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PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION
 12 Months Ended
Dec. 31, 2019
Property, Plant and Equipment [Abstract]  
PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION

Utility property, plant and equipment is recorded at original cost.  Original cost includes materials, labor, construction overheads and AFUDC for regulated property.  The cost of repairs and maintenance is charged to Operations and Maintenance expense as incurred.  

The following tables summarize property, plant and equipment by asset category:
Eversource
As of December 31,
(Millions of Dollars)
2019
 
2018
Distribution - Electric
$
15,880.0

 
$
15,071.1

Distribution - Natural Gas
3,931.1

 
3,546.2

Transmission - Electric
10,958.4

 
10,153.9

Distribution - Water
1,726.5

 
1,639.8

Solar
200.2

 
164.1

Utility
32,696.2

 
30,575.1

Other (1)
1,025.6

 
778.6

Property, Plant and Equipment, Gross
33,721.8

 
31,353.7

Less:  Accumulated Depreciation
 
 
 
Utility    
(7,483.5
)
 
(7,126.2
)
Other
(387.4
)
 
(336.7
)
Total Accumulated Depreciation
(7,870.9
)
 
(7,462.9
)
Property, Plant and Equipment, Net
25,850.9

 
23,890.8

Construction Work in Progress
1,734.6

 
1,719.6

Total Property, Plant and Equipment, Net
$
27,585.5

 
$
25,610.4

 
As of December 31,
 
2019
 
2018
(Millions of Dollars)
CL&P
 
NSTAR
Electric
 
PSNH
 
CL&P
 
NSTAR
Electric
 
PSNH
Distribution - Electric
$
6,485.5

 
$
7,163.7

 
$
2,271.1

 
$
6,176.4

 
$
6,756.4

 
$
2,178.6

Transmission - Electric
5,043.0

 
4,411.9

 
1,498.7

 
4,700.5

 
4,065.9

 
1,338.7

Solar
—

 
200.2

 
—

 
—

 
164.1

 
—

Property, Plant and Equipment, Gross
11,528.5

 
11,775.8

 
3,769.8

 
10,876.9

 
10,986.4

 
3,517.3

Less:  Accumulated Depreciation
(2,385.7
)
 
(2,895.3
)
 
(799.9
)
 
(2,302.6
)
 
(2,702.0
)
 
(772.9
)
Property, Plant and Equipment, Net
9,142.8

 
8,880.5

 
2,969.9

 
8,574.3

 
8,284.4

 
2,744.4

Construction Work in Progress
483.0

 
592.3

 
159.6

 
335.4

 
510.3

 
135.7

Total Property, Plant and Equipment, Net
$
9,625.8

 
$
9,472.8

 
$
3,129.5

 
$
8,909.7

 
$
8,794.7

 
$
2,880.1


(1) 
These assets are primarily comprised of computer software, hardware and equipment at Eversource Service and buildings at The Rocky River Realty Company.

In 2019, Eversource recorded an impairment charge for the NPT project costs, which had been recorded within both Construction Work in Progress and the Transmission - Electric asset categories. For further information regarding the impairment of NPT, see Note 1D, "Summary of Significant Accounting Policies - Impairment of Northern Pass Transmission," to the financial statements.

Depreciation of utility assets is calculated on a straight-line basis using composite rates based on the estimated remaining useful lives of the various classes of property (estimated useful life for PSNH distribution and the water utilities).  The composite rates, which are subject to approval by the appropriate state regulatory agency, include a cost of removal component, which is collected from customers over the lives of the plant assets and is recognized as a regulatory liability.  Depreciation rates are applied to property from the time it is placed in service.

Upon retirement from service, the cost of the utility asset is charged to the accumulated provision for depreciation.  The actual incurred removal costs are applied against the related regulatory liability.  

The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows:
(Percent)
2019
 
2018
 
2017
Eversource
3.0
%
 
2.9
%
 
3.0
%
CL&P
2.8
%
 
2.8
%
 
2.8
%
NSTAR Electric
2.8
%
 
2.8
%
 
2.9
%
PSNH
2.8
%
 
2.8
%
 
3.1
%


The following table summarizes average remaining useful lives of depreciable assets:
 
As of December 31, 2019
(Years)
Eversource
 
CL&P
 
NSTAR Electric
 
PSNH
Distribution - Electric
34.3
 
35.3

 
33.7

 
33.2

Distribution - Natural Gas
43.2
 
—

 
—

 
—

Transmission - Electric
40.4
 
36.8

 
44.9

 
42.1

Distribution - Water
33.5
 
—

 
—

 
—

Solar
24.2
 
—

 
24.2

 
—

Other (1)
11.2
 
—

 
—

 
—



(1) 
The estimated useful life of computer software, hardware and equipment primarily ranges from 5 to 15 years and of buildings is 40 years.