Internet Surfer 2.0

home *** CD-ROM | disk | FTP | other *** search

/ Internet Surfer 2.0 / Internet Surfer 2.0 (Wayzata Technology) (1996).iso / pc / text / mac / faqs.032 < prev next >

Wrap

Text File | 1996-02-12 | 27.9 KB | 598 lines

Frequently Asked Questions (FAQS);faqs.032 The two pairs of connections on a GFCI outlet are not symmetric. One is labeled LOAD; the other, LINE. The incoming power feed *must* be connected to the LINE side, or the outlet will not be protected. The LOAD side can be used to protect all devices downstream from it. Thus, a whole string of outlets can be covered by a single GFCI outlet. Subject: Where should GFCIs be used? The NEC mandates GFCIs for 110V, 15A or 20A single phase outlets, in bathrooms, kitchens within 6' of the sink, garages, unfinished basements or crawl spaces, outdoors, near a pool, or just about anywhere else where you're likely to encounter water or dampness. There are exceptions for inaccessible outlets, those dedicated to appliances ``occupying fixed space'', typically refrigerators and freezers, and for sump pumps and laundry appliances. The CEC does not mandate as many GFCIs. In particular, there is no requirement to protect kitchen outlets, or most garage or basement outlets. Basement outlets must be protected if you have a dirt floor, garage outlets if they're near the door to outside. Bathrooms and most exterior outlets must have GFCIs. Even if you are not required to have GFCI protection, you may want to consider installing it anyway. Unless you need a GFCI breaker (see below), the cost is low. In the U.S., GFCI outlets can cost as little as US$8. (Costs are a bit higher in Canada: C$12.) Evaluate your own risk factors. Does your finished basement ever get wet? Do you have small children? Do you use your garage outlets to power outdoor tools? Does water or melted snow ever puddle inside your garage? Subject: Where shouldn't I use a GFCI? GFCIs are generally not used on circuits that (a) don't pose a safety risk, and (b) are used to power equipment that must run unattended for long periods of time. Refrigerators, freezers, and sump pumps are good examples. The rationale is that GFCIs are sometimes prone to nuisance trips. Some people claim that the inductive delay in motor windings can cause a momentary current imbalance, tripping the GFCI. Note, though, that most GFCI trips are real; if you're getting a lot of trips for no apparent reason, you'd be well-advised to check your wiring before deciding that the GFCI is broken or useless. Subject: What is the difference between a GFCI outlet and a GFCI breaker? For most situations, you can use either a GFCI outlet as the first device on the circuit, or you can install a breaker with a built-in GFCI. The former is generally preferred, since GFCI breakers are quite expensive. For example, an ordinary GE breaker costs ~US$5; the GFCI model costs ~US$35. There is one major exception: if you need to protect a ``multi-wire branch circuit'' (two or more circuits sharing a common neutral wire), such as a Canadian-style kitchen circuit, you'll need a multi-pole GFCI breaker. Unfortunately, these are expensive; the cost can range into the hundreds of dollars, depending on what brand of panel box you have. But if you must protect such a circuit (say, for a pool heater), you have no choice. One more caveat -- GFCI outlets are bulky. You may want to use an oversize box when installing them. On second thought, use large (actually deep) boxes everywhere. You'll thank yourself for it. Incidentally, if you're installing a GFCI to ensure that one specific outlet is protected (such as a bathroom), you don't really have to go to all of the trouble to find the first outlet in the circuit, you could simply find the first outlet in the bathroom, and not GFCI anything upstream of it. But protecting the whole circuit is preferred. When you install a GFCI, it's a good idea to use the little "ground fault protected" stickers that come with it and mark the outlets downstream of the GFCI. You can figure out which outlets are "downstream", simply by tripping the GFCI with the test button and see which outlets are dead. Subject: What's the purpose of the ground prong on an outlet, then? Apart from their use in electronics, which we won't comment on, and for certain fluorescent lights (they won't turn on without a good ground connection), they're intended to guard against insulation failures within the device. Generally, the case of the appliance is connected to the ground lead. If there's an insulation failure that shorts the hot lead to the case, the ground lead conducts the electricity away safely (and possibly trips the circuit breaker in the process). If the case is not grounded and such a short occurs, the case is live -- and if you touch it while you're grounded, you'll get zapped. Of course, if the circuit is GFCI-protected, it will be a very tiny zap -- which is why you can use GFCIs to replace ungrounded outlets (both NEC and CEC). There are some appliances that should *never* be grounded. In particular, that applies to toasters and anything else with exposed conductors. Consider: if you touch the heating electrode in a toaster, and you're not grounded, nothing will happen. If you're slightly grounded, you'll get a small shock; the resistance will be too high. But if the case were grounded, and you were holding it, you'd be the perfect path to ground... Subject: Why is one prong wider than the other? Polarization Nowadays, many two-prong devices have one prong wider than the other. This is so that the device could rely (not guaranteed!) on one specific wire being neutral, and the other hot. This is particularly advantageous in light fixtures, where the the shell should neutral (safety), or other devices which want to have an approximate ground reference (ie: some radios). Most 2-prong extension cords have wide prongs too. This requires that you wire your outlets and plugs the right way around. You want the wide prong to be neutral, and the narrow one hot. Most outlets have a darker metal for the hot screw, and lighter coloured screw for the neutral. If not, you can usually figure out which is which by which prong the terminating screw connects to. Subject: What kind of outlets do I need in a kitchen? The NEC requires at least two 20 amp ``small appliance circuits'' for kitchens. The CEC requires split-duplex receptacles. Outlets must be installed such that no point is more than 24" (NEC) (900 mm CEC) from an outlet. Every counter wider than 12" (NEC) or 300 mm (CEC) must have at least one outlet. The circuit these outlets are on may not feed any outlets except in the kitchen, pantry, or dining room. Furthermore, these circuits are in addition to any required for refrigerators, stoves, microwaves, lighting, etc. Non-dedicated outlets within 6' of a sink *must* be protected by a GFCI (NEC only). Split duplex receptacles are fed with a 220V circuit. The tab is broken on the hot side of the outlet, and one hot goes to the upper outlet, and the other hot goes to the lower outlet. The neutral connects to both outlets through one screw. When "carrying through" to another outlet, the neutral must be pigtailed, such that removing the outlet, or having the neutral connection fall off doesn't cause the neutral to disconnect from downstream outlets. Subject: Where must outlets and switches be in bathrooms? There must be at least one outlet in each bathroom, adjacent to the sink, in addition to any outlet that may be incorporated in the light fixture. All such outlets *must* be GFCI-protected. Subject: What is Romex/NM/NMD? What is BX? When should I use each? Romex is a brand name for a type of plastic insulated wire. Sometimes called non-metallic sheath. The formal name is NM. This is suitable for use in dry, protected areas (ie: inside stud walls, on the sides of joists etc.), that are not subject to mechanical damage or excessive heat. Most newer homes are wired almost exclusively with NM wire. There are several different categories of NM cable. BX cable -- technically known as armored cable or "AC" has a flexible aluminum or steel sheath over the conductors and is fairly resistant to damage. TECK cable is AC with an additional external thermoplastic sheath. Protection for cable in concealed locations: where NM or AC cable is run through studs, joists or similar wooden members, the outer surface of the cable must be kept at least 32mm/1.25" (CEC & NEC) from the edges of the wooden members, or the cable should be protected from mechanical injury. This latter protection can take the form of metal plates (such as spare outlet box ends) or conduit. [Note: inspector-permitted practise in Canada suggests that armored cable, or flexible conduit can be used as the mechanical protection, but this is technically illegal.] Additional protection recommendations (these are rules in the Canadian codes - they are reasonable answers to the vague references to "exposed to mechanical damage" in both the NEC and CEC): - NM cable should be protected against mechanical damage where it passes through floors or on the surface of walls in exposed locations under 5 feet from the floor. Ie: use AC instead, flexible conduit, wooden guards etc. - Where cable is suspended, as in, connections to furnaces or water heaters, the wire should be protected. Canadian practise is usually to install a junction or outlet box on the wall, and use a short length of AC cable or NM cable in flexible conduit to "jump" to the appliance. Stapling NM to a piece of lumber is also sometimes used. - Where NM cable is run in close proximity to heating ducts or pipe, heat transfer should be minimized by means of a 25mm/1" air space, or suitable insulation material (a wad of fiberglass). - NM cable shall be supported within 300mm/1' of every box or fitting, and at intervals of no more than 1.5m/5'. Holes in joists or studs are considered "supports". Some slack in the cable should be provided adjacent to each box. [while fishing cable is technically in violation, it is permitted where "proper" support is impractical] - 2 conductor NM cable should never be stapled on edge. [Knight also insists on only one cable per staple, referring to the "workmanship" clause, but this seems more honoured in the breach...] - cable should never be buried in plaster, cement or similar finish. - cable should be protected where it runs behind baseboards. - Cable may not be run on the upper edge of ceiling joists or the lower edges of rafters where the headroom is more than 1m (39"). Whenever BX cable is terminated at a box with a clamp, small plastic bushings must be inserted in the end of the cable to prevent the clamps forcing the sharp ends of the armor through the insulation. BX is sometimes a good idea in a work shop unless covered by solid wall coverings. In places where damage is more likely (like on the back wall of a garage ;-), you may be required to use conduit, a UL- (or CSA-) approved metal pipe. You use various types of fittings to join the pipe or provide entrance/exit for the wire. Service entrances frequently use a plastic conduit. In damp places (eg: buried wiring to outdoor lighting) you will need special wire (eg: CEC NMW90, NEC UF). NMW90 looks like very heavy-duty NMD90. You will usually need short lengths of conduit where the wire enters/exits the ground. [See underground wiring section.] Thermoplastic sheath wire (such as NM, NMW etc.) should not be exposed to direct sunlight unless explicitly approved for that purpose. Canada appears to use similar wire designations to the US, except that Canadian wire designations usually include the temperature rating in Celsius. Eg: "AC90" versus "AC". In the US, NM-B is 90 degrees celcius. NOTE: local codes vary. This is one of the items that changes most often. Eg: Chicago codes require conduit *everywhere*. There are very different requirements for mobile homes. Check your local codes, *especially* if you're doing anything that's the slightest out of the ordinary. Wire selection table (incomplete - the real tables are enormous, uncommon wire types or applications omitted) Condition Type CEC NEC Exposed/Concealed dry plastic NMD90 NM armor AC90 AC TECK90 Exposed/Concealed damp plastic NMD90 NMC armor ACWU90 TECK90 Exposed/Concealed wet plastic NMWU90 armor ACWU90 TECK90 Exposed to weather plastic NMWU TW etc. armor TECK90 Direct earth burial/ plastic NMWU* UF Service entrance RWU TWU armor RA90 TECK90 ACWU90 [* NMWU not for service entrance] Subject: Should I use plastic or metal boxes? The NEC permits use of plastic boxes with non-metallic cable only. The reasoning is simple -- with armored cable, the box itself provides ground conductor continuity. U.S. plastic boxes don't use metal cable clamps. The CEC is slightly different. The CEC never permits cable armor as a grounding conductor. However, you must still provide ground continuity for metallic sheath. The CEC also requires grounding of any metal cable clamps on plastic boxes. The advantage of plastic boxes is comparatively minor even for non-metallic sheathed cable -- you can avoid making one ground connection and they sometimes cost a little less. On the other hand, plastic boxes are more vulnerable to impacts. For exposed or shop wiring, metal boxes are probably better. Subject: Junction box positioning? A junction box is a box used only for connecting wires together. Junction boxes must be located in such a way that they're accessible later. Ie: not buried under plaster. Excessive use of junction boxes is often a sign of sloppy installation, and inspectors may get nasty. Subject: Can I install a replacement light fixture? In general, one can replace fixtures freely, subject to a few caveats. First, of course, one should check the amperage rating of the circuit. If your heart is set on installing half a dozen 500 watt floodlights, you may need to run a new wire back to the panel box. But there are some more subtle constraints as well. For example, older house wiring doesn't have high-temperature insulation. The excess heat generated by a ceiling-mounted lamp can and will cause the insulation to deteriorate and crack, with obvious bad results. Some newer fixtures are specifically marked for high temperature wire only. (You may find, in fact, that your ceiling wiring already has this problem, in which case replacing any devices is a real adventure.) Other concerns include providing a suitable ground for some fluorescent fixtures, and making sure that the ceiling box and its mounting are strong enough to support the weight of a heavy chandelier or ceiling fan. You may need to install a new box specifically listed for this purpose. A 2x4 across the ceiling joists makes a good support. Metal brackets are also available that can be fished into ceilings thru the junction box hole and mounted between the joists. There are special rules for recessed light fixtures such as "pot" lamps or heat lamps. When these are installed in insulated ceilings, they can present a very substantial fire hazard. The CEC provides for the installation of pot lamps in insulated ceilings, provided that the fixture is boxed in a "coffin" (usually 8'x16"x12" - made by making a pair of joists 12" high, and covering with plywood) that doesn't have any insulation. (Yes, that's 8 *feet* long) NEC rules are somewhat less stringent. They require at least 3" clearance between the fixture and any sort of thermal insulation. The rules also say that one should not obstruct free air movement, which means that a CEC-style ``coffin'' might be worthwhile. Presumably, that's up to the local inspector. [The CEC doesn't actually mandate the coffin per-se, this seems to be an inspector requirement to make absolutely certain that the fixture can't get accidentally buried in insulation. Ie: if you have insulation blown in later.] There are now fixtures that contain integral thermal cutouts and fairly large cases that can be buried directly in insulation. They are usually limited to 75 watt bulbs, and are unfortunately, somewhat more expensive than the older types. Before you use them, you should ensure that they have explicit UL or CSA approval for such uses. Follow the installation instructions carefully; the prescribed location for the sensor can vary. There does not yet appear to be a heat lamp fixture that is approved for use in insulation. The "coffin" appears the only legal approach. Subject: What does it mean when the lights brighten when a motor starts? This usually means that the neutral wire in the panel is loose. Depending on the load balance, one hot wire may end up being more than 110V, and the other less than 110V, with respect to ground. This is a very hazardous situation - it can destroy your electronic equipment, possibly start fires, and in some situations electrocute you (ie: some US jurisdictions require the stove frame connected to neutral). If this happens, contact your electrical authority immediately and have them come and check out the problem. Note: a brief (< 1 second) brightening is sometimes normal with lighting and motors on the same 220V with neutral circuit. A loose main panel neutral will usually show increased brightness far longer than one second. In case of doubt, get help. Subject: What is 3 phase power? Should I use it? Can I get it in my house? Three phase power has three "hot" wires, 120 degrees out of phase with each other. These are usually used for large motors because it is more "efficient", provides a bit more starting torque, and because the motors are simpler and hence cheaper. You're most likely to encounter a 3 phase circuit that shows 110 volts between any hot and ground, and 208 volts between any two hots. The latter shows the difference between a normal 220V/110V common neutral circuit, which is 240 volts between the two hots. There are 3 phase circuits with different voltages. Bringing in a 3 phase feed to your house is usually ridiculously expensive, or impossible. If the equipment you want to run has a standard motor mount, it is *MUCH* cheaper to buy a new 110V or 220V motor for it. In some cases it is possible to run 3 phase equipment on ordinary power if you have a "capacitor start" unit, or use a larger motor as a (auto-)generator. These are tricky, but are a good solution if the motor is non-standard size, or too expensive or too big to replace. The Taunton Press book ``The Small Shop'' has an article on how to do this if you must. Note that you lose any possible electrical efficiency by using such a converter. The laws of thermodynamics guarantee that. Subject: Is it better to run motors at 110 or 220? Theoretically, it doesn't make any difference. However, there is a difference is the amount of power lost in the supply wiring. All things being equal, a 220V motor will lose 4 times less power in the house wiring than a 110V motor. This also means that the startup surge loss will be less, and the motor will get to speed quicker. And in some circumstances, the smaller power loss will lead to longer motor life. This is usually irrelevant unless the supply wires are more than 50 feet long. Subject: What is this nonsense about 3HP on 110V 15A circuits? It is a universal physical law that 1 HP is equal to 746 watts. Given heating loss, power factor and other inefficiencies, it is usually best to consider 1 HP is going to need 1000-1200 watts. A 110V 15A circuit can only deliver 1850 watts to a motor, so it cannot possibly be more than approximately 2 HP. Given rational efficiency factors, 1.5HP is more like it. Some equipment manufacturers (Sears in particular, most router manufacturers in general ;-) advertise a HP rating that is far in excess of what is possible. They are giving you a "stall horsepower" or similar. That means the power is measured when the motor is just about to stop turning because of the load. What they don't mention is that if you kept it in that condition for more than a few seconds hopefully your breaker will trip, otherwise the motor will melt -- it's drawing far more current than it can continuously. When comparing motors, compare the continuous horsepower. This should be on the motor nameplate. If you can't find that figure, check the amperage rating, which is always present. Subject: How do I convert two prong receptacles to three prong? Older homes frequently have two-prong receptacles instead of the more modern three. These receptacles have no safety ground, and the cabling usually has no ground wire. Neither the NEC or CEC permits installing new 2 prong receptacles anymore. There are several different approaches to solving this: 1) If the wiring is done through conduit or BX, and the conduit is continuous back to the panel, you can connect the third prong of a new receptacle to the receptacle box. NEC mainly - CEC frowns on this practise. 2) If there is a copper cold water pipe going nearby, and it's continuous to the main house ground point, you can run a conductor to it from the third prong. 3) Run a ground conductor back to the main panel. 4) Easiest: install a GFCI receptacle. The ground lug should not be connected to anything, but the GFCI protection itself will serve instead. The GFCI will also protect downstream (possibly also two prong outlets). If you do this to protect downstream outlets, the grounds must not be connected together. Since it wouldn't be connected to a real ground, a wiring fault could energize the cases of 3 prong devices connected to other outlets. Be sure, though, that there aren't indirect ground plug connections, such as via the sheath on BX cable. The CEC permits you to replace a two prong receptacle with a three prong if you fill the U ground with a non-conducting goop. Like caulking compound. This is not permitted in the NEC. Subject: Are you sure about GFCIs and ungrounded outlets? Should the test button work? We're sure about what the NEC and CEC say. Remember, though, that your local codes may vary. As for the TEST button -- there's a resistor connecting the LOAD side of the hot wire to the LINE side of the neutral wire when you press the TEST button. Current through this resistor shows up as an imbalance, and trips the GFCI. This is a simple, passive, and reliable test, and doesn't require a real ground to work. If your GFCI does not trip when you press the TEST button, it is very probably defective or miswired. Again: if the test button doesn't work, something's broken, and potentially dangerous. The problem should be corrected immediately. The instructions that come with some GFCIs specify that the ground wire must be connected. We do not know why they say this. The causes may be as mundane as an old instruction sheet, or with the formalities of UL or CSA listing -- perhaps the device was never tested without the ground wire being connected. On the other hand, UL or CSA approval should only have been granted if the device behaves properly in *all* listed applications, including ungrounded outlet replacement. (One of us called Leviton; their GFCIs are labeled for installation on grounded circuits only. The technician was surprised to see that; he agreed that the NEC does not require it, and promised to investigate.) Subject: How should I wire my shop? As with any other kind of wiring, you need enough power for all devices that will be on simultaneously. The code specifies that you should stay under 80% of the nominal capacity of the circuit. For typical home shop use, this means one circuit for the major power tools, and possibly one for a dust collector or shop vac. Use at least 12 gauge wire -- many power tools have big motors, with a big start-up surge. If you can, use 20 amp breakers (NEC), though CEC requires standard 20A receptacles which means you'd have to "replug" all your equipment. Lights should either be on a circuit of their own -- and not shared with circuits in the rest of the house -- or be on at least two separate circuits. The idea is that you want to avoid a situation where a blade is still spinning at several thousand RPM, while you're groping in the dark for the OFF switch. Do install lots of outlets. It's easier to install them in the beginning, when you don't have to cut into an existing cable. It's useful if at least two circuits are accessible at each point, so you can run a shop vac or a compressor at the same time as the tool you really want. But use metal boxes and plates, and maybe even metal-sheathed cable; you may have objects flying around at high speeds if something goes a bit wrong. Note that some jurisdictions have a "no horizontal wiring" rule in workshops or other unfinished areas that are used for working. What this means is that all wiring must be run along structural members. Ie: stapled to studs. Other possible shop circuits include heater circuits, 220V circuits for some large tools, and air compressor circuits. Don't overload circuits, and don't use extension cords if you can help it, unless they're rated for high currents. (A coiled extension cord is not as safe as a straight length of wire of the same gauge. Also, the insulation won't withstand as much heat, and heat dissipation is the critical issue.) If your shop is located at some remove from your main panel, you should probably install a subpanel, and derive your shop wiring from it. If you have young children, you may want to equip this panel with a cut-off switch, and possibly a lock. If you want to install individual switches to ``safe'' particular circuits, make sure you get ones rated high enough. For example, ordinary light switches are not safely able to handle the start-up surge generated by a table saw. Buy ``horsepower-rated'' switches instead. Finally, note that most home shops are in garages or unfinished basements; hence the NEC requirements for GFCIs apply. And even if you ``know'' that you'd never use one of your shop outlets to run a lawn mower, the next owner of your house might have a different idea. Note: Fine Woodworking magazine often carries articles on shop wiring. April 1992 is one place to start. Subject: Underground Wiring You will need to prepare a trench to specifications, use special wire, protect the wire with conduit or special plastic tubing and possibly lumber (don't use creosoted lumber, it rots thermoplastic insulation and acts as a catalyst in the corrosion of lead). The transition from in-house to underground wire is generally via conduit. All outdoor boxes must be specifically listed for the purpose, and contain the appropriate gaskets, fittings, etc. If the location of the box is subject to immersion in water, a more serious style of water-proof box is needed. And of course, don't forget the GFCIs. The required depths and other details vary from jurisdiction to jurisdiction, so we suggest you consult your inspector about your specific situation. A hint: buy a roll of bright yellow tape that says "buried power line" and bury it a few inches above where the wire has been placed. Subject: Aluminum wiring During the 1970's, aluminum (instead of copper) wiring became quite popular and was extensively used. Since that time, aluminum wiring has been implicated in a number of house fires, and most jurisdictions no longer permit it in new installations. We recommend, even if you're allowed to, that do not use it for new wiring. But don't panic if your house has aluminum wiring. Aluminum wiring, when properly installed, can be just as safe as copper. Aluminum wiring is, however, very unforgiving of improper installation. We will cover a bit of the theory behind potential problems, and what you can do to make your wiring safe.