voltage drop

[redfish]

Does it matter which end of the circuit you install the larger wire to compensate for voltage drop?

 

[peter d]

Re: voltage drop

Good question. I am guessing the larger wire goes at the end of the circuit, because the further you get from the source, the more voltage drop you will get. But then again, maybe it doesn't matter at all.

 

[infinity]

Re: voltage drop

Electrically it doesn't matter.

 

[iwire]

Re: voltage drop

Originally posted by redfish:
Does it matter which end of the circuit you install the larger wire to compensate for voltage drop?

Generally no.

However if you where feeding multiple loads that are spread out from one circuit (think parking lot poles) placement of wire sizes will make a difference.

Using a smaller wire from the panel to the first 5 poles, than larger wire for the last 5 poles of a 10 pole circuit will not help as much as doing it the opposite way.

 

[physis]

Re: voltage drop

A run of wire is a resistor and that's how it should be thought of when considering voltage drop.

Another reason that I don't like using resistivity or "K" value when calculating voltage drop. It makes the whole concept seem like something different than it is.

It's Voltage drop = current x resistance. Or V=IR

Using the typically taught method for voltage drop calculation seems to hide how simple it actually is.

If there are two wire sizes in series then their resistances are simply summed.

Edit: Or you can calculate the voltage drop of each conductor separately and sum that.

[ July 30, 2005, 03:10 PM: Message edited by: physis ]

 

[rattus]

Re: voltage drop

Why would you use different sizes in the same circuit?

 

[physis]

Re: voltage drop

To bug engineers.

Sorry Rattus, I couldn't resist.

 

[iwire]

Re: voltage drop

A 120 volt single circuit run from a panel 200' to a 10 amp load then on another 200' and another 10 amp load.

From panel to the first load.

Using 10 AWG 9.6 volt drop or 110.4 volts

Using 6 AWG 3.9 volt drop or 116.1 volts

From first load to second load

Using 6 AWG fed from the 10 AWG @ 110.4 volts 1.59 volt drop or 108.8 volts

Using 10 AWG fed from the 6 AWG @ 116.1 volts 4.8 volt drop or 111.30 volts


I am 2.5 volts better off with the larger wire at the front of this simple circuit.

 

[iwire]

Re: voltage drop

Originally posted by rattus:
Why would you use different sizes in the same circuit?

Value engineering.

 

[hardworkingstiff]

Re: voltage drop

Originally posted by iwire:

I am 2.5 volts better off with the larger wire at the front of this simple circuit.

I think to classify this as a "simple circuit" you would need only one load. How about you calculate it again with one load and a JB in the middle instead of a load dropping off.

 

[iwire]

Re: voltage drop

Originally posted by hardworkingstiff:
I think to classify this as a "simple circuit" you would need only one load. How about you calculate it again with one load and a JB in the middle instead of a load dropping off.

It's my circuit and I will wire it how I want.

 

[physis]

Re: voltage drop

I needed a 10 amp load so I stold the one you have in the middle Bob.

[ July 30, 2005, 04:35 PM: Message edited by: physis ]

 

[iwire]

Re: voltage drop

OK I will try it in a 'T'.

 

[iwire]

Re: voltage drop

Originally posted by physis:
Bob you should calculate your 6 AWG for only 10 amps. to make your voltage drop 1.96 v. instead of 3.9.

Which one?

One way it has 20 amps of load and the other way it does not.

Help me out here, it's Saturday and the grill is fired up along with a beverage or two...

 

[rattus]

Re: voltage drop

Generally speaking you would use the larger wire where the current is greatest, but depending on the relative wire lengths, this might not always be the best solution. Each case would have to be computed individually.

 

[physis]

Re: voltage drop

Sorry Bob. You were right. I left out the distance "2".

BBQ in' and beer, sounds way cool.

No, I did it right. .000491 x 2 x 200 x 10 = 1.96

Ok you're right again. That should be a 20 and not a 10.

Now I'm hiding the calculator from myself. (I only have like twenty at my desk ).

[ July 30, 2005, 04:33 PM: Message edited by: physis ]

 

[iwire]

Re: voltage drop

Originally posted by rattus:
Generally speaking you would use the larger wire where the current is greatest, but depending on the relative wire lengths, this might not always be the best solution. Each case would have to be computed individually.

No doubt.