Increase in size Ground article 250

[brother]

Could use a little help here. I forget the exact article number, but when we had a circuit 20amp and #12 awg copper was originally good to use, but we decided to upsize to # 10 for voltage drop on the distance, its my understanding we have to upize the ground also to # 10 because of us upsizing from #12's even though its a 20 amp breaker/circuit.

Can some one point me to the right exact section. I know they changed the language a some years ago to supposely to help make it clearer, but some of us still get confused. Is my understanding correct on this still?

Thanks,

 

[Dennis Alwon]

section 250.122(B)

 

[brother]

section 250.122(B)

Thanks. so am I correct in the upsizing the ground even though its a 20 am circuit even though the language has changed?

 

[GoldDigger]

Yes.
In some edge cases you even end up having to increase the size of the EGC just because you put in a smaller breaker than the original!

 

[brother]

Yes.
In some edge cases you even end up having to increase the size of the EGC just because you put in a smaller breaker than the original!

Can you elaborate on this statement please?

 

[ActionDave]

Can you elaborate on this statement please?

Table 250.122 tells you that 10AWG equipment grounding conductor is good for up to 60A. Put 6AWG on a 50A breaker and all you need is a 10AWG equipment ground. Put those same 6AWG conductors on a 20A breaker and section 250.122(B) forces you to use a 6AWG equipment ground.

 

[LarryFine]

The EGC sizing becomes dependent on the circuit-conductor sizing, rather than the OCP sizing.

 

[infinity]

Table 250.122 tells you that 10AWG equipment grounding conductor is good for up to 60A. Put 6AWG on a 50A breaker and all you need is a 10AWG equipment ground. Put those same 6AWG conductors on a 20A breaker and section 250.122(B) forces you to use a 6AWG equipment ground.

Yes that's true, and for that reason this section still ranks as one of the worst pieces of junk in the NEC. And in some instances a #8 conductor can be protected at 50 amps so by using #6 you've increased the size of the circuit conductors and the #10 EGC is now too small. Simple right?

 

[kwired]

Yes that's true, and for that reason this section still ranks as one of the worst pieces of junk in the NEC. And in some instances a #8 conductor can be protected at 50 amps so by using #6 you've increased the size of the circuit conductors and the #10 EGC is now too small. Simple right?

it was written as a one size fits all rule, though reality is it isn't always necessary.

 

[charlie b]

250.122(B) used to say simply that if the ungrounded conductors are "increased in size," you must also increase the EGC. But it never said "increased from what"; it never gave the starting point. That is what was changed recently (2014 edition). It now says essentially that if a wire size has enough ampacity (under the conditions of use), and if you use a bigger wire, then you must increase the EGC.

Example: Put 5 single phase, 120V, 20A circuits in the same conduit, using THHN wire. That's 10 current-carrying conductors, so you must derate by 50%. You can start at the 90C column, so a #12 derates from 30 amps to 15 amps. Since you cannot protect a wire with a 15A ampacity with a 20 amp breaker, you must use a #10 wire. In the context of 250.122(B), that is NOT an increase in size "from the minimum size that has sufficient ampacity for the intended installation." Therefore, you can still use a #12 EGC.

 

[kwired]

Thanks. so am I correct in the upsizing the ground even though its a 20 am circuit even though the language has changed?

As written if you increase the ungrounded conductor size you must increase the EGC proportinally in size.

Since 15, 20 and 30 amp circuits require minimum of 14, 12 and 10 AWG conductors and also require same size minimum EGC's, an increase of 12 to 10 AWG circuit conductor would require same proportional increase of EGC so that would also be 12 to 10 AWG.

This is one of the easy applications, gets more complex when you can have 60 amp circuit with 6 AWG and a 10 EGC and increase the 6 AWG - now you must calculate how much proportionally larger the EGC must be and determine which standard conductor size is at least that large.

 

[infinity]

Example: Put 5 single phase, 120V, 20A circuits in the same conduit, using THHN wire. That's 10 current-carrying conductors, so you must derate by 50%. You can start at the 90C column, so a #12 derates from 30 amps to 15 amps. Since you cannot protect a wire with a 15A ampacity with a 20 amp breaker, you must use a #10 wire. In the context of 250.122(B), that is NOT an increase in size "from the minimum size that has sufficient ampacity for the intended installation." Therefore, you can still use a #12 EGC.

After you have derate the conductors to 15 amps doesn't that become the conductor ampacity?

 

[kwired]

250.122(B) used to say simply that if the ungrounded conductors are "increased in size," you must also increase the EGC. But it never said "increased from what"; it never gave the starting point. That is what was changed recently (2014 edition). It now says essentially that if a wire size has enough ampacity (under the conditions of use), and if you use a bigger wire, then you must increase the EGC.

Example: Put 5 single phase, 120V, 20A circuits in the same conduit, using THHN wire. That's 10 current-carrying conductors, so you must derate by 50%. You can start at the 90C column, so a #12 derates from 30 amps to 15 amps. Since you cannot protect a wire with a 15A ampacity with a 20 amp breaker, you must use a #10 wire. In the context of 250.122(B), that is NOT an increase in size "from the minimum size that has sufficient ampacity for the intended installation." Therefore, you can still use a #12 EGC.

After you have derate the conductors to 15 amps doesn't that become the conductor ampacity?

It does, but I think I agree this is one example of where that 10 AWG on a 20 amp breaker can have a 12 AWG EGC, because the minimum required conductor needs to have an ampacity of 20 amps or greater, though I also think one can consider the load served - receptacle outlets definitely must use the 10 AWG for the 20 amp circuit in that case. Fixed hardwired loads, could get by with 12 AWG if the fixed load is not over 15 amps in his example, especially if a motor or other load that allows increased branch circuit device for SCGF protection.

 

[Carultch]

250.122(B) used to say simply that if the ungrounded conductors are "increased in size," you must also increase the EGC. But it never said "increased from what"; it never gave the starting point. That is what was changed recently (2014 edition). It now says essentially that if a wire size has enough ampacity (under the conditions of use), and if you use a bigger wire, then you must increase the EGC.

Do you necessarily have to account for 240.4(B) when determining your starting point of this calculation?

A couple examples:
A 150A circuit on a transformer secondary, which only needs 130A for the load. 240.21(C) requires a full 150A worth of wire (i.e. not less than the OCPD rating), until you are behind the first breaker. Then 240.4(B) allows #1 Cu for the feeder. Suppose one wanted to unify the sizes, and stick with #1/0 Cu for both the feeder and secondary. Would #1/0 Cu be considered "upsized" on the load side of the 150A breaker, and therefore require a larger ground than #6 Cu?

Future expansion is a possibility, up to a possible full future capacity of 600A. "Today", only a 500A circuit is necessary for the active loads. The circuit originates at device A, a 600A OCPD, which leads to a junction box (device B) where the future expansion might be added. Suppose it contains 5-terminal Polaris blocks each phase, with a vacant position future circuit as a feeder tap. The active branch then leads to a 500A main breaker panelboard (device C). The circuit between A and B = 2x 350's Cu for the full 600A. The circuit between B and C = 2x 250's Cu, taking credit for 240.4(B), because that part of the circuit won't need more than 500A, even when the future branch is added to the junction box. It is understood that the 600A device governs the entire circuit to at least need #1 Cu as the EGC. Is the circuit between devices A and B considered "upsized", because it is larger than the circuit between B and C, thus requiring larger than #1 Cu?

 

[LarryFine]

. . . I think I agree this is one example of where that 10 AWG on a 20 amp breaker can have a 12 AWG EGC, because the minimum required conductor needs to have an ampacity of 20 amps or greater . . .

Couldn't the same thing be said about the #12s before you upsized them: that they already had the required ampacity?

Besides, isn't this the exact scenario that the requirement to proportionately upsize the EGC is meant to address?

 

[kwired]

Couldn't the same thing be said about the #12s before you upsized them: that they already had the required ampacity?

Besides, isn't this the exact scenario that the requirement to proportionately upsize the EGC is meant to address?

If supplying receptacles no, you would need 20 amp conductor if protecting such a circuit with 20 amp overcurrent device.

The thing here is even for fixed loads 15 amps is a standard overcurrent device size so you can't go to next size up of 20. If the load and conductor ampacity were both 16 instead then yes you could go next size up on overcurrent protection.

 

[brother]

250.122(B) used to say simply that if the ungrounded conductors are "increased in size," you must also increase the EGC. But it never said "increased from what"; it never gave the starting point. That is what was changed recently (2014 edition). It now says essentially that if a wire size has enough ampacity (under the conditions of use), and if you use a bigger wire, then you must increase the EGC.

Example: Put 5 single phase, 120V, 20A circuits in the same conduit, using THHN wire. That's 10 current-carrying conductors, so you must derate by 50%. You can start at the 90C column, so a #12 derates from 30 amps to 15 amps. Since you cannot protect a wire with a 15A ampacity with a 20 amp breaker, you must use a #10 wire. In the context of 250.122(B), that is NOT an increase in size "from the minimum size that has sufficient ampacity for the intended installation." Therefore, you can still use a #12 EGC.

Thanks for all the responses. So basically it appears the intent was to have an increase in size for mostly voltage drop type installations and not amperage. It just appears they could write the language better and make it more clear of what is needed. I would have increase the size of the ground in your amperage example thinking it was required.

Anyone have any suggestions on how to better write that section?

 

[infinity]

Anyone have any suggestions on how to better write that section?

Change the table to make the EGC size according to the size of the ungrounded conductors.

 

[kwired]

Change the table to make the EGC size according to the size of the ungrounded conductors.

Sort of like we already do with grounding electrode conductors or supply side bonding jumpers.

It has been like it is for so long you would need to present something pretty convincing I would bet before the CMP will even consider it.

 

[infinity]

Sort of like we already do with grounding electrode conductors or supply side bonding jumpers.

It has been like it is for so long you would need to present something pretty convincing I would bet before the CMP will even consider it.

If I remember correctly something similar has been proposed in the past possibly by one of our mods. It really makes sense, if the ungrounded conductor is up-sized for any reason then the EGC will automatically be up-sized too. No dumb calculations involved.