2008 NEC SER Cable Requirements

[aline]

I have a situation where I'm upgrading from a 100amp service to a 200amp service for a residential single family dwelling. The existing panel will also be replaced with a 200amp panel and the homeowner wants 200amp rated conductors feeding the new panel. The homeowner is adding central air and a hot tub.

If my understanding of the 2008 Nec is correct, if the SER cable from the 200amp main breaker to the 200amp panel feeds the entire load of the home then Table 310.15(B) can be used and 4/0 al SER cable can be installed.

The issue is that the new location of the meter main with 200amp breaker is on the opposite side of the home from the new 200amp panel. The new A/C unit will be right next to the new 200amp meter main. I plan to install a 200amp meter main with 200amp main breaker with 8-16 circuit breaker spaces. I want to install a breaker at the meter main to feed power to the A/C instead of running all the way to the panel on the other side of the home.

Since the A/C load would not be carried by the SER cable, then the entire load of the home would not be carried by the SER cable, meaning I would now have to use Table 310.16 and the 60 deg. column to size the SER cable.

This makes no sense to me.
I'm reducing the load on the SER cable going to the panel by running the A/C from the meter main instead of the panel, yet I now have to increase the size of the SER cable to the panel?

Is this correct?
Am I missing something here?

 

[augie47]

You are correct.
There have been proposals for the 2011 NEC to address that issue, but as of '08, it is clear that in order to use 310.15(B)(6) the cable must carry the entire load of the dwelling unit.
In your situation, since you are using a 8-16 circuit panel at the meter, it might be best to install a 100-150 amp breaker to feed your interior panel.
Note that in most jurisdictions, your interior SE would need to be sized by the 60? ampacity.

 

[aline]

You are correct.
There have been proposals for the 2011 NEC to address that issue, but as of '08, it is clear that in order to use 310.15(B)(6) the cable must carry the entire load of the dwelling unit.
In your situation, since you are using a 8-16 circuit panel at the meter, it might be best to install a 100-150 amp breaker to feed your interior panel.
Note that in most jurisdictions, your interior SE would need to be sized by the 60? ampacity.

The home owner is adamant about having the full 200amp capacity at the interior panel.

I guess I'll just have to run the A/C unit from the interior panel so the entire load will be carried by the SER cable and then I can use the smaller 4/0 SER cable. This is funny. Increase the load on the SER cable so that I can reduce it's size.

I talked to the supply house and they don't stock or sell any SER cable larger than 4/0.
They also said the larger SER cable would not fit in the breaker lugs.

 

[jwjrw]

The home owner is adamant about having the full 200amp capacity at the interior panel.

I guess I'll just have to run the A/C unit from the interior panel so the entire load will be carried by the SER cable and then I can use the smaller 4/0 SER cable. This is funny. Increase the load on the SER cable so that I can reduce it's size.

I talked to the supply house and they don't stock or sell any SER cable larger than 4/0.
They also said the larger SER cable would not fit in the breaker lugs.

Unless you want to pvc and thhn not much choice...

 

[RUWired]

I talked to the supply house and they don't stock or sell any SER cable larger than 4/0.
They also said the larger SER cable would not fit in the breaker lugs.

How about a 4/0 cu. ser cable or 3/0 cu mc cable?

 

[Sierrasparky]

How about refeeding the A/C after you have the panels installed and inspectected then pull a permit if need be for the a/c.
Or you can ask your AHJ for a exception as you would be reducing the load on the 200 amp feed to the sub.

 

[infinity]

If he really wants his full 200 amps at the panel then he'll have to pay for larger conductors. Take your pick, run conduit and pull in conductors sized according to 310.16 or just run #3/0 MC cable as suggested. The latter would be my choice.

 

[curt swartz]

If he really wants his full 200 amps at the panel then he'll have to pay for larger conductors. Take your pick, run conduit and pull in conductors sized according to 310.16 or just run #3/0 MC cable as suggested. The latter would be my choice.

How about 4/0 AL MC? Assuming the load is <180 amps

We are still on the 05 NEC but I'm surprised that more electricians haven't changed to AL MC instead of using larger SER. One of my supply houses stocks and cuts larger MC and the price is not much more than SER.

 

[infinity]

How about 4/0 AL MC? Assuming the load is <180 amps

We are still on the 05 NEC but I'm surprised that more electricians haven't changed to AL MC instead of using larger SER. One of my supply houses stocks and cuts larger MC and the price is not much more than SER.

That would work too if you could convince the owner that his 180 amp cable is really giving him 200 amps.

 

[One-eyed Jack]

You are correct.
There have been proposals for the 2011 NEC to address that issue, but as of '08, it is clear that in order to use 310.15(B)(6) the cable must carry the entire load of the dwelling unit.
In your situation, since you are using a 8-16 circuit panel at the meter, it might be best to install a 100-150 amp breaker to feed your interior panel.
Note that in most jurisdictions, your interior SE would need to be sized by the 60? ampacity.

You guys are ignoring the last part of 310.15 b,6 that states. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity greater than their service entrance conductors.

 

[Dennis Alwon]

You guys are ignoring the last part of 310.15 b,6 that states. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity greater than their service entrance conductors.

Be careful here Jack, because this states allowable ampacity not larger wire size. The ampacity of a 4/0 alumin can be less than a 3/0 alum in certain situations. The same for other conductors.

Let me give an example. T. 310.15(B)(6) states that 2/0 copper is good for 200 amps. Now T. 310.16 states that 2/0 copper se cable is only good for 145 amps. So I would have to use 4/0 copper se cable to get the same ampacity as 2/0 copper at the service. Since the 4/0 copper se cable is not a conductor with an ampacity larger than 2/0 copper at the service then it would appear it would be needed to satisfy code even tho the wire is larger in size.

 

[infinity]

Be careful here Jack, because this states allowable ampacity not larger wire size. The ampacity of a 4/0 alumin can be less than a 3/0 alum in certain situations. The same for other conductors.

Let me give an example. T. 310.15(B)(6) states that 2/0 copper is good for 200 amps. Now T. 310.16 states that 2/0 copper se cable is only good for 145 amps. So I would have to use 4/0 copper se cable to get the same ampacity as 2/0 copper at the service. Since the 4/0 copper se cable is not a conductor with an ampacity larger than 2/0 copper at the service then it would appear it would be needed to satisfy code even tho the wire is larger in size.

I would guess that you're using this based on the words allowable ampacity?

 

[Dennis Alwon]

I would guess that you're using this based on the words allowable ampacity?

Yes, of course

 

[One-eyed Jack]

Be careful here Jack, because this states allowable ampacity not larger wire size. The ampacity of a 4/0 alumin can be less than a 3/0 alum in certain situations. The same for other conductors.

Let me give an example. T. 310.15(B)(6) states that 2/0 copper is good for 200 amps. Now T. 310.16 states that 2/0 copper se cable is only good for 145 amps. So I would have to use 4/0 copper se cable to get the same ampacity as 2/0 copper at the service. Since the 4/0 copper se cable is not a conductor with an ampacity larger than 2/0 copper at the service then it would appear it would be needed to satisfy code even tho the wire is larger in size.

I am in agreement with the above statement. In the OP,s case he would have to use 350kcm al. to get a full 200 amp capability. All because of the 60 degree requirement of 334. Allowable ampacity being the killer phrase. If you use 250kcm the allowable ampacity is less than 200. 300kcm is still less than 200. 350 is more than the allowable of the se. This is a no win for SE cable.

 

[One-eyed Jack]

The next question. Have we overcome our wire bending space when we go to 300 or 350kcm. Now to stuff that 300 into a 4/0 lug!!!!!

 

[aline]

If he really wants his full 200 amps at the panel then he'll have to pay for larger conductors. Take your pick, run conduit and pull in conductors sized according to 310.16 or just run #3/0 MC cable as suggested. The latter would be my choice.

Unless I run the A/C from the panel inside the home so the entire load of the home is carried by the SER cable running to the panel.

Then I can install 4/0 Alu SER cable protected by a 200amp breaker.

This is the flaw with this code rule.

Add the A/C on to the SER cable and I can reduce it's size even though I'm adding more load on it.

Take the A/C off of the SER cable and run it from the meter/main panel and now I have to increase the SER cable size even though I'm reducing the load on it.

 

[infinity]

Unless I run the A/C from the panel inside the home so the entire load of the home is carried by the SER cable running to the panel.

Then I can install 4/0 Alu SER cable protected by a 200amp breaker.

This is the flaw with this code rule.

Add the A/C on to the SER cable and I can reduce it's size even though I'm adding more load on it.

Take the A/C off of the SER cable and run it from the meter/main panel and now I have to increase the SER cable size even though I'm reducing the load on it.

I agree that the rule is flawed but it is what it is. As it stands right under the 2008 NEC you're stuck with it.

 

[stars13bars2]

What is the load calculation of the house, with and without the A/C load?