MV Circuits Direct Bury

[bwat]

How often are people seeing direct bury with MV circuits rather than any conduit or concrete encased conduit? Specifically with decent sized (1MW+) solar sites.

It seems to be more common in this sector than others.

 

[bwat]

I should have also added: and your thoughts on the matter?

 

[electrofelon]

Are you talking about like 15 kV class stuff or 2 KV PV wire?

For 15KV CN cable, we did some solar sites down in Georgia and the utilities would just direct bury it. Of course that Clay is pretty soft friendly stuff there. Up here in New York when we do underground utility line extensions they require either sand bedding or PVC conduit.

For PV wire, we have always put in conduit, I've never seen it direct buried but with appropriate soil or sand bedding, I'm sure it would be fine.

Also I think 300.50(A)(3) , requiring metal conduit or nonmetallic conduit with concrete encasement for non shielded cables in other than industrial establishments is ridiculous.

 

[bwat]

Are you talking about like 15 kV class stuff or 2 KV PV wire?

For 15KV CN cable, we did some solar sites down in Georgia and the utilities would just direct bury it. Of course that Clay is pretty soft friendly stuff there. Up here in New York when we do underground utility line extensions they require either sand bedding or PVC conduit.

For PV wire, we have always put in conduit, I've never seen it direct buried but with appropriate soil or sand bedding, I'm sure it would be fine.

Also I think 300.50(A)(3) , requiring metal conduit or nonmetallic conduit with concrete encasement for non shielded cables in other than industrial establishments is ridiculous.

Sorry, the 15kV class is what I was asking about. Yeah it seems like utilities in NE will often require PVC and/or concrete encasing, but if it's privately owned (not utility in this case) I'm wondering how common it is to see the MV direct buried from pad to pad.

 

[electrofelon]

Sorry, the 15kV class is what I was asking about. Yeah it seems like utilities in NE will often require PVC and/or concrete encasing, but if it's privately owned (not utility in this case) I'm wondering how common it is to see the MV direct buried from pad to pad.

Around here (upstate NY). One of the utilities here owns and maintains an UG extension to a pad xformer. The customer has to dig the trench and provide sand bedding under and over. POCO throws in the cable. The other utility allows a customer owned MV line extension, where we buy and install and own the primary. Despite being customer owned, we do have to meet their specs. We can protect with sand or put in PVC conduit. I have always put in conduit as that seemed cheaper than dealing with sand which is sometimes thousands of feet through the woods so a real logistical nightmare (I'm reconsidering that now though with the cost of PVC). Long story short, I wouldn't have a problem with direct bury CN cables in friendly soil or with sand backfill. My thinking is these cables are quite tough, and the concentric neutral surrounds and protects the semicon and insulation,and that is fine to touch the dirt if the outer covering is knocked. Note that concentric neutral cable is sometimes not even covered, in other words it's just the concentric neutral on the outside with no covering and that is directly buried! But I always get the covered stuff.

 

[pv_n00b]

I see a lot of cable thermal studies and they are all for direct buried MV cables in the collector circuits. Great to lower the install cost, a pain for O&M.

 

[ron]

Direct bury for cheaper install, but there is a trade off with time to repair and the likelihood that it would be damaged in the first place.