Template · Commercial and industrial

240/120V three-phase delta service single line diagram

A high-leg delta service, with the three-phase and single-phase loads kept where they belong. Use this for an older shop or small industrial building on a 240/120V three-phase delta service, where one phase is 208V to neutral. The drawing shows which loads go on which phases.

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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240/120V three-phase delta service single line diagram: A high-leg delta service, with the three-phase and single-phase loads kept where they belong. — 240/120V three-phase delta service. 14 devices on an 11 × 17 in sheet with a title block and notes column.

What the reviewer checks on this drawing

The inspector checks that the high leg is identified and on the centre bus position, that no 120V load is on it, and that two- and three-pole breakers on it carry a straight 240V rating.

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	240/120V 3φ 4W delta
Meter	Utility meter	200A socket	Service conductors, per utility
Circuit breaker	200A 3P	Main breaker	4 #3/0 Cu, high leg marked orange
Panel	Panel A	200A bus · 240/120V 3φ 4W
Ground	Grounding electrode system	#4 Cu GEC
Circuit breaker	50A 3P	Compressor
Disconnect switch	Disconnect	60A · within sight, of motor	3 #8 Cu + #10 G
Motor	Air compressor	10 HP · 230V · 28A
Circuit breaker	30A 2P	Phases A-C
Heater	Water heater	4.5 kW · 240V	2 #10 Cu + #10 G
Circuit breaker	20A 1P	Phase A
Lighting	Lighting	120V
Circuit breaker	20A 1P	Phase C
Receptacle	Receptacles	120V	2 #12 Cu + #12 G

Notes on the sheet

The B phase is the high leg: 208V to neutral. It is marked orange wherever it is accessible and lands on the centre bus position (NEC 110.15, 230.56 and 408.3). In the meter socket the utility usually wants it on the right-hand jaws: follow the utility’s standard there.
No 120V load on the high leg. Single-pole breakers go on phases A and C only, so every third space stays empty or takes part of a two- or three-pole breaker.
Two- and three-pole breakers that include the high leg are rated 240V, not the 120/240V slash rating (NEC 240.85).
Compressor 10 HP at 230V: 28A (NEC Table 430.250) × 125% = 35A, on #8 Cu with a 50A breaker. The compressor has its own controller with overload protection (NEC 430.32).
Water heater 4.5 kW ÷ 240V = 18.8A; × 125% = 23.4A, protected at 30A.
Balance the 120V load between A and C: the transformer winding between them carries all of it.

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.