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



## General Zod (Sep 27, 2021)

As the title states. I need a 400V 3-pole circuit breaker. The 3-pole breakers at my local big box stores are rated at 240V. What would you use?


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## woodchucker (Sep 27, 2021)

I don't know what I would use, I would go to an electrical supply house... around here we have cooper, and I would ask for what I needed.
Because, I don't know enough to substitute .


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## mksj (Sep 27, 2021)

Might help to know the size/Amperage you are looking for and if is for DIN rail or direct panel mount.
It depends on the enclosure, I would check Automation Direct, Mouser Electronics, etc.
UL489 is rated for  480Y / 277 VAC / 125 VDC, I have been using their MCB breakers for 240VAC


			https://www.automationdirect.com/adc/shopping/catalog/circuit_protection_-z-_fuses_-z-_disconnects/ul_489_miniature_circuit_breakers/gladiator_miniature_circuit_breakers_(gmcbu_series)/3-pole_(1a-63a)#
		


600VAC


			https://www.automationdirect.com/adc/shopping/catalog/circuit_protection_-z-_fuses_-z-_disconnects/ul_489_rated_molded_case_circuit_breakers_(mccb)/3-pole_mccbs,_15a-600a_(3p_series)/15a-100a_(100a_g-frame)#
		




			https://www.mouser.com/ProductDetail/Phoenix-Contact/2907687?qs=WfzemSix46tB4UMLh%2FCoVw%3D%3D
		



			https://www.mouser.com/ProductDetail/Phoenix-Contact/2907689?qs=WfzemSix46sjz2dEBfd2dg%3D%3D


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## Al 1 (Sep 27, 2021)

It sounds like you should contact a licensed electrician.  Al.


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## rabler (Sep 27, 2021)

Is this just for the Stel S300 you recently posted about?  Or are you using the 400V transformer for something else too?
A question to run by the more code/wiring safety knowledgeable folks - wouldn't an appropriate sized breaker on the input to the transformer work fine?  I.e., put a 400/230 * 25A breaker= 43.5, so roughly 40 amps, on the low side of the transformer?  I would *guess* that would actually be safer as it covers shorts in the transformer.


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## Bi11Hudson (Sep 27, 2021)

Rule Nr1: Hire an electrician that knows heavy industrial electrical systems. Avoid a residential "wireman", find someont that knows what the hell he's doing. There isn't space here, or the time, to bring you up to speed on all of what you need to know.

With that caveat out of the way, I must assume (ass out of me) that you have a rotary converter and need to wire the downside. The first comment is that a circuit breaker will protect the wiring, transformers, switches, and such like. It *will not protect the machine itself*. That's what the overloads on the starter and the local control fuse are for. 

Using a fusable disconnect or breaker to protect the wiring, with THHN class insulation and AWG 10 wire to the machine. A 30 amp breaker will do fine, do not try to size the breaker to the machine load. EMT conduit is fine, it needn't be rigid pipe. Rigid pipe is "better' but a PITA to work with. Do not run the wiring concealed behind wallboard, use conduit. In my day, SO insulation on portable cable was rated for 600 volts. I don't know what the class is today.

A cartridge fuse for a 240 volt circuit is rated for 300 volts. A similar fuse for 480 (600 volts) is about twice as long and usually twice the diameter. Most any breaker for that class will be rated for 600 volts. I have seen such breakers on eBay, they come and go for availability. The important issue is that when you find one, it *must be 600 volt class*. 300 volt insulation will not hold up and is a shock hazard.

All 480 wiring needs to be enclosed in metal boxes. And *never* run 480 in the same enclosure as 240. There are exceptions, but they are the field of serious electricians, not for amateurs.

I should have scared you enough with this overview that you will find someone qualified to  do this sort of work. *Find him. . . *

.


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## JimDawson (Sep 27, 2021)

Maybe these?



			https://www.automationdirect.com/adc/shopping/catalog/circuit_protection_-z-_fuses_-z-_disconnects/ul_489_miniature_circuit_breakers/eaton_480y-z-277vac_miniature_circuit_breakers_(faz-na_series)/3-pole_(0.5a-32a)#Amperage_Rating_ms=%2225A%22&start=0


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## Aukai (Sep 27, 2021)

I'm sure if your playing with this voltage you know how dangerous it is, if it's like 440v you don't have to touch it, it will jump to you. I just had to say it out loud.


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## General Zod (Sep 27, 2021)

rabler said:


> Is this just for the Stel S300 you recently posted about?  Or are you using the 400V transformer for something else too?
> A question to run by the more code/wiring safety knowledgeable folks - wouldn't an appropriate sized breaker on the input to the transformer work fine?  I.e., put a 400/230 * 25A breaker= 43.5, so roughly 40 amps, on the low side of the transformer?  I would *guess* that would actually be safer as it covers shorts in the transformer.



Yes, it's for the Stel S300.  I do have breaker on the low-side of the transformer, coming from the phase converter, but I still want a breaker between the transformer and the welder.




Bi11Hudson said:


> Rule Nr1: Hire an electrician that knows heavy industrial electrical systems. Avoid a residential "wireman", find someont that knows what the hell he's doing. There isn't space here, or the time, to bring you up to speed on all of what you need to know.
> 
> With that caveat out of the way, I must assume (ass out of me) that you have a rotary converter and need to wire the downside. The first comment is that a circuit breaker will protect the wiring, transformers, switches, and such like. It *will not protect the machine itself*. That's what the overloads on the starter and the local control fuse are for.
> 
> ...


 

Nope, you haven't scare anyone.   At least not me.....





Aukai said:


> I'm sure if your playing with this voltage you know how dangerous it is, if it's like 440v you don't have to touch it, it will jump to you. I just had to say it out loud.



I'm quite aware.



Al 1 said:


> It sounds like you should contact a licensed electrician.  Al.



No, thanks.

mksj, JimDawson,  thanks for the links.


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## markba633csi (Sep 28, 2021)

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


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## General Zod (Sep 28, 2021)

markba633csi said:


> 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.
> ...



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.


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## mksj (Sep 28, 2021)

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.




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						StackPath
					





					www.ecmweb.com


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## General Zod (Sep 28, 2021)

mksj said:


> 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.
> 
> 
> 
> ...



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


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## mksj (Sep 28, 2021)

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."


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## General Zod (Sep 28, 2021)

mksj said:


> 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.


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## mksj (Sep 28, 2021)

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


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## General Zod (Sep 28, 2021)

mksj said:


> 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.
> 
> 
> 
> ...



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?


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## Weldingrod1 (Sep 28, 2021)

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


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## MikeInOr (Sep 29, 2021)

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


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## sdelivery (Sep 29, 2021)

mksj said:


> 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.
> 
> 
> 
> ...


This is FACT.


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## General Zod (Sep 29, 2021)

sdelivery said:


> This is FACT.


Yes, and as I mentioned it is not an _issue _what so ever_ for me_, therefore in _my _particular system, it is insignificant by my perspective.


I'm pretty sure I will go with the DIN rail circuit breakers that mksj linked from the Direct Automation website.   I see they have the 480V models which should pose no problem with a lower-voltage system, and the mounting scheme makes it quite easy to integrate into my setup with out too much hassle; just a little fab work here and there.


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## General Zod (Nov 11, 2021)

Thanks to everyone for their unwavering support!   Took me this long since I been working long hours and only have like 20-30min free on the weekdays after I get home, and weekends are for traveling around Texas 

Receptacles from Left to Right:

240A (just pass through, same 3-Φ coming from the rotary phase converter, not up/down converted)
up-converted 400V with a 25A B-curve breaker (right above, breaker on the left).  They were out of stock on C-curve breakers, so I'm thinking it will be fine.
up-converted 480V on a 20A B-curve breaker (right above, breaker on the right).












I still need to protect the wiring that comes out from the transformer, but for now it's no big deal as I don't work anywhere near there.


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## sdelivery (Nov 11, 2021)

mksj said:


> 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.
> 
> 
> 
> ...


This is fact. Motors experience similar high inrush also. 
There are reasons for the national electric code and the calculations in it.


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## tq60 (Nov 11, 2021)

A suggestion...

All outlets look alike, not good.

Twist lock devices have different size and shape of ground prong to allow "matched" plugs.

The your outlets have the prongs close to the sides, may be a hazard if you plug in live.



Sent from my SM-G781V using Tapatalk


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## General Zod (Nov 12, 2021)

tq60 said:


> A suggestion...
> 
> All outlets look alike, not good.
> 
> ...



Thanks for your suggestions.   No need to worry on any of those accounts; they don't present any issues/problems.


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