Safety Clearance for Indoor & Outdoor Power Distribution Equipment

In the substation layout, the safety clearance between distribution devices refers to the minimum distance maintained between distribution devices or between distribution devices and other equipment or facilities. The safety clearance is crucial for the safe and efficient operation of the power system, involving aspects such as operational safety, equipment safety, and environmental safety.

1. Personnel safety: Ensures operators and maintenance staff can safely approach, operate, and maintain distribution equipment without coming into contact with live parts or hazardous areas, preventing electric shocks or other accidents.
2. Equipment safety: Proper safety clearance helps prevent electrical interference, short circuits, or fires, ensuring stable and reliable equipment operation.
3. Fire safety: The safety clearance between devices prevents fire spread, providing adequate space for firefighting and evacuation in case of fire, enhancing the substation’s fire protection.
4. Ease of maintenance and expansion: Adequate safety clearance makes maintenance and repair work easier and provides space for future expansion and modifications.
5. Electromagnetic compatibility: The safety clearance helps avoid electromagnetic interference between devices, ensuring normal operation and reducing impact on communication systems or other equipment.

Indoor and Outdoor Safety Clearance, especially for Wall Bushings and Busbar Installation

According to IEC 60137, wall through bushing is device that enables one or several conductors to pass through a partition such as a wall or a tank, and insulates the conductors from it; the means of attachment (flange or fixing device) to the partition forms part of the bushing

Note 1 to entry: The conductor may form an integral part of the bushing or be drawn into the central tube of the bushing.

The safety clearance for indoor power distribution equipment shall comply with the specifications in Table 3.1.14-1,

The outdoor power distribution equipment shall comply with the specifications in Table 3.1.14-2.

The actual voltage exceeds the rated voltage levels listed in Tables 3.1.14-1 and 3.1.14-2, the safety clearance values corresponding to the next higher rated voltage level shall be adopted for both indoor and outdoor power distribution equipment.

Mark	Application Scope	Rated Voltage (kV)
		3	6	10	15	20	35	60	110J	110	220J
A1	1, Clearance between live parts and grounded parts.2, Clearance between mesh or plate barriers extending 2.5m above the ground and the live parts above the barrier.	70	100	125	150	180	300	550	850	950	1800
A2	1, Clearance between different phase equipment during transportation2, Clearance between live parts on both sides of circuit breakers and disconnectors.	75	100	125	150	1800	300	550	900	1000	2000
B1	1, Clearance between grating barriers and live parts.2, Clearance between live parts of different circuits undergoing separate maintenance without barriers.	825	850	875	900	930	1050	1300	1600	1700	2550
B2	Clearance between mesh barriers and live parts	175	200	225	250	280	400	650	950	1050	1900
C	Clearance between exposed conductors without barriers and the ground (floor)	2375	2400	2425	2450	2480	2600	2850	3150	3250	4100
D	Clearance between parallel exposed conductors of different circuits undergoing separate maintenance	1875	1900	1925	1950	1980	2100	2350	2650	2750	3600
E	Clearance between outdoor outgoing bushings and road surfaces.	4000	4000	4000	4000	4000	4000	4500	5000	5000	5500

① 110J and 220J refer to Neutral Point directly grounded power grids.

② For mesh barriers, if replaced with plate barriers, the B1 value may be taken as A1 + 30mm.

③ The clearance between outdoor wall bushings and outdoor pathways shall not be less than the C values specified for outdoor installations in Table 3.1.14-2.

④ For altitudes exceeding 1000m, A values should be corrected according to Figure 3.1.14-6.

⑤ The values in this table do not apply to factory-manufactured complete power distribution assemblies.

Figure 3.1.14-1 Outdoor Verification of A1, A2, B1, B2, C and D Values

Figure 3.1.14-2 Outdoor Verification of B1, and E Values

Figure 3.1.14-3 Outdoor Verification of A1, A2, B1, and D Values

Safety Clearance for Outdoor Power Distribution Equipment

Mark	Application Scope	Rated voltage (kV)
		3~10	15~20	35	60	110J	110	220J	330J	500J	750J
A1	1, Clearance between live parts and grounded parts.2, Clearance between mesh barriers extending 2.5m above the ground and the live parts above the barrier	200	300	400	650	900	1000	1800	2500	3800	5600/5950
A2	1, Clearance between live parts of different phases.2, Clearance between live parts on both sides of circuit breakers and disconnectors.	200	300	400	650	1000	1100	2000	2800	4300	7200/8000
B1	1, Clearance between transported equipment and live parts without barriers.2，Clearance between grating barriers and insulators/live parts3, Clearance between live parts of different circuits undergoing separate maintenance without barriers.4，Clearance between live parts and grounded parts during live-line maintenance	950	1050	1150	1400	1650	1750	2550	3250	4550	6250/6700
B2	Clearance between mesh barriers and live parts.	300	400	500	750	1000	1100	1900	2600	3900	5600/6050
C	1，Clearance between exposed conductors without barriers and the ground.2，Clearance between exposed conductors and the top of buildings/structures.	2700	2800	2900	3100	3400	3500	4300	5000	7500	12000
D	1. Clearance between parallel exposed conductors of different circuits undergoing separate maintenance.2. Clearance between live parts and the edges of buildings/structures.	2200	2300	2400	2600	2900	3000	3800	4500	5800	7500/7950

Notes:

•  110J, 220J, 330J, 500J, and 750J refer to neutral point directly grounded power grids.；

② The clearance between grating barriers, insulators, and live parts at 220kV and above may be verified using the corresponding B values based on the actual potential distribution of the insulator. In such cases, the clearance between the grating barrier and the insulator may be less than the B1 value. If no potential distribution data is provided, a linear distribution calculation should be applied. For phase-to-phase clearance in 500kV and above systems, verification should also be based on the actual potential distribution of the insulator; if no potential distribution data is available, a linear distribution calculation shall be used.

• During live-line work, the clearance between live parts and grounded parts (110J–500J), as well as between live parts of different phases or intersecting circuits, shall be B1 = A2 + 750mm.
• For 500kV systems, the A1 clearance for twin-bundle flexible conductors to ground shall be 3500mm.
•  Except for a rated voltage of 750J, A values shall be corrected according to Figure 3.1.14-6 for altitudes above 1000m. For 750J, the value before “/” applies to 1000m altitude, and the value after “/” applies to 2000m altitude.
• This table does not apply to factory-manufactured complete power distribution assemblies.

Figure 3.1.14-5 Outdoor Verification of A2, B1, and C Values

Figure 3.1.14-4 Outdoor Verification of A1, B1, B2, C, and D Values

Figure 3.1.14-6 Correction of A Values for Altitudes Above 1000m
(A2 values and indoor A1, A2 values may be proportionally increased according to this figure) 

Baoding Hewei Power Technology Co., Ltd. is a well-established and constantly growing company focusing on designing, developing, and manufacturing transformer bushing, including:

Wall bushing

Wall bushings with CT

Transformer Bushing

High current bushing

Capacitive current transformer

Air-air bushing

Since 2017, Our bushing products have often been exported to Europe, America, Africa, and other countries. Hewei Power has got many patents, type-test reports and ISO certificates:

IS09001, IS014001, ISO45001, OHSAS1800.