# 208v to 120/240v using buck boost



## Jhellwig (Jun 18, 2014)

Use two buck boosts. Or a 208 primary 120/208 secondary.

What is it that makes it unable to be used on 208? Lots of stuff is rated for 240 but can be used on 208 systems.


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## tates1882 (Sep 3, 2010)

Why bother with a boost xformer at all? If the equipment has a ul stamp it will operate within a 10% tolerance of nameplate voltage. So it should be able to handle 208 maybe not the most efficient. Also you could do a single phase xformer, straight 208 on primary side and 120/240 on secondary side 


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## Vert15 (Apr 29, 2015)

tates1882 said:


> Why bother with a boost xformer at all? If the equipment has a ul stamp it will operate within a 10% tolerance of nameplate voltage. So it should be able to handle 208 maybe not the most efficient. Also you could do a single phase xformer, straight 208 on primary side and 120/240 on secondary side
> 
> 
> Sent from my iPhone using Tapatalk



At 208v, the 240v equipment will operate at about 86% of its rating. This is nearly 13% under, hence the need for a 13.3% boost xformer. Also, im trying to help the client establish a price effective installation. Taking into account the price difference of a 1kva auto xformer to a 7.5kva iso xformer. 

It still remains unclear as to how i would do this without spending too much on equipment.


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## micromind (Aug 11, 2007)

It's not possible to boost 120/208 to 120/240 using buck-boost transformers. 

The only way to get genuine 120/240 from a 120/208 system is by using a transformer that has either a 120 or a 208 primary and a 120/240 secondary.


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## tates1882 (Sep 3, 2010)

Vert15 said:


> A client has requested an L1430R receptacle. This receptacle is a 4 prong, 120/240v outlet. This outlet will be used for a piece of equipment with a nameplate requirement of 30amps @ 120/240v. His electrical service consists of 120/208v. So i decided to use a 13.3% buck boost transformer rated at 1kva with voltages of 120/240v primary & 16/32v secondary. However, this only takes care of the 240v secondary of the transformation; this does not take care of the 120v(line to neutral). Should a general purpose transformer, rated at 7.5kva 240vprimary to 120/240v secondary, be used to establish a neutral point. This installation will require two transformers; a buck boost and a general purpose xformer. Or am i missing something? Is there an easier way of doing this?


 thinking about this the machine uses one leg of the 240v for the 120 side, the cord cap and recp won't work for what you want to do. also you would be making a circle, boost then transform for your neutral. the second transformer would have to after the cord cap on the machine its self. like micro said below 



micromind said:


> It's not possible to boost 120/208 to 120/240 using buck-boost transformers.
> 
> The only way to get genuine 120/240 from a 120/208 system is by using a transformer that has either a 120 or a 208 primary and a 120/240 secondary.


 thanks was trying to figure out how to make this work with the ops design and couldn't wrap my mind around it.


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## Vert15 (Apr 29, 2015)

I figured this was the only way. 7.5kva 208 pri to 120/240v sec xformer will have to do. Thanks for the help.


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## Southeast Power (Jan 18, 2009)

Vert15 said:


> A client has requested an L1430R receptacle. This receptacle is a 4 prong, 120/240v outlet. This outlet will be used for a piece of equipment with a nameplate requirement of 30amps @ 120/240v. His electrical service consists of 120/208v. So i decided to use a 13.3% buck boost transformer rated at 1kva with voltages of 120/240v primary & 16/32v secondary. However, this only takes care of the 240v secondary of the transformation; this does not take care of the 120v(line to neutral). Should a general purpose transformer, rated at 7.5kva 240vprimary to 120/240v secondary, be used to establish a neutral point. This installation will require two transformers; a buck boost and a general purpose xformer. Or am i missing something? Is there an easier way of doing this?


I don't see a practical way to use a couple of auto transformers here.
You need to find a properly sized transformer that is going to give you a nice three 3 phase delta. It can be an open delta if you want to try to save some money but, I can't see using auto transformers for this application.


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## Southeast Power (Jan 18, 2009)

Vert15 said:


> I figured this was the only way. 7.5kva 208 pri to 120/240v sec xformer will have to do. Thanks for the help.


Just make sure you completely know how they are using the 120volts in that machine. You are for sure going to have a high leg.


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## hardworkingstiff (Jan 22, 2007)

jrannis said:


> You are for sure going to have a high leg.


I think he is talking about a single-phase transformer, 208 x 120/240. I don't think a high leg will be involved.


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