HELP for cathodic protection Groundbed Design

Instructions
for using
Groundbed Design Program

Introduction
The following items present very broad guidelines with respect to each of the data entry items used in this program. These statements are not to be considered absolutes, but rather as general guidelines.

Groundbed current output
Suggested Values:
Current required to provide sufficient protection to your structure.
Acceptable range of values:
Values must be in AMPS
Minimum 0.1 amps Maximum 200 amps
Affect on Calculations:
Output current is used to calculate the number of anodes required, length of the backfill column (or depth and number of holes), current density at the backfill to earth interface, and the rectifier operating voltage. Output current requirement should be determined as accurately as possible through independent tests before initiating the design.

Groundbed hole diameter
Suggested Values:
An 8 inch diameter hole is commonly recommended. A 12 inch hole is also quite common.
For horizontal designs, the number entered as hole diameter is used as width and height of the groundbed, necessary depth of calculated spare backfill is added to the top.
Acceptable range of values:
Values must be in inches. When designing a deep or shallow vertical groundbed, this dimension must be the diameter not the radius. When designing a continuous horizontal groundbed, this dimension must be the width of the groundbed.
Minimum 6 inches
Affect on Calculations:
Changes in the diameter changes the surface area of the backfill column but the affect on final design is less significant than changing the length of the column.

Backfill-soil max. current density
Suggested Values:
Recommended values are dependent on soil conditions:

Backfill Current Density - Design Values

Soil Condition	Amps/ft²	Amps/m²
Very Dry Soil	0.10	1.08
Dry Soil	0.15	1.61
Partially Dry - Not in Water Table	0.20	2.15
Moist - In Water Table	0.30	3.22
Open Hole	0.46	4.95

Acceptable range of values:
Values must be in AMPS per SQ. FT.
Minimum 0.00001 amps per sq. ft. Maximum 1000 amps per sq. ft.
Affect on Calculations:
In most deep groundbeds, this value should not exceed 100 - 200 mA/ft² Higher values will result in a higher consumption rate for the backfill.

Inactive depth
Suggested Values:
In addition to the normal reasons for including an inactive length in a groundbed design, this length can be used to force anodes below a high resistance surface soil layer.
Acceptable range of values:
Values must be in feet
Affect on Calculations:
The inactive depth will affect cable length.It will therefore affect cable resistance, which is part of total groundbed resistance. Inactive depth will also affect drilling costs.

Soil resistivity
Suggested Values:
Soil resistivities should match the soil resistivity values in the area of the groundbed.
Acceptable range of values:
Values must be in ohm cm
Minimum 10 ohm cm Maximum 500,000 ohm cm
Affect on Calculations:
Higher soil resistivities imply higher total resistance which in turn demands higher voltage values.

Cable length above ground
Suggested Values:
This is the length of cable from the junction box or header cable to the top of hole. For a shallow vertical or a horizontal design, the most accurate results are obtained if a short distance to header cable is used. When multiple strings or multiple holes are used, the program will calculate the corresponding cable lengths for the additional strings.
Acceptable range of values:
Values must be in feet
Minimum 0 feet Maximum 500 feet
Affect on Calculations:
When multiple strings or multiple holes are used, the program will calculate the corresponding cable lengths for the additional strings. This influences total cable length and hence influences total groundbed resistance.

Backfill resistivity
Suggested Values:
For LIDA deep groundbeds, ELTECH recommends using petroleum coke which has been calcined at high temperatures. Actual backfill resistivities may be obtained from the manufacturer. A conservative suggested value is 2 ohm cm.
Acceptable range of values:
Values must be in ohm cm
Minimum 0.005 ohm cm Maximum 50 ohm cm
Affect on Calculations:
A lower backfill resistivity results in lower total groundbed resistance.

Desired Groundbed total resistance
Suggested Values:
It is recommended to design for 2 ohms or less.
Acceptable range of values:
Values must be in ohm
Minimum 0.001 ohm Maximum 50 ohm
Affect on Calculations:
Increasing groundbed total resistance will also increase voltage and therefore increase cost.

Desired Rectifier operating voltage
Suggested Values:
A value that corresponds with your existing rectifier or your planned operating costs.
Acceptable range of values:
Values must be in volts
Affect on Calculations:
Increasing voltage will increase resistance and vicea versa.

Backfill Consumption Rate
Suggested Values:
For LIDA deep groundbeds, ELTECH recommends using petroleum coke which has been calcined at high temperatures. Actual backfill consumption rates may be obtained from the manufacturer. A conservative suggested value is 2.2 lbs. per amp year.
Acceptable range of values:
Values must be in lbs./amp yr
You should use the consumption rate for the backfill you plan to use in the groundbed.
Affect on Calculations:
A lower backfill consumption rate results in a shorter spare length in the design. If consumption rate used here is larger than the actual consumption rate, the design will indicate a longer spare length than actually required for the design life. Conversely, if you specify a consumption rate smaller than the actual rate, the design will indicate an insufficient spare length for the design life of the groundbed.

Vent Pipe Diameter
Suggested Values:
For LIDA deep groundbeds, ELTECH recommends using a one inch vent pipe.
For Shallow Vertical and Horizontal designs vent pipes are seldom used Enter 0 inches into the blank when no vent pipe is used.
Acceptable range of values:
Values must be in inches
Must be diameter not radius of the vent pipe.
Obviously you should not enter a diameter larger than the diameter of the hole.
Affect on Calculations:
The volume of the vent pipe is considered when calculating the volume of coke in the groundbed.

Backfill Density
Suggested Values:
A value of 70 lbs. per cu.ft.is common.
Acceptable range of values:
Values must be in lbs per cu.ft.
Backfill density of the planned backfill should be obtained from the manufacturer.
Affect on Calculations:
Backfill density is used to calculate the number of lbs. of backfill required. If you use a backfill density smaller than the actual backfill density, you will very likely not buy enough backfill material. Conversely, if you use a backfill density which is greater than the actual backfill density, it is likely that you will buy an excessive amount of backfill.

Hole Spacing
Suggested Values:
Values of 10 feet to 30 feet are common.
Acceptable range of values:
Value must be in feet
Right-of-way, company policy, and other physical considerations may well be the determining factor for hole spacing.
Affect on Calculations:
Hole spacing for shallow vertical groundbeds is a factor in computing total groundbed resistance. Larger spacing produces slightly smaller total resistance at the coke column to earth interface.

#6 HMWPE
Selection Guidelines :
Soils or water rich in chloride are the source of chlorine when the anodes are energized.

HMWPE (high molecular weight polyethylene) is non-resistant to chlorine and should be chosen only for situations where chlorine will not be present.

#6 cable may be more costly than #8 cable, but because of its larger diameter, resistance of #6 cable will be less than resistance of #8 cable. Maximum current capacity will be greater for #6 cable and that may result in fewer strings.

#6 PVDF/HMWPE
Selection Guidelines :
Soils or water rich in chloride are the source of chlorine when the anodes are energized.

PVDF/HMWPE is resistant to chlorine and should be selected where chlorine will be a factor.

#8 HMWPE
Selection Guidelines :
Soils or water rich in chloride are the source of chlorine when the anodes are energized.

HMWPE (high molecular weight polyethylene) is non-resistant to chlorine and should be chosen only for situations where chlorine will not be present.

#8 PVDF/HMWPE
Selection Guidelines :
Soils or water rich in chloride are the source of chlorine when the anodes are energized.
PVDF/HMWPE is resistant to chlorine and should be selected where chlorine will be a factor.

Groundbed Type
You may select only one of the listed groundbed types.

Checking Anode Types
You may select as many anode types as you wish. The program will construct a design for each one that you select. This feature provides a convenient method to compare several designs.

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