-->/images/PowerCableUpdate.jpg/images/southwire_100x70.jpgWaste-Water Applications Go for Thicker InsulationsWasteWaterApplicationsGoforThickerInsulations.htmIn harsh environments, thicker is better when it comes to power cable insulation.
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Waste-Water Applications Go for Thicker Insulations

In harsh environments, thicker is better when it comes to power cable insulation.

Power cables lead a tough life for in waste-water treatment plants. The chlorine used in the treatment process creates an acidic environment that can be hard on cables – especially PVC-insulated THHN conductors.

“The harsh conditions around waste-water processing motivate many treatment facility operators to switch from THHN-rated conductors to cables carrying an XHHW or RHH/RHW type conductor,” says David Cooper, Southwire senior product engineer.

What’s the difference? Any of them can be used in cable trays (if listed) or in conduit. All of them are rated for continuous 90°C operation in wet and dry locations. But there are differences in materials properties and insulation thickness – and those differences count in harsh environments.

 

How do you choose?

Southwire type THHN or THWN-2 conductors carry a polyvinyl chloride (PVC) insulation that’s protected by a nylon jacket.  The nylon jacket offers good resistance to oil and gasoline. But if you nick the nylon during installation, you get a couple of problems. First, the PVC insulation can suffer from exposure to chlorine and other chemicals commonly used in waste-water treatment. The exposure to chemicals is especially critical when you pull THHN into conduit, because any barbs left in the conduit can cut into the nylon jacket – and a lot of THHN goes into conduit.

RHH/RHW-2 and XHHW are showing up as alternatives to THHN in acidic environments for two reasons: They both use cross-linked polyethylene (XLPE) insulation rather than PVC. Second, they both offer more insulation thickness than THHN. XHHW offers a little more thickness, RHH/RHW offers quite a bit more. In general, in the demanding waste-water treatment environment, the thicker the insulation, the better off you are.

Here’s an example: A single-conductor 350 kcmil THHN cable uses 60 mils of PVC. An XHHW conductor delivers 65 mils of XLPE. RHH-RHW gives you 95 mils of XLPE. The table below summarizes the constructions.

 

Thicker is better

“The cost differential for the upgraded insulation is very small compared to the cost of unscheduled downtime,” Cooper says. “And for maximum performance, Southwire can supply XHHW insulation with a PVC jacket. On a 350kcmil conductor, you get 65 mils of XLPE and a 65 mil PVC jacket, for a total of 130 mils of protection. That will absorb a lot of abuse.”

Table:

600V Power Cable Comparison

 

 

THHN/THWN-2

XHHW-2

RHH/RHW-2/USE-2

Insulation

PVC, nylon jacket

XLPE

XLPE

Example insulation thickness:

350 kcmil copper conductor

60 mils

65 mils

95 mils

Resistant to

Heat; moisture; gasoline; oil; AWG 2 and larger are sunlight resistant

High-heat; moisture; AWG 2 and larger are sunlight resistant

High-heat; moisture; sunlight resistant

Applications

conduit, all sizes;

1 /0 AWG and larger are CT-rated

conduit, all sizes;

1 /0 AWG and larger are CT-rated

conduit, all sizes; direct burial; 1/0 AWG and larger are CT-rated

Temperature ratings

90ºC wet/dry,

75ºC when exposed to oil or coolant

90ºC wet/dry

90ºC wet/dry

Other Southwire ratings

MTW; AWG 8 and up rated THWN-2; AWG 14 - AWG 6 rated AWM (105ºC)

AWG 14 - AWG 8 rated SIS

AWG 6 - AWG 4 rated SIS