I Need a 400V, 3-pole, 25A circuit breaker.....what would you use?

[General Zod]

I doubt any electromechanical breaker will do you much good if there is a short in the welder.
The solid state components in there will destroy themselves way before the breaker even thinks about tripping.
Solid state stuff usually is fused, but even that is just to prevent fires not save the equipment.
Skip the breaker and save yourself some money. If the welder is not fused internally you could provide it externally.
Personally, I probably wouldn't bother. If you shut down the system when you leave it should be safe.
-M

Yes I do understand your point, but I'd still rather have a breaker post-transformer. Saving money is not a concern, (but at the same time I don't let others dictate what I do or don't do with my hard-earned money ). I didn't even need this welder nor the 30kva transformer needed to run it, LOL.

 

[mksj]

I believe the NEC would require a secondary side breaker/fusing in most cases to protect the wiring on that side, there are some exceptions. With a 30 kva transformer the inrush current when it is switched on will be significant.

NEC Guidelines for Transformer and Transformer Feeder Protection

When overcurrent protection is not required

www.ecmweb.com

 

[General Zod]

I believe the NEC would require a secondary side breaker/fusing in most cases to protect the wiring on that side, there are some exceptions. With a 30 kva transformer the inrush current when it is switched on will be significant.

NEC Guidelines for Transformer and Transformer Feeder Protection

When overcurrent protection is not required

www.ecmweb.com

It's not switched On under load though. The inrush of just simply turning it on with zero-load is rather insignificant.

 

[mksj]

Not a factor of loading, has to do with first energized or reenergized after a short interruption, the transformer may draw inrush current from the system due to the core magnetization being out of sync with the voltage. "Inrush Current is a form of over current that occurs during energisation of a transformer and is a large transient current which is caused by part cycle saturation of the magnetic core of the transformer. For power transformers, the magnitude of inrush current is initially 6 – 10 times or higher of the rated load current."

 

[General Zod]

Not a factor of loading, has to do with first energized or reenergized after a short interruption, the transformer may draw inrush current from the system due to the core magnetization being out of sync with the voltage. "Inrush Current is a form of over current that occurs during energisation of a transformer and is a large transient current which is caused by part cycle saturation of the magnetic core of the transformer. For power transformers, the magnitude of inrush current is initially 6 – 10 times or higher of the rated load current."

I appreciate your input, but I don't agree that the in-rush is anywhere near that much (180 to 300 kW worth! - according to your quote). That much juice should pop the 3-phase breaker it gets it's power from (240V, 40A, 3-pole), and heck that would pop the single phase breaker that my RPC gets it's power from (240V, 125A, 2-pole), since that powers the transformer. Neither have tripped. The lights don't even dim at all when I turn on the 3-pole breaker it is powered from. So with my empirical observations, I have to say that your conjecture is not that accurate. However, if you would like to send test equipment to me, I would be more than happy to provide numerical data & measurements for you. But for now I will agree to disagree, since all my gear is working just fine with no ill electrical effects.

 

[mksj]

Not theory, but fact. The reason breakers do not rip is because it is for a very short period of time and it has to do with the trip curve. Whatever works for you is fine, but there are quite a few threads over at the Practical Machinist that this is a reality and can be an issue.

Inrush current - Wikipedia

en.wikipedia.org

RE: Transformers

 

[General Zod]

Not theory, but fact. The reason breakers do not rip is because it is for a very short period of time and it has to do with the trip curve. Whatever works for you is fine, but there are quite a few threads over at the Practical Machinist that this is a reality and can be an issue.

Inrush current - Wikipedia

en.wikipedia.org

RE: Transformers

Yes I do know about inrush current. While I may not be an "industrial electrician" or have all the experience that others may have, I do have a degree in Physics & Mathematics, so I'm not as clueless as some people here quickly assume others to be. Like Bi11Hudson who says there isn't enough time/space to teach me, presumably because he assumes I know nothing or can't learn. That's fine if he thinks that. My learning rate is actually quite rapid, because I taught myself how to learn at a young age. Heck, I taught myself Calculus-I with only 3 books from my public library when I was 16 yrs old, aced the HS class, placed at state-level competitions, went on and took and passed about 8 classes in different areas of Calculus in college while obtaining my degree. But I digress for the moment.

What I'm getting at, is the "can be an issue" part you mentioned. So even if the inrush is significant, it actually isn't an issue. Because the breakers don't trip. I can go to my garage right now, flip the RPC on, then flip the transformer on, and nothing in my house "freaks out" in any way shape or form. So what does that tell me? That there is no issue. Do you understand me now?

 

[Weldingrod1]

I've had my (big) welding machine end up with a magnetized core and pop the house breaker when I tried to turn it on. Took a couple of tries to pump enough energy into the core to pull down the remnant magnetization and allow me to start it. It's only happened once, but the in rush is a real phenomenon, just something where you have to get unlucky at turn-off.

Sent from my SM-G892A using Tapatalk

 

[MikeInOr]

I usually go to ebay for things like this. It seems like 3 phase anything is cheap on ebay. Most all of my machines that I have rebuilt have 3 phase contactors for single phase motors because 3 phase contactors are so cheap on ebay. I would bet you could pick up the breaker you a looking for at a reasonable price with a little searching.

https://www.ebay.com/sch/i.html?_fr...TitleDesc=0&_odkw=dan+wesson+barrel&_osacat=0

 

[sdelivery]

Not theory, but fact. The reason breakers do not rip is because it is for a very short period of time and it has to do with the trip curve. Whatever works for you is fine, but there are quite a few threads over at the Practical Machinist that this is a reality and can be an issue.

Inrush current - Wikipedia

en.wikipedia.org

RE: Transformers

This is FACT.