Stud welding power supplies split cleanly into two camps: single-phase capacitor-discharge (CD) machines running on 110 V or 230 V residential/light-commercial service, and three-phase drawn-arc (DA) machines wired for 400 V at 32 A [S1]. The phase choice is dictated by stud diameter, weld rate, and whether the work happens at a fixed shop or a temporary site.
CD units typically draw 500–3000 W and complete welds in milliseconds, while DA units step that up to 100–1400 A of welding current from a 400 V three-phase feed [S1]. Drawn into a 120-degree rotating supply, the arc energy stays below 5% voltage ripple, versus the 120 Hz pulsing inherent in any single-phase feed [S2][S3].
How the Two Power Topologies Behave Under Load
Single-phase service uses one hot conductor and a neutral, delivering an alternating wave that peaks and returns to zero twice per cycle; in a 60 Hz system that is 120 power pulses per second, and the arc visibly responds to each one [S2][S3]. Three-phase service uses three hot conductors offset by 120 degrees, so the instantaneous power never collapses to zero and voltage ripple on a welding bus stays under roughly 5% [S2].
For a stud welding process where the weld time is in the millisecond range, that ripple matters less for the fusion event itself than for the consistency between welds. Single-phase systems produce small power variations that show up as bead-to-bead variation, a non-issue on a CD weld of a small fastener, but visible when an operator is laying a string of larger studs on stainless or sanitary tubing [S2]. Three-phase drawn-arc machines exploit the smoother supply to hold longer weld times, higher current, and a more repeatable heat input on studs above about 10 mm.
Stud Welder Specifications by Phase: CD vs DA
On a single-phase CD platform, the Taylor CDM range runs from a 110 V or 230 V dual-voltage input and welds 2–10 mm studs at 10–50 studs per minute with 35–200 V of open-circuit output, while the CDi range welds 2–10 mm studs at 5–30 studs per minute from 25–200 V [S1]. On a three-phase DA platform, the same manufacturer's DA i12 welds 3–10.8 mm (M12 PD) studs at 3–20 studs per minute and the DA i16 welds 3–14.6 mm (M16 PD) studs at 3–30 studs per minute, with welding current of 100–800 A and 100–1400 A respectively, all from a 400 V 32 A three-phase feed [S1].
The decision splits along four axes: stud diameter, weld rate, site power, and duty cycle. Up to 10 mm stud diameter and rates below 30 studs per minute, a single-phase CD unit on a 230 V outlet is the workhorse and is the same architecture used in the capacitor-discharge stud welder class that dominates field work. Above 10 mm, or when the line has to run above 20 studs per minute for full shifts, a three-phase DA unit on 400 V 32 A is the only realistic option. The TIG welder world runs into the same wall at much higher currents, which is why the same three-phase-vs-single-phase reasoning appears in both spec sheets.
Site Power, Cable, and Breaker Sizing
Single-phase CD units plug into 110 V or 230 V outlets that exist in nearly every shop, vehicle workshop, and construction trailer, which is why they are the default for offsite and repair work [S1]. The trade-off is current draw: a 230 V CD unit pulling 3000 W draws roughly 13 A, well within a standard 16 A or 20 A branch circuit, while a comparable three-phase DA unit at 100 A of welding current needs a 400 V 32 A dedicated feeder, which is rarely present outside a fixed industrial installation [S1].
Inverter-based welders have narrowed the gap, but basic electrical physics still sets the ceiling: a three-phase machine cannot pull more than its input breaker allows, and a single-phase machine cannot deliver more instantaneous power than its single conductor can carry without unacceptable voltage drop [S2][S5]. Field practice when only single-phase is available is to either pick a CD unit sized to the stud, or add a phase converter / step-down transformer to feed a smaller three-phase DA machine, accepting reduced output and a longer weld time [S5].
Decision Matrix: When to Pick Single-Phase vs Three-Phase
Use single-phase when the largest stud is 10 mm or below, the weld rate is under 30 studs per minute, the site only has 110/230 V service, and the welds are intermittent or mobile. Use three-phase when the stud diameter is above 10 mm (M12 and up), the production line needs 3–30 studs per minute sustained, the arc energy must stay within tight consistency limits for code work, and the facility already has a 400 V three-phase feeder with at least 32 A of headroom [S1][S2][S6].
A direct comparison on the four decision criteria: maximum stud diameter is 10 mm on single-phase CD versus 14.6 mm on three-phase DA (M16 PD) [S1]; maximum sustained weld rate is 50 studs per minute on the top single-phase CD model versus 30 studs per minute on the largest three-phase DA, but three-phase maintains that rate over long shifts where single-phase CD overheats [S1]; input service is 110/230 V single-phase versus 400 V three-phase 32 A [S1]; arc energy ripple is roughly 5% or more on single-phase versus under 5% on three-phase [S2]. For arc welder processes in general, this same pattern of single-phase portability versus three-phase stability is the rule, not the exception, and stud welding is no different [S6].
Limitations, Failure Modes, and Cross-Process Context
Single-phase CD units are not built for studs above 10 mm; pushing the open-circuit voltage or extending the weld time to compensate usually ends in stud blowout or a cold set, not a clean fusion zone. Three-phase DA machines, conversely, are not portable in any practical sense: a 400 V 32 A three-phase feeder, the correct plug, and a matching breaker must already be on the wall, and trying to back-feed one from a small rotary phase converter caps the available welding current well below the nameplate rating [S1][S5].
Field reports also note that transformer-based three-phase welders are generally locked to either single-phase or three-phase operation and cannot be rewired in the field, while many modern inverter machines accept either input but draw noticeably more line current on single-phase for the same welding output [S5]. The same phase-selection logic shows up in the electroslag pressure welder class, where the heavier-duty variants are three-phase only for the same reason: stable, high-current delivery over a long weld cycle. Trigger timing on the gun side, including lift, plunge, and the weld sequence itself, interacts with this power topology; finer details on that sequence are covered in the stud welder gun trigger timing walkthrough, which complements the power-side choice made here.
For sites that already have a 400 V three-phase drop but only need to weld small fasteners intermittently, an inverter-based single-phase machine on a 230 V outlet will usually outperform a three-phase DA unit run at reduced capacity, because the inverter's electronics smooth out the single-phase ripple well enough for small-diameter studs [S2][S5]. The opposite is also true: forcing a single-phase CD unit onto a high-volume M16 stud production line is the most common mis-spec in this category, and the failure mode shows up as inconsistent fillet geometry, not as a tripped breaker.