150-458-100-05
Appendix B - Technical Reference
HRE-458 List 1, List 1B, and List 2
February 23, 2000
23
Figure 10.
Lightning Protection Unit (LPU)
Cable Stub and Pressurization
Every HRE-458 comes equipped with a single 30-foot (9.144 m), screened, cable stub (refer to
for a complete description of the cable stub). The stub is available as List 1, List 1B (gel-filled) or List 2
(air-filled).
The stub is secured to the enclosure baseplate by a cable strain relief adapter. The cable pair is splayed out and
encapsulated in the polyurethane that is poured into the enclosure base. This provides an airtight seal at the cable
entry point.
The List 2 cable-pressurized enclosure has an air inlet tube that accompanies the air-filled stub. The air inlet tube
connects the inside of the enclosure to the main feeder cable. This tube enables dry air or dry nitrogen to flow from
the main cable into the cable stub through the air cutoff valve and into the enclosure. The air cutoff valve
(
) controls the flow through the air inlet tube as described in the
section beginning on page 2.
The pressure relief valve is not intended to control the pressure that is supplied to the enclosure. The external
network pressure control system, usually located at the front end of the main feeder cable in the servicing CO,
performs this function. Instead, the pressure relief valve should be used as a safety device for limiting the
maximum internal pressure in the enclosure.
The HRE-458 enclosures have been safety tested to 36 PSI. This amount of pressure can
severely damage most cables and cable stubs. Pressure above 60 PSI is dangerous because
the v-band is forced away from the flange and the dome could be impelled away from the
housing causing damage and injury.
The common pressure supplied through the air core cable is about 9 PSI. This is sufficient
pressure to prevent any water from entering the housing. ADC recommends pressurizing the
enclosure to a maximum of 12 PSI.
The pressure release valve is set to release at a maximum pressure of 15 PSI. Due to
manufacturing tolerances of the springs, this maximum 15 PSI pressure has a tolerance of
±3 PSI. This pressure and tolerance are well within any safety concerns that might apply to the
housing, personnel, or cable.
