Underground 33 KV cable burial/protection requirements
Underground 33 KV cable burial/protection requirements
(OP)
The Power Company contractor is installing an undergroung HV feeder, the ground is rocky and in spots they can only go 20-30cm deep. the cable is in black hddp conduit with red stripes and is coverde with cement blocks and cement. The customer is concerned that the installation is unsafe.
The cable is being installed along a public road with limited access. The feeders are protected at each end with fuses and the load is minimal (less than 3 amps)and there is only one load at the end of the 600 meter installation a 60 kva transformer.
Opinions please on safety and code requirements if avaliable but the power company is doing the job so the code doesn't apply!!!!!
Thanks
Farang
The cable is being installed along a public road with limited access. The feeders are protected at each end with fuses and the load is minimal (less than 3 amps)and there is only one load at the end of the 600 meter installation a 60 kva transformer.
Opinions please on safety and code requirements if avaliable but the power company is doing the job so the code doesn't apply!!!!!
Thanks
Farang






RE: Underground 33 KV cable burial/protection requirements
600V - 50Kv Min. = 76cm, prefered = 90cm, Max. = 122cm
Allowable exception due to rocky soil conditions are as follows:
All cable in schedule-80 conduit, allowable trench depth to top of conduit = 46cm.
All cable in DB 120 conduit with a 10cm thick concrete cap, allowable trench depth to top of conduit = 30cm.
All cable in schedule-80 PVC with a 10cm thick concrete cap, allowabletrench depth to top of conduit = 15cm.
Hope this helps.
RE: Underground 33 KV cable burial/protection requirements
RE: Underground 33 KV cable burial/protection requirements
The NEC dors not apply to utilities.
RE: Underground 33 KV cable burial/protection requirements
But if it is necessary for some reason (eg political interference), it might be an idea to fill the trench with concrete.
Bung
Life is non-linear...
RE: Underground 33 KV cable burial/protection requirements
I agree with Bung. That seems like a very expensive way to get 60kVA.
RE: Underground 33 KV cable burial/protection requirements
IT's not safe. 20 cm deep is less that 8" deep. Normal practice here would be 36". What does the utility say? It sounds like the contractor doesn't have the equipment to trench in rock and is trying to get someone to agree with his scheme for doing it on the chrap. Trenching in rocky ground is not cheap - no way around it.
A semi public road is a public road, Murphys law applies. IT may be the gardner or some yahoo digging fishworms but sooner or later someone may get into it.
The cable in conduit is a good way to go. Back fill with some red dyed flowable fill and that's about as safe as it gets.
RE: Underground 33 KV cable burial/protection requirements
Table 1, Case 8 of State of California Public Utilities Commission General Order #128 (Rules for construction of underground electric supply and communication systems") requires depth of 751-35000V supply cables and ducts to be 24" (minimum), above 35000V: 36".
Fig.1 of the referenced document shows the dimensions to concrete encasement