Sizing Conductors & Breaker for Arc welder

I

IanO3

Member
Location
Florida
Occupation
Electrician
The nameplate of a Syncrowave 350LX Arc welder (Cant figure out how to attach photo) does not specify an Effective (eff) or a Max current value. So I'm of the assumption (😬) That the Current value given on the nameplate (i1) is the primary rated current at its given voltage.

It will be wired 240V (230v) and shows an i1 of 131.1A.
Its my understanding that duty cycles can be adjusted by the the person welding when adjusting the output amperage, And the nameplate represents this showing multiple duty cycle percentages at different output currents (i.e. 30% @ 400A, 40% @350A ... , 100% @ 250A).

The question is how to determine the duty cycle to use in Table 630.11(A) when given primary rated current, and adjustable duty cycles.

Questions solve ignorance.
Thanks in advance,
- Ian
 
infinity said:
Did you take a glance at the owners manual? It has some specifications:

View attachment 2575299
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Yes, I currently have that document (2-9 electrical service guide) and (2-3 specifications) page printed out. I didn't just go with this, as my initial concern was that #4AWG seems incorrect for a 112A input rating. That concern is why I opened Art. 630 to try and size everything myself off the nameplate.

If the "With Power Factor Correction" table was to be used than why provide the first table "Without .. Correction"?
I was also concerned with the "Note" at the top letting me know they are calculated at 60% duty cycle, as if to say "If not being used at 60% duty cycle this would be irrelevant."

I'm sure I'm misunderstanding or overthinking this.
Any help is appreciated.
 
IanO3 said:
The question is how to determine the duty cycle to use in Table 630.11(A)
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You'll have to ask the customer about that, that is whether they plan to use the machine full-tilt all the time or occasionally at half the capacity.

BTW, I haven't checked and it probably hasn't changed, but the quoted table references the 1996 code and it's pretty likely that Florida is using a newer one.
 
zbang said:
You'll have to ask the customer about that, that is whether they plan to use the machine full-tilt all the time or occasionally at half the capacity.

BTW, I haven't checked and it probably hasn't changed, but the quoted table references the 1996 code and it's pretty likely that Florida is using a newer one.
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I noticed that as well, and checked a 1996 NEC ampacity table to ensure it hadn't changed.

As for asking the customer, I don't like the idea of something being sized based on someones promise of how they'll use it. I feel it should be sized based on the largest possible amperage especially since its as simple as the turn of a dial for output amperage?

If a welder is capable of a 100% duty cycle (Adjustable) do you just size directly from the Rated Primary Current (1.00 Multiplier)?
I'm aware if I do that it takes away any fears I would have, but would like to know the proper procedure.
 
A welder should know better. The manual talks about duty cycle and overheating. If they exceed the duty cycle, the welder shuts down with a HLP message and it runs its cooling fans. Most welders know this and pay attention to their welding time. The manual warns that the warranty can be void if you overheat the welder. I think the issue here is they want the welder (person) to be cognizant about the duty cycle, but the thermal shutdown circuit will protect the welder unless that mechanism fails in which case you can burn up the welder. A burnt up welder could also burn up your branch circuit wiring though.

So leaving a bit of margin in the branch circuit ampacity would be prudent, but sizing the circuit to 100% Imax when it can't do that at a 100% duty cycle is overkill. If you use the table value in 630.11(a) and calculate them at the various duty cycles and input amp values, they tend to give values that are all about the same. That value is probably about the ampacity of a #4 wire for this welder.
 
Attached is the nameplate from the welder in question.
And for starters that word "Should" know better is my issue.
suemarkp said:
A welder should know better. The manual talks about duty cycle and overheating. If they exceed the duty cycle, the welder shuts down with a HLP message and it runs its cooling fans. Most welders know this and pay attention to their welding time. The manual warns that the warranty can be void if you overheat the welder. I think the issue here is they want the welder (person) to be cognizant about the duty cycle, but the thermal shutdown circuit will protect the welder unless that mechanism fails in which case you can burn up the welder. A burnt up welder could also burn up your branch circuit wiring though.

So leaving a bit of margin in the branch circuit ampacity would be prudent, but sizing the circuit to 100% Imax when it can't do that at a 100% duty cycle is overkill. If you use the table value in 630.11(a) and calculate them at the various duty cycles and input amp values, they tend to give values that are all about the same. That value is probably about the ampacity of a #4 wire for this welder.
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I don't believe the value I have is the Imax. I believe it's the Rated Primary current. 630.11 Speaks of using the rated primary current Multiplied using Table 630.11(A) "Based on THE duty cycle of the welder", seems to imply a welder has a set duty cycle (or is it interpreted as the "Desired" duty cycle?), because the duty cycle is adjustable.
Rated primary current at 30% - 131A*.55 = 72A
Where at 100% its 131A.

I'm misunderstanding something I'm sure but, if you have a single value in amperage (Rated primary current), how does Table 630.11(A) at different duty cycles, give values that are all about the same?
 

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Many welder nameplates list the primary current at different secondary currents and design duty cycles. The current drawn at the 100% duty cycle usage is less than the current drawn at the 40% duty cycle setting. The duty is variable because it can do a longer duty at a lower setting, but sometimes you need more current for a larger weld (and you can't use it so hard in that case). Multiplying the 630.11 table values by these currents tends to give the same number because overall there is a given thermal load that the welder can accommodate without burning up. This is usually enforced with a thermal element (circuit breaker) in the welder that shuts it down but keeps the fans running. But those thermal elements can fail, especially when they are used a lot. So their guideline is to tell the welder operator to follow a duty cycle and watch the clock.

This welder seems to only show the secondary currents at various duty cycles. If you use it at 100%, you need to set it to 250A. If you can use it at 30% you can turn it up to 400A. If it showed the primary current as well, you could multiply those by the 630.11 table values to see what you get. You could probably make a guess of it by applying the 400/131 ratio to the other secondary currents, but I'm not sure if welders work this way or not. I did that here:

400A / 131A = 3.05 Duty cycle is 30% 630.11 multiplier is .55 Duty cycle limited amp draw is 131*.55 = 72A
350A / 3.05 = 115A Duty cycle is 40% 630.11 multiplier is .63 Duty cycle limited amp draw is 115*.63 = 72A
300A / 3.05 = 98.4A Duty cycle is 60% 630.11 multiplier is .78 Duty cycle limited amp draw is 98.4*.78 = 77A
250A / 3.05 = 82A Duty cycle is 100% 630.11 multiplier is 1 Duty cycle limited amp draw is 82A

These values should be safe on a #4 copper conductor rated at 75C since it is rated at 85A continuous. Welding at 100% duty cycle seems nearly impossible as you need to change sticks, reposition work, etc so the 82A load would still have have breaks.

If it makes you feel better, run this circuit with #2 copper. This way you should melt the welder before melting the branch circuit wiring.
 
Thank You Mark,
Now I understand what you mean math wise, and it already makes more sense, finding the ratio between the primary and secondary currents and using that ratio to find the other primary currents at various secondary currents (Different duty cycles). Also begins to make sense why the specs from welder manual show the #4 AWG (Not that I thought they would be wrong, just wasn't understanding).

I certainly have enough now to move on from this.

Last question - on the nameplate I attached it shows a Primary current value of 131A @230V (Apologize for the photo being upside down).
You used that value against the 400A output current (max Output current) to rework the other duty cycles. All makes sense to me. But, does that mean we are reading that Primary Current value as the Imax? (Even though its not labeled as any of the following: Imax, Ieff, or Rated Primary Current).
I'm Thinking now the term "Rated Primary Current" is referring to the Primary current at each given duty cycle? (As the input current changes depending upon the output current)
 
I'm not really sure what the rules are on calculating Imax or Ieff. It is supposed to be on the nameplate, but it isn't on this one (maybe it is too old). Based on the nameplate and the user manual, it seems like 131 should be the Imax.

I also notice the manual says the input amps is 112A at a 60% duty cycle (only duty cycle they listed). So maybe my 400/131 ratio scheme isn't quite accurate since I got 98.4A. But the idea is the same and a welder manufacturer should know how it works at all duty cycles when they came up with their conductor size recommendation. The welder manual seems to be referencing the 1996 code, so using the lastest rules can be difficult when you have older stuff that was labeled differently back then.
 
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