Thread Tools
Old 01-01-2006, 12:03 AM
Guest
Join Date: May 1999
Location: Up there, waiting
Posts: 17,203
Why do some electrical devices have polarized plugs and others do not?

Well?
Old 01-01-2006, 12:26 AM
Charter Member
Join Date: Jan 2003
Location: Richmond, VA
Posts: 22,536
Generally, if it is important for safety that the hot and neutral be in one arrangement rather than the other, then a polarized plug is used. One example of this is in a lamp. Since unscrewing a bulb to replace it necessarily exposes one of the electrical connections, it is best that this connection be the neutral. The only way to guarantee this is to have a polarized plug--of course it's a guarantee only if the electricians that wired your house did their jobs right. Other things are equally safe (or equally dangerous) no matter which way the hot and neutral are arranged. These can be made with a nonpolarized plug, though either kind may be used.
Old 01-01-2006, 12:53 AM
Charter Member
Join Date: Jun 1999
Location: Milwaukee, WI
Posts: 26,647
Quote:
Originally Posted by Q.E.D.
The only way to guarantee this is to have a polarized plug--of course it's a guarantee only if the electricians that wired your house did their jobs right.
AND the device must be wired properly. A GREAT example is a toaster. If it's wired backwards, then even when it's off the heating elements are still live and reaching in to grab your toast could result in a shock. In general, (IANAElectrician) the neutral and ground should never be on a switch.
Old 01-01-2006, 01:07 AM
Charter Member
Join Date: Jan 2003
Location: Richmond, VA
Posts: 22,536
Quote:
Originally Posted by Joey P
If it's wired backwards, then even when it's off the heating elements are still live and reaching in to grab your toast could result in a shock.
Not so much anymore. Most toasters (certainly all the ones with the UL symbol) are made with a double pole switch which cuts out both the hot AND the neutral. Even this isn't entirely foolproof, as I have seen cheap switch contacts fuse closed under fault conditions.
Old 01-01-2006, 02:15 AM
Guest
Join Date: Mar 2003
Location: Minneapolis, MN
Posts: 13,654
A few electronics devices only work properly if the hot & neutral are connected properly. So they would need to have polarized plugs.

Other devices have polarized plugs to improve chances for safety, as QED said. (But unscrewing a light bulb exposes both both lines -- one in the threads, the other in the bottom button. It's safer if the hot line is only available in that small button at the bottom of the connector. This protects people who are so dumb they stick their whole thumb into the socket.)

Finally, some devices may have polarized plugs just for economic reasons. A manufacturer buys large quantitites of plugs, and it might be cheaper to just keep 1 kind (polarized) in stock at the factory.


So there's no particular pattern to this. Of the many lamps in my house, at least half have normal, non-polarized plugs. Including some new ones.
Old 01-01-2006, 04:51 AM
Charter Member
Join Date: Nov 2001
Posts: 12,684
Devices with transformers at their input don't need polarized plugs. Those plug-in, low voltage power supplies nearly always have non-polarized, 2 prong connections. I assume that's so that you can connect them either way depending on how much room there is at the outlet.

I believe that either 2 0r 3 prong polarized plugs are now standard for all other devices although not required in many locales.
Old 01-01-2006, 05:39 AM
Guest
Join Date: Dec 2005
Posts: 36
Polarized plugs are good. I have a 1964 Fender guitar amp that will give you a pretty good jolt through the guitar strings (which are connected to the case of the amp) if you get the non-polarized plug backwards.
Old 01-01-2006, 09:54 AM
Guest
Join Date: Aug 2000
Location: Location: Location:
Posts: 10,483
Related question:

Heavy duty power tools (mitre saws, reciprocating saws, etc) that are 'double insulated' do not have the third ground wire/plug.

Why?
Old 01-01-2006, 09:56 AM
Guest
Join Date: May 1999
Location: Up there, waiting
Posts: 17,203
As an example, I have a cheapo plastic fan with a polarized plug, while the plug on the charger for my MP3 player is a straight plug.
Old 01-01-2006, 10:15 AM
Charter Member
Join Date: Nov 2001
Posts: 12,684
Quote:
Originally Posted by orangetruck
Polarized plugs are good. I have a 1964 Fender guitar amp that will give you a pretty good jolt through the guitar strings (which are connected to the case of the amp) if you get the non-polarized plug backwards.
This indicates a lot of "leakage," [i]i.e.[/b]a relatively low resistance connection of the "hot" lead to the case and isn't the way the thing was designed. In other words, something is wrong and I would have it fixed.
Old 01-01-2006, 10:34 AM
Charter Member
Join Date: Jun 2003
Location: Portlandia
Posts: 38,698
The importance of polarized plugs and proper polarization of the entire circuit becomes readily apparent to Americans living overseas. Or at least those Americans who are using 110v appliances plugged into autotransformers. At one embassy they fried thousands of dollars worth of mother boards prior to my arrival.
Old 01-01-2006, 11:33 AM
Guest
Join Date: Feb 2005
Location: Hampshire, UK
Posts: 626
If you're talking AC applicances, then the functionality of the device shouldn't be affected if all parts of the circuit are isolated from earth (US: ground). Any distinction between live and neutral is mainly for safety reasons, e.g. only the live line will be fused. Occasionally there'll be a mains applicance that needs an earth reference, and one such example of this is flame-sensing gas ignitors. The ignition electrode is biased with current-limited mains voltage, and the flame is sensed by the electrical model it presents* between the electrode and ground. As neutral is at roughly earth potential anyway, the circuit here needs to be cunningly designed so it will work with live and neutral swapped.

Even low voltage AC plugs benefit from polarisation. There's a range of music effects pedals that use AC output mains adaptors, and if you're running a number of these from the same mains adaptor then they all need to be oriented the same way or the ground interconnects will crowbar the power supply.

*An electrical model of a flame looks a bit like a perfect diode in series with a huge resistor of about 100Mohm or so.
Old 01-01-2006, 11:34 AM
Guest
Join Date: Jul 2003
Location: City of the Red Chicken
Posts: 1,120
Quote:
Originally Posted by Philster
Related question:

Heavy duty power tools (mitre saws, reciprocating saws, etc) that are 'double insulated' do not have the third ground wire/plug.
The ground wire is connected to the normally non-energized metal parts of a tool. It is designed to provide a positive path to complete a circuit if the innards of the tool get wonky and a live wire touches the normally non-energized parts. It protects you by the short circuit being directed in to the electric system rather than through your arm. But this method is not foolproof, as if the short happens while you are holding the tool, it generally takes less time to give you a good shock than it does to blow your breaker.

Most old metal tools have the wires floating around in direct contact with metal, and all it takes for a short is for the insulation to crack or rub off. The double insulated tools add more protection between the live wires and any metal parts. The idea is that rather than attempting to direct away the current if you get a short to the metal, they make it almost impossible to make that short in the first place.
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 04:54 AM.

Copyright © 2017
Best Topics: ingest glass klingon discommendation trusted credentials senora vs senorita marcus aurelius gods landkreuzer p.1500 waze sucks dynabeads review piss hardon buzz the tower colymbosathon ecplecticos prn status moccasins socks predator pee flossing slang ancient booby traps pig dog german cats and bread pp. pages human neutering cannon vs gun sumo wrestlers testicles eating yourself drano for toilets toes picking up hot muscular women reddit banjo damprid lowes center in football frosted light bulbs gregg ruled paper soup to nuts flavorless ice cream games like syberia boycott china animal cruelty best way to clean rocks how many people does the average person know what animals eat cockroaches i fucking hate cats removing surgical tape residue velvet worm for sale does unopened mayonnaise go bad dr strange amazon prime breaking in a tempurpedic mattress black polo khaki pants torrid job interview questions why does valerian root smell so bad thank you gift doctor does fedex ever deliver early fs1 on time warner cable how to remove a sidewalk what are butterfingers made of change of address jury duty food starting with e is it laid off or layed off house number on curb how many people are needed for an orgy sneaking a cat into an apartment best tasting cough syrup toro electric start lawn mower won't start laptop won't connect to printer what time is taps played on military bases are black babies born black what time does the mailman stop running feet itchy after shower what does the sky look like by a black hole?