used. General household appliances have come with cords with an integral molded-on plug for decades, but you can pick up most of the smaller types of replacement plugs in almost any hardware store. Extension leads sold in your average places also have molded plugs and sockets, but wireable inline sockets are also easily obtainable as well if you want to make up your own. Cordsets sold for connecting domestic appliances such as dryers and ranges also generally come with an appropriate molded-on 30 or 50A plug, but wireable plugs are also sold. Then there are all the heavier commercial/industrial connectors, including locking types, three-phase etc.

    As in the sleeved pins on newer 13A plugs in Britain? No. But over the years the smaller molded 2-prong plugs as found on most 120V appliances which don't require a ground have grown a raised "lip" around the face which is generally absent on older plugs.

    Many of what might be termed general-purpose 120V circuits in homes are now required to have GFCI protection by the NEC (National Electrical Code). It started in the early 1970's with GFCI protection required for outdoor receptacles near swimming pools, then extended to all outdoor receptacles, bathroom receptacles in 1975, garages in 1978, and so on. They gradually added places like basements, boat houses, receptacles within 6 ft. of a kitchen sink then all kitchen receptacles, crawlspaces, etc. The latest revision (2014) just added GFCI requirements for 120V receptacles in laundry areas.

    The GFCI is designed for a nominal 5mA trip current, and similar to RCD protection in the U.K., you can get circuit-breakers which incorporate GFCI protection (like the British RCBO) and you can get GFCI receptacles which have feed-through terminals to protect downstream outlets. GFCI protection at this level is on a per-circuit (or part of circuit) basis, so there are no split-load type of arrangements with a common GFCI protecting multiple final circuits.

    There's still no GFCI requirement for things like dedicated dryer, range, air conditioning, water heater circuits etc., but the 2014 code did just add a requirement for dishwashers, even if hardwired.

    Then there is the separate issue of the AFCI, which is a whole different story since it was first introduced about 15 years ago.

    The various TN/TT designations aren't used here, but what would be classed as TN-C-S is the norm as far as all regular public supplies are concerned. TN-S exists only as a separately derived system in some environments, e.g. where a private transformer is used on the premises for some reason. TT isn't used at all, and is prohibited by the NEC.

    Well that opens up the field of discussion a little!

    Starting at the supply level, the U.S. has rather more options for sub-kilovolt supplies than exist in the U.K. Regular residential and light commercial supplies are single-phase 3-wire 120/240V (in the typical home, the 240V being used for the range, dryer, and larger fixed electric heating and air-conditioning units). The two most common three-phase supplies nowadays are wye systems at 120/208 and 277/480V. In some places you can also find older 240 & 480V delta supplies, the former of which is commonly found as the 4-wire delta arrangement so that 120V loads can also be supplied. In general, these are typically regarded by the utilities as "legacy" systems now, and only the 120/240, 120/208 & 277/480 wye systems can be had for new or upgraded installations.

    Moving into the home, as you're probably aware the ring final circuit isn't used, everything being wired as radials, and plugs aren't fused. General-use 120V 15A receptacles are fed from either 15 or 20A branch circuits, and general purpose circuits feed both receptacle outlets and fixed lighting. At least two dedicated 20A branch circuits feed receptacles in the kitchen & dining areas (an NEC rule which dates back to 1959). Over the years the NEC has also added requirements for some other individual circuits as loads have increased, e.g. a dedicated circuit for the laundry area in 1968 and most recently (2008, maybe 2005?) a dedicated 20A circuit for the bathroom because of the ridiculously high-power hair dryers on sale now.

    In terms of the physical equipment, type NM (Non Metallic sheathed) cable is the equivalent of British T&E and used in pretty much the same way, although it has a slightly different construction. Conduit systems can use two different thicknesses of PVC conduit (known as Schedule 40 & Schedule 80) depending upon requirements, and as well as heavy gauge steel conduit there are also thinner types, such as EMT (Electrical Metallic Tubing), which is something akin to the thinwall metal conduit which can still sometimes be found in British homes of the 1930's. There's nothing really equivalent to British SWA cable here. Armored cables are an interlocking metallic sheath containing the conductors inside, looking something like a metallic flexible conduit in overall appearance.

    The "Wire Nut" has become the almost universal connector for conductors within boxes these days and the typical British/European "choc block" isn't generally found. As I just mentioned in another thread, duplex receptacles (double sockets) have the neat feature of having separate terminals for each half (supplied with a bridging link), so that if you want you can wire them separately, either on completely different circuits or, as is commonly done in some locations, so that one half is permanently live and the other half can be controlled by wall switch for plug-in lamps.

    That's just about begun to scratch the surface probably, but should set the ball rolling!

    Yes, if it's the main distribution panel for the house. Supplies are the equivalent of TN-C-S, and at the main panel the neutral busbar is bonded to the panel cabinet (which is always metal - should please the latest U.K. amendment crowd!). Unlike TN-C-S in the U.K., there is also always a local earth electrode connected to the incoming supply neutral, typically either where the neutral passes through the meter base or directly to the busbar in the panel itself. The panel can have separate neutral & ground bars, with the neutral bonded to ground, or can just use a single combinbation bar into which the branch circuit neutrals and grounds are connected.

    When we come to a sub-panel, however, it's a different story and the neutrals & grounds have to be kept separate on separate bars, with the neutral floating and not bonded to the casing & ground bar. Panels are normally supplied with a bonding strap or screw so that the connection from neutral bar to ground can be put in place or omitted as required.

    That's another one which could open a long debate, so we'll probably come back to details later. Obviously there are pros & cons for both the American and the British systems, but in general I think they're perfectly good, with reservations I have about certain things which have crept in over time.

    The push-in terminations found on some receptacles and switches are an abomination in my mind, and I think it would be good if they were abandoned entirely for the sake of the few seconds it takes wrap a wire around a terminal screw and make a more secure job of the connection.

    But on the other side of the coin, thinking of something mentioned in another recent thread about incoming service conductors, all incoming services here are run in solid metallic conduit from where the cables enter the house to the meter, whether underground or overhead.
     
    Last edited: 6 Jan 2016
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  4. eveares

    eveares

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    That seems a bit of a bad idea, what protects one from getting a shock of the line and neutral pins on a plug as it's inserted into a socket.

    But how about general things like fixed lights, your general socket in the living room/bedroom/hall, etc... I guess not.

    Well I did not know that... You learn something new every day.

    But I guess it just as strong against mechanical damage and the metallic sheath is earthed, right?


    Eeek! :eek::censored: Having the CPC's and Neutrals linked together after the main incoming fuse cut out seems very wrong and like a bad idea to me. The main DB could end up floating live should the neutral return to the fuse cutout from the main DB become broken with no dedicated earth from the DB to the Cut-Out as a fault return path!

    I guess factory's what need 400v/415v 3 phase would have their own local transforms to generate the voltages they need.

    Also what is DIY electrics like in America regarding the law, do you have the equivalent of notifiable work as is defined in Part P (Approved Document P) over here?
     
  5. winston1

    winston1

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    IMG_0484.jpg

    This moulded plug was on a fan for sale in New York last year.
     

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    Last edited: 7 Jan 2016
  6. PBC_1966

    PBC_1966

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    O.K., I should have said not routinely used. :) There were also some unpolarized plugs around years ago which were fitted with two fuses. But fused plugs are the exception rather than the rule.

    It's no worse than existed in the U.K. for decades before sleeved pins became the norm. I guess it's just not something that has ever been considered a big enough potential concern here.

    On a somewhat related note though, "tamper resistant" receptacles have been required by the NEC for all the general 120V 15 & 20A outlets in homes from 2008. These are the U.S. equivalent of shuttered sockets, operated on the "equal pressure on two pins" principle, since the receptacles have to accept plugs both with and without a ground pin. There are some exceptions - Receptacles for dedicated appliances which are normally not easily accessible (one for and behind a refrigerator, for example), receptacles mounted high up, etc.

    Not to the 5mA level specified for elsewhere, but the AFCI (Arc-Fault Circuit Interrupter) which is now required for just about all "regular" 120V circuits in the house includes ground-fault protection at a higher level, around 30 - 50mA.

    The general approach as far as what might be called general-use 120V circuits are concerned is to provide two 20A branch circuits for the receptacles in the kitchen & dining area (the receptacles themselves are normally the regular 15A types). The NEC requires that all general receptacles in these areas be fed from these specific circuits, and that these circuits feed nothing else (no fixed lights, sockets in other rooms etc.).

    Apart from where other specific dedicated circuits are required, all of the general-purpose receptacles and fixed lighting in the rest of the house can be wired on any combination of 15 & 20A circuits as the designer likes to use, based on a minimum of 3 watts per square foot. So if you have a 1500 sq. ft. house, for example, you need to provide for a minimum of 3 x 1500 = 4500 watts, or 37.5A at 120V, and thus you would need as a minimum either two 20A circuits or three 15A circuits. Receptacles in the living room, bedrooms, hallways etc. plus lighting throughout the whole house are then distributed among these general-purpose circuits. As you might expect, there are some specific rules about loading, e.g. if a circuit feeds both general receptacles and fixed equipment then the latter mustn't account for more than 50% of the circuit capacity.

    As I mentioned earlier, the laundry area is required to have a dedicated 20A circuit for receptacles, which normally means it will feed the washing machine (no integral heaters here) and provide power for the motor and timer where a gas dryer is in use, as well as any other sockets provided in the room for general use. And there's the newer (and slightly convoluted) rule about providing bathrooms with a dedicated 20A circuit now; previously bathroom receptacles were just included with the general circuits above.

    While going through the typical lineup, I might as well mention the dedicated circuits for a few other things as well. Electric dryers are generally provided with a 30A 120/240V outlet, and where an electric range is used for cooking it's usually a 40 or 50A circuit (also 120/240V). Full-size electric water heaters, where used, are also on their own dedicated 240V circuit of appropriate rating, as are central electric heating and air-conditioning systems.

    Dedicated circuits can be, but are not always required, to be provided for other larger appliances. For example, a refrigerator in a kitchen can just run from one of the 20A kitchen circuits, but can also be provided with its own dedicated 15 or 20A circuit. Garbage disposals and dishwashers are other candidates, and that brings us to the multiwire circuit, since this is a place where it's commonly found.

    Since we have a 3-wire single-phase supply, the 120V loads are normally distributed as evenly as possible between the two poles. It also makes it possible to save on copper by running a 3-wire (not counting ground) circuit where convenient to provide the equivalent of two 2-wire circuits. A duplex outlet below the kitchen countertop is a very common example where this is done in the home, one half for the dishwasher and the other half via a switch above the counter for the garbage disposal. Multiwire circuits can be used anywhere, but this is a particularly common usage.

    Yes and yes. For underground work though, there's a type of cable known as UF which is a non-armored type suitable for direct burial, otherwise it's usually done with conduit.

    Ah, I should have explained that we don't have an equivalent of the British cut-out, nor does the main circuit-breaker open the supply neutral. The incoming neutral just goes straight through the meter base and connects directly to the neutral busbar in the main panel, which will then be bonded to the casing (and have the local earth electrode, bonding for water etc. connected to it). So it's really pretty much the same as the U.K., just with N-E bonding point at the main panel instead of ahead of the meter.

    They often have a local transformer, but 400-415V is not a standard utilization voltage here, the closest being the 480V which was originally supplied in delta configuration (and hence the choice of 277/480V as the wye replacement). But yes, facilities which have a 277/480V supply will then typically have a transformer to provide a 120/208V system internally as well, since at the very least 120V will normally be needed for general office equipment and similar things.

    Sort of, but that will take some more explanation and this is quite a long post already, so let me get back to you on that one!
     
    Last edited: 7 Jan 2016
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  7. winston1

    winston1

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    Would you be allowed to fit a 240 volt socket anywhere? I'm thinking if I lived there I would like to bring a decent kettle with me.
     
  8. PBC_1966

    PBC_1966

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    No problem with that at all - In fact when I get to re-doing our kitchen here, I'm planning on adding a couple of 240V sockets for just that reason!

    As well as the 120/240V receptacles provided for range and dryer, if applicable, you can also find straight 240V receptacles in specific locations in some homes. A typical use for a 240V 15A receptacle is to feed a fixed unit air-conditioner/heater in a single room.
     
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  10. PBC_1966

    PBC_1966

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    To get to this question now:

    The general approach is that to do certain things (electrical, plumbing, reroofing, building an extension, converting a garage into living area, building a new home from scratch etc.) you're supposed to get a relevant permit from the city or county, for which there is a fee, then the city or county inspector will come out and check that the work meets the relevant codes and (assuming it does) issue a final inspection certificate.

    As with many things in the U.S., there is no single set of rules which apply nationwide, or even statewide in many cases, so the details about what work requires a building permit and what does not can vary considerably from one place to another, as can the fees. In terms of electrical work, some places can be very strict and demand a permit for almost anything more than just replacing an existing switch, light, or receptacle, while in other places you can pretty much do anything short of replacing or installing a new distribution panel or main service without a permit. But for smaller jobs, the starting level of the fees does tend to be much more reasonable than the charges imposed by U.K. local authorities: I believe the fees here in the City of Redding for small electrical works start at around $30, for example.

    The permit and inspection process applies not only to DIY householder work, by the way, but also to professional electricians, plumbers, builders, etc. I'm not aware of anywhere which prevents DIY work on one's own house of any sort, but just about every state requires electricians working for remuneration to be licensed (generally ditto for plumbing, HVAC, and other trades).
     
  11. PBC_1966

    PBC_1966

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    A few photos to go with some of the answers above.

    Here's a "valise" style rewireable plug, Hubbell brand in this case; note the terminal screws - plain brass for "hot," silver for neutral, green for ground:

    DSCN3803.jpg DSCN3801.jpg

    These are armored plugs and sockets, good for making up rugged extension cords or for fitting on power tools (these are Leviton):

    DSCN3796.jpg

    Here are a couple of tough nylon bodied plugs (Hubbell again); these are intended for 240V use - note the different blade orientation:

    DSCN3798.jpg

    And here's an illustration of the changing style of molded appliance plugs; on left is an older type, 1960's in this case, on the right the current style with a raised "lip" around the front of the plug:

    DSCN3845.jpg

    Note also in that last picture the blade with a flared end to make it slightly wider and provide polarization. It seems to have become common nowadays to use polarized plugs even when there's no real need. The plug on the left has identical blades, and so is reversible.
     
  12. PBC_1966

    PBC_1966

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    The ubiquitous Wire Nut, seen here in two common sizes for household work:

    DSCN3821.jpg

    In this particular range from Ideal, the yellow will take up to four #14 conductors or up to three #12; the red is good for up to four #12 or two #10 (in general, 14 AWG cable is used for 15A circuits, 12 AWG for 20A, and 10 AWG for 30A).

    A typical duplex receptacle (Hubbell); note the different color terminal screws again, and the links between the two halves which can be removed to wire them independently:

    DSCN3818.jpg

    And here's a switch, a commercial type in this partcular example (Hubbell again):

    DSCN3820.jpg

    This is NM-type cable (Non Metallic sheathed), commonly known as Romex after a brand name:

    DSCN3840.jpg

    The particular example above is 12 AWG. Somewhere just into the beginning of the 21st century the manufacturers adopted a sheath color identification scheme for the smaller sizes: White is #14, yellow is #12, orange is #10. Larger sizes are normally black. With older cables the sheath color was of no significance and could vary. The 3-core (plus ground) versions add red and have the conductors in a spiral rather than being flat-in-line like the British equivalent.
     
  13. PBC_1966

    PBC_1966

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    A typical distribution panel - This is a 125A 24-position board I just purchased for the home, Cutler-Hammer CH type (now owned by Eaton):

    DSCN3850.jpg DSCN3849.jpg

    Note the bonding strap on the right-hand side which can be connected into the neutral bar when used as a main panel, or discarded when used as a sub-panel where neutral & ground are kept separate. (For main panel use, the lugs at the top would normally be replaced with a suitable main breaker as well.)

    And some of the breakers used with this particular panel:

    DSCN3808.jpg DSCN3809.jpg DSCN3853.jpg DSCN3833.jpg
     
    Last edited: 14 Jan 2016
  14. wundaboy

    wundaboy

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    Whenever I see American MCBs and RCBOs they remind me of the Crabtree C50s of the 1970s - far bulkier and better built than what we have now in Europe. What is the quality like?
     
  15. PBC_1966

    PBC_1966

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    Yes, they still have a much more rugged feel to them than the newer MCB's in the U.K. Those Cutler Hammer breakers pictured above are actually a few years old now (1980's manufacture), as I picked up a whole new-old stock batch to use with the new C-H board also pictured, which will be going in as a sub-panel as we remodel the house. But the current production breakers still have a much more solid feel about them than current British types.

    Speaking of Crabtree C50's, when I was young we moved into a real "fixer upper" house which had been built in the 1930's and had little done to it since, including any wiring. It still had the old 2-pin 15A sockets in some rooms and, naturally, rubber-insulated cable which was in a pretty bad state of decay by then. My father completely rewired it, and the "cupboard under the stairs" acquired a nice shiny new C50 board with, as I recall, about six breakers. That was 1971. I suspect that it was the only house in the street sporting C50's, and at that time possibly the only house in the street with circuit breakers rather than fuses.
     
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