"Properly" hook up an ancient IdealArc 250/250?

[Jawn]

I have an old Lincoln IdealArc 250/250 (probably 1970s vintage) that I'd like to hook up in a new detached garage/workshop at my house. Plenty of anecdotal evidence of these running on normal 50A welder circuits at lower power settings, but I'd like to have this thing hooked up "right" in my new workshop.

Local (GA) code is NEC 2020 and inspections will occur as there is a new service being installed.

It's a little vague on its specifications, the manual has a table which assumes 200A secondary current even though it's a 250 amp welder. At 200 amps secondary, the primary is stated to be 70A and 50% duty cycle. It also specifies a 90A "superlag" fuse... not sure how to correlate that to a suitable breaker.



I can work from the 70A at 50% duty cycle to get that I need conductors sized for 49.7A (using .71 multiplier from 630.11(a)), but overcurrent protection I'm a little less sure of. Am I interpreting this correctly that 630.12(A) says overcurrent protection cannot exceed 200% of that 70A? So... 140A? Seems crazy high. Or is it not that critical, so long as it's under that 200% and big enough to not nuisance trip? What size breaker should I choose?

 

[nadogail]

When wiring a feed to a welder you are allowed to take into consideration the fact that your welding will not represent a continuous load and the supply conductors can be reduced in size.

This is an area where I know just enough to be dangerous and do not profess to have expert knowledge.

 

[u2slow]

Wiring welders is an 'in the ballpark' situation. Meet the minimums and don't exceed the maximums. With this size of machine, you're beyond 6-50R. (Much cheaper to hardwire.)

Super lag fuses are most likely a brand reference to a time delay fuse.

The safest way is to choose OCP at the low end and then if nuisance tripping is a problem, increase it. I would probably do a 60, 70 or 100 breaker because they're common and cheaper.

 

[MoonRise]

Note that the recommended 70 amp Super-Lag fuse is only if you have the optional power-factor correction capacitor kit installed.

Without the PF capacitor kit, the recommended fuse is a 90 amp Super Lag.

(one way or another, those input recommendations already take into account the machine's duty cycle with regard to the input amperage protection. No way would you be running 90 amps continuously through some #8 AWG copper wiring in the wall, it only has a rated ampacity of 40 amps, not including another other possible derating factors)

You can NOT run that machine as a plug and receptacle configuration. It has to be hard wired to a wall disconnect (think AC unit wall disconnect or similar).

Your minimum required service for hooking up that welder is a 90 amp breaker and #8 AWG copper wire from the panel to the disconnect and some more #8 AWG cable (hot-hot-ground) hardwired from the wall disconnect to the machine. Pay attention to connecting the ground wire to the machine chassis, via either the existing grounding stud or if that is missing or nonexistent then by adding a grounding lug to the chassis or connecting to a clean bare chassis bolt.

Those 'old' transformer machines pull a LOT of inrush current when first powered on. In addition to being an 'industrial' type machine where it is rated at 200 amps output @ 50% duty cycle but can go up to 250 amps @ 30% duty cycle. So no, you can't usually just say 'I'll run it at less than full power and then I can run it on a less-than-recommended input breaker/fuse and I'll be fine.'

Or you can call or contact Lincoln and ask them for clarification. https://www.lincolnelectric.com/en/Ask-the-Experts

 

[MoonRise]

Oh, and if you are wiring up a dedicated circuit for that welder (which you MUST do, just in case you didn't realize that aspect), and you are using less-than-breaker-ampacity wiring (#8 AWG copper on a 90 amp breaker in this case) you should label the circuit as such.

(old NEC code used to require labeling such less-than-ampacity circuits, just so someone doesn't end up connecting a continuous-duty device on a circuit wired with a reduced duty-cycle rating). example: welder circuit on a 50 amp breaker using #12 AWG copper, then someone later connects a space heater or heavy-duty motor on that circuit and the wiring in the walls ends up overheating and failing or starting a fire.

Also, an inspector would/should fail the wiring if they see a 90 amp breaker with #8 AWG copper wire (which only has an ampacity rating of 40 amps, not including any other possible derating factors). Like I mentioned above.

 

[Jawn]

When wiring a feed to a welder you are allowed to take into consideration the fact that your welding will not represent a continuous load and the supply conductors can be reduced in size.

This is an area where I know just enough to be dangerous and do not profess to have expert knowledge.

Right, which is where I'm getting conductors sized for 49.7A despite rated current of 70A (at 200A secondary).

I found a manual for a later version of the welder... also shows 70A at 50% duty cycle for 200A secondary current as well as 86A at 30% duty cycle for 250A secondary current... applying that duty cycle reduction calculates to less than the 50% at 70A does, so wire sized for at least 50A should be ok. I'm pretty confident about that.

Wiring welders is an 'in the ballpark' situation. Meet the minimums and don't exceed the maximums. With this size of machine, you're beyond 6-50R. (Much cheaper to hardwire.)

Super lag fuses are most likely a brand reference to a time delay fuse.

The safest way is to choose OCP at the low end and then if nuisance tripping is a problem, increase it. I would probably do a 60, 70 or 100 breaker because they're common and cheaper.

The guy I got it from ran it on a 6-50R, but he said it'd pop the breaker above 125A or so. I tested it at similar output on a 50A breaker. Obviously both the 6-50R and 50A breaker is insufficient for anything beyond that. I do plan to hardwire it. I don't have a need to move it around, so no real reason to invest in a plug/receptacle combo big enough for this monster as expensive as they are.

My knee jerk thoughts were to either put a 70A (matches what the welder nameplate says [although for less than 100% output]) or 90A (matches the fuse rating specified in the manual). Run #6 THHN to a 100A non-fused disconnect and hope the inspector approves.

I could ask him what he expects it to have... but I have no idea if calling attention to it will open a bigger can of worms with the inspector. Maybe I'll just pre-wire and approach the topic with him once he shows up for rough-in inspection.

Note that the recommended 70 amp Super-Lag fuse is only if you have the optional power-factor correction capacitor kit installed.

Without the PF capacitor kit, the recommended fuse is a 90 amp Super Lag.

(one way or another, those input recommendations already take into account the machine's duty cycle with regard to the input amperage protection. No way would you be running 90 amps continuously through some #8 AWG copper wiring in the wall, it only has a rated ampacity of 40 amps, not including another other possible derating factors)

You can NOT run that machine as a plug and receptacle configuration. It has to be hard wired to a wall disconnect (think AC unit wall disconnect or similar).

Your minimum required service for hooking up that welder is a 90 amp breaker and #8 AWG copper wire from the panel to the disconnect and some more #8 AWG cable (hot-hot-ground) hardwired from the wall disconnect to the machine. Pay attention to connecting the ground wire to the machine chassis, via either the existing grounding stud or if that is missing or nonexistent then by adding a grounding lug to the chassis or connecting to a clean bare chassis bolt.

Those 'old' transformer machines pull a LOT of inrush current when first powered on. In addition to being an 'industrial' type machine where it is rated at 200 amps output @ 50% duty cycle but can go up to 250 amps @ 30% duty cycle. So no, you can't usually just say 'I'll run it at less than full power and then I can run it on a less-than-recommended input breaker/fuse and I'll be fine.'

Or you can call or contact Lincoln and ask them for clarification. https://www.lincolnelectric.com/en/Ask-the-Experts

Well, there *are* plugs/receptacles that would handle it... but they'd probably cost at least several times what I paid for the welder and new cables.

Oh, and if you are wiring up a dedicated circuit for that welder (which you MUST do, just in case you didn't realize that aspect), and you are using less-than-breaker-ampacity wiring (#8 AWG copper on a 90 amp breaker in this case) you should label the circuit as such.

(old NEC code used to require labeling such less-than-ampacity circuits, just so someone doesn't end up connecting a continuous-duty device on a circuit wired with a reduced duty-cycle rating). example: welder circuit on a 50 amp breaker using #12 AWG copper, then someone later connects a space heater or heavy-duty motor on that circuit and the wiring in the walls ends up overheating and failing or starting a fire.

Also, an inspector would/should fail the wiring if they see a 90 amp breaker with #8 AWG copper wire (which only has an ampacity rating of 40 amps, not including any other possible derating factors). Like I mentioned above.

My calculations based on info from the manual did show a required ampacity of just under 50A, which is why I had in mind #6 THHN in conduit.

 

[u2slow]

I question if the local disconnect is required when the panel breaker is close enough (don't know the NEC distance rule).

Also, an inspector would/should fail the wiring if they see a 90 amp breaker with #8 AWG copper wire (which only has an ampacity rating of 40 amps, not including any other possible derating factors). Like I mentioned above.

Actually not a fail. Code is allowing the mismatched wire and breaker because of the duty cycle. (do the appropriate code calc) This presumes the machine is hardwired.

 

[Jawn]

I question if the local disconnect is required when the panel breaker is close enough (don't know the NEC distance rule).

Actually not a fail. Code is allowing the mismatched wire and breaker because of the duty cycle. (do the appropriate code calc) This presumes the machine is hardwired.

Disconnect may or may not be required, I'd feel better about having something within arm's reach. That said, come to think of it... I may end up putting this thing right next to the breaker box, so I may be ok without a separate disconnect.

As to wire size #6 vs #8... it depends on the type of wire. NM-B will require #6 for 50A, THHN inside conduit would technically be ok with #8 but I'd feel better about having #6 there. Same mental process that's making me put #12 THHN in for my 20A receptacles even though it'd be ok with #14.

At least if I decide to run more than one circuit in a single conduit, #12 gives me enough headroom to handle the derating for the number of conductors needed for two 20A receptacle circuits.

 

[alfredeneuman]

you are using less-than-breaker-ampacity wiring (#8 AWG copper on a 90 amp breaker in this case) you should label the circuit as such.

(old NEC code used to require labeling such less-than-ampacity circuits, just so someone doesn't end up connecting a continuous-duty device on a circuit wired with a reduced duty-cycle rating).

The "old NEC" had no such rule.