220 CMR, § 125.23

Current through Register 1538, January 3, 2025

Section 125.23 - Clearances

(1)General.

(a)Application. 220 CMR 125.23 covers all clearances, including separations involving wires and supporting structures for effectively grounded systems.

(b)Maintenance of Clearances. The clearances required by 220 CMR 125.23 shall be maintained at not less than the specified values.

(2)Horizontal Clearances of Supporting Structures from Other Objects. Supporting structures and their guys and braces shall have the following horizontal clearances from other objects. The clearance shall be measured between the nearest parts of the objects concerned.

(a)From Fire Hydrants. Not less than four feet.

(b)From Curbs. Not less than six inches measured to the street side of the curb.

(c)From Railroad Tracks. Structures supporting transmission conductors or wires which cross railroad tracks shall have a horizontal clearance, if practicable, of not less than 12 feet from the nearest track rail, except that at sidings a minimum clearance of seven feet may be allowed. At loading sidings, sufficient space shall be left for a driveway. The horizontal clearance to the structure or its attachments shall be maintained from base of rail elevation to an elevation 22 feet above top of rails.

Structures supporting transmission conductors or wires which parallelrail road tracks shall have a horizontal clearance of not less than seven feet from the nearest track rail. The horizontal clearance to the structure, its attachments, or climbing space shall be maintained from base of rail elevation to an elevation 22 feet above top of rails.

Where necessary, to provide safe operating conditions which require an uninterruped view of signals, signs, etc. along tracks, the parties concerned shall cooperate in locating structures to provide the necessary clearances.

(d)From Pipelines. Structures, structure attachments and structure foundations supporting transmission conductors or wires should have a minimum horizontal clearance of seven feet from a pipeline. Where this clearance cannot be attained, a lesser clearance may be established by mutual agreement.

(3)Vertical Clearances of Wires Above Ground, Rails or Water. The vertical clearance of all wires above ground, rails or water shall not be less than the values specified in Table 1 in 220 CMR 125.23 under either of the following conditions:

(a) Final unloaded sag, no wind, with the conductor at maximum continuous operating temperature, but not less than 120°F. In computing conductor temperature, an ambient air temperature of 100°F and a transverse wind of two feet per second should be used.

(b) Final sag, no wind, 32°F conductor temperature with not less than 1/2 inch radial ice on conductor.

Table 1

MINIMUM VERTICAL CLEARANCE, IN FEET, ABOVE GROUND, RAILS OR WATER

Nature of Ground, Rails or Water	Guys	Phase to Phase Voltage (KV) for Effectively Grounded Systems
69	115	230	345
Track rails of railroads (except electrified railroads using overhead trolley conductors) handling freight cars on top of which men are permitted.	25	30	31	33	36
Track rails of railroads (except electrified railroads using overhead trolley conductors) not included above.	18	22	23	25	28
Track rails of trolley systems and areas accessible to trackless trolleys.	27	28	29	31	34
Streets, alleys, roads or other areas accessible to vehicles (except trackless trolleys) and bodies of water not used by sailboats.	18	22	23	25	28
Driveways to residence garages.	10	22	23	25	28
Spaces or ways accessible to pedestrians only (minimum clearance in any direction).	8	17	18	20	23
Bodies of water used for sail boating.	35	40	40	40	40

Note: No clearance from ground is required for guys not crossing streets, driveways, roads, or pathways, nor for guys provided with traffic guards and paralleling sidewalk curbs.

(4)Underground Risers. Open transmission conductors connecting to underground systems in unguarded areas shall not be run closer to the ground than the clearances given in Table 2 in 220 CMR 125.23.

Table 2

MINIMUM CLEARANCE ABOVE GROUND, IN FEET

Phase to Phase Voltage (KV) for Effectively Grounded Systems	Clearance Above Ground
69	22
115	23
230	25
345	28

(5)Crossing Clearances of Wires Carried on the Same or Different Supports. The clearance between any two conductors or wires crossing each other and carried on the same or different supports shall be not less than the values specified in Table 3 (220 CMR 125.23) under any of the following conditions:

(a) Upper conductor or wire at final unloaded sag, no wind, maximum continuous operating temperature, but not less than 120°F and the lower conductor or wire at existing unloaded sag, no wind, 100°F. In computing conductor temperature, an ambient air temperature of 100° F and a transverse wind of two feet per second should be used.

(b) Upper conductor or wire coated with not less than 1/2 inch radial ice, no wind, 32°F, final sag and the lower conductor or wire at existing unloaded sag, no wind, 32°F.

(c) Upper conductor or wire at final unloaded sag, no wind, maximum operating temperature in 0°F ambient air with a two feet per second transverse wind and the lower conductor or wire at existing unloaded sag, no wind, 0°F.

Table 3

MINIMUM CLEARANCES, IN FEET, AT CROSSINGS OF WIRES CARRIED ON THE SAME OR DIFFERENT SUPPORTS

Nature of Wires Crossed Over	Guys	Phase to Phase Voltage (KV) for Effectively Grounded Systems
69	115	230	345
Communication, including cables and messengers.	2	6	7	9	12
Supply cables having effectively grounded continuous metal sheath or insulated conductors supported on and cabled together with an effectively grounded messenger, all voltages; messengers associated with such cables.	2	4	5	7	10
Trolley contact conductors.*	6	6	7	9	12
Guys; span wires; lightning protection wires; service drops 0 to 750 V.	2	4	5	7	10
Open supply wires:
0 to 750 V phase to phase	2	4	5	7	10
750 to 50,000 V phase to phase	4	4	5	7	10
Transmission conductors: Phase to phase voltage (KV) for effectively grounded systems
69	4	6	7	9	11
115	5	**	8	10	12
230	7	**	10**	12	14
345	10	**	12**	14**	17

* For minimum clearance above ground or rails, see Table 1 in 220 CMR 125.23.

** It is preferred to install the higher transmission voltage at the higher level, where practicable.

(6)Separation Between Essentially Parallel Conductors or Wires.

(a) Separation Between Transmission Conductors and Conductors or Wires Carried on the Same Structure -- Fixed Conductor Supports.

1. Transmission Conductors or Wires of the Same or Different Circuits. The minimum separation at the structure between transmission conductors which are not free to swing and other transmission conductors or wires shall not be less than the larger value required by 220 CMR 125.23(6)(a)1.a. or 220 CMR 125.23(6)(a)1.b.

a. Minimum Separation: Separations at the structure shall be not less than the values given in Table 4 in 220 CMR 125.23.

Table 4

MINIMUM SEPARATION, IN FEET, BETWEEN TRANSMISSION CONDUCTORS AND OTHER TRANSMISSION CONDUCTORS OR WIRES

Clearance of Transmission Conductors From	Phase to Phase Voltage (KV) for Effectively Grounded Systems
69	115	230	345
Conductors of the same circuit.	4	5	9	13
Grounded or insulated lightning protection wires.	2.5	3.5	6.0	8.5
Conductors of different transmission circuits (phase to phase voltage for effectively grounded systems).
69	6	7	9	11
115	7	8	10	12
230	9	10	12	14
345	11	12	14	17

b. Separations According to Sag. Separation at the structure between transmission conductors and other transmission conductors or wires shall be not less than given by the following expression:

Separation, in feet =.033 (KV) + D

where:

(KV) is calculated as specified in Table 5 in 220 CMR 125.23.

D is given in Table 6 in 220 CMR 125.23.

Table 5

VALUE OF (KV) TO BE USED IN SEPARATION EXPRESSION

Conductors or Wires Under Consideration	Value of (KV)
Conductors of the same transmission circuit	Phase to phase voltage of transmission circuit, in kilovolts.
Transmission conductor and grounded lightning protection wires	Phase to ground voltage of transmission circuit, in kilovolts.
Tranmission conductor and insulated lightning protection wire or trans-	Maximum effective continuous voltage between conductors or
mission conductor and conductor of different transmission circuit	wires, in kilovolts.

Table 6

VALUE OF D TO BE USED IN SEPARATION EXPRESSION (VALUES OF SAG AT 60°F, FINAL, UNLOADED, NO WIND)

Sag, in Feet	D	Sag, in Feet	D	Sag, in Feet	D
2	0.94	18	2.83	55	4.95
4	1.33	20	2.98	60	5.17
6	1.63	25	3.34	65	5.48
8	1.89	30	3.66	70	5.58
10	2.11	35	3.95	75	5.78
12	2.31	40	4.22	80	5.96
14	2.50	45	4.48	85	6.15
16	2.67	50	4.72	90	6.33
95	6.50
100	6.67

Notes

(1) Interpolate for intermediate sag values.

(2) Where conductors or wires have different sags, use greater sag to determine value of D.

2. Subconductors of the Same Phase. The requirements of 220 CMR 125.23(6)(a)1. do not apply where the two or more conductors of the same circuit are operated with no potential difference between them, such as bundled phase conductors.

3. Transmission Conductors and Supply or Communication Conductors. The minimum separation at the structure between transmission conductors and supply or communication conductors shall be not less than the values given in Table 7 in 220 CMR 125.23.

Table 7

MINIMUM SEPARATION, IN FEET, BETWEEN TRANSMISSION CONDUCTORS AND SUPPLY OR COMMUNICATION CONDUCTORS

Phase to Phase Voltage (KV) for Effectively Grounded Systems
69	115	230	345
Communication conductors and open supply wires 0 to 50 KV phase to phase.	6	7	9	12

(b) Separation Between Transmission Conductors and Conductors or Wires Carried on the Same Structure -- Insulators Not Restrained from Movements. Where suspension insulators are used and are not restrained from movement, the conductor separation shall be increased so that one string of line insulators may swing transversely through an angle of 30° from a vertical position without reducing the values required by 220 CMR 125.23(6)(a). The insulator swing of 30° may be changed when such changes are supported by engineering studies that include the use of authenticated weather data and contemporary technology, provided the resultant swing angle does not reduce the clearance given in 220 CMR 125.23(6)(a).

(7)Separation Between Transmission Conductors and Conductors or Wires of Another Structure. The minimum separation between a transmission conductor and any conductor or wire carried on another structure shall not be less than the values specified in Table 8 in 220 CMR 125.23 for any of the following conditions:

(a) Final unloaded sag, no wind, with the transmission conductor at maximum continuous operating temperature, but not less than 120°F.

(b) Final sag, no wind, 32°F conductor temperature, with not less than 1/2 inch radial ice on transmission conductor.

(c) Initial unloaded sag, no wind, 0°F transmission conductor temperature.

(d) Final sag, 6 psf. horizontal wind with the transmission conductor at not less than 60°F.

Note: In determining minimum separation for all conditions listed above, it shall be assumed that the conductor or wire on the other structure is in a vertical position and is at the temperature (between 0° and 60°F) which produces the minimum separation between the conductor or wire on the other structure and the transmission conductor in its equilibrium position for the loading condition under consideration.

Table 8

MINIMUM SEPARATION, IN FEET, BETWEEN TRANSMISSION CONDUCTORS AND CONDUCTORS OR WIRES CARRIED ON ANOTHER STRUCTURE

Nature of Wires Carried on Another Structure	Phase to Phase Voltage (KV) for Effectively Grounded Systems
69	115	230	345
Communication, including cables and messengers; trolley contact conductors.	6	7	9	12
Supply cables having effectively grounded continuous metal sheaths or insulated conductors supported on and cabled together with an effectively grounded messenger, all voltages; messengers associated with such cables; guys; span wires; lightning protection wires; service drops and open supply wires 0 to 50,000 volts phase to phase.	4	5	7	10
Transmission conductors: Phase to phase voltage (KV) for effectively grounded systems
69	6	7	9	12
115	7	8	10	12
230	9	10	12	14
345	11	12	14	17

(8)Clearances of Transmission Conductors from Structures and Guys.

(a)Clearances from Structures to Which They are Attached. The clearance in any direction from transmission conductors to structures and to span wires and guys attached to the same structure shall be not less than the values given in Table 9 in 220 CMR 125.23 with the conductors at final, unloaded sag, at 60°F.

Table 9

CLEARANCES, IN FEET, OF TRANSMISSION CONDUCTORS FROM STRUCTURES AND EFFECTIVELY GROUNDED PARTS

Clearances of Conductors From	Phase to Phase Voltage (KV) for Effectively Grounded Systems
69	115	230	345
Surfaces of structures; conduits; effectively grounded switch parts and effectively grounded parts of span wires and guys.	1.5	2.5	4.5	6.5

Where suspension insulators are used and are not restrained from movement, the conductor clearances shall be such that the values of clearance required above will be maintained with an insulator swing of 30° from the vertical position.

The insulator swing of 30° may be changed when such changes are supported by engineering studies that include the use of authenticated weatherdata and contemporary technology, provided the resultant swing angle does not reduce the clearances given above.

(b)Clearances from Supporting Structures of Another Line, from Bridges and from Buildings -- General. Clearances shall be not less than the values given in Table 10 for any of the following conditions:

1. Final unloaded sag, no wind, with the conductor at maximum continuous operating temperature, but not less than 120°F.

2. Final sag, no wind, 32°F conductor temperature with not less than 1/2 inch radial ice on conductor.

3. Final sag, six pounds per square foot horizontal wind, with the conductor at not less than 60°F.

4. Initial unloaded sag, no wind, 0°F conductor temperature.

Table 10

CLEARANCES, IN FEET, OF TRANSMISSION CONDUCTORS FROM STRUCTURES OF ANOTHER LINE, BUILDINGS AND BRIDGES

Clearances of Transmission Conductor	Phase to Phase Voltage (KV) for Effectively Grounded Systems
69	115	230	345
From structure of another line (grounded parts)	4	5	7	9
* From building surface where conductors are attached and are guarded or made inaccessible	1.5	2.5	4.5	6.5
From building surface where conductors pass by the building which is accessible	10	11	13	16
* Passing over buildings and over or near bridges	17	18	20	23

^* Above roof level of buildings, pass-by clearances shall be maintained horizontally if the angle of the diagonal with the horizontal is 50° or less. If this angle is greater than 50°, the diagonal clearance shall be not less than the pass-over clearances given.

(c)Clearances from Supporting Structures of Another Line, from Bridges and from Buildings -- Special Requirements.

1. Clearances from Buildings. Transmission conductors shall be arranged and maintained so as to hamper and endanger firemen as little as possible in the performance of their duties.

Transmission conductors carried along the surface of a building shall be guarded or made inaccessible. Clearances given in Table 10 in 220 CMR 125.23 shall be maintained from the building or its attachments (balconies, platforms, etc.).

2. Clearances from Bridges. Clearances given in Table 10 in 220 CMR 125.23 shall be maintained from the bridge, its attachments or wing walls. Where the conductors pass over traveled ways, the clearances of 220 CMR 125.23(3) shall apply if they are greater than those required by Table 10 in 220 CMR 125.23.

(9)Clearance of Transmission Conductors from Gas Pipeline Blow-Offs. The minimum horizontal clearance between transmission conductors and gas pipeline blow-offs should be 100 feet.

220 CMR, § 125.23