Sat, 28 May 2016 23:17:05 GMT in alt.home.repair, wrote:
On Sat, 28 May 2016 20:04:33 -0000 (UTC), Diesel
wrote:
Thu, 26 May 2016 05:50:22 GMT in alt.home.repair, wrote:
"Continuous load" means you size the circuit to 125% of total
load (14.6*1.25=18.25a)
so 18.25a is OK on a 12 ga wire with a 20a breaker
You're going over the 80% trade standard load (16amps on a 20amp
circuit) at that point,
Excuse me but the load is 14.6a. The 18.25a IS 125% of the load so
the 80% has been accounted for.
The load is 14.6A under perfect conditions of a wire 100ft or less
in total length, yes. However, if the last heater happens to be a
bit further away from the panel than 100ft as the OP suggested,
there's a real risk of voltage drop to the last heater with
the others running because the 12/2 wire just can't provide the full
load that far out to the last device. A voltage drop will increase
the amount of amps required by that heater to do it's job. The 12/2
isn't going to appreciate that and neither will the breaker. It will
tolerate being over 20amps until it heats up enough to trip.
It's why I suggested 10/2. So, the OP won't even have to worry about
problems down the road if their estimates are off. It certainly
won't hurt the situation.
http://handymanwire.com/ubbthreads/u...ngest_distance
100feet is the normal usual maximum spec'd
The code does not rule on lenghts and voltage drop.. --only
suggests!
The end of run outlet is where the starvation is the worst and any
inductive load will suffer the worst at that point so you must
consider this as you overall design limit at 100feet.
A 20amp circuit fully loaded at this outlet will drop 5.6% where 5%
is the RECOMMENDED maximum and we must install 10gage wiring if we
still insist on a 20amp rated circuit. The other choice is to derate
this long run to a 15 amp circuit on this 12g wire and you could
possibly expect to be at 5% drop at 140-150feet. Tthe full 15 amp
dribbles off at around 120 feet!
20amp circuit loaded at 18amp is 5%
16amp will result in 4.5% missing at that far outlet.
The loss will be accumulative along the run as other 'stuff' is
plugged in.
Most equipment that uses electricity is designed to function well at
plus or minus 10%,whetner it is a resitive load like light bulb or
an inductive load like a lighting ballast or motor.
This all becomes even more crucial when the power company is
experiencing voltage sags in the summer high loads and the volatage
that arrives at the pole down the street is already considerably
LOW!!!---and if you designed your circuit lengths at the extra long
end ---you are causing motor loads to labor,and lights to be dim!
Go with the far outlet at 100feet MAX...and you will be with the
majority!!!
from the OPS original post:
From the main panel to the farthest unit is less than 100ft.
So, the last heater on the circuit, depending on how far away it
actually is from the panel and if the others are all running or not,
could exceed the rated capacity for the wire and/or the breaker. IE:
it's too far and the wire is too skinny to get the needed amps to
the device.
I understand there is a cost difference going with 10/2 and some
individuals consider that to be more important than the total amount
of amps the circuit might pull when fully energized (all heaters on
- high) So, for short distance, and if the OP is very close with his
figure on distance to last device on the circuit, your suggestion
will save him money and work fine. If he's wrong or a bit off and
it's a bit further, he might have to break up the heaters into
seperate fed circuits to keep the amps low enough. Which will use
additional wire and another breaker or two in his panel, assuming
there's room for that.
At this point, whatever cost savings the OP had by not running 10/2
have disappeared.
Why even have to be concerned with it? Use the thicker wire, you
KNOW each device will get all the amps it needs, without any
possibility of an overload condition.
Like I said though, whatever choice the OP makes, it looks fine from
here.
--
MID:
Hmmm. I most certainly don't understand how I can access a copy of a
zip file but then not be able to unzip it so I can watch it. That
seems VERY clever!
http://al.howardknight.net/msgid.cgi?ID=145716711400