building feeding another building

[Grouch1980]

Hi all,
We have an existing building that will feed a new building about 300 feet away from it. Both buildings are on the same lot, management, owner, etc. Based on NEC article 225, this would be allowed. I'm looking at having the feeder between the buildings trenched 24" below grade. However, the owner wants to save money and have the feeder routed overhead instead of trenched. it's 3 sets of PVC conduit. would the NEC code allow this? can the feeder be routed overhead? and how would 3 sets of conduits even be supported?

Thanks!

 

[zbang]

Not going to save any money putting conduits above ground- you'd have to build a lot of support structures for them. Why not go full overhead with a 3-4 poles and messenger-supported wire?

What kind of load are we talking about? (Any reason not to just put in another service and let the PoCo get the wire there?)

 

[Grouch1980]

the load is about 700 amps. the client wanted to go with building feeding building. using the utility company was talked about, but in the end it was decided for bldg to feed bldg. don't know the details though. so, from the looks of it, it looks like yes the code allows to go overhead. we would just need a lot of supports from what you're saying. perhaps we can use messenger supported wiring, i haven't looked at that though yet.

 

[zbang]

Voltage matters, too. If you need 208/120 at the end and have 480/277 at the main bldg, put the transformer at the far end. If all you have is 208, might make $ sense to boost that to 480 (or 600), go overhead with that, and drop back at the end.

AFAICT, outside of factory plants nobody runs conduit "overhead" between buildings, and not for that length; it's either buried conduit or messenger-supported overhead from poles. (I'm sure someone will correct me .)

 

[infinity]

RMC has a burial depth of only 6" so not much trenching is required. Can the conduit be run sitting on the ground?

 

[Grouch1980]

Voltage matters, too. If you need 208/120 at the end and have 480/277 at the main bldg, put the transformer at the far end. If all you have is 208, might make $ sense to boost that to 480 (or 600), go overhead with that, and drop back at the end.

AFAICT, outside of factory plants nobody runs conduit "overhead" between buildings, and not for that length; it's either buried conduit or messenger-supported overhead from poles. (I'm sure someone will correct me .)

yes... the feeder is actually 480 volts... we are putting the transformer at the far end, where the second building is located. There we are stepping down to 120/208 volts.

I've never seen overhead conduits either. right now i have it designed as buried. maybe i can look into messenger supported wiring.

 

[Grouch1980]

RMC has a burial depth of only 6" so not much trenching is required. Can the conduit be run sitting on the ground?

it cannot... we are going through driveways / parking lots.

 

[jusme123]

Just put It underground, the idea of building a tressle system for 3 conduits is ridiculous jmo. Also, run a 2” spare conduit for future whatever

 

[zbang]

it cannot... we are going through driveways / parking lots.

Directional drilling and pull in DB cable?

 

[Jerramundi]

You could do a comparative cost analysis and see which one would be cheaper and then present that to the higher ups, but I highly doubt you're going to save money going overhead with the amount of supports you would need.

How would one even calculate the number of supports needed? The maximum distance allowable for messenger cables? Which I think is 40 ft?

I would just bore it through the lot. That's what we used to do on cell tower sites. I was a grunt laborer at the time so other than telling you that it's a good amount of work, I wouldn't know exactly what the equipment is called... we bored a hole, used a pulley system to pull PVC through, then pulled the wire.

I guess it could be close in cost when you add the equipment needed to bore a hole... vs the cost of mounting supports. Not gonna be cheap either way.

The cheapest thing would probably be utilizing the utility company for a separate drop if available nearby.