[TheForge] Light bulbs and shop power

[Ed Eccleston]

Bruce,

   Correct.  My blanket statement was from the standpoint of "normal" 
residential and commercial construction practices.  It's rare for a house to 
have a run of 100' pulling a full 20amps.  Actually, the allowable load on a 
breaker is usually calculated at no more that 75% max. continuous usage, 
anyway.  If you've ever dismantled an electric oven,  the wires connected 
directly to the element are quite small even though the supply wires must be 
#8 or so.  And Mike is also correct.  When a breaker trips a number of 
times,  both the trip threshold current seems to lessen, and the "slo-blow" 
capability drops.  Has anyone noticed that the lights may dim when the 
refrigerator starts up, but then return to normal?  The power draw of a 
compressor (motor) starting up is quite a bit more than is required to keep 
it running.  Most breakers will allow a heavier than allowable current for a 
short time (NPI), before actually popping.
----- Original Message ----- 
From: "Bruce ." <freemab222 at gmail.com>
To: "Blacksmithing List Sponsored by ABANA" <theforge at mailman.qth.net>
Sent: Friday, August 03, 2012 9:23 AM
Subject: Re: [TheForge] Light bulbs and shop power


> Ed,
>
> Thanks for your contribution.
>
> I'd like to point out that from the standpoint of the physics involved
> (i.e, behavior of electricity and conductors) it is NOT true that the
> length of the run doesn't matter.  The longer the run, the more the
> resistance and the greater the voltage drop.  Voltage drop = heat
> dissipation AND extra load on the circuit (and as the wire heats, its
> resistance increase further, compounding the problem).  Just because
> you can run a light bulb using a 6-foot extension cord, does NOT mean
> you can safely run it using a 500-ft extension cord of the same gauge.
>
> I suspect what you were saying is that given the wire sizes you
> mention, the length of the run is not an issue.  With sufficiently
> large wire, the voltage drop is minimal in any event, so a multiplier
> (longer length) does not necessarily increase the voltage drop enough
> to worry about.
>
> However, there are on-line calculators for determining   Play with
> this one, for example:  http://www.csgnetwork.com/wiresizecalc.html
> It told me that a 10' run of 20A requires 14ga wire, but a 100' run of
> 20A requires 8ga wire!
>
> And thanks for the comment about circuit breakers "getting weaker".
> But exactly what does that mean?  Will they fail safe (open the
> circuit before there's a real overload) or fail dangerously (not open
> the circuit when they should)?  Any idea what the typical lifetime of
> your typical household circuit breaker might be?
>
> On Fri, Aug 3, 2012 at 11:10 AM, Ed Eccleston <edeccleston at att.net> wrote:
> <snip>
> Rule of thumb is:
>> 15amp breaker requires minimum #14 ga. wire...20amp= #12
>> ga....30amp=#10ga....40amp=#8ga....
>>     The length of the run is not so critical as long as the wire size is
>> sufficient.  It's when you have a combination of long run, small wire 
>> size
>> and larger draw that you get into hot water.
> <snip>
> Oh, and final
>> note, generally the more that a breaker pops, it gets weaker.
>>       Yes, it's not inexpensive to get set up properly,  but it's sure a 
>> lot
>> safer.
>>
>> Thanks for letting me blather.
>>
>> Ed Eccleston
>>
>
> -- 
> Bruce
> NJ
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