Template · Commercial and industrial

Telecom site with −48V DC plant single line diagram

A cell site service with a generator, rectifiers, a battery string and DC distribution. Use this for a cell site or equipment shelter: a 200A service through a transfer switch with a standby generator, an AC panel, and a −48V DC plant with rectifiers, a battery string and DC distribution.

A free template with typical ratings, conductor callouts and general notes. Open it, change what differs on your job, fill in the title block and export a PDF.

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Telecom site with −48V DC plant single line diagram: A cell site service with a generator, rectifiers, a battery string and DC distribution. — Telecom site with −48V DC plant. 21 devices on an 11 × 17 in sheet with a title block and notes column.

What the reviewer checks on this drawing

The reviewer checks the transfer switch as the service disconnect, the rectifier input at 125%, the battery overcurrent protection and conductors, which DC conductor is grounded, and the bonding of everything on site to the ground ring.

What the drawing shows

Every device on the sheet, in the order power reaches it.

Symbol	Label	Rating or detail	Conductors feeding it
Utility source	Utility service	120/240V 1φ 3W
Meter	Utility meter	200A socket	Service conductors, per utility
Transfer switch	Automatic transfer switch	200A · service rated, 200A utility breaker inside
Circuit breaker	100A 2P	Generator breaker
Generator	Standby generator	20 kW · 120/240V, diesel	3 #3 Cu + #8 G
Ground	Site ground ring	#2 solid tinned Cu
Panel	AC power panel	200A bus · neutrals isolated	3 #3/0 Cu + #6 G
Surge protective device	SPD	Type 2
Circuit breaker	40A 2P	Rectifiers
Rectifier or charger	Rectifier plant	6 kW · 54V DC · 111A	2 #8 Cu + #10 G
Circuit breaker	150A DC	Battery breaker
Battery	Battery string	48V · 200 Ah · 9.6 kWh	2 #1/0 Cu
Panel	DC distribution	48V DC · 200A	2 #1/0 Cu
Circuit breaker	60A DC	Radios
Load	Radio units	48V DC · 40A	2 #6 Cu
Circuit breaker	30A DC	Transmission
Load	Microwave and fibre	48V DC · 15A	2 #10 Cu
Circuit breaker	30A 2P	HVAC
Load	Cabinet cooling	MCA 18A · MOCP 30A
Circuit breaker	20A 1P	GFCI
Receptacle	Service receptacle		2 #12 Cu + #12 G

Notes on the sheet

The DC plant is −48V: the positive (return) bus is the grounded conductor, bonded once to the site ground bar. Breakers and fuses are in the negative.
Rectifiers 6 kW at 54V float = 111A DC. AC input 6 kW ÷ (240V × 95%) = 26A; × 125% = 33A, on a 40A circuit with #8 Cu.
Battery string 200 Ah carries the 55A site load for about three hours. Battery breaker and conductors sized for the full rectifier output: 150A on 1/0 Cu (150A at 75 °C).
Generator 20 kW ÷ 240V = 83A, protected at 100A. The transfer switch does not switch the neutral, so the generator neutral is not bonded at the generator. Sign at the service equipment giving the type and location of the standby source (NEC 702.7).
Transfer switch is the service disconnect, with a 200A breaker on its utility side as the service overcurrent protection (NEC 230.90 and 230.91). Grounding electrode conductor and main bonding jumper terminate at it; neutrals isolated at the AC power panel.
Everything on site bonded to the ground ring: tower, shelter or cabinets, fence, generator and the service ground. Battery installation per NEC Article 480 (CEC Section 64).

Diagram is schematic and not to scale. Field-verify existing equipment ratings. Ratings and conductor sizes shown are typical. Confirm against the adopted code, the equipment listing and a load calculation before installation. Code references are to the 2023 NEC and the 2024 Canadian Electrical Code: see references and editions.