Vendor VS POCO... both are correct...

[altarengineering]

Recently a situation arose where a vendor installed a 200 HP motor with 18.5 amps or variable load (irrigation). The POCO installed 35 feet of 350 mcm USE-2 Quadraplex direct buried from the POCO's TX to the customers 800 amp disconnect (Franklin motor starter for irrigations). The vendor raised the issue that the terminations inside the cabinet were rated at 75C and that the derated 350 mcm according to NEC was inadequate. The POCO stood on the principle that the point of service was the terminations inside the cabinet and that the cable was not under the jurisdiction of the NEC and according to cable manufacturer was rated at 305 amps at 90C.

Additional facts; POCO claims to provide service at 480 and not the 460 referenced in NEC tables.
200 HP motor rated at 240 amps plus 18.5 - total full coincident LOAD 258.5

Questions; Does POCO have the ability to stand on the exemption from NEC considering the "point of service" rule. Are there any issues or rules which would reinforce either case...?

 

[jim dungar]

Questions; Does POCO have the ability to stand on the exemption from NEC considering the "point of service" rule. Are there any issues or rules which would reinforce either case...?

Any conductors under the exclusive control of the POCO may be sized per their methods. Any conductors under the control of the customer must follow NEC rules. This means that often there is a demarcation point (e.g. the meter/CT cabinet) where two different size conductors are joined.

Even if the utility sizing applies, they are not able to ignore the UL Listing of the equipment restricting them to the 75?C ratings of the lugs. Have you considered in-line compression splices? You would need about 4ft of conductors.

The voltage rating of the source, 480V, and that of the utilization equipment, 460V, are for all intents identical and proper for the purpose of the service conductor sizing.

 

[Cavie]

POCO is not goverened by the NEC.

 

[jim dungar]

POCO is not goverened by the NEC.

No, but they are by Listing requirements and manufacturer's instructions.

 

[Smart $]

No, but they are by Listing requirements and manufacturer's instructions.

I agree... but the question that I see that remains unanswered is how altarengineering can establish that 4ft (or any length) of conductors with a minimum ampacity of 258.5A at 75?C is required.

Also, OP didn't specify copper or aluminum. 350Kcmil copper conductors are NEC rated 310A at 75?C, so I'm assuming POCO installed aluminum conductors, which are NEC rated 250A at 75?C.

From there ambient temperature correction factor comes into play. If conductors are aluminum, a correction of 258.5 ? 250 = 1.03, which is entirely reasonable for direct buried conductors, would make the installation NEC and UL compliant. Ambient correction factor for 21-25?C is 1.05 for 75?C conductors.

Being underground and only 35', the emerged conductor distance shouldn't come into play, but thought I'd mention it since we don't have the necessary details to rule it out.

 

[texie]

My question is, why is the PoCo connecting the disconnect? Is there not a CT cabinet where the PoCo lands the service conductors (where there may well be 90 degree terminals)? Then the owner runs NEC compliant conductors from the CT to the main. What am I missing here?

 

[jim dungar]

... can establish that 4ft (or any length) of conductors ...

The UL test for terminal temperature, among other factors, uses 4ft of appropriately sized conducotrs, therefore the standard industry thought is that amount of conductor buffers the device from any other condition.

 

[Smart $]

The UL test for terminal temperature, among other factors, uses 4ft of appropriately sized conducotrs, therefore the standard industry thought is that amount of conductor buffers the device from any other condition.

I understand that... but I was inferring there should be UL documentation altarengineering can reference.

 

[mivey]

The UL test for terminal temperature, among other factors, uses 4ft of appropriately sized conducotrs, therefore the standard industry thought is that amount of conductor buffers the device from any other condition.

What about the 15 foot heat sink also used by the industry? That seems to be the basis for the 10 ft transitioning exception. To err on the side of caution perhaps a 10-15 ft section would be better.

 

[mivey]

Recently a situation arose where a vendor installed a 200 HP motor with 18.5 amps or variable load (irrigation).

The POCO does not have to use the loads as calculated by the NEC rules. They can if they want, but they can also use other source tables, empirical data, and specific calculations.

The POCO installed 35 feet of 350 mcm USE-2 Quadraplex direct buried from the POCO's TX to the customers 800 amp disconnect (Franklin motor starter for irrigations).

The POCO probably used a 350 kcmil aluminum XLPE type cable but whatever the case may be it was probably rated for 90?C like USE-2.

The vendor raised the issue that the terminations inside the cabinet were rated at 75C and that the derated 350 mcm according to NEC was inadequate.

If they did bring the cable to the cabinet, they would need to allow for the 75?C termination. They could have required the customer to meet them at a splice point with 90?C rated cable sized for 75?C per the NEC (but the utility cable from the splice back towards the transformer would be sized for 90?C).

They could also have required the customer bring their cable to the transformer. Even if installed by the customer, this cable could be under the NESC if the control was turned over to the utility (quite common). If the customer owns and maintains the cable, it would have to meet NEC (and any specific POCO service requirements).

The POCO stood on the principle that the point of service was the terminations inside the cabinet and that the cable was not under the jurisdiction of the NEC and according to cable manufacturer was rated at 305 amps at 90C.

They are correct but still have to consider the 75?C termination.

Additional facts; POCO claims to provide service at 480 and not the 460 referenced in NEC tables.
200 HP motor rated at 240 amps plus 18.5 - total full coincident LOAD 258.5

They do not have to use the customer NEC load calcs.

Questions; Does POCO have the ability to stand on the exemption from NEC considering the "point of service" rule.

Absolutely. Their facilities fall under the NESC (or whatever they choose to use) as long as it does not provide things for non-restricted use. An example would be that lighting on customer property supplied from the POCO distribution system falls under the NESC as long as they don't provide receptacles at the base of the pole that can be used by unqualified persons.

Are there any issues or rules which would reinforce either case...?

The NESC and NEC show that this cable is under the NESC. However, the NESC performance design would support consideration of the 75?C termination.

Even after all is said and done, the cable is more than adequate. Suppose we use the NEC loads and ampacities, after adjusting for the 20?C buried ambient we have a 278 amp capacity at a 75?C rating. From Table 310.15(B)(16) and Table 310.15(B)(2)(A): 250 amps * 1.11 = 277.5 amps.

 

[petersonra]

No, but they are by Listing requirements and manufacturer's instructions.

what law makes that so?

 

[texie]

Any conductors under the exclusive control of the POCO may be sized per their methods. Any conductors under the control of the customer must follow NEC rules. This means that often there is a demarcation point (e.g. the meter/CT cabinet) where two different size conductors are joined.

Even if the utility sizing applies, they are not able to ignore the UL Listing of the equipment restricting them to the 75?C ratings of the lugs. Have you considered in-line compression splices? You would need about 4ft of conductors.

The voltage rating of the source, 480V, and that of the utilization equipment, 460V, are for all intents identical and proper for the purpose of the service conductor sizing.

I agree on all points. But I go back to my post #6, is there not a CT cabinet in this installation to solve this issue? It would appear the OP would need conductors connected to his disconnect with an ampacity at 75 degrees of 240A * 1.25 plus the 18.5A of non continuous load (assuming it is non continuous) which is 318.5 A. This would be a 400 CU or a 600 AL.

 

[mivey]

what law makes that so?

Not sure there is one other than the law of common sense. I can't think of anything at the moment but the utility could vary from specific manufacturer instructions if they had valid reason. If things go south they better have good validation. As for the temperature limit of the equipment: I don't see how you would get around that one and nor do I see a good reason in general.

 

[mivey]

I agree on all points. But I go back to my post #6, is there not a CT cabinet in this installation to solve this issue?

Probably has CTs in the pad-mount transformer with a meter mounted next to the transformer. Sounds like the cable goes directly from the transformer load-side terminals to the customer equipment terminals.

It would appear the OP would need conductors connected to his disconnect with an ampacity at 75 degrees of 240A * 1.25 plus the 18.5A of non continuous load (assuming it is non continuous) which is 318.5 A. This would be a 400 CU or a 600 AL.

Not if it is utility conductor.

 

[kwired]

I agree on all points. But I go back to my post #6, is there not a CT cabinet in this installation to solve this issue?

There is likely metering somewhere, but that apparently is not the service point in this case otherwise the POCO would not have run the conductors in question. I see the service point in this case as the line side terminals of the service disconnect. Still possibly complicates things with the temperature rating of those terminals though. Is POCO going to pay for repair/replacement of the disconnect if the line side terminals fail? My guess is no.

 

[texie]

OK, I guess if the OP has no CT can to use a demarcation point because the metering is done in a pad mount (we think), then he will need a tap box to act as a demarcation point. I've done them in the past in cases like this. It's just a big box with busbars in it with lugs for line and load and can be had with 90 degree terminations. They are commercially available. PoCo runs to the line side with the service conductors and customer runs NEC compliant load conductors from the load side to the service disconnect. This is the only way I would accept it if I was the AHJ. The way the OP describes is not compliant and will probably lead to problems.

 

[mivey]

There is likely metering somewhere, but that apparently is not the service point in this case otherwise the POCO would not have run the conductors in question. I see the service point in this case as the line side terminals of the service disconnect.

I agree.

Still possibly complicates things with the temperature rating of those terminals though. Is POCO going to pay for repair/replacement of the disconnect if the line side terminals fail? My guess is no.

With the conservative parameters, if they do fail I highly doubt it will be because of the temperature rating. The conductor is more than adequate as is.

 

[mivey]

OK, I guess if the OP has no CT can to use a demarcation point because the metering is done in a pad mount (we think), then he will need a tap box to act as a demarcation point.

Does not necessarily need it, but it is an option if so desired.

I've done them in the past in cases like this. It's just a big box with busbars in it with lugs for line and load and can be had with 90 degree terminations. They are commercially available. PoCo runs to the line side with the service conductors and customer runs NEC compliant load conductors from the load side to the service disconnect.

If you insist on a separation point ahead of the equipment, a simple UG splice would make more economic sense. A splice box would be more practical with multiple service taps, not just one load.

This is the only way I would accept it if I was the AHJ.

That is a bit overboard IMO.

The way the OP describes is not compliant and will probably lead to problems.

I disagree and doubt you can substantiate your suspicions. Unless you have evidence that has not been provided here, there is nothing wrong with the OP installation.

 

[jim dungar]

what law makes that so?

In Wisconsin it is the same Administrative Code that enforces the NEC.
Among, other items, this code specifically prohibits the utility from providing service (e.g. connecting) to installations that do not meet the NEC.

 

[mwm1752]

If the wire is rated @ 90C & the terminals are 75C -- do we not start derating from the conductor 90C rating & land on the terminal 75C rating as max amps , when the derate solution is more than the 75C rating? It seems that all are starting the derate from the 75C column.