Maybe
PBC_1966 could eighteen me on a few questions I have about electrics in the US:
I'll try! (I might even try for nineteen.....
)
1) Do you have rewire-able plugs and are they common?
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.
2) Do modern plugs have the insulated ends to stop one from getting a shock when plugging them in?
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.
3) Do all modern circuits from the DB have RCD's/GFCI's?
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.
4) How common is each earthing system in the states? (i.e. TT, TN-S, TN-C-S)
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.
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...
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!
6) Is it true that the Neutrals and CPC's are often connected together at the DB?
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.
7) How do you rate the electrical standards in the US compared to the UK?
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.
