Electrical Cables in Directionally Drill Sleeve

[wirestu]

All,

My questions relate to installation of cables in directionally drilled conduits. For those of you who are unfamiliar with the technique it basically a horizontal drilling method in which a bit is pushed underground and conduit (usually HDPE - High Density Polyethelene) is pulled back in the borehole and used as a sleeve.

In our area, most of the time directional drilling is used for water, gas lines, and utility primary/secondary cable. The sleeves are usually roll out HDPE and vary in size from 3" to 18" which are fused to join the lengths. Our questions relate to the installation of electrical cables in these sleeves. The HDPE has no U/L listing as electrical conduit. The utility usually install their primary and secondary cables since they are not concerned with the NEC and U/L.

1) We are wondering if we install a cable or cable assembly (i.e. 3 conductor with ground shielded cable assembly similar to Coreflex) which is rated for direct burial can we install it inside the HDPE sleeve since the sleeve serves no electrical purpose?

2) In a second part of the project the directional driller is to install 4 - 3" HDPE sleeves in a common borehole, from a well house to a well vault pit for our electrical cables. We plan to install a shielded power cable assembly for the well pumps (2 conduit with a cable in each), a shielded direct burial instrumentation cable for the 4-20 mA signals in the pit and the final sleeve is for the float switches in the pit. The pit is a Class 1 Division 1 location. These switches are not explosion proof and must be powered through intrinsically safe barriers in a control panel. Our interpretation of the NEC says the conductors from the control panel to the probes must be in a metal grounded conduit. We are wondering if we install a corrugated metal jacketed cable assembly with say 14 #14 gauge conductors, if this would meet the intent of the code.

3) Our final question is related to local disconnect for the well and product pump. The pits are below ground and aside from explosion proof are corrosive locations due to salt water being just below the surface. The well houses are about 150' away from the well pits. The motor starters for the pumps are capable of being locked in the open position. We are in NYC and are governed by the 1999 NEC. Our question is are local explosion proof disconnect required in the vaults?

Thanks in advance for everyone's help.

Stu

 

[don_resqcapt19]

Re: Electrical Cables in Directionally Drill Sleeve

Stu,
A1) UL listed HDPE conduit is available up to 4" diameter. However, if the cable is suitable for direct burial, I see no reason that a protective sleeve would have to be listed conduit.
A2) What code section requires grounded metal conduit for the IS circuit? 504.20 permits the use of any wiring method that is suitable for use in unclassified locations.
A3) Under the '99 code, the exception to 430-102(b) clearly permits the remote lockable disconnect for this application.
Don

 

[rbalex]

Re: Electrical Cables in Directionally Drill Sleeve

1) Yes; but remember from Table 300-50, minimum cover is based on the direct burial conductor depth. No mechanical protection in is assumed from the HDPE. (I assumed MV Cable since it was shielded)

2. A bit tough. I would first want to see the IS control drawing, the area classification documentation and the pit details for a definitive answer. In general, cable listed as MC-HL or ITC-HL with appropriate termination fittings is an acceptable wiring method in Division 1. [See 501-4(a)(1) Exceptions 2&3 ] I would also want to see a vapor barrier created in the sleeves. Div 1 is serious business.

3.) From 1999 NEC no additional disconnect is required (see exception) :

430-102 (b) Motor. A disconnecting means shall be located in sight from the motor location and the driven machinery location.
Exception: A disconnecting means, in addition to the controller disconnecting means as required in accordance with Section 430-102(a), shall not be required for the motor where the disconnecting means for the controller is individually capable of being locked in the open position .