More on upgrading ECG's

[jdengr]

Following up on this topic, I have a similar question:

I'm installing several 120v, 20-amp branch circuits. The conductors are run from the panel to a pull box in one 2" conduit, and then spliced to serve individual loads branching out from the PB in seperate conduits. Because of the number of conductors in the 2" conduit, the wire was resized to #8, but is still spliced to #12 in the PB going out to the individual loads.

Question:
In reference to 250.122(B), would the EGC still need to be upgraded to #8 in the 2" conduit going to the PB even though it is spliced to #12 in the PB?

 

[charlie b]

Re: More on upgrading ECG's

I would have to say "yes." I can't think of a way to twist the rule to do otherwise.

 

[infinity]

Re: More on upgrading ECG's

I'm with Charlie, yes you would need to use #8.

 

[ronaldrc]

Re: More on upgrading ECG's

Since we upped the size of the #12 to a #8 because of the number of wires in a conduit and not voltage drop shouldn't we consider
250.122 para (C) Multiple circuits,instead of 250.122 (B)? and base it on the size of the 20 amp. breaker?

 

[steve66]

Re: More on upgrading ECG's

Since we upped the size of the #12 to a #8 because of the number of wires in a conduit and not voltage drop shouldn't we consider
250.122 para (C) Multiple circuits,instead of 250.122 (B)? and base it on the size of the 20 amp. breaker?

I think you still have to consider both. Size the EGC per (C) and then increase the size per (B).

Steve

 

[jdengr]

Re: More on upgrading ECG's

Thanks for the replies...

Another consideration:

If I install a #12 EGC for each ckt in the 2" conduit, and splice them all together using a ground busbar in the PB, then the equivelant circular mills would be sufficient, correct?

[ October 11, 2005, 09:30 AM: Message edited by: jdengr ]

 

[charlie b]

Re: More on upgrading ECG's

I think not. You could have used a #12 phase conductor for a single circuit, and had enough ampacity. But because of multiple-conductors in a conduit, you upsized the phase conductor to #8. Therefore, you have to use a #8 EGC to the junction box.

Also, you can't use #12 EGCs that are connected at both the PB and the juction box. The code does not permit paralleling wires that small.

[ October 11, 2005, 10:24 AM: Message edited by: charlie b ]

 

[jdengr]

Re: More on upgrading ECG's

Thanks for the help. I was looking at 250.122(F)(1), but wasn't aware of 310.4 limiting the size of paralleled conductors.

 

[charlie b]

Re: More on upgrading ECG's

Originally posted by jdengr: . . . but wasn't aware of 310.4 limiting the size of paralleled conductors.

Someone pointed out to me that 310.4 does not appear to apply to EGCs. What a surprise: It didn't say what I thought it did.

In any event, I can't think of anything that permits paralleling of EGCs, regardless of size. I know that if you have the phase conductors in multiple conduits, then each conduit gets a full-sized EGC, and you connect (i.e., parallel) those EGC conductors at each end. But that is not the same as the code saying you need a minimum #8 EGC, and the installer trying to achieve that by substituting a set of parallel #12s. 250.122 does not give the option of using a set of conductors with equivalent total cross-sectional area.

 

[ronaldrc]

Re: More on upgrading ECG's

I still think one Number 12 Equipment grounding conductor would satisfy the code why would you pull a separate EGC for each conductor? We don't normally do that code says one equipment ground ,and it only has to be as large as your largest ungrounded conductor.

[ October 11, 2005, 03:07 PM: Message edited by: ronaldrc ]

 

[charlie b]

Re: More on upgrading ECG's

Originally posted by ronaldrc: I still think one Number 12 Equipment grounding conductor would satisfy the code.

It would not satisfy 250.122(B).

Why would you pull a separate EGC for each conductor? We don't normally do that

The original question had to do with using only one EGC from the panelboard to the junction box. The issue at hand is the required minimum size of that one EGC.

. . . code says one equipment ground ,and it only has to be as large as your largest ungrounded conductor.

The code does not assign an EGC size on the basis of the ungrounded conductor. It does say that the EGC never has to be larger than the ungrounded, but that is not the whole picture.

It starts off by assigning the EGC size on the basis of the overcurrent device. Then it says that if you pick an ungrounded conductor that is larger than is necessary, if ampacity were the only consideration, then you also must increase the size of the EGC.

[ October 11, 2005, 03:20 PM: Message edited by: charlie b ]

 

[iwire]

Re: More on upgrading ECG's

Ronald you lost me on that last one.

There is no escaping 250.122(B) in any installation.

What really gets funny is if you ran 6 AWG for a 20 amp circuit for any reason from a 100 amp panel you would end up with a 6 AWG EGC for that branch circuit and an 8 AWG with the 100 amp feeder.

[ October 11, 2005, 03:21 PM: Message edited by: iwire ]

 

[james wuebker]

Re: More on upgrading ECG's

I believe you should only have to step up to a #10 ground wire. It's had to figure but with derating to using a #8 Hot & neutral conducts in this circuit,you ground should be OK with a #10 gr. In a standard 20 amp circuit we use #12 H-N-G but if using a #10g you can use it up to 60 amps. A #8g is good for 100 amps without figuring any derating in it. Am I missing something here. Let me know.
Jim

 

[james wuebker]

Re: More on upgrading ECG's

I believe you should only have to step up to a #10 ground wire. It's had to figure but with derating to using a #8 Hot & neutral conducts in this circuit,you ground should be OK with a #10 gr. In a standard 20 amp circuit we use #12 H-N-G but if using a #10g you can use it up to 60 amps. A #8g is good for 100 amps without figuring any derating in it. Am I missing something here. Let me know.
Jim

 

[iwire]

Re: More on upgrading ECG's

Jim I don't think you missing anything but what 250.122(B) says.

It is short and to the point.

250.122(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.

 

[tadavidson]

Re: More on upgrading ECG's

How do you get that #8 to fit under the screw of a 20 amp breaker?

 

[iwire]

Re: More on upgrading ECG's

Originally posted by tadavidson:
How do you get that #8 to fit under the screw of a 20 amp breaker?

Many 240/120 volt 20 amp breakers will have terminals rated for 6 or 8 AWG.

Once you get to 480/277 20 amp breakers it would not be unusual to have terminals rated for 1 AWG or larger.

You can also splice a short length of smaller conductor on to the larger conductor in order to get it to fit, this will not noticeably effect the voltage drop.

In larger sizes you can get "Pin Terminals" that are made for this. You can get a pin terminal that accepts a 750 Kcmil but has a 500 Kcmil pin.

This is a pin terminal

It is installed with a hydraulic compression tool, the black piece is an insulator you slide over it after installation.

 

[james wuebker]

Re: More on upgrading ECG's

iwire, I did read 250.122(B) and we must remember the word proportionately. If you base that off the table 250.122 I still think #10 is good in this case. It's really hard to do it because it jumps from #12 for 20 amps to #10 for 60 amps. Trying to find that proportion gets a little harder because of this jump. But I can't disagree with your answer.
Thanks!
Jim

 

[infinity]

Re: More on upgrading ECG's

iwire, I did read 250.122(B) and we must remember the word proportionately. If you base that off the table 250.122 I still think #10 is good in this case.

A 20 amp circuit would require #12 conductors with a #12 EGC. So proportionately the ratio is 1 to 1. Therefore an increase to #8 circuit conductors would require the same ratio, so the EGC must be increased to # 8 also.

 

[ronaldrc]

Re: More on upgrading ECG's

Good Morning Bob was very busy yesterday.

I will explain my thinking on this subject.As I have heard many on here say the NEC is a mini mun guide line for the Electrical trade and not an instructions book and I couldn't agree more.

And it can't explain every Art. in detail.

In Art.250.122 (B) the reason it says to up size your equipment ground with your ungrounded conductors was mainly because of voltage drop.


According to the original poster there was no voltage drop issue here.It was because of the number of conductors in the conduit.

If you will look at 310.10 of the NEC you will see that the NEC tries to limit the heat produced in a conduit to a low enough point or below the temperature rating of the conductor to keep the heat from destroying the insulation on the wire over a long period of time.

Okay that said now consider this.

If we over size the conductors from a #12 to a #8 like the table of 315.15(2)(a) says to do which would be a 50 percent increase to a #8 this should correct the excessive heating of these conductors in this 2" conduit.

Presumably this will bring the temperature of this conduit system down to the NEC standards.

The equipment ground is not normally a conductor and is not going to be adding any heat to the conduit.

Now the equipment grounding conductor for a 20 amp. circuit breaker is a #12 and there is no voltage drop issue here. A #12 wire will handle the fault current to clear the circuit by kicking the breaker.

Other than just satifying what 250.122 (b) says why would I upsize my Eq. grd. to a #8?

I understand that 250.122 (b) says to oversize but I am also considering that the authors thought the electricians doing the installing would think about why they are ask to over size here.

Maybe 250.122 (b) should have an exception.

By the way if I was to do this installation I would pull 1, #12 thwn green copper equipment ground.And if my inspector wanted a #8 I would tell him what I just said above and reluctantly use the #12 to pull a #8 in with.

This is all I have to say about the subject.

Ronald