Reducing conductor size for equipment lug and it's effect on VD

[mark32]

I had to disagree with an electrician today that has many more years experience than I do. He was trying to fit #6 onto a lighting contactors terminal, which wasn't happening. So he was looking for a lug that would work. The lugs he found were just a bit too big, then his phone rang. While he was talking I grabbed a crimp on lug for #8, which looked like it would fit in the terminal's recess. When he finished his call I showed him what I had, but scoffed at the idea of reducing the #6 to #8 because it would create too much VD. I said you're only going to use like 6" of #8. He said no way because it's at the beginning of the circuit, it would be different if it were at the end of the run. I didn't calculate 6" of #8 on a 200' run with a 20 amp load, but I can't imaging there would be a concernable difference at the load(s). What do you say?

 

[petersonra]

the Vd is the same regardless of whether the smaller wire is at one end or the other, or in the middle somewhere.

however, i don't know that the lug is identified fr being terminated with a ferrule like you wanted to do.

 

[augie47]

see it done all the time. as long as the smallest conductor is protected by the overcurrent device, no problem. That short a piece of wire...as noted anywhere in the system, will make negligible difference.

 

[Carultch]

I had to disagree with an electrician today that has many more years experience than I do. He was trying to fit #6 onto a lighting contactors terminal, which wasn't happening. So he was looking for a lug that would work. The lugs he found were just a bit too big, then his phone rang. While he was talking I grabbed a crimp on lug for #8, which looked like it would fit in the terminal's recess. When he finished his call I showed him what I had, but scoffed at the idea of reducing the #6 to #8 because it would create too much VD. I said you're only going to use like 6" of #8. He said no way because it's at the beginning of the circuit, it would be different if it were at the end of the run. I didn't calculate 6" of #8 on a 200' run with a 20 amp load, but I can't imaging there would be a concernable difference at the load(s). What do you say?

As long as it is factors that are not local to the termination, it is perfectly OK to do this. In any case, make sure 110.14(C) can be satisfied with the size.
(Voltage drop, conditions of use in other parts of the circuit...etc)

1 ft of #8 wire compared to 100 ft or more of #6 wire, is not going to affect voltage drop enough to matter. The uncertainty of circuit length during the design process, is a lot more than that.

it would be different if it were at the end of the run

Not true. The performance of a circuit with a series of resistors is independent of the order of resistors. All that matters is the individual difference of voltage across each, and therefore how it affects the power delivered from source to load.

Think of a battery, an LED, and a resistor. Does the location of the resistor, before or after the LED affect the power delivered to the LED?

 

[mark32]

As long as it is factors that are not local to the termination, it is perfectly OK to do this. In any case, make sure 110.14(C) can be satisfied with the size.
(Voltage drop, conditions of use in other parts of the circuit...etc)

1 ft of #8 wire compared to 100 ft or more of #6 wire, is not going to affect voltage drop enough to matter. The uncertainty of circuit length during the design process, is a lot more than that.



Not true. The performance of a circuit with a series of resistors is independent of the order of resistors. All that matters is the individual difference of voltage across each, and therefore how it affects the power delivered from source to load.

Think of a battery, an LED, and a resistor. Does the location of the resistor, before or after the LED affect the power delivered to the LED?

Thanks guys, I just did a calculation using the numbers he gave, 200' one way, #6 thhn, 20 amp load. (It's 277v by the way). VD with all #6 is 3.928. VD with one foot of #8 is 3.943 for a difference of .015 volts. It was bizarre hearing such illogical talk from this particular fellow as he's a well seasoned electrician. Talking with him on this topic was like having a disagreement with your wife in which she's totally wrong on something and you're in disbelief because she actual believes what's she's arguing about. Perhaps I'll show him my calculations, but on second thought he's one of those guys that no matter what you say he's right.

the Vd is the same regardless of whether the smaller wire is at one end or the other, or in the middle somewhere.

however, i don't know that the lug is identified fr being terminated with a ferrule like you wanted to do.

Good one, I didn't think of that. Do you normally see such info in the manufacturer's instructions?

 

[kwired]

You have in many ways the same thing when a fuse link is inserted into a circuit. The main conductors have less resistance per inch then the fuse link, there is voltage drop across the fuse link but it is minimal as long as it doesn't heat up enough to melt and open the circuit. The length of smaller conductor that is the topic of this thread is not as high of a resistance as a fuse link would be (at least not the fuse needed for the circuit in question).