This page is from the original Code Check website. To see the latest version choose "Home Page New"
This page is from the original Code Check website. To see the latest version choose "Home Page New"
|
Electrical Q & A
|
|||||||||||||||||
Could you possibly tell me, according to the code book, can i install a outlet to the interior floor of a house. what section would i find this in the code book... BENJAMIN HERRERA <benjaminX_m_herrera@ccm.rr.intel.com>
I know of no restriction on the use of floor outlets in residential construction in the National Electric Code. If the outlet is being used to comply with the requirements for receptacle outlet spacing(6ft. rule) it must not be farther than 18" from the wall.Section 210-51(a). Also, if there are hanidcap requirements a floor outlet would not qualify.
My kitchen was renovated recently and the receptacle mounted at the washing machine was a three prong grounded recpt, the inspector said there has no ground so it must be replaced. It was replaced with an old two prong non-grounded recpt. Doesn't this require a GFIC recept? Even though the kitchen was renovated, the receptacle was an original. Doesn't it still require ground protection since it does feed the washing machine and is located approx 5 inches from the washing machine water pipe? February 9, 1997Mr. William R. Davis<QKRE82A@PRODIGY.COM>
Hazard- Current finding a path through a human heart via a faulty appliance chasis to a grounded surface. Electrocution
The National Electric Code does not require a GFCI(Ground Fault Circuit Interupter) receptacle for a washing machine. Even in a garage where GFCI's are the rule a GFCI might not be required if the receptacle is dedicated and the receptacle outlet is made inaccessible by the appliance, some would argue exempts the GFCI requirement.
If the work you are doing is considered new work by the JHA this could mean it needs to meet 1993 NEC standards which would mean a grounded three prong receptacle. If the outlet is within 6 feet of sink it would require GFCI protection.
If it is considered existing construction it may either be installed with a 2 prong receptacle, replaced with an ungrounded GFCI or the code makes provision to run a separate equipment ground wire(green #12 min.) to bond the metal of the appliance to a well grounded cold water system..
A GFCI does not require an equipment ground to operate under a ground fault condtion. The equipment ground is only required to utilize the test button(there are other safe ways to test ungrounded GFCI's receptacles).
Under all circumstances installing a GFCI would be a good idea anywhere in proximity to a grounded surface such as metal piping, earth/soil or exposed concrete.
See: Grounding for more information.
A reader wrote and asked if a steel stud framing system needs to be grounded.
The National Electric Code(NEC) does not specifically deal with this question. No surprise there. Like a Medieval alchemist scouring the esoterica of the Kaballah, one has to dig deep into the arcane reaches of Section 250 of the NEC (for more see grounding) to answer this question.
In Section 250 there are two citations that mention "structural metal frame of a building".
Section 250-58a says the metal frame must not be used as the equipment grounding conductor for ac equipment. The intent here is to make sure that any electrical faults to equipment are carried off to the equipment grounding conductor that must be run with the conductors supplying the piece of equipment(250-57b & 250-59 ) and not through an unreliable path like the steel studs.
Section 250-81b says the metal frame must be part of the Grounding Electrode System when the frame is intentionally grounded. This is most commonly interpreted to mean that the steel structure of a large commercial building will be electrically connected to the earth. In a one or two family dwelling structure this may or may not be true. Steel studs are often used in conjunction with wooden laminated beams or isolating treated wood mud sills. If the entire structure is framed in metal and lightning is a significant threat then the structure should be effectively bonded to the GES. (see NFPA 780-1992(ANSI) and local jurisdiction)
The key to these apparently contradictory requirements is the need to understand the two distinct functional systems being written about. Although electrically connected, the Equipment Grounding System and the Grounding Electrode System have two different purposes.
The Equipment Grounding System is designed to clear equipment faults(shorts to metal surfaces of appliances or tools) that are part of the premises wiring. The Grounding Electrode System is primarily there to provide an alternative path for external voltages(lightning and utility surges) so they do not find their way through your home.
In the California city where I have been an electrical inspector for 11 years we do not require any specific grounding requirements for steel studs. Any steel electrical boxes or metal equipment that might be attached to steel studs must always be grounded, effectively grounding the studs to the equipment grounding system.
"In my opinion: Steel frames in residential building serve-as support and as pass-thru of NMC cables, as such there is a possibility to become energized. Thus, steel frames should be "grounded". On this type of construction it is not mandated to install metal boxes, therefore the "grounding...through metal boxes" should not be taken for granted. see 250-80(b) and (FPN)."
We discussed this further and agree that a bonding jumper from the frame should be provided if plastic boxes are used in a steel frame and should be sized to the largest breaker size that feeds the specific section of wall.
"I ground by using at least one metal box in each circuit. I would be interested in responses to this practice."
First of all, lightning rods are not designed to attract or conduct current from lightning. They are designed to dissapate and prevent the build up of the negative static charge that is necessary to cause a lightning strike. That is why they are made with a sharp point on the end. A sharp point on the end of a conductor will force ions into an ever-decreasing amount of space until their electrical potential forces them to "escape" or "jump" into the surrounding atmosphere thereby neutralizing the difference in potential of the lightning static field to ground.. If lightning rods were intended to be conductors of lightning, they would be spherical on top to retain, and therefore attract, as much of the opposite charge (negative), to lightning static field charge (positive). After all, in electricity, as in other things, opposites attract. The spherical top retaining a charge can be observed at work in a Van DeGraff (sp?) generator.
Also, if a lightning rod were meant to safely conduct the thousands and thousands of amps of a lightning strike, it would be a few feet in
diameter with a cable the diameter of a tree trunk running to a ground rod as big as the lightning rod. Anything else would melt under the demands of such a large current surge before the full charge was transmitted to the ground. All this, however, has little to do with the subject at hand. What course lightning (millions of volts) takes and what course standard household current (240/120VAC - nominal) takes, are two different things.
Lightning can jump several miles through air with no other apparent conductor, household voltage can do 1/2" tops. If lightning can go through
even 1000 feet of air, why can't it go through a few layers of 3/4" plywood and 1/2" sheetrock and, conversly, through you, like a microwave
through a cheap burrito in a convienence store? :) Therefore, attracting lightning is a worse idea than repelling it. Hence, lightning rods.
Air conditioners/refrigerators/multi-phase electrical appliances:
Often the coils are being held at ground potential to prevent the build-up of eddy currents (I'm phrasing this horribly -- it's 1:15 AM and it's been about a dozen years since I learned/used this stuff) which can ultimately cause a fire to erupt. These eddy currents can also cause the casing to rise in potential (voltage), thus creating a serious hazard to the user (you).
Microwaves, Computers, similar electronic appliances:
The ground serves to establish a baseline voltage as a reference point for all internal circuitry operations. Having used instrumentation systems on a poorly grounded electrical system, I can tell you that the ground can be VERY important for instrumented experiments; however, they are also important for these devices. [Some may argue that the Common and Ground are equal, but I'm not sure that the internal wirings make that assumption.] A floating ground can drive these devices nuts!
Automotive Circuits:
The ground also serves as the return, and provides the final leg of the circuit.
Electrical shielding/Cable TV/Antennas/Coaxial cables:
The ground serves to nullify the effects of stray signals by "grounding out", or reducing to a zero potential, the voltages which are picked up by the outer shield. This prevents much of that signal potential from reaching the inner wire core. Your home: Prevents ground loops (mentioned in the next paragraph) which could enable your lamp, air conditioner, and bathtub to be at various potentials when referenced to each other. In other words, it prevents you from being able to touch two devices at the same time and get shocked. [Note that modern homes have so many redundancies in this area that the grounding isn't as critical as it once was -- especially if you have copper plumbing. On the other hand, if you have PVC and poly plumbing, then it may be quite essential.
Your lightning rod or roof antenna:
The ground wire provides a direct path for the electrical current to reach ground, so that the lightning current (theoretically) doesn't attempt to burn its way through your homestead. Thus, much damage is avoided. The term "ground", from what I've learned, comes from connecting the circuit to the ground itself (as in soil) which serves as a theoretically unlimited source of electrons to nullify any potentials (voltages) which may build. Having worked instrumented experiments in the outdoors, I can also tell you that ground loops can be fun to deal with. In these situations, two grounds are emplaced without interconnection, and they thus have a potential difference between them. This can also wreak havoc on an experiment (or body) if they are assumed to be at the same potential. Hope that helps. I'm sure it will fuel some valuable conversation from our news group compatriots.
I understand that the motor to a Whirlpool tub requires a disconnect. Would the test button on a GFI installed near the service access panel qualify? The motor would be hard wired through the GFI on the load side of the receptacle.
Terms
Hydromassage is the word used in the NEC to describe an electrically driven pump used in a bathtub whose water is replaced with each usage. The commercial names Jacuzzi or Whirlpool are commonly used to describe a hydromassage.
A Spa on the other hand is used to define a tub that holds water from bath to bath.
Disconnects (more info.)are required for any motor. This can be any switch that is rated for the running load(amps) imposed. The basic rule is the "In sight rule", requiring that the disconnect be visible from the motor but never more than 50 feet away(unless it has provision for a padlock.
Safety Consideration
Motors require servicing. When a service person is installing or removing a motor they want to be absolutely certain the equipment they are working on will not become energized or start rotating without warning, hence the requirement for an "in sight disconnect".
Discussion
In all the jurisdictions I've worked, a cord cap(plug) is an acceptable and prefered disconnect for this application. Strict interpretation of the code would disallow it, so you have to check with the specific jurisdiction. It would almost certainly not be acceptable to use the test button on the GFI as this would violate the manufacturers listing and would not clearly display that the motor was disconnected.
There are special GFI's that are listed as switches, however, in 15 years of inspecting electrical systems I have yet to see one, so it is unlikely the GFI you mentioned is so listed.
Subject: Re: 310-19 Note 3
Date: Sat, 19 Apr 1997
Reply-To: redwood@codecheck.com
Organization: CodeCheck.com
To: jjjones@primenet.com
J.Joe Jones wrote:
>
> Redwood,
>
> Having read some of your positions on electrical questions relating to the NEC I would like your opinion on a specific circumstance.
>
> An existing 100 ampere electrical service is to be upgraded to 200 amperes. The location of the new 200 ampere service will be approximately 60 feet from the existing service location.
>
> Because of the location of the existing 100 amp service no additional loads are likely to be installed at any time in the future due to the physical constraints of the panel.
>
> The service entrance conductors of the existing service are typical #4 AWG copper and there has never been an overload of the 100 ampere service disconnect. Aside from the other considerations of converting the existing service into a subpanel, would you accept a feeder circuit consisting of #4 copper conductors protected with a 100 ampere circuit breaker to used for the feeder, which is essentially what is occuring presently.
IMHO- Sounds reasonable, but my opinion isn't what counts. If I was Master of the Universe your job would pass, but I'm not. Your inspector will be the judge and jury of this decision. His take on this will probably be based on Note 3 at the back of Table 310-19. Strickly interpreted the code text disallows the special upratings allowed for sub-feeders which don't "...serve as the main power feed". Your sub-panel would only be a portion of the "...main power feed". Many interpret this to mean a 100 amp feeder may be sized to the special exemptions allowed in this table only if they are the only load coming out of the service. Extending the logic the Note 3 sizing would be allowed for a 200 amp feeder from a 200 amp panel(2/0 AWG copper).
IMHO- the intent of this section is to recognize the reality of
residential electric loads. They are intermittent. Lots of cush is built into residential load calcs. I would say re-feeding the old service with a 4/3 copper cable assembly is a safe and reasonable installation.Performance record should contribute to the figuring here.
Date: Tue, 22 Apr 1997
Newsgroup: misc.consumers.house
Andrew Crabtree wrote:
I have recently been looking at houses that were built in the 20's and 30's and some of them still have the original electrical wiring. These have no ground. I was wondering what my main problem with the two pronged wiring would be, and approximately how much it would cost to upgrade a house of approximately 1400sqf. The house has a crawl space, if that helps.
For the most part, houses of this vintage were *originally* wired in a style of wiring called knob and tube wiring.To see some illustrations of this wiring method go to:
Knob & TubeThere is no longer an easy way to install an equipment ground with Knob and Tube. Until 96' codes it was okay to ground to water piping at any convenient location. Since 96' you have to take equipment grounds all the way back to within 5ft. of the main grounding electrode. Two pronged wiring is only a problem where you have appliances that require an equipement ground(3 prongs).
2 prong plugs that are located in shock hazard areas(plumbing, concrete floors and soil) can be replaced with ground fault circuit interrupters(they can protect against shock even when an equipment ground is not connected).
Left alone, knob and tube wiring is a safe and reliable system. The problems with knob and tube have to do with later day modifications and additions that were done by unqualified installers.
A further caution about house wired in the twenties: For about 8 years during the twenties it was permitted to fuse and switch neutrals(now strictly forbotten). This makes for some shocking experiences for young electricians who havn't been wisened to this aberration in the code.
Furthermore, because the neutrals might be fused in a 20's house one can easily think there are twice as many circuits as there really are.
A sign that work was "boot-legged" by underqualified installers is if you see knobs installed on the underside of floor joists in a crawl space or on the top of ceiling joists in the attic. This was never to
code and is the sign of amateur work. Knob and Tube wiring is designed to be installed in the concealed spaces between joists. If you peek into a crawl space and see wires running under joists the system probably needs to be rewired.I havn't "worked with the tools" in a while so can't begin to give you price estimates of such work.
In the late 30's when household appliances started to take hold, systems were often upgraded with a type of cable assembly called Armor Clad Cable(commonly refered to as BX). 2 prong outlets that are fed with BX cabling can usually be ground very easily because the metal sheathing of the cable is an acceptable grounding path.
Subject: Re: Birds
on Wires
Date: 5 May 1997 20:35:50 GMT
From: "Bill Harnell" <bharne@adss.on.ca>
Organization: None
The potential present is determined by Ohm's Law and will be the result of
the voltage drop in the one inch or so (a small bird <G>) of the conductor
caused by the current flow through it.The formula for determining that voltage drop is: E=IR or, Voltage (E) is
equal to the current flow in Amperes (I) multiplied by the resistance (R)
of that portion of the conductor.So, if 10 Amps of current are flowing through an AWG #6 conductor (whose
resistance per mile is 2.229 Ohms or .0000351 Ohms per inch) the
Voltage=10*.0000351 which equals 0.000351 Volts or 351 microvolts, hardly
enough to do any harm to anything!
Subject: What is 2
phase and 3 phase mean?
Don Klipstein wrote:
> JBOBST (jbobst@aol.com) wrote:
> : Three phase power is almost never available for
residential use. It's a
> : pity because a 3Ph motor for a given HP rating is much
smaller and less
> : complicated than single Ph (no starting windings or starting
capacitors),
> : not to mention cheaper to buy and operate.
> : Two phase is some kind of oddity. I have never seen it
in use.
>
> I have seen a 2-phase motor. This is indeed uncommon. 2-phase
power
> is even more uncommon. You can convert 3-phase to 2-phase
with
> transformers (requires some knowledge of trig and electrical
engineering
> to figure out how it works).
>
> 3-phase involves three phases 120 "electrical degrees"
(1/3 cycle)
> apart. 6-phase is similar enough; converting from one to
another merely
> involves reversing transformer sedcondary windings or using
centertapped
> secondary windings. (There could be an alternate definition
of 6-phase,
> involving phases 30 degrees apart, and as interchangeable
with "12-phase"
> [Ha!!!!] as the
above definition of 6-phase is with 3-phase.)
>
> "2-phase" is sometimes incorrectly used as referring
to 240 volt
> centertap usable to make separate 120 volt circuits. True
2-phase
> involves circuits 90 degrees apart, meaning approx. 169 volts
betewwn 120
> volt "hots" of the different phases. As I mentioned
above, 2-phase and
> 3-phase can be converted from one to the other (either way)
by an oddball
> combination and voltage of transformers. This means that
if you have a
> 2-phase motor, you are likely to need a "phase changer"
(oddball
> transformer setup). I think that 2-phase motors, although
rare, are muchç> less common than 2-phase power to run
them.
In article wegrzyn@garbagedump.com (Chuck Wegrzyn) writes:
> I am installing an in-ground, liner pool that is framed
with metal
> walls. In reading the NEC manual, it states that a properly
wired
>pool system requires the pool walls (the metal frame) to be
grounded.
> This seems pointless to me - the metal walls are in contact
with
> the ground, and given that I live in the Boston area, the
surrounding
soil is damp. As a result the pool is already grounded.
>
> [snip]
>
> Also, the electrican stated that if I have a metal fence
put up,
> will need to have it grounded as well. I told him that I
would just
> sink the poles in the ground a little further than the concrete
edge
> and that would do it. He said I was wrong - I think he's
an idiot.
> Anything wrong with this?
He is not an idiot. And neither is code.
The key word here is 'equipotential'.
It means all these bits of metal (or other conductive stuff) which
you
may come in contact with are at the same voltage potential, so
you don't
get a potential differece across your body.
The only way you can ensure equipotential condition is
met is to 'bond'
all these bits of metal and stuff together. The concept of 'ground'
has
little to do with this, as the potential across bits of ground
(as in
soil) varies.
If you rely on soil as a 'ground' then you can fall foul of
potential
gradients between grounding conductors. This can be more serious
than
it sounds. The voltage across ground can be fairly high, in the
range
of several tens of volts. There used to be a very neat diagram
in an
older version of the IEE regs (the UK equivalent of 'code') showing
a
cow getting fried due to fault current between grounding eletrodes
causing a potential gradient across a farm enough to kill a cow.
In another newsgroup recently there was a case of a fish hatchery
having
all it's (fishy) inmates electrocuted on a regualr basis due to
faults
on an overhead line several miles away.
I would treasure your electrician. I (speaking from the UK) have
this
view that Yanks in general don't take earthing (or socket polarity)
seriously, and view much American electricity (particularly the
rural
domestic variety) as downright dangerous. Sounds like you've found
a
spark that takes earthing seriously.
----------------------------------------+------------------------------------
David Buckley of Electric Solutions Ltd | Email: dbuckley@esl.tex.com
Services to the Computing,Electronics |
and Entertainment industries. |
Calling from South London, in the UK |
Back to Table of contents
Subject: Receptacle Ground Up or Down?
Date: Fri, 09 Jan 1998
From:
Code Question of The Day <codeedit@ecmag.com>
Dear Subscriber:
Here's a comment on Question 84 that you might find interesting.
Joe Salimando
moderator
************
> QUESTION 84
>
> Does the NEC require that the standard 125v, 15A & 20A
grounded > receptacles be installed in such a manner that the
> ground position is in the down (closest to the floor) position?
>
> ANSWER
>
> The NEC has no requirement for the receptacles in question
to be > installed in any particular orientation. >
> However, some areas of the country have required a > specific
orientation.
************
COMMENT FROM MR. SMITH
Seeing how gravity is un avoidable, it is a good idea to install receptacles so that the ground is up, or the neutral up (horizontally) to help prevent accidental contact with live circuit conductors.
I once went on a service call where a paper clip had fallen behind a desk and shorted a isolated ground receptacle, causing a total failure of the point of sales system. this receptacle was installed in the traditional ground down "sleepy face" position.
Richard Smith
[For you electrical code buffs this is a very interesting mail server http://www.ecmag.com/freebies/freebies.htm]
>Ok, I can't figure this out. If anyone can help, I will
be very grateful. All of a sudden the electric in my house is
freakin out.
>Everything sends surges (I think), when they turn on (fridge,
washer,
>microwave, heaters, water heater, etc.). This never used to
happen, it's
>just all of a sudden. If anyone wants more details, let me
know.
To: mrjones@nvsn.com
Out at the street is the power companies transformer. The secondary winding is at 240 VAC with a center tap. That means the transformer supplies two 120 VAC circuits or a single 240 VAC supply, depending on what it is that your house happens to need in various places around the house. It takes three wires -- two hots and a neutral -- to deliver that service. (The safety ground wiring is another topic.)
Now, consider what happens if that center tap is not securely connected all the way through to your house and it's circuit breaker panel. The center voltage between the two opposite 120 VAC rails can wander around and can wander around considerably if the connection is completely open by a loose connection. 240 VAC appliances, such as the clothes dryer, don't care about the wandering center line. But your lights etc do very much care. If per chance the lighting etc load on both sides happens to be in balance, then lighting will be in balance. But if more lights etc are drawing current on one side, then that side will load down, lets say to 90 volts, in which case the other side will be up at 150 VAC which is plenty enough to start frying light bulbs, even explosively. So, a few light bulbs blow up, reducing the load on that side and so the imbalance gets even worse.
Quite often the symptoms that you describe are due to a loose connection owned by the power company. So, I'd call them up immediately and report the problem. It is also possible that the loose connection may be one that you own, in which case you may need to call an electrician. The chances are most likely that the power company has a problem to fix for you. I'd be surprised if you have any trouble getting them to hussle out and take a look. In the mean time you might consider shutting down the main breaker before you fry any light bulbs or worse around the house.
If I've miss read the symptoms, tell me more. If I've read you right, you have a serious problem that you need to solve right away.
Subject: Re: Light
Bulbs....Open Neutral
Date: Thu, 29 May 1997
From: redgate@tulsa.oklahoma.net (Kirk Kerekes)
Newsgroups: alt.home.repair
In article <338b7f89.3866335@parlor.hiwaay.net>, vpdura@hiwaay.net
(Vic
Dura) wrote:
. hicks@millcomm.com wrote:
.
. >Simple: The source is 220V (okay, 240V), not 110V. The pole
transformer
. >puts out 240V, but the center tap is grounded so that you
get two 120V to
. >ground legs. But if the center tap isn't properly connected
with the
. >house's neutral, and if there's a higher load resistance
on one side vs
. >the other, then you can get a higher voltage on the high
resistance side.
In most defective systems there isn't a "high resistance side", if the tap to neutral is poor or (sigh) nonexistent then both 120V "sides" see a poor (or zero) neutral connection. As a result, if side A has the the highest current draw at any given instant, it has the lowest line voltage, while the other side has (240V - A) volts. This leads to the signature symptom of bad neutral -- lights getting _brighter_ when a major 120V appliance comes on.
This does not only afflict older homes -- I saw this in a very nice, 1980's era suburban home in an affluent suburb of Dallas -- and the residents had been living with it for _years_. A call (well, two calls) to their power utility got the problem resolved.
Most houses these days are wired with ROMEX(tm) or its equivalent, so that each branch circuit has its own neutral running back to the breaker box, where the neutrals are all ganged together on a buss-bar and tied into the service neutral. As a result, there are very few places to look for a bad connection if you have a house-wide open neutral condition. An electrician or knowledgeable homeowner can spend 10 minutes with a screwdriver and fix most in-house neutral defects in such a system by tightening all the neutral screws. If this doesn't fix the problem, the difficulty probably resides with stuff belonging to the power company, and a phone call to them is in order.
A new house (or new breaker box) can frequently benefit from a round of screw-tightening after it has been in service for a few months -- the copper wires tend to deform under the screw pressure. This applies to the clamping screws in circuit breakers also, although they use pressure-distributing clamps that appear to minimise the problem.
Some homes are wired "Edison style" in which each branch circuit is sort of a miniature version of the service circuit: two 120V branches with a common neutral. Defects in that common neutral can generate very bewildering symptoms that mimic whole house neutral defects. Edison circuits also cannot be used with normal 120V GFCI breakers -- although you ought be able to use the new (and expensive) 240V GFCI breakers on them.
--
Kirk & Diane Kerekes
Redgate@Tulsa.oklahoma.net
Check ©1998
by Redwood Kardon
