Welder wiring?

[raferguson]

In my new shop, I had them pull in a 100 amp 240V subpanel, as well as wire two 240V outlets, 8 ga wire, on 50 amp breakers. (one circuit for the compressor, one for the welder). As I read the code, I could have gone to a 55 amp breaker, but the contractor would not go bigger on the breaker, since the outlet was a 50 amp outlet.

I know that welders have a special section in the NEC, and that it is possible to use smaller wire for a larger breaker, than would be permitted in other applications. As I understand it, this is based on the duty cycle of the welder.

1. Given the 8 ga wire, and the 50 amp outlet, how large a breaker would be reasonable? The primary load would be a Syncrowave 200 welder. It can put out 200 amps, but is rated at 150 amps at 40% duty cycle. The rated input current at 150 amps is around 50 amps at 230V, depending on TIG vs stick, and AC vs DC. I have been living with a 50 amp breaker without difficulty, but this is a new shop with a new breaker, so I don't know if I am going to trip it or not. I suppose that the short answer is that I should not change the breaker unless needed. I would label the outlet as "Welder only," if I were to increase the breaker size. My guess is that I could go up to a 60 amp breaker without being crazy. Going up a wire size would not be a huge deal, since the run is about 6 feet in 1/2 inch conduit.

2. My dream welder is a Syncrowave 250, which is rated for 250 amps at 40% duty cycle, and up to 310 amps output. I would probably hard wire it in on its own circuit. The spec sheet says 250 amps out requires 96 amps in at 230 volts. Presumably I would install a 100 amp breaker for such a welder, although I am unsure what wire size would be appropriate. Even on a 100 amp circuit, I might trip the breaker at full power. Thoughts? I might end up with a welder similar to the Syncrowave 250, if I get a good deal on craigslist. I could use more power for the rare times that I weld thicker aluminum. Whether I need it or not is a separate question. ;-)

Conveniently, the new subpanel has lots of room for additional circuits. I will be adding a 30 amp 240/120 RV outlet, using a 30 amp breaker left over from the subpanel project.

Thanks,
Richard

 

[Norcal]

Was the 8 gauge in conduit, or was it NM cable AKA "Romex®"? 8 AWG NM cable is 40A max.,

 

[wyliesdiesels]

The 55a rating you got for #8 THWN cannot be used to size OCPD.

That rating is found in the 90* c ampacity column which is for derating purposes only.

#8 THWN is limited to 50a

#8 NM-b is limited to 40a as said above.

What is the HP rating on the compressor?

 

[sberry]

It's a welder circuit, if wevread the instruction manuals the minimums are for single circuit in pipe and a cord or cable needs to be upsized. I don't recall anywhere it says we need to limit the breaker if cable isbused. Millions of circuits installed by masters and inspected were 10 cable to 50 fuses for welders.
A machine that does not come with a plug is sposed to be hard wired. I believe the 200 is an 8 wire with 100 breaker.

 

[sberry]

whoops, the 200 is a 8/60 machine. There are so many models its a problem doing it from memory. There are models within models, a couple of them allow 8/100, maybe a red one. But once the breaker goes over 50 the recept is out due to the fact a smaller machine could be plugged in to it where the internals are not designed for short circuit that high. Most,,,, 50A machines come with a 12 cord. Some of the bigger feeders with higher duty have larger ones.
In the case above as Norcal pointed out that the 8 cable is too small for the machine regardless of the breaker.

but the contractor would not go bigger on the breaker, since the outlet was a 50 amp outlet.

The contractor would be correct and I have never heard of a 55 breaker, why would one want an oddball anyway?

I would probably hard wire it in on its own circuit.

All of these need their own hardwired.
Comps over 3 hp and welders over 50A

 

[mcbane]

My synchrowave 250 is from the mid 1990s so might not be the same as a new version but: the nameplate says use a 50 amp minimum breaker. The welder came with no cord but the shop that sold it added a short 8-3 cord and standard 50 amp plug.

While the welder can draw a lot more than 50 amps they have taken credit for the duty cycle when they suggest that a 50 amp breaker might be acceptable. As a practical matter, that welder has a huge inrush current and will reliably trip a 50 amp breaker if you power cycle it, on-off-on, within about a one minute period or you weld a little too long at high current. Mine has been running on a 60 amp breaker for over 20 years without tripping the breaker. The old 50 amp breaker was maddening. My in-conduit wiring is 6ga.

NEC says: Each welder shall have overcurrent protection
rated or set at not more than 200 percent of I1max. Alternatively,
if the I1max is not given, the overcurrent protection shall be rated
or set at not more than 200 percent of the rated primary current
of the welder.
An overcurrent device shall not be required for a welder
that has supply conductors protected by an overcurrent device
rated or set at not more than 200 percent of I1max or at the rated
primary current of the welder.
If the supply conductors for a welder are protected by an
overcurrent device rated or set at not more than 200 percent of
I1max or at the rated primary current of the welder, a separate
overcurrent device shall not be required

NEC is pretty generous re: breaker size because larger shops might run several welders on one breaker. Your two biggest welders on that circuit will govern in terms of overcurrent protection and conductor sizing. Keep in mind that your wiring must be appropriate to the breaker size.

 

[mcbane]

I just checked the online synchrowave manual dated 2002 and it recommends a maximum of 125 amps for the disconnect, with minimum 6 ga wire. You can also spend $$$ more and get the power factor correction kit that will lower the current draw of that welder.

 

[sberry]

My synchrowave 250 is from the mid 1990s so might not be the same as a new version but: the nameplate says use a 50 amp minimum breaker. The welder came with no cord but the shop that sold it added a short 8-3 cord and standard 50 amp plug.

While the welder can draw a lot more than 50 amps they have taken credit for the duty cycle when they suggest that a 50 amp breaker might be acceptable. As a practical matter, that welder has a huge inrush current and will reliably trip a 50 amp breaker if you power cycle it, on-off-on, within about a one minute period or you weld a little too long at high current. Mine has been running on a 60 amp breaker for over 20 years without tripping the breaker. The old 50 amp breaker was maddening. My in-conduit wiring is 6ga.

NEC says: Each welder shall have overcurrent protection
rated or set at not more than 200 percent of I1max. Alternatively,
if the I1max is not given, the overcurrent protection shall be rated
or set at not more than 200 percent of the rated primary current
of the welder.
An overcurrent device shall not be required for a welder
that has supply conductors protected by an overcurrent device
rated or set at not more than 200 percent of I1max or at the rated
primary current of the welder.
If the supply conductors for a welder are protected by an
overcurrent device rated or set at not more than 200 percent of
I1max or at the rated primary current of the welder, a separate
overcurrent device shall not be required

NEC is pretty generous re: breaker size because larger shops might run several welders on one breaker. Your two biggest welders on that circuit will govern in terms of overcurrent protection and conductor sizing. Keep in mind that your wiring must be appropriate to the breaker size.

Good perspective and working on general understanding.
The allowances for the high breakers may not apply across the board. The machine itself may have a separate listing thru nema, if it comes plug and cord it needs to be installed like its listed.
The code limits the breaker size on the receptacle, there is an allowance for the wire under some circumstances. Another reason for hard wire. Not only is it designed to be adequate its often designed to be current limiting.
An example being an electric range, the only wire in it that is 50A is the cord and none of the rest of it has additional over current, lots of 30A machines that way as well as lots or sposed to be all equipment to plug in to 120V 20A till further protection may be added or components sized adequately to provide short circuit protection.
AC buzz box, 48A at rated and 12 cord. No thermal beyond. Duty limited depending on load. Can wire it with a 10 cable and not be unsafe. Now,,,,,,,,,, we have small mig and inverters, come 50A plugs. Used to be a 50 required a 12 so they used the same cord as the buzzer, allowed it to 50A, machine used half that allowing for 2 machines to the same circuit and maybe even tap wire under some circumstances in the nature of the electric range.

 

[sberry]

Some of the things one can do might not be a great idea in the home residential. Even on my farm keep the cobble jobs to a minimum and simple. While the code allows some welders to be connected like that the cord may need change, the outlet done away with, a listed switch, other internal components changed etc.
Over the years have corrected lots of my own faults, I have remodeled, put new equipment, along with it better code compliance and not so many ambushes.

 

[sberry]

About the onlyist thing I can think of that comes cord and plug ready with 6-50-r that would overload a 10 cable is a 250 feeder. Most ranges/ovens are 4 wire, compressors don't come with them and even then would be limited 3 hp which wouldn't overload the wire. Even if it gets violated with 5 hp wont burn the place down,,,, lots of them on 10/30 cable circuits.
Lots of factors to size wire but a decent general place to start is a cord or building wire should be a size larger than the cord comes on it. A size bigg3er than whats listed in the manual. It may be ok to pipe single circuit to them with Thhn the same as the cord but if its a high load like an AC buzzer the performance droops, duty becomes more of an issue, move up a size and all the worry goes away and may be able to connect some other machines to the same circuit.

 

[sberry]

Basically you cannot apply a load that is going to overheat the wire if you use a larger breaker. If the calculated load wont overheat the wire a welder can be connected to a larger breaker than the standard limitations.
I have a 300 synch, its not really wired legal. I hooked a number 2 from main lug feed thru to a 100A breaker box I had and used 6 to a 6-50. While the 6 would be ok for short circuit the machine really requires 2 to the point that the duty cannot overheat the wire. I should find a 60 and change it to protect it from thermal. I don't use it anymore and the breaker is off but at one point tripped a 60 once back in the day really smoking on it way beyond what I needed to run it, some big seam on a boat I will never do again.
A 250 synch calls for 6 at 100, you wont trip it. The machine would burn up the common hardware, torch, tungsten etc. before it would trip. Even though the breaker is 100 its not really protecting the wire from thermal even at top loads.
Same way with a 180 mig, may be connected to a smaller 12 wire with its 12 cord on a 50A breaker.

 

[raferguson]

The compressor is on it's own 50 amp circuit.

The wire is in metal conduit.

Good point in terms of using the welder's own cable as a starting place in terms of sizing the wire.

All outlets are within 10 feet of the subpanel, so not much voltage loss there.

Thanks to all for your comments.

 

[wyliesdiesels]

The compressor is on it's own 50 amp circuit.

The wire is in metal conduit.

Good point in terms of using the welder's own cable as a starting place in terms of sizing the wire.

All outlets are within 10 feet of the subpanel, so not much voltage loss there.

Thanks to all for your comments.

Whats the HP rating on the compressor motor?