Medium Voltage feeder under building

[EEJaime]

Good morning,
Just trying to confirm what I believe to be the truth, but getting other 'eyes' on the problem never hurts.

We have a couple of buildings under construction at a high school here in southern California. Contractor ripped up an on-site 4160V feeder with his backhoe. Well we are investigating the damage and will get it fixed, however the routing of the on-site, customer owned feeders was not as the "as-built" drawings indicated. Big surprise there. Luckily no one was injured. There is a problem with the system coordination as neither the feeder breaker, nor the main system breaker cleared the fault before some SCE faciities on the service pole were damaged. But that is not the issue I am asking about here.

Anyway, the routing is such that now it will be below the slab of the new classroom building. The District asked if code required them to re-route the conduit outside the building footprint. We stated that since the feeder bypasses the building and was sufficiently deep to clear the footings, there was no code (NEC/CEC), that would require that. Just wanted to know if anyone out there has any code references that would NOT allow such an installation. I know that this is not the ideal situation, but I don't believe it is a code issue.

If anyone has information to the contrary, please enlighten me.

Thank you and regards,
EEJaime

 

[dpc]

I believe it would be allowed by NEC, as long as you have the necessary concrete thickness (2"). Article 230.6 seems to say (to me) that this is explicitly OK, since the feeder is considered outside the building.

As you say, it is not an ideal solution, but I'm sure I've probably done something similar in the past.

David Castor

http://www.cvoes.com

 

[jghrist]

Look at it this way. If the conduit is beneath the building, it will be damn unlikely to be dug up again. On the other hand, if the cable fails and you can't get it pulled out of the conduit, it will be damn hard to get to to repair.

 

[EEJaime]

jghrist,
That is why I say it isn't an ideal solution. I think the District is looking for a way to offset costs to someone else. If we had a code violation in the design, (even though the "as-built" drawings they provided to us showed this line twenty feet away from actual location), they could say that we should have indicated the line needed to be re-routed, or should have warned the contractor to avoid it, or who knows what else, but they might be able to get some E & O mileage out of it. If they want it relocated, we will direct the contractor to do so, but it will need to be a District preferance and on their dime. I don't know off-hand how much the Contractor is liable for, but there is standard language in the doc's about damaging existing facilities. Hopefully we can arrive at a reasonable fix.

 

[dpc]

They should be down on their knees giving thanks that no one was injured or killed and that the personal injury lawyers were not unleashed.

David Castor

http://www.cvoes.com

 

[alehman]

Did anyone call the local utility locate service before digging?

It's not necessarily a code violation.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[resqcapt19]

Alan,
The original post said that the feeder that was hit was customer owned. Around here the utility locate services do not locate customer owned lines. He also said that the as-builts did not show the cable in the correct location.

That being said, the cable should have been located by the contractor before digging. If the contractor does not have locating equipment, other than the back hoe, he could hire a contractor that does. Often electrical equipment testing companies provide that type of service.

 

[rbulsara]

Such situations are best resolved by skillful negotiations and not throwing books at each other, even if it may not be a outright code violation.

One can always argue that the contractor was negligent in not making efforts to located existing underground utilities before digging. Even the engineers can share a blame for not specifying so. Relying on as-built is not an excuse or a good practice. It should have an appropriate disclaimer, when used.



Rafiq Bulsara

http://www.srengineersct.com