Street lights Interview Q/A

 Street lights Interview Q/A

Street lights Main components

1.  Lighting poles 
2.  LED fixtures/luminaires Drivers/ ballasts.
3.  Feeder pillars/control panels 
4.  Underground cable 
5.  Earthing system
6.   lighting control (timer, photocell, contractors)

Common defects

1. Burnt Lamps /LED failure 
2. loose wiring/terminations 
3. Faulty photocell or timers’
4. Damaged pools or leaning poles.
5. Underground cable faults 
6. Tripped breakers in feeder pillars 
7. corrosion in panels.

Check Lux level

1. Conduct night inspection 
2. Use a Lux meter 
3. compared measured 
4. lux with project specs/Standards 
5. Identify dark spots, dim areas, and non-functional 
6. poles Report and tallow up on corrective action.

Standard for lighting

1.  IEC (installation equipment) 
2.  NEC/NFPA 70 (Electrical Safety) 
3. IES (Illumination standards) 
4. Saudi Building code SBC 401/504

Light pole not working

1. check breaker Status in feeder pillar 
2. Inspect wiring fuses and connection 
3. Test photocell/Timer 
4. check LED driver and luminaire 
5. check grounding and voltage 
6. if cabling fault suspected→ perform Megger test 
7. Report findings and follow up with maintenance team.

Inspect before lighting poles

1.  Check straightness 
2.  verify galvanization/Painting 
3. Conform height and Type 
4.  check foundation bolts and base plate 
5. Ensure correct earthing provision 
6. Review Shop drawing.

Safety precautions

1.  Lockout/Tag out 
2.  Voltage absente test
3. PPE (gloves, helmet insulated tools
4. safe ladder or man-lift use 
5.  Safety distance from live circuits

 Inspect UG lighting cables

1.  Confirm cable Size and type
2. Check Sand bedding 
3. Warning tape 
4. proper depth 
5. proper jointing
6. Megger test results
7.  As-built verification.

Photocell why used

A photocell automatically switches street lights on at night and off in the morning, based on light level.

Handle non-compliance

1.  Document with photos 
2.  issue NCR/observation report
3.  follow up until correction is completed
4. re-insect the work.

LED Technology

Mention: LED drivers efficacy life span, voltage range, IP rating, Surge protection, heat dissipation etc.

Daily/weekly reports

1. inspection summary
2. Pending faults
3. completed corrective actions
4. status of all zones/streets 
5. Pictures and Location references.

Check during night inspection,

1. Dark areas 
2. Flicking light 
3. Dim fixtures 
4. wrong orientation 
5. Non-functional poles 
6. Timer/photocell malfunction.

Excavation size depends

1. Pole height
2. Pole type (Gl/steel/conical /octagonal
3. wind load 
4. Foundation design 
5. Manufacturer requirement.

Typical Foundation Excavation Sizes

Pole Height	Typical Excavation size (Length x width x depth)
6m	0.6mx0.6x1.0m
8m	0.7mx0.7x1.2m
10m	0.8mx0.8x1.5m
12m	1.0mx1.0x1.8m

Key Inspection Points.

1.      Correct Location per drawing.

2.       proper depth (check wilt measuring Tape)

3.       Compacted soil at bottom.

4.       correct anchor bolt cage installed –

5.       Proper alignment and orientation-

6.       concrete grade as per spec (usually 25 MPa or higher)

7.       Curing and backfilling done properly.

Common Defects You May, Report

1. incorrect depth 
2. Leaning bolts
3. wrong bolt Template 
4. Poor compaction 
5. Honeycombing in foundation concrete.

Cable Trench Excavation for Lighting Calles

Lighting cables usually range from 20/4C 6mm² -16mm² -35mm²Depending on load.                  Typical cable Trench Dimensions

cable Type	Trench Width	Trench Depth
1V Lighting cable (single run)	30-40cm	60- 80cm
Multiple cable/main feeder	50-60cm	80-100cm

1. Depth increase if 
2. Road Crossings 
3. High voltage Area
4. Extra protection required,

Standard cable Laying Procedure

Step-by-step 

1. Excavation as per drawing 
2. Lay 10-15cm sand bedding 
3. Place the cable (maintain bending radius) 
4. cover with 10-55cm Sand bedding 
5. Install protection tiles / concrete slabs
6. Lay warning tape 300m above cable 
7. Backfill with approved material.

Inspection checklist!

1.  Correct depth & width 
2. cable Type, size and route 
3. No sharp stones under cable 
4. Proper joints with heat shrink kits 
5. Megger test before back-fill 
6. Warning Tape installed 
7. correct backfilling & compaction

Test Method connect

 megger positive lead to conductor. Connect negative Lead to Armoring or metallic sheath or Earth, Test voltage LV cable- (0,6 /1Kv) and MV cable(3,3-33kv)

Acceptance criteria → LV cable→ 1MΩ MVcable→100MΩ HV cable → 1000 MΩ

- 10m lighting pole depth is 1.5m & 0.8x0.8m dimensions.

- Street light cable Trench typically 60-80 cm including sand bedding Cable, protection tiles and warning tape.

- Use Sand under & above the cable to protect cable from sharp objects and prevent insulation damage.

- Warning→ To alert workers during future digging that live cable

Check concrete pouring for light pale foundation:

1. Correct depth 
2. Position of anchor bolts 
3. vertical alignment 
4. proper shuttering 
5. steel and template 
6. Earth pit location.

Typical Pole Heights by Road/street Type

Road	street Type	use Typical Pole height (m)
Narrow	residential street, smalls private Road	6-8m
medium	Urban streets, city local Roads	8-10 m
Major urban	arterials/city main street	10-12m
High-traffic roads	multi-lane, highways	12 - 14m higher depending on width, lanes, design.

Why the Variation

+ Narrow or residential roads: Lower height helps avid glare, light spill onto Houses and fits smaller road width.

+ Wider roads or roads with high speed traffic: taller pole help distribute light over wider carriageways and cover more area per pole, reducing the number of poles needed.

+ For major high-speed roads or highways! Higher mounting may also improve visibility and road Safety under varied conditions.

Relation between Pole light, Road with, Spacing & Layout

→A common rule: The pole height should roughly equal lights are on one the road width

→For even light distribution, Typical spacing between poles us often about 2.5 - 3x Pole height.

→If using two-sided or staggered lighting: you might use taller and greater spacing to cover full width.

The Standard of street-lighting, SASO2927/2019,

defines lighting classes based on road function (vehicle roads, intersections, pedestrian areas) but it doesn't fix a precise universal pole-height per class, instead the lighting design (including height, fixture type, spacing, light level) is based on appropriate class and road geometry.

In practice (per local suppliers/ manufactures, for "main roads" (Urban arterials, multi-lanes) typical pole height are given as 10-12m for secondary roads or local street" as 6-8m

If I were you inspecting a project in KSA_

For residential / small street → expect 6-8m pole

For Urban city roads Medium Street-expect 8-10 m

For main arterials multi-lane/busy roads → expect 10-12m

Possibly 12+m - but check road geometry, traffic, design requirement-

Road Type	Residential Lanes/ Internal streets.	Secondary Roads	Main Urban Roads.	(Single/Double)
multi-lane Road	High ways	Pole Height	pole spacing	LED Wattage
NOTE	-	For narrow roads & residential	6m-8m	20-30 m
30w-6ow	Areas, prevents glare into houses.	8m- lom	30 - 40m	6ow-gow
moderate traffic roads inside towns/cities,	10m- 12m	35 - 45m	90w- 120w	used for commercial zones
40- 50m	120w-150w	Need high uniformity & wider	Beam.	Spread.
150w- 200W	Expressways, high speed.	Service Road Next 12m- 14m	12m- 14m	45— 55m
(Sometime 1Sm)	8m-10m	30 - 40 m	to Highways	Parks/ walkways
4m 6m	15 - 20m	50w -90w	20w - 40w	Lower illumination requirement
Than the main carriage way	Low mounting height to reduce glare and improve comfort.	Parking Lots/	8m- 12m	Depends on
60w -150w	Based on area and	Open Area	Layout	Required uniformly.

NOTE Exact height depends on road width, number of lanes, lighting Class and the projects approved lighting design calculations.

1. 6-8m → Residential
2. 8-10m →Secondary
3. 12m →main urban
4. 12m-14m → highways / major materials

Mounting height vs. spacing Rule

Typical Spacing = 2.5 to 3 x Pole height

if pole 10m .. Spacing will be 25-30m

LED wattage

1. - Residential → 30-60w
2. - Urban →60-120w
3. - Highways → 120w-200w

SLD for street Lighting

Shows the electrical power flow from the source to each lighting Circuit.

Parts you will seen

1. Incoming supply (LV panel or feeder) 
2. Feeder Pillar (with MCBs/MCCB 
3. Individual lighting circuits, 
4. Cable Size (e.g., 4C X16mm² CU) 
5. Overcurrent protection devices 
6. Earthing connection
7. contactor/timer/photocell system
8. Load distribution (KW per circuit)

What you check: 

1.  correct cable size
2. correct breaker ratings 
3. proper earthing layout
4. circuit separation (not overloading one circuit)
5. Whether protection coordination is correct.

Pole Detail Drawing 

1.  Pole height (e.g, 12m 10m) 
2. Arm Length (single Arm, double Arm)                
3. Luminaire mounting height 
4. Door opening for wiring 
5. earthing bolt Location.
6. Anchor bolt dimensions
7. Matesial (galvanized steel, aluminum)

You check 

 correct pole type delivered to site 

1. Door opening direction 
2. Material certification.
3. wind load compliance (especially in Sandi Arabia)

Pole Foundation Drawing/ shows the civil foundation for the pole.  

Includes/, 

1.  Foundation depth
2. Foundation diameter 
3. concrete grade (C30,C35)                        
4. Rebar details (steel cage, number of bars) 
5. Anchor bolt size and spacing 

Backfilling instructions. Inspection 

1. Excavation depth match drawing 
2. rebar cage installed correctly 
3. Anchor bolt aligned vertically 
4. concrete poured without segregating 
5. Foundation curing as required.

Cable Trench & Duct Bank Drawing Show how Underground lighting cables run.                                                                                              

 Contains 

1. Trench depth usually 80cm to 1.2m depending on Standard
2. Sand bedding (10-15cm)    
3. warning tape location 
4. concrete encasement(if heavy traffic area 
5. Duct Sizes (63mm/10mm, HDPE/PVC) 
6. Manhole and pull-chamber drawings.

You check> 

1. Depth and Wight match design 
2. Proper compaction 
3. Cable Separation 
4. Warning tape is placed 30cm above cables
5. Duct slope and bend radius are correct.

Feeder Pillar (FP)/ Control cabinet Drawing                                                                                             shows wiring inside the feeder pillar.                                                                                                       Includes > 

1.  incoming/outgoing cable glands 
2. breaker arrangement 
3. photocell/timer
4. contactor wiring 
5. earthing links 
6. neutral bar layout 
7. surge protection devices.

You check> 

1. correct breaker size installed
2. Proper termination (lugs, tightening torque) 
3. no lose connection 
4. phase labeling and cable identification
5. earthing continuity.

Lighting Fixture drawing LED / Sodium fixture.

1. Driver (LED diver) connection
2. Wattage rating
3. Light distribution type (Type II,III,IV) 
4. IP rating (P65,66) 

You will check >

1. Proper tilt angle
2. correct wattage installed
3. Surge protector included 
4. No water ingress
5. Orientation fallows design.

Light calculation sheet (Dialux/calculux)

Includes

1. Lux level (Average, min, Max 
2. Uniformity 
3. Pole Spacing 
4. Light distribution cures    
5. mounting height 
6. overhang values.

You check > 

1. Installed poles follow calculation layout 
2. Lux level meet saudi/SBC-201 Standards    

Pole height and arm length match design

Road Type	Pole height	Typical Spacing
Highways	12-14m	35- 45m
Major roads	10-12m	30 - 40m
Secondary Roads	8 - 10m	25-35 m
Residential streets	6-8m	20-30m
Pedestrian walkways	4-6m	15 - 25m

How Many Poles can be connected in one circuit

This depends on > 

1. luminance wattage (50W, 100W, 150W, 200w etc) 
2. circuit breaker rating (typically 16A/20A/25A) 
3. Maximum voltage drop allowed (3-5%) 
4. Cable Size (4cx10m², 16 mm², 25mm² etc)                                                                               

  Typically Rules Used in Sandi Projects  > 

circuit design Based on Total Load Limit Max 3000w per circuit One lighting circuit should not exceed 3kw-

Practical Example (most common)

Case 1= Using LED Street lights → 3000w=150w= 3000w=150w= pole/circuit (max) But consultant usually reduce for Safety_ Recommended=12-16                                                                                        Case 2= using 100W LED Street lights→ 3000w=100w = 30 pale/circuit (Max) Recommended = 18-22 Case 3= Using 200W LED (Major Roads/ Highways) → 3000W →200w= 15 pole /circuit (Max Recommended = 8-12

Luminaire wattage cable	Poles pre circuit.
60W LED	18-24 poles
90W-100W LED	16-22 poles
120W-150W LED	12-16 poles
180W–200W LED	8-12 poles
250W MH/HPS (old roads)	6-10 poles

Most used (standard Saudi project)

Cable Type	Circuit Rating	Usage
4CX10mm2 CU	16A /20A	Short circuits, residential, areas.
4c x16mm2 CU	20A/25A	Major Roads, long distances.
4C x 25mm2 CU	25A+	Long circuits, heavy load.
4c x35mm2 CU	Special case	When voltage drop is high.

Most Practical

Luminaire wattage	Poles/circuit	Cable
60-100W	12-20	4CX10mm2 cu
100-150W	12-16	4Cx16 mm2cu
150—200w	8-12	4C x16mm2 cu or 25mm2 cu
200W+	6-10	4c x25-35mm2 cu

Voltage Drop maximum allowed → 3%%

If voltage drop exceeds limit → increase cable size or reduce circuit length.

Key Points

1. Review approved shop drawings, Method of Statement and ITPs before execution.
2. Verify cable Type, Size, insulation, and Standards compliance (EC, NEC)
3. Inspect conduit, trunking and tray installations for alignment and
4. Ensure Segregation of power, lighting, instrumentation and ELV systems as per design.
5. Check cable pulling Methods, bending radius, and Mechanical protection-Verify proper earthing, bonding and continuity of grounding inspect terminations, torque tightening, labeling and identification
6. Confirm fire-rated wiring sealing at fine-rated penetrations.
7. Conduit insulation resistance and continuity testing with records.
8. Final CA/QC approval prior to energization and commissioning.