Quote:
Originally Posted by artbyjody
Oversizing wire however actually generates more load resistance to begin with and should not be overly done or practiced as you decrease the overall cpacity of your storage system...which is the making the batteries work harder and deplete faster...
Oversizing you have to consider also distance and gauge ensure sure you do not see more than a 3% drop in voltage over the run... (if you can make sense of it - the charts American Wire Gauge table and AWG Electrical Current Load Limits)
A checklist however somewhat related:
Marine Electrical Check List (good site in general)
Not that it is an evil practice -however....really should be avoided...
VD= 2*K*I*L/ CSA
WHERE:
VD= VOLTAGE DROP
I= CURRENT
L= DISTANCE OF THE LOAD FROM THE OUTLET (IN FT)
K= 12 FOR COPPER AND 19 ALUMINUM (FOR MAXIMUM TEMP OF 75 DC)
CSA= CONDUCTOR CROSS SECTIONAL AREA IN CIRCULAR MILS. |
Over sizing the wire will DECREASE load resistance as the wiring runs will add less resistance to the circuit as a whole. The equation you posted says exactly that. For a given load, the larger the CSA, the less inherent resistance the wire adds to the circuit, hence the lower the voltage drop.
Oversized wire does not increase the available fault current of a circuit, a protective deveice with a larger rating does. If you size the breaker (or fuse) for the wire, which you should, then the breaker (or fuse) should trip LONG before the wire melts and burns. If it doesn't, there was no point in the protective device in the first place. Minimizing your "risk" by using a small wire that won't burn as long is the definition of false security. How about preventing the wire from burning in the first place? As far as I'm concerened, I don't want any fire on my boat, no matter what size.
As Hartley18 stated, oversizing your wiring, as SD has done (as well as myself) will hurt nothing but your wallet.
Now I certainley agree that if you use grossly oversized wire, and size the breaker or fuse to protect that wire, you have created a situation that will produce more fault current before the protective deveice activates. It does not, however, increase the risk of the wire burning because the wire and breaker are sized to match each other and the breaker will trip long before the wire reaches its burning point.