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I just bought a lower-mid priced 120V/20A welder (Forney Easy Weld 140MP), and the manual details that the welder be plugged into a 20A outlet (with a 30A circuit breaker), or you can use a provided adapter to plug into a 15A outlet (with a 20A circuit breaker) for welds requiring lower power draw.

I’ve researched a bunch on breaker/receptacle amperage and building code, and thus am now aware that multiple 15A receptacles can be on a 20A circuit.

That aside, is the suggestion from the manual common practice? I would assume that a 20A outlet be on a 20A breaker, not a 30A breaker. I would assume that a 15A outlet would be on a 15A breaker (unless I was specifically informed otherwise).

I’d figured that a 20A welder on a 20A circuit would be a-ok. I definitely don’t have 30A circuits to plug into in my humble garage.

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b. insler
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2 Answers2

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You're correct that 20A receptacles are not allowed on 30A circuits. 30A receptacles only.

The manufacturer is competent and the item is UL-listed. What the UL-approved instructions really mean is you would be allowed to wire a dedicated 20A welder circuit.

Special rules for a dedicated welder circuit: since it is dedicated to the welder, certain NEC rules allow a breaker size "bump" to avoid nuisance trips. The rules essentially allow the welder to surge above 20A for short time periods (see "Duty cycle") since the short overload times and long cool down times will prevent wire overheat. To avoid the surges tripping breakers, a breaker bump is authorized.

But that bumped circuit must be dedicated to that one appliance. Preferably the appliance should be hard-wired; your AHJ might allow you to use a single socket (not the usual duplex) which is labeled "Welder only" or some such.

You are NOT allowed to bump the breaker for a general-purpose circuit that is used for other stuff.

Harper - Reinstate Monica
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12

Generally the NEC prohibits 20A receptacles on 30A breakers, but Instructions are part of the NRTL Listing (UL/CSA/ETL), and override general NEC provisions. So if the product is listed it's code legal.

If you have a 20A receptacle on a 20A breaker you will need to operate at a less than max setting.

2017 NEC 110.3(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

NoSparksPlease
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