Voltage drop wire size reduction

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DonaldSparkyDog

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Blueprints designed a voltage drop for a 20 amp 240 volt branch circuit that requires a #2 XHHW, (long run). Submittals approved 2 pole 20 amp CB that only accepts #8 max wire size. EE says just splice the #8 to the #2 right below the panelboard and terminate to the CB. I am of the understanding that a circuit that is increased in size for voltage drop is to remain that size through out the circuit loop. Would not the #8 develop heating issues under load? Thanks.
 
DonaldSparkyDog said:
Blueprints designed a voltage drop for a 20 amp 240 volt branch circuit that requires a #2 XHHW, (long run). Submittals approved 2 pole 20 amp CB that only accepts #8 max wire size. EE says just splice the #8 to the #2 right below the panelboard and terminate to the CB. I am of the understanding that a circuit that is increased in size for voltage drop is to remain that size through out the circuit loop. Would not the #8 develop heating issues under load? Thanks.
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What the EE suggests is acceptable.
 
181129-1153 EST

DonaldSparkyDog:

Think.
Would not the #8 develop heating issues under load?
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Why would it? Just analysis heat production per unit length of wire. Report back what you figure out.

.
 
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DonaldSparkyDog said:
I am of the understanding that a circuit that is increased in size for voltage drop is to remain that size through out the circuit loop. Would not the #8 develop heating issues under load?
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With a 20a or less load on a 20a breaker, even a section of #12 wire won't overheat. The larger wire does not cause more current to flow, it merely minimizes the reduction of current (which is a by-product of voltage drop.)

There is no requirement that a wire up-size remain throughout a circuit; it merely can not be undersized for the breaker used. Don't forget, though, that the EGC needs to be proportionately up-sized where the conductors are.
 
ActionDave said:
Do that and a crack will open in the center of the earth and swallow us all.
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LOL! In the extremely unlikely event you are right, at least it would take all the arc fault breakers with it.

I agree with actiondave in that I would splice a number 12 to it right in the panel, unless I had a gutter to work with to keep the panel a little bit neater.

And on the other end, that number two would get spliced into number 12 conductors in a junction box before all of the outlets.
 
Back way back when we had to run a circuit around four hundred feet from the panel... then runabout ten 20amp outlets and a set of lights... to a blacksmiths shed... boss had me run a full set of number sixes to the box in the shed.. through the conduit that was buried...
in the panel he ran a 20 amp double pole breaker, but did not connect the one wire... just capped it and taped it to the others that were in the group... the neutral and the ground at the time ran to the ground bar... there was not a separate ground bar at the time. Then he ran a number ten from the other live wire to the breaker... telling me to pay attention.
in the blacksmiths shed he taped a label in the box stating the panel and the breaker number and that it was a 20 amp circuit only. He then hooked in a fusible switch of some sort with a blank spot next to it. Then he had me run number twelve wire to everyplace in the shed following his directions, and we wired it all up... he tested it all and called in the inspector, who wanted to know about how he sized the wires and such..voltage drop, etc... that was when he introduced me to his guidebook... until then I had never seen a code book, or the rules or anything... I just did what he said for me to do and until that job he never even let me strip a wire..just pull them...
 
DonaldSparkyDog said:
Blueprints designed a voltage drop for a 20 amp 240 volt branch circuit that requires a #2 XHHW, (long run). Submittals approved 2 pole 20 amp CB that only accepts #8 max wire size. EE says just splice the #8 to the #2 right below the panelboard and terminate to the CB. I am of the understanding that a circuit that is increased in size for voltage drop is to remain that size through out the circuit loop. Would not the #8 develop heating issues under load? Thanks.
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Heating is a product of amperage, and more specifically amperage as it travels across a resistance. Wire has resistance which is spread out across its length. Amperage only increases when voltage goes down with loads that "compensate" for that. Like a motor. And if the current increases to the point that a #12 wire is getting too hot, then the breaker will trip first. Basically, I wouldn't even use #8. Look at the back of your code book, find out what the resistance of a 1 foot piece of #12 is. THAT is the amount of resistance that terminating in #12 will add to the run. Will that actually push you resistance up above the allowed value?
 
DonaldSparkyDog said:
Blueprints designed a voltage drop for a 20 amp 240 volt branch circuit that requires a #2 XHHW, (long run). Submittals approved 2 pole 20 amp CB that only accepts #8 max wire size. EE says just splice the #8 to the #2 right below the panelboard and terminate to the CB. I am of the understanding that a circuit that is increased in size for voltage drop is to remain that size through out the circuit loop. Would not the #8 develop heating issues under load? Thanks.
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Your understanding is incorrect. As long as the derated ampacity of the smaller conductor is adequate to carry the current, heating will not be an issue and the impact on the overall voltage drop will be minuscule. This is a common situation and the remedy suggested by the EE is fine.
 
LarryFine said:
With a 20a or less load on a 20a breaker, even a section of #12 wire won't overheat. The larger wire does not cause more current to flow, it merely minimizes the reduction of current (which is a by-product of voltage drop.)

There is no requirement that a wire up-size remain throughout a circuit; it merely can not be undersized for the breaker used. Don't forget, though, that the EGC needs to be proportionately up-sized where the conductors are.
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Ok Larry - I'm going to question the rationale of upsizing the EGC
 
buffalonymann said:
Ok Larry - I'm going to question the rationale of upsizing the EGC
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Because the voltage-drop concerns that trigger the need for up-sizing the circuit conductors also affect the ability of the EGC to effectively cause the over-current device to operate correctly.

In other words, if there is a short circuit at the far end of the circuit, you don't want there to be so much voltage drop along the length of the EGC that it heats up without tripping the breaker.
 
LarryFine said:
Because the voltage-drop concerns that trigger the need for up-sizing the circuit conductors also affect the ability of the EGC to effectively cause the over-current device to operate correctly.

In other words, if there is a short circuit at the far end of the circuit, you don't want there to be so much voltage drop along the length of the EGC that it heats up without tripping the breaker.
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And of course there's the rationale that the code requires it so we do it. :D
 
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