# 240v 1Ø from 480v 3Ø Service



## Pmartens07 (May 14, 2018)

Hello all, I have only worked on 240v 3Ø Systems before and now have been presented with a project requiring not only 120v lighting and convenience circuits but also 2 240v 1Ø circuits for welder receptacles that will be used for the initial construction and later for occasional repairs and maintenance. 

What’s the best way to obtain the power required for these circuits and maintain balance? I had thought of putting in a 480-240 stepdown transformer feeding a small (100a main) 240v 3 phase panel and doing my best to balance the loads out of that but wanted to check with people who have done this before. The 120v circuits are not really a problem but the 50a 240v 1Ø loads are what has me a bit unsure. 

Thanks in advance.


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## Pmartens07 (May 14, 2018)

I should have specified, this project is a 480v 3Ø service requiring both 120v and occasional 240v single phase loads


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## 460 Delta (May 9, 2018)

Does it have to be true 240 volt, or will 208 suffice? If 208 is fine, then a 208/120 star, 3 phase transformer would be my suggestion. About 30 kva should do it. 
Depending on how you tap it , the voltage can be up around 215 or so, pretty common around here.


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## just the cowboy (Sep 4, 2013)

Do you need 240v or will 208 be OK?

You can do what you said using a high leg delta xformer for the 240 volt.

But if the welders are able to work on 208 I would put in a 208/120v wye system.

Yes I would go 3 phase.


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## telsa (May 22, 2015)

All modern welders use ELECTRONICS to produce the desired application voltages. 

For them 208VAC is the same as 240VAC. They don't even care if it's 60Hz or 50Hz.

208VAC is so common that no manufacturer of welders can dare produce a machine that can't tolerate it. ( Actually, because of electronics, dirty power is no problem for them. )

The universal design is to rectify the AC and then to generate the desired current with power electronics.

I've even seen welders that can take 480VAC and manipulate it. ( high end machines ) 

Though I'd not expect you to see them on a construction site.

So... you want a 480 to 208Y120 scheme. I've worked with such devices set on rollers and skids.


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## 460 Delta (May 9, 2018)

telsa said:


> All modern welders use ELECTRONICS to produce the desired application voltages.
> 
> For them 208VAC is the same as 240VAC. They don't even care if it's 60Hz or 50Hz.
> 
> ...


 Umm not all modern welders use inverter technology, plenty still use tried and true transformers that will have low OCV if they don't have a 208 tap available. Now it's not the end of the world if it's a 230 machine on 208, Iv'e welded plenty with machines like that, it just makes it a little harder to hold an arc, you have to run your arc a litte tighter.
Ole 460 is more than a conduit puller and a wire bender, he may have run a few beads of weld too.:wink:


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## paulengr (Oct 8, 2017)

The other scheme is splitting the 480 which gives you true 240/120 instead of 208/120. Use single phase 480/tapped 240/120 transformers, 3 of them.

Sent from my SM-T350 using Tapatalk


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## Cow (Jan 16, 2008)

Pmartens07 said:


> I should have specified, this project is a 480v 3Ø service requiring both 120v and occasional 240v single phase loads


It sounds like a single phase transformer would suffice since there is no mention of any 3 phase loads. I'd probably install a 25kva if there was no interest in future expansion. You could probably get away with a 15kva, but I don't know what your loads are beyond "welder receps and few lights."


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## Pmartens07 (May 14, 2018)

This facility will have around 70kW of 3 phase motor loads once operational. The single phase loads will be strictly lighting, convenience, and these 2 welder receptacles. I would not expect the 240 single phase loads to ever be active while the much larger three phase loads are drawing

Thanks for the advice!


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## tmessner (Apr 1, 2013)

I would use a 50 kva 480 x 120/240 single phase transformer and a 200 amp single phase loadcenter. We have done a lot of this on large sites with minimal single phase loads. Loadcenters are cheaper than 3 phase. all of the lighting is 277v so the only load on the loadcenter is the welder and whatever 120 outlets loads you would have.


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## 460 Delta (May 9, 2018)

One thing to keep in mind is many industrial size welding machines are 230-460 volt, it may pay to inquire about the machines the intend to use.


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