Type USE Ampacity 400A (320A continuous)

[Sparky555]

Please check my work:
Usually the utility provides service laterals but this is a non-residential project (dairy, office, and retail sales), so I would need to provide it. As non-residential Table 310.15(B)(6) does not apply.

So according to Table 310.16 (USE) it is:
75 degree column...600 kcmil copper or 900 kcmil aluminum.
90 degree column...500 kcmil copper or 700 kcmil aluminum.

...and the 75 degree column applies because of the termination at the meter pedestal?

 

[mwm1752]

Have no load calcs to determine -- what code cycle? -- shall carry the load m -- voltage drop? -- IMO way over kill on your answers but is compliant -- never seen a 320 pedestal just the wall mount type

 

[Carultch]

Please check my work:
Usually the utility provides service laterals but this is a non-residential project (dairy, office, and retail sales), so I would need to provide it. As non-residential Table 310.15(B)(6) does not apply.

So according to Table 310.16 (USE) it is:
75 degree column...600 kcmil copper or 900 kcmil aluminum.
90 degree column...500 kcmil copper or 700 kcmil aluminum.

...and the 75 degree column applies because of the termination at the meter pedestal?

That would be if the "next size up rule" doesn't apply, 240.4(B). If it is my choice, I would parallel.

The 90 C column usually applies for temperature corrections and ampacity adjustments to find wire ampacity. Termination ampacity of 75C must also apply, unless you are in a very rare situation where you have 90C terminations and 90C equipment.

Also note that USE without a -2 dual rating, is only rated for 75C.

 

[Sparky555]

That would be if the "next size up rule" doesn't apply, 240.4(B). If it is my choice, I would parallel.

The 90 C column usually applies for temperature corrections and ampacity adjustments to find wire ampacity. Termination ampacity of 75C must also apply, unless you are in a very rare situation where you have 90C terminations and 90C equipment.

Also note that USE without a -2 dual rating, is only rated for 75C.

I'm not following the 240.4(B) reference. The utility provides the overcorrect protection at the pole. The parallel is a good suggestion I hadn't thought of. Although it is a service lateral (130') it needs to go up the pole with RMC, IMC or Schedule 80 RNMC with a service head similar to an overhead service. With that in mind at 75 degrees I get 3/0 copper or 250 kcmil aluminum.

To the other OP, I'm not aware that Table 310.16 has changed in any recent code cycle. I'm not following the load calc question. I have a 200A service and the load calc comes in at 65A so I use a 6ga copper service lateral? I don't think so.

The oversized comment is why I'm asking. The utility engineer said they would use 350 kcmil aluminum. There is UG Triplex, if that's what it's called, which is 350-2 & 4/0 aluminum which seems to be what's commonly used. I find nothing in the NEC to support that (other than utilities don't follow NEC allowable ampacities). Utilities do size conductors on expected load. The utility is not providing this lateral.

 

[kwired]

I'm not following the 240.4(B) reference. The utility provides the overcorrect protection at the pole. The parallel is a good suggestion I hadn't thought of. Although it is a service lateral (130') it needs to go up the pole with RMC, IMC or Schedule 80 RNMC with a service head similar to an overhead service. With that in mind at 75 degrees I get 3/0 copper or 250 kcmil aluminum.

To the other OP, I'm not aware that Table 310.16 has changed in any recent code cycle. I'm not following the load calc question. I have a 200A service and the load calc comes in at 65A so I use a 6ga copper service lateral? I don't think so.

Utility protection if any doesn't really matter if this is service conductors the only overcurrent device that matters is your service disconnect(s) and their respective overcurrent devices.

If you have a single 200 amp service disconnect with 200 amp overcurrent device you must supply it with a conductor that has at least 176 ampacity and can round the protection up to next standard overcurrent device which is 200 - unless the calculated load is over 175 then the conductor ampacity must be at least that of the calculated load. This is why you often see 4/0 aluminum which is only a 180 amp conductor used for 200 amp circuits - as long as the load is not over 180.

But you could have multiple multiple service disconnecting means (up to 6) that add up to more then 200 amps according to overcurrent device settings and still have as single supply of only 6AWG if the load calc is only 65 amps. Would be somewhat rare installation but not impossible.

 

[mwm1752]

400 MCM Cu @ 75 C = 335Amps, 600 MCM Al @ 75 c = 340Amps both would be a max size needed, without any derating factors for a 320Amp max(calculated continuous & non continuos) load as stated. I might be missing something here though but not sure for whay you've given in the original post.

 

[Sparky555]

So you're both saying that the service lateral conductors are sized at 80% of the rating of the first breaker/disconnect unless a load calculation shows that the load is over 80% of that rating? I don't find this anywhere in allowable ampacities. Do you have an NEC reference?

 

[mwm1752]

I am assuming that the calculated load is 320 amps -- I do not see how dwelling services would apply for the 80%

 

[mwm1752]

220.40 General
The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted by Part III or IV or required by Part V have been applied.
230.23 Size and Rating
(A) General. Conductors shall have sufficient ampacity to carry the current for the load as calculated in accordance with Article 220 and shall have adequate mechanical strength

 

[Sparky555]

220.40 General
The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted by Part III or IV or required by Part V have been applied.
230.23 Size and Rating
(A) General. Conductors shall have sufficient ampacity to carry the current for the load as calculated in accordance with Article 220 and shall have adequate mechanical strength

Then I suppose as the load increases above the original calculation the service laterals would be required to be replaced?

 

[mwm1752]

code is minimum -- does not anticipate" what if " just calculates on what is -- options & decisions above & beyond code does not make it non compliant

 

[kwired]

So you're both saying that the service lateral conductors are sized at 80% of the rating of the first breaker/disconnect unless a load calculation shows that the load is over 80% of that rating? I don't find this anywhere in allowable ampacities. Do you have an NEC reference?

No. Art 220 load calculations will give you a number that doesn't need further adjustments.

A 320 meter socket is rated 320 continuous 400 non continuous but has nothing to do with conductor ampacity.

Remember the minimum size conductor must be selected based on load, you can use next higher standard device for overcurrent protection for 800 amps or below circuits. A conductor can be larger then minimum size needed to carry load but still must have proper overcurrent protection, which also can be next standard size higher.

Or if you only have say 278 amps of calculated load your choices are to go with at least 278 amps conductor and 300 overcurrent device or many would choose to go with 400 amp supply to allow for some growth - but that means you need at least 351 amp conductor if the load is less then 350 but you are using a 400 amp overcurrent device because 350 is a standard size and next up is 400.

If you select 500 copper which has 380 ampacity or 700 aluminum which has 375 ampacity those would be fine on 400 amp device as long as load is not more then 380 or 375.

This is for conductors feeding a single overcurrent device - my example earlier with multiple service disconnects being fed is one situation where you could have less conductor size - say you were feeding two 200 amp disconnects but load calculation were only 300 between the two - a 300 amp conductor is all that is needed for a common supply conductor - but a conductor allowed to be protected at 200 amps is needed for the tap to each disconnect.

 

[Sparky555]

I appreciate the clarity of your reply kwired. Thanks!

 

[Dennis Alwon]

The 320 amp meter base always causes trouble since it is really a 400 amp meter base. As Kwired stated it is rated 320 for continuous load---

 

[Sparky555]

So if I understand this correctly (it is a 400A with (2) 200A mains) if the load calc comes in under 160A I could run 2/0 copper (175A) or 4/0 aluminum (180A).

 

[Dennis Alwon]

Not exactly. 175 amp is a standard size overcurrent protective device so you cannot use the next higher size breaker. I am not sure where the 160 amps came from other than 80% of 200 amps which has nothing to do with this.

A 200 amp breaker can have 200 amps of load but it cannot be be 200 amps of continuous load. The continuous load can be 160 and non continuous load can be 40 amps on a 200 amp breaker. In this case the wire must be 3/0 at 75C

Now if the calculated load of continuous plus non continuous load was 180 amps or less then I could use 4/0 aluminum at 75C (180 amps) and still maintain the 200 amp breaker.

If you use 2/0 copper you would have to change the overcurrent protective device to 175 amps

 

[kwired]

So if I understand this correctly (it is a 400A with (2) 200A mains) if the load calc comes in under 160A I could run 2/0 copper (175A) or 4/0 aluminum (180A).

Now that you have told us you do have multiple mains, what I was mentioning earlier can apply. You don't necessarily need full 400 amps of supply conductor but do need to have enough ampacity for calculated load. You do need over 175 amp tap conductors (because 175 is a standard overcurrent device size) to each 200 amp main even if the main supply conductor is less then a 400 amp conductor.

Then comes instances where you are supplying motor loads where you may be able to increase the overcurrent setting.

Clear as mud isn't it?

 

[mwm1752]

If this is a 320amp meter with 2 - 200 amp mains the tap conductors are already installed as part of the assembly. One common install has been parallel 4/0 service laterals into a ct can, the laterals are tied together prior to passing through the CT's, some use split bolts, or feed thru taps, then they continue to separate 200 amp disconnect with OCPD mains. The 4/0 Al is rated @ 180 amp 75C which complies with an unfused tap terminating into a 200 amp OCPD.

 

[Sparky555]

Thanks to all for the clarifications. I didn't know 175A breakers existed, I thought they were 150, 200. It is a 320 with 2/200s.

Now I understand the utility engineer's suggestion of 350 kcmil lateral, which they would use and which is ample for the load.

 

[Dennis Alwon]

Thanks to all for the clarifications. I didn't know 175A breakers existed, I thought they were 150, 200. It is a 320 with 2/200s.

Now I understand the utility engineer's suggestion of 350 kcmil lateral, which they would use and which is ample for the load.

Look at art. 240.6 for a list of standard breakers