Northern Natural Gas Company

Fifth Revised Volume No. 1

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Effective Date: 11/01/2007, Docket: RP08- 67-000, Status: Effective

Fifth Revised Sheet No. 206A Fifth Revised Sheet No. 206A : Effective

Superseding: 1 Revised 2 Revised Sheet No. 206A




Tolling Agreement. A tolling agreement or arrangement means that the owner of the

electric generator has agreed with an LDC to convert natural gas owned and provided by

the LDC to electricity owned by the LDC.


Total or Gross Heating Value. The term "total or gross heating value" means the total

calorific value, expressed in Btus when one cubic foot of anhydrous gas at sixty

degrees Fahrenheit (60 F) is combusted with dry air at the same temperature and the

products of combustion are cooled to sixty degrees Fahrenheit (60 F). The Btu

specified is on a higher heating value (HHV) basis. A conversion factor is required

to convert lower heating value to a higher heating value basis to correctly calculate

the expected fuel usage of certain equipment. For estimating purposes, the higher

heating value of natural gas is approximately 10 percent more than the lower heating



Town Border Station (TBS). The term "Town Border Station" ("TBS") shall mean the

physical location where the LDC receives gas from Northern. The TBS generally

consists of facilities to regulate gas pressure and measure gas quality and volumes.


Unauthorized Gas. "Unauthorized Gas" shall mean any volumes delivered to Northern

from receipt points which have not been nominated in any amount by any Shipper for

that month and which have not been scheduled by Northern.


Valid Request. Any reference in this Tariff to a "valid request" used in conjunction

with Section 26 "Requests for Service" shall also include any requests submitted

electronically through Northern's Internet website.


Wobbe Index - The term "Wobbe Index" shall mean a number which indicates the

interchangeability of gas. The Wobbe Index is determined by dividing the higher

heating value of the gas in Btu per standard cubic foot by the square root of its

specific gravity with the respect to air. Wobbe Index is used as an indicator of the

heat release rate of combustion equipment employing fixed orifices such as boilers,

stoves, water heaters, and furnaces.