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maximum direct burial hv cable depth
- Thread starter hooman17
- Start date
NEC 2017
FIGURE 310.60(C)(3) Cable Installation Dimensions for Use with Table 310.60(C)(77)
Through Table 310.60(C)(86).
Note 1: Minimum burial depths to top electrical ducts or cables shall be in accordance with 300.5. Maximum depth to the top of electrical duct banks shall be 750 mm (30 in.) and maximum depth to the top of direct-buried cables shall be 900 mm (36 in.)
Since the cable ampacity depends on thermal resistance of the ground [RHO] and the bury depth the ampacity indicated in the FIGURE 310.60(C)(3)Tables is calculated for Rho=90 °C-cm/watt. and 900 mm depth. For deeper burying one has to recalculate the ampacity. No other limitation -in my opinion-it could be.
FIGURE 310.60(C)(3) Cable Installation Dimensions for Use with Table 310.60(C)(77)
Through Table 310.60(C)(86).
Note 1: Minimum burial depths to top electrical ducts or cables shall be in accordance with 300.5. Maximum depth to the top of electrical duct banks shall be 750 mm (30 in.) and maximum depth to the top of direct-buried cables shall be 900 mm (36 in.)
Since the cable ampacity depends on thermal resistance of the ground [RHO] and the bury depth the ampacity indicated in the FIGURE 310.60(C)(3)Tables is calculated for Rho=90 °C-cm/watt. and 900 mm depth. For deeper burying one has to recalculate the ampacity. No other limitation -in my opinion-it could be.
Another consideration needs to be practicality of access in the future for repair if the cable ever goes faulty. Going deeper will increase the cost of excavation and the complexity of the excavation.
Consider using conduits. If you are direct burying for rating then an option is to fill the conduits with bentonite which can be removed if need be by pressure jetting.
Regards
Marmite
Consider using conduits. If you are direct burying for rating then an option is to fill the conduits with bentonite which can be removed if need be by pressure jetting.
Regards
Marmite
I do not see any technical limitations for the maximum allowable depth of HV cable.
It is preferred to install the buried cable as closes to the surface to maximize ampacity, cost reduction, and resolve maintenance issue among other benefits. However, if there is any interference with subsurface underground utilities, highway, rail crossing or underwater lake sections, deeper cable installation may be required beyond the limits exposed by the NEC.
If you are in the NEC jurisdiction, take advantage of the clause "under engineering supervision" as allowed by the code
Enclosed is a sample of ampacity reduction with the cable depth
It is preferred to install the buried cable as closes to the surface to maximize ampacity, cost reduction, and resolve maintenance issue among other benefits. However, if there is any interference with subsurface underground utilities, highway, rail crossing or underwater lake sections, deeper cable installation may be required beyond the limits exposed by the NEC.
If you are in the NEC jurisdiction, take advantage of the clause "under engineering supervision" as allowed by the code
Enclosed is a sample of ampacity reduction with the cable depth
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