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wire connection

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chajakedude

New Member
is it ok to connect a small wire (30AWG) to a larger wire (18AWG) directly? i am going to connect the 18 fan power cord to the 30 wire to make an electromagnet. i know that the 30 has to be sufficiently long enough so that it has enough internal resistance to handle 120V, but do i need to have any special connection between the two wires?
 

Gene

New Member
This is a bit of a puzzle. First off, I would never connect a wire smaller than the wire required to handle the current of the appliance. If the manufacturer of the fan used an 18 gauge wire, you can bet that is the smallest gauge you can safely attach.

Your post sounds very dangerous!

Perhaps you would like to be a little more specific about your project??
 

chajakedude

New Member
what i had in mind was using the small wire to make the coils for the magnet. the more coils the better the magnet and small wire makes more coils. so i was going to put the "magnet" in the middle of the hot leg of the fan cord. but i need that current to run through some resistance before it gets back to the wall.
thanks for your information.
 

stevez

Active Member
Gene's point about safety is most important so let's always keep that out front in any discussion.

In most situations wire is the means to conduct electricity from the source to the load. Voltage and current are two important things to address in determining whether or not a wire is appropriate for the task.

The insulation addresses the voltage. Normally hookup wire on battery or lower (50 volts) voltage applications is sufficient - check to be sure if you are connecting to higher voltages.

The wire size addresses the current or amps. Heat and voltage drop are two "current" related issues. If voltage drop is not critical then you can use the smallest wire possible that will not get hot - there are tables that show how much current a wire can carry. As a wire gets smaller the resistance per foot goes up - and the resulting voltage drop along the wire increases. The energy lost to voltage drop is converted to heat but we've already addressed that. If you are concerned about voltage drop then you need to know what current will flow and calculate the voltage drop for the wire size. There are also tables for that.

All of the above presumes that conditions will be "normal" in that the current flow will be what you expect. You need to plan on some not normal things. Current at startup of a motor, for example, is much higher than the run current. If there is a short circuit that results from a component failure or otherwise the current can be much higher. Fuses, fuseable links, circuit breakers, etc were made to address this issue - the let normal currents flow but open the circuit to prevent excess current from flowing.

So, Gene's rule of thumb to not reduce the size is a good guideline unless you 1) know how much current is flowing and 2) are certain that you've addressed the overcurrent problems (short circuits, startup, etc). In your situation you could add a fuse to the points where you connect the smaller wires - the fuse size appropriate for the wire or the weakest link.

Hope this helps.
 

Gene

New Member
I still don't understand what you are trying to accomplish but I do understand how you plan to wire it up. DON'T DO IT!

If the magnet winding has too few turns, the 30 AWG wire will burn up. If it is too many turns, the motor will not run - the field winding in the motor will heat up and the fan will die.

Could you do your magnet winding experimentation with a battery operated fan? If not, buy a pre-wound coil made for 120 VAC and put it in parallel with your fan (not series).

Other than an occasional transformer, I never connect anything directly to the house mains.
 
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