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Old 07-04-2012, 09:47 AM   #1
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Circuit size for Amp loading?


I have a Hobart welder that states it draws 20.5A. Does this mean it must go on a 30 Circuit, or is that a startup current that is short enough that a 20A circuit would suffice?

Similarly, I have a Wood Lathe that draws 21A, same question?

Here's the specs on the welder:

Rated Output at 30% Duty Cycle
130 A at 21.5 VDC
Current Range: 25 - 190 A
Max. Open-Circuit Voltage: 31 V
Wire Feed Speed Range: 40 - 700 IPM
50 - 740 IPM at no load
Amps Input at Rated Load: 60 Hz., 230 V., 20.5A
kVA: 4.7
kW: 3.88
Dimensions
H: 12-3/8 in (315 mm)
W: 10-5/8 in (270 mm)
D: 19-1/2 in (495 mm)
Net Weight: 68 lb (31 kg)
Rated Output at 30% Duty Cycle130 A at 21.5 VDCCurrent Range25 - 190 AMax. Open-Circuit Voltage31 VWire Feed Speed Range40 - 700 IPM
50 - 740 IPM at no loadAmps Input at Rated Load, 60 Hz 230 V20.5kVA4.7kW3.88DimensionsH: 12-3/8 in (315 mm)
W: 10-5/8 in (270 mm)
D: 19-1/2 in (495 mm)Net Weight68 lb (31 kg)
Rated Output at 30% Duty Cycle130 A at 21.5 VDCCurrent Range25 - 190 AMax. Open-Circuit Voltage31 VWire Feed Speed Range40 - 700 IPM
50 - 740 IPM at no loadAmps Input at Rated Load, 60 Hz 230 V20.5kVA4.7kW3.88DimensionsH: 12-3/8 in (315 mm)
W: 10-5/8 in (270 mm)
D: 19-1/2 in (495 mm)Net Weight68 lb (31 kg)

Thanks in advance.

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Old 07-04-2012, 10:58 AM   #2
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Circuit size for Amp loading?


Id figure a heavy load like those at 125% of name plate rating myself anyway

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Old 07-04-2012, 11:07 AM   #3
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Circuit size for Amp loading?


Does it have a cord on it? To plug it in?
From your description and specs I see a 30 amp circuit with number ten conductors.
It never hurts to give the manufacturer a call. But since its rated for 20.5 amps, it needs a 30 amp circuit unless it comes with a cord and plug.

Edit: Article 240.6 indicates a 25 amp breaker or fuse as standard.

Last edited by J. V.; 07-04-2012 at 11:11 AM.
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Old 07-05-2012, 05:35 PM   #4
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Circuit size for Amp loading?


I don't weld, but here's my take on these spec's:

Rated Output at 30% Duty Cycle
130 A at 21.5 VDC
>equals 2800w (2800/230 = 12A), average, so while the arc is struck you will pull 2800/0.3 = 9320w and 9320/230 = 41A, so if you want the breaker to never trip use a 40A breaker.
>A 25A breaker will be running at 41/25 = 1.6x rated value and will hold for many seconds while the arc is struck, depending on the breaker's trip curve.

Amps Input at Rated Load: 60 Hz., 230 V., 20.5A
>This implies that for most welding jobs the duty cycle is 100x(20.5/41) = 50% and the length of time the arc is struck is such that most/some 20A breakers won't trip.

Last edited by Yoyizit; 07-05-2012 at 05:40 PM.
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Old 07-05-2012, 06:03 PM   #5
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Circuit size for Amp loading?


I agree with JV ... 230 volt supply, double pole 30 amp circuit breaker, #10 awg copper conductors for the branch circuit. This will be Murphy proof..... It may even exceed the minimums (rated) that the manufacturer is stating on the specifications ...
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Old 07-05-2012, 08:48 PM   #6
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Circuit size for Amp loading?


you have to go 30A, i set up temp power for guys with 20A welders all the time at work and even the 20A tack welders for duct insulation that are rated at 20A exactly will trip a 20A breaker. whether or not it's legal save yourself the trouble and go a size bigger. Odds are the welder has a 30A twistlock receptacle on it.
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Old 07-05-2012, 10:39 PM   #7
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Circuit size for Amp loading?


read nec art 630.11(a).multiply the 20.5 input amps by the 30%duty cycle factor which is .55 and you get 11.275 amps.that means a 20 amp ckt is fine.should give a min breaker req.25 amp breaker for lathe.

Last edited by oleguy74; 07-05-2012 at 10:42 PM.
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Old 07-06-2012, 09:17 AM   #8
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Circuit size for Amp loading?


Quote:
Originally Posted by oleguy74 View Post
read nec art 630.11(a).multiply the 20.5 input amps by the 30%duty cycle factor which is .55 and you get 11.275 amps.that means a 20 amp ckt is fine.should give a min breaker req.25 amp breaker for lathe.
With the trip curve in Fig. 1,
http://static.schneider-electric.us/...0600DB0105.pdf
at 41/20 = ~2x rated current, arcs lasting less than 28 seconds will never trip it and arcs lasting longer than 110 seconds will always trip it. Possibly it's 50-50 that an arc lasting 60 seconds will trip the particular breaker the OP finally selects, assuming this trip curve is typical.

But, Andrew79 has some real world data on this and he says 30A.

Last edited by Yoyizit; 07-06-2012 at 09:20 AM.
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Old 07-06-2012, 10:01 AM   #9
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Circuit size for Amp loading?


should have said #12 wire instead.also weldershould say req breaker size.just put a 30 amp breaker on it.IMO these trip curv tables are good,i doubt any one posting here will ever test a breaker for actual values in a residential setting.only time i have had it done was for power up-grades for teleco central offices.breakers from manufactures allready pass min values.just my view...

Last edited by oleguy74; 07-06-2012 at 10:57 AM.
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Old 07-06-2012, 12:32 PM   #10
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Circuit size for Amp loading?


Quote:
Originally Posted by oleguy74 View Post
just put a 30 amp breaker on it.
Agreed.
You may pay a little more but you will have a substantially increased likelihood that you won't be tripping this breaker.

Last edited by Yoyizit; 07-06-2012 at 12:43 PM.
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Old 07-06-2012, 12:32 PM   #11
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Circuit size for Amp loading?


minimum and what will actually hold are two totally different things, remember the code book is the MINIMUM allowed by law. There's nothing saying anywhere that you can't cover your @ss and go above the minimum

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