Seperate voltage panel

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jamesguy10

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Location
Amsterdam NY
Got a restaurant with a 400 amp single phase service. Cant upgrade to 3 phase. They just purchased a bunch of (well not that much) 208v single phase(2 wire+ground) equiptment. I was originally going to use a buck/boost at each piece of equiptment, but i thought it might make sense to put in a 8 space single phase subpanel, but step the voltage down to 208 for it. WHat kind/size of transformer would you use for this? Ill figure out the load draw and post it when i do.
 

iwire

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Location
Massachusetts
If you don't need a neutral you could use a relatively small, single properly sized buck transformer to supply the separate panel.

What is the total KW of 208 load?
 

iwire

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Location
Massachusetts
jamesguy10 said:
Why cant i have a neutral?,

'Cause I am not sure you deserve one. :grin:



You can have a neutral, it just adds to the cost.

If you can live without a neutral all you will need is one very small buck transformer.

If you want a neutral you would need two bucks or forget the autotransformer and go with a standard transformer.


the draw will be about 10kva

That is really not that high, but if I recall transformers like to live around 70 to 80% loading and considering this is a restaurant I think it is prudent to think of these as continuous loads.

IMO the least expensive route is a new sub panel without a neutral supplied via one buck transformer. But there are many ways to get the job done. :)
 

iwire

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Location
Massachusetts
jamesguy10 said:
i found a 25kva transformer on ebay, except the primary is 208 and the secondary is 240, can i still use it to make 240 into 208?

Maybe, but considering it would be 'backward' you may not be able to get a neutral out of it.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
jamesguy10 said:
Nope, cant change them (well one i can but they want it on 208 becuase it draws 800 less watts)

I always get a kick out of customers that think in terms of watts.Its there money so spend it for them.Had they done the homework first they mighta saved dollars
 

micromind

Senior Member
If the load is 10KW at 208V, that's around 48 amps.

I know there are all sorts of fancy formulas for figuring the exact xfmr size, use them if you want. In reality, the low volt side of a buck/boost xfmr will see the current of the load, or very close to it.

Since you're going from 240 to 208, you'll need an xfmr with a 32V secondary, and a 240V primary. It'll likely be 120/240, or 240/480. It doesn't matter which. The secondary will likely be 16/32V. Connect it for 240 in and 32 out. To connect it as a buck, you can look on a xfmrs website.

1.5KVA at 32V is about 46 amps. Too small. 2KVA is about 62 amps. Good if nothing else is to be added later. I would intentionally fill up the new 208 panel, or someone will certainly add load to it, possibly overloading the xfmr. Code sized overcurrent protection will NOT keep a xfmr from burning up. I would also completely remove the neutral bus, as one leg will be 120V and the other 88V.

I really don't like buck/boosting an entire panel, but in this case it might be the best way to go.

Rob.
 

iwire

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Location
Massachusetts
Jim W in Tampa said:
I always get a kick out of customers that think in terms of watts.

Jim, watts are what matters, these are heating appliances, watts have a direct impact.

If you drive a heating appliance designed only for 208 at 240 it will very likely overheat and shut down or maybe even be a fire hazard.
 

jim dungar

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Location
Wisconsin
Occupation
PE (Retired) - Power Systems
jamesguy10 said:
Why cant i have a neutral?, the draw will be about 10kva

There is no buck-boost transformer arrangement that will provide a proper neutral. Bucking down to 208V means your line-neutral voltage will only be 104V.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
iwire said:
Jim, watts are what matters, these are heating appliances, watts have a direct impact.

If you drive a heating appliance designed only for 208 at 240 it will very likely overheat and shut down or maybe even be a fire hazard.

Not suggesting 240 unless its rated but many things run fine at 208.Only do this when plate says 208/240.At 208 it is just bit underpower and likely fine.Dont read into this that i am saying a rated 208 appliance can take 240 they cant.
 

iwire

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Location
Massachusetts
Jim W in Tampa said:
Not suggesting 240 unless its rated but many things run fine at 208.

Well Jim that is not exactly news. :grin:

But Jame's has stated the equipment he is wiring is 208 only.
 

iwire

Moderator
Staff member
Location
Massachusetts
220/221 said:
I think I have only seen ONE piece of kitchen equipment that said 208 only.

Maybe you don't get around much? :grin:

We recently installed over 100 sandwich ovens for a sandwich shop chain that all where labeled 208 only, I saved a tag, maybe I will post it. :)
 

jamesguy10

Senior Member
Location
Amsterdam NY
iwire said:
Maybe you don't get around much? :grin:

We recently installed over 100 sandwich ovens for a sandwich shop chain that all where labeled 208 only, I saved a tag, maybe I will post it. :)

Thats one of the things im installing, btw i got a couple transformers and the jobs done.... works great
 
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