Reducing Wire

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Alwayslearningelec

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Say you have a 20A breaker for the circuit but you must run 1/0 because of voltage drop what's the most practical way to reduce down to #10 or #12 to land the wires on the breaker? Thanks
 
I agree with Strat, I would put a pull box adjacent to the panel and make the transitions there with a Ilsco style connector.

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horsegoer said:
Say you have a 20A breaker for the circuit but you must run 1/0 because of voltage drop what's the most practical way to reduce down to #10 or #12 to land the wires on the breaker? Thanks
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If you change wire sizes the tap rules gets you in trouble.

The best way is change lug sizes if that’s available. Otherwise you can use pigtail adapters.


This comes up all the time on larger size long runs.


But this is the biggest adapter I can find. It gets you to #2. But you are asking for #10. That’s a huge jump.

Second option is it’s a wire size change but you are going up, not down. If you like/need to stick with crimped connections you will have to crimp both and bolt two lugs together jump like doing a motor. If you want something more pretty I’d use a simple DIN rail terminal.


These terminal blocks will go from 1/0 to #14 which allows you to make the connection. Look at the DN-T1/0 model. Just need DIN rail for mounting, an end cover, and two stop blocks but you can just use grounding blocks for stops. Unfortunately 25 per box but I use them all the time.

If you prefer bolt down these work:


Just be very careful with power distribution blocks. Some are NOT Listed as assemblies so you can’t use them except as panel components. So the EPDB101 will work (need 2) or the HPB series gives you more poles but it’s an open frame style. The HP series doesn’t meet NEC.
L
 
horsegoer said:
Just for the section of the run that has the 1/0 correct? And what code section is that? Why does it have to be the same size as the phase conductors?
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For a 20 amp circuit your typical conductors are #12 which require a #12 EGC according to T250.122. The EGC to ungrounded conductor size ratio is 1 to 1 meaning that both conductors are the same size. When you up size the ungrounded conductors to #1/0 the EGC is also required to #1/0 which is the same 1 to 1 ratio.
 
infinity said:
For a 20 amp circuit your typical conductors are #12 which require a #12 EGC according to T250.122. The EGC to ungrounded conductor size ratio is 1 to 1 meaning that both conductors are the same size. When you up size the ungrounded conductors to #1/0 the EGC is also required to #1/0 which is the same 1 to 1 ratio.
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But that is not always the case. Many cases I see the EGC much smaller than the ungrounded conductors. Maybe I'm not following.
 
horsegoer said:
But that is not always the case. Many cases I see the EGC much smaller than the ungrounded conductors. Maybe I'm not following.
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For circuits larger than 30 amps that is true but not for 15, 20, or 30 amp circuits. In those case the EGC to ungrounded conductor ratio is 1 to 1.
 
For #14,#12 & #10 (15,20 and 30 amp OCP) the EGC will be same same size as the phase conductors If you increase the phase on those circuits (15,20,30) the EGC will be the same size as the phase.


opps posted along with infinity
 
Which also means that when upsizing a 120V circuit for VD, it could be cheaper to upsize the grounded conductor more than the ungrounded conductors.

For example, on a 20A circuit, #12 solid copper has a DC resistance of 1.93 ohms/kft (per Chapter 9 Table 8, although maybe I should be using Table 9 instead). Say for VD reasons you need to get that down to 0.9 ohms/kft. You could use #8 stranded conductors (0.778 ohms/kft), and you'd need (3) #8s (ungrounded, grounded, EGC).

Or you could use a #6 grounded conductor (0.491 ohms/kft) and a #10 stranded ungrounded conductor (1.24 ohms/kft), for an average of 0.866 ohms/kft. That would let you use a #10 EGC. So if (2) #10s + (1) #6 is cheaper/easier than (3) #8s, that's an option (with a bit more VD, as 0.866 > 0.778).

Cheers, Wayne
 
wwhitney said:
Which also means that when upsizing a 120V circuit for VD, it could be cheaper to upsize the grounded conductor more than the ungrounded conductors.

For example, on a 20A circuit, #12 solid copper has a DC resistance of 1.93 ohms/kft (per Chapter 9 Table 8, although maybe I should be using Table 9 instead). Say for VD reasons you need to get that down to 0.9 ohms/kft. You could use #8 stranded conductors (0.778 ohms/kft), and you'd need (3) #8s (ungrounded, grounded, EGC).

Or you could use a #6 grounded conductor (0.491 ohms/kft) and a #10 stranded ungrounded conductor (1.24 ohms/kft), for an average of 0.866 ohms/kft. That would let you use a #10 EGC. So if (2) #10s + (1) #6 is cheaper/easier than (3) #8s, that's an option (with a bit more VD, as 0.866 > 0.778).

Cheers, Wayne
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You also have to make sure that the impedance of the combined EGC and the ungrounded line was low enough to open the OCPD on a short circuit. You would need perhaps 100 Amps of short circuit current to reliably open the OCPD with a 20 A rated OCPD.

That would make your maximum circuit resistance about 120 volts/100 Amps, or about 1.2 Ohms.

A # 10 going out and a #10 coming back is 2.48 Ohms/1000 ft of circuit length. So your maximum circuit distance would be about 485 feet using two # 10's.

In reality, it would likely be somewhat less by the time you used Ac numbers instead of DC.
 
horsegoer said:
But that is not always the case. Many cases I see the EGC much smaller than the ungrounded conductors. Maybe I'm not following.
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Yes, but the rule is that if you increase the CCCs you have to increase the EGC by the same ratio. If the EGC is the same size as the CCCs before the upsize then it will be the same size afterwards as well. One thing to note, though is that if the EGC is already larger than it needs to be, you start with the minimum size it could be before you do the proportional upsizing.
 
Here are some examples for base Ratio calculations. Be careful when doing motors. Wire size and over current device(s) for motors can trip you up.
Hope it helps
 

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