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#174364 - 02/02/08 10:25 PM Basic electrical question & safety  
Clueless  Offline
New Member
Joined: Feb 2008
Posts: 2
Asia Pacific
Hi all,

Not being from an electrical field, I was hoping to get some clarification from you guys regarding the use of extension cords vs. plugging into a regular wall socket.

One of the electrical/fire safety recommendations is to never overload a power socket, i.e. from plugging too many appliances into a single wall socket, or to daisy-chain extension cords off a single wall socket. They always recommend installing more wall sockets if you require more plugs, to avoid overloading / overheating.

However, I have seen electricians installing additional wall sockets by just connecting the new sockets in parallel to the existing one, i.e. they are not running a new cable from the DB. Is this the right way of doing it, cos wouldn't that be the same as using an extension cord off a single wall socket?

Sorry if my post sounds ignorant, but I really am with regards to electrical matters, and would really appreciate some help. Thanks!


Arc Flash PPE Clothing, LOTO & Insulated Tools

#174368 - 02/02/08 11:36 PM Re: Basic electrical question & safety [Re: Clueless]  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
It's not as ignorant a question as it may seem.

The connection of any plug with the receptacle isn't likely to be nearly as sure as the connection made in a properly use wire-nut.
Pull the plug out just a little, and there's even less contact area ... which leads to heating, which may start a fire, etc.

More important, perhaps, is that most extension cords are a lot thinner wire than what is used in the walls. Overload the wire, and the wire itself gets hot.

I'm sure you've removed plugs that felt warm, even hot. Not only is the cord overloaded, but the connections inside the plug probably aren't very good.

Finally, a cord is out there to get tripped over, stepped on, squashed ... and might very well be damaged. That damage can then cerate additional risks.

#174375 - 02/03/08 10:00 AM Re: Basic electrical question & safety [Re: renosteinke]  
Clueless  Offline
New Member
Joined: Feb 2008
Posts: 2
Asia Pacific
Thanks.. good point about the thickness of the wires in the walls vs extension cords. However, was the electrician right in creating a new wall outlet by just connecting the wires in parallel to an existing socket, instead of pulling a new connection from the main circuit breaker?

#174376 - 02/03/08 10:58 AM Re: Basic electrical question & safety [Re: Clueless]  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
In general, yes. Or, to be more correct, he was not 'wrong.' That is, he broke no rules.

There are circumstances where various codes require dedicated circuits, or limit the number of receptacles on a circuit, but these rules probably don't apply to the receptacle you describe.

This brings up the next question: Was simply extending the circuit the wise thing to do? The answer to that has a lot to do with what the electrician knew about the intended use of the receptacle.
For example, if this was to add a receptacle to a mud room, so that you could plug in a space heater .... it would have been wiser to run a new circuit from the panel.
If the intent was to have the bedside table served by a receptacle that wasn't buried behind the bed, extending the existing circuit made wonderful sense.

#174391 - 02/03/08 08:29 PM Re: Basic electrical question & safety [Re: Clueless]  
hardwareguy  Offline
Joined: Jun 2007
Posts: 50
Not only are the conductors in most extension cords thinner, the contacts inside are not robust. They aren't rated for continuous duty at their rated current in the majority of cases.... you may have seen the phrase "temporary power tap" on multiple outlet extension cords and plug strips and the intermittent duty ability of the contacts is the main reason for this.

For high drain appliances, the rule is one size thicker than the appliance cord. So, if your space heater has a 16AWG cord, the proper extension cord would be 14AWG. The bigger cords have more robust contacts and the increased wire size minimizes resistance which lessens power lost as heat along the line.

For power strips, it's different: no more than about 8A per outlet even though the total rating may be 15A. The outlets on most strips are designed with lower drain electronic equipment in mind for the most part. While fixing computers, I have seen space heaters plugged into strips and the scary thing is the plug has melted itself to the strip and is inseparable!

The heater was only drawing 12A while the strip was good for 15A total but clearly each individual plug cannot handle the full load. To my dismay, this is almost never mentioned in any handbook that comes with one of these strips.

#174403 - 02/04/08 08:05 AM Re: Basic electrical question & safety [Re: hardwareguy]  
SteveFehr  Offline
Joined: Mar 2005
Posts: 1,213
Chesapeake, VA
The national electric code does not (generally) restrict the number of electrical receptacles that can be put on a single breaker. This is because the breaker is designed to protect the cabling. No matter how much you plug into those receptacles, the breaker will prevent you from overloading the wire. In a typical home, most are either unused or serving loads with negligible or very low current draw. (DVD players and TVs don't draw all that much. Clock radios draw practically nothing at all.) The largest cord & plug current loads in a house are things like coffee pots, hair dryers, curling irons, space heaters, microwaves- basically things designed to heat up as quickly as possible. With the exception of space heaters, most of these are on for very little. And kitchens and bathrooms- the location of most of the high-current appliances- DO have special restrictions on receptacles.

Appliances are designed and tested for power consumption. They are designed to never draw more than 15A, which is the maximum design current for a typical 3-prong plug, which is what protects the plug from overloading- even if there is a 20A breaker, that coffee pot or hair dryer will never draw more than 15A. This is all fine and good until the homeowner plugs in a 10A extension cord with a splitter and plugs several "15A" plugs into it, defeating the deliberate rating and testing process. (This is why power strips are so frowned upon, even if they do have that worthless little 15A breaker.)

The electrical code prohibits "permanant" extension cords because they present a much higher risk of fire than permanant electrical cabling, as they're more exposed to damage. The national fire protection association doesn't care that you have your lamp further away from the outlet than the cord will reach- they just would rather you have a safe place to plug it in.

#174425 - 02/04/08 08:15 PM Re: Basic electrical question & safety [Re: SteveFehr]  
richxtlc  Offline
Joined: Sep 2007
Posts: 10
Tampa, FL
Actually the code does limit the number of recepticles that can be placed on a circuit. A 15 amp circuit is 10 and a 20 amp circuit is 13. This is based on 180VA per common bus on each outlet. Therefore, you cannot just add an outlet just because you need one. See below:
220.14(I) Receptacle Outlets. Except as covered in 220.14(J) and (K), receptacle outlets shall be calculated at not less than 180 volt-amperes for each single or for each multiple receptacle on one yoke. A single piece of equipment consisting of a multiple receptacle comprised of four or more receptacles shall be calculated at not less than 90 volt-amperes per receptacle. This provision shall not be applicable to the receptacle outlets specified in 210.11(C)(1) and (C)(2).

#174430 - 02/04/08 09:21 PM Re: Basic electrical question & safety [Re: richxtlc]  
electure  Offline

Joined: Dec 2000
Posts: 4,262
Fullerton, CA USA

220.14(I) Receptacle Outlets. Except as covered in 220.14(J)

You're right, but only for other than dwelling occupancies and guest rooms of hotels.

Read on:
(J) Dwelling Occupancies. In one-family, two-family, and
multifamily dwellings and in guest rooms or guest suites of
hotels and motels,

#174447 - 02/05/08 07:59 AM Re: Basic electrical question & safety [Re: electure]  
SteveFehr  Offline
Joined: Mar 2005
Posts: 1,213
Chesapeake, VA
Yes, I was referring to residences specifically because that was the OP's question. Nothing stopping an electrician from putting every room but the kitchen and bathroom on a single 15A AFCI receptacle circuit.

Well, aside from fear of bodily harm when the HO moves in wink

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