# 120/208 1-ph load in 120/240 environment



## mikewillnot (Apr 2, 2013)

This unit (commercial steam table, (@5kva) requires 120/208 power SINGLE PHASE (from a 3-phase source, i.e. uses two hot legs and a neutral from a three phase system) and we are installing it in a building with 120/240 1-ph.* I am intending to supply power via a buck-boost transformer in such a way as to provide 120/208, but one leg of the incoming power to the unit will have (A) 120 volts, and the other will have (B) 88 volts (total 208). *

I have the same problem as this post from two years ago, only bigger. 

http://www.electriciantalk.com/f2/208v-vs-240v-heater-elements-35009/#/forumsite/21022/topics/35009

the alternative would be to supply the machine with 120 / 240, and risk frying the heating elements.

with the buck boost, It seems important that any of the table?s internal 120 volt loads be connected to the A (120-volt) leg, not the B (88-volt) leg, and there is an expensive looking digital control panel on the front.

I would prefer not to rewire the table, or even get inside and monkey around. 

Thoughts / suggestions welcome. 
THX


----------



## daks (Jan 16, 2013)

Tone each hot going into the table and see which one goes to the controls... ?

Resistance to N MAY give a clue...

Power up with a 120V source on "one side" of the table connection points and see which "side" powers on the controls...

Call the manufacturer, maybe it will run on 240 also...


----------



## mikewillnot (Apr 2, 2013)

The second idea, powering up one side, is great. THX. 

The manufacturer, Vollrath, of Sheboygan, WI, has been quite unhelpful, and so far unable to provide a wiring diagram for this unit, one of a series that are all custom built. Grrrrrr. 

Years ago I worked for a couple of years in a company that manufactured custom control equipment and cabinetry for industrial machinery. EVERYTHING was custom made, and EVERYTHING had drawings, and EVERYTHING was built as drawn, or the drawings were revised. Of course, the drawings were all on really large sheets of paper back then. Harder to email.


----------



## telsa (May 22, 2015)

*Typical ignorant screwed up specification*



mikewillnot said:


> This unit (commercial steam table, (@5kva) requires 120/208 power SINGLE PHASE (from a 3-phase source, i.e. uses two hot legs and a neutral from a three phase system) and we are installing it in a building with 120/240 1-ph.* I am intending to supply power via a buck-boost transformer in such a way as to provide 120/208, but one leg of the incoming power to the unit will have (A) 120 volts, and the other will have (B) 88 volts (total 208). *
> 
> I have the same problem as this post from two years ago, only bigger.
> 
> ...



Such a unit is sure to be constructed of compounded -- as in a series -- resistors...

Each of which is set to 120 VAC to the neutral.

The VAST bulk of their customer base is wired 208Y120 so they've put this spec out to STOP guys messing around with buck/boost transformers -- which are sure to over voltage one of the legs -- (140VAC ish)

The unit under discussion will accept center tapped 240/120 single phase PERFECTLY.

The "unhelpful" tech at the factory has absolutely no idea what the heck you're talking about - - phase angles -- three phase -- it's all mumbo-jumbo to him... which shows as defensive "unhelp."

&&&&&&&

There are virtually no systems -- resistive or motor -- that can't tolerate the both 208Y120 and 240Y120 -- single phase -- without further ado.

There are countless 'techs' who don't know any of this -- and are put on the spot the moment the discussion drifts over to power circuits.

You will never find a digital logic power supply -- in this digital age - - that is NOT constructed as a switching power supply -- meaning that it can AUTOMATICALLY adjust to the delivered voltage -- dynamically -- moment by moment. It's the LEAST sensitive element to voltage in the entire assembly.

These switching power supplies are cheaper than Chicklets -- and are embedded in every PC you've seen in the last forty-years -- and are now everywhere.

They, like VFDs, ALWAYS convert the juice to DC in a rank of capacitors. This is then ported into a new voltage and new frequency by solid state switches (transistors/ power transistors/ Insulated Gate Bipolar Transistors/ IGBTs with stunning efficiencies. With digital tricks it's possible to either create a new DC voltage (seen in PCs) or a new AC waveform at a new frequency. (seen in VFDs)

Wise up: NEVER worry about the power quality fed to modern digital systems. They can eat mud and spit out chocolate!

As for the resistors... just how can you ruin them? You're raising steam!


----------



## MDShunk (Jan 7, 2007)

Steam table? Wire that bitc& for 240. There's millions of them out there in the field in little shops and whatnot wired that way, when originally rated for 208. You've given them the benefit of quicker hot food.


----------



## oliquir (Jan 13, 2011)

should be ok if there is some thermostat, elements will cycle on and off so they wont overheat


----------



## Hawkrod (Mar 19, 2012)

I just rebuilt a Vollrath last week. They have an overheat sensor next to the heating element, it would be tough to burn one out with voltage. That being said, the one I rebuilt had been very wet and they use a nasty insulation that acts like a sponge and the temp sensors had been bypassed! Burned all of the elements out and killed one thermostat!


----------



## telsa (May 22, 2015)

....


----------



## telsa (May 22, 2015)

If this underslab work was done before your arrival... 

Then imagine this: A strut rail system anchored with concrete forming stakes (the round steel ones) attached with stirrup style strut straps -- with two (2) rails in each row of stubs -- tops and bottoms -- so as to keep all of the GRC/ RMC straight up and down -- perfectly -- before the mud covered all. In the second rank, additional strut rails, twinned, so as to keep them in perfect alignment -- and a SET spacing between all of the stubs -- just 'so.' 

This scheme is DRASTICALLY faster than screwing around with EMT and tie-wire -- the typical improv hidden underneath slabs all across America.

Now that the mudding is done, your foreman is figuring to drop a slew of THREADLESS bonding bushings with lay-in-lugs -- just 'so' -- all across the entire array. 

Notions of a transition to vertical branch piping, never!

Any such attempt would have the boys on their knees for days on end -- trying to get the raceways to look even half-way professional. When, in fact, the branch conductors are racing all over the facility -- crossed over -- and over -- and over. 

Why? 

Emergency panel -- Isolated ground panels -- lighting panels -- etc. 

So each branch underslab run is stuffed with conductors from 'alien' panels. You're in for a real treat when these are pulled in and landed. You'll just love the extra bonding conductors, hence the 1" pipe minimum.

&&&&&

Like casinos and other LARGE structures that support vast numbers of 'strangers' the wiring to any particular spot in the building can NEVER be loaded entirely through one panel. Darkness at any time, under any condition is PROHIBITED. So you'll have multiple back-ups -- to include multiple generator-sets -- and multiple fuels for same -- ... 

You might even see multiple taps to the Poco primary distribution loops... or that the hospital is on a SPECIAL (double secret probation style) Secret Primary Loop -- that is triply backed up by the Poco. { For the noobs out there: every decent sized American city has a core primary loop that the Poco will hold as its 'last bastion' of reliability. (Typically, the Poco, itself, is on this loop) This primary loop will NEVER participate in 'brown outs' -- rotating black outs -- or any other nonsense. 

The Services permitted to tap into this primary distribution loop are strictly by permission or accident. (as in accident of history... being at the magic place at the right time) 

This structure is mimicked in EVERY nation on Earth. 

Saddam's electric grid was a pity, rolling blackouts were constant. He never let them touch his government, though. Is it any wonder that no-one wants to build away from the capital in Third World nations? 

&&&&&

The NEC is oriented towards FIRE HAZARDS caused by electric power distribution and utilization. With concrete slab and steel containment all around, you'll never hear a AHJ 'kick' about a beauty gutter down on the slab. They never 'let the smoke out.'


----------



## telsa (May 22, 2015)

*Raising steam is an ISOTHERMAL process*

_"I just rebuilt a Vollrath last week. They have an overheat sensor next to the heating element, it would be tough to burn one out with voltage. That being said, the one I rebuilt had been very wet and they use a nasty insulation that acts like a sponge and the temp sensors had been bypassed! Burned all of the elements out and killed one thermostat!"_

A steam table -- the use of current to raise steam -- common as dust in kitchens -- functions ISOTHERMALLY. Put a thermometer in a pot of boiling water -- in the middle of the water -- not the metal sides -- and you'll discover that the temperature doesn't move AT ALL while it boils. 

It's a law of chemistry and physics that boiling and freezing are ISOTHERMAL events -- as long as the material involved is a PURE SUBSTANCE. With the crappy water out there, that may not be so true in the real world. 

What destroys steam tables -- EVERY TIME -- is minerallized water. Conventional water softening is NO HELP. It doesn't address chlorine, just swaps evils.

The plain vanilla Culligan scheme uses table salt -- pelletized -- to refresh an 'exchange ion resin bead column' (PhD Chemistry speak) The 'HARD' ions: Mg, Ca, are captured by the resin beads and 'SOFT' ions: Na are released. 

{ Wiki your hearts out on the process } 

Whereas the steam table is crudded all to H with ANY of the above ions. They are all 'stay behinds' that can't boil into steam. 

So, it's high time that EVERY steam table be fed from a RO (Reverse Osmosis) water supply. These are now punched out like Chicklets in retail sizes appropriate for steam tables. They do produce volumes of cast-off water flow (to carry away the ions -- still in solution) -- which the kitchen can surely use as potable water/ janitorial water. 

At the point of failure, the ions have crudded up the water intake port/ valving to the point that the steam table is STARVED of water. ONLY then can the temperature begin to rise -- and REALLY do some damage. Then, by the time a tech is called, the entire table needs a re-build. 

If the typical steam table were torn down -- and 'flossed' -- it'd never develop cavities.

(salt build-ups and corrosion -- which really takes off at steam temperatures, BTW.) 

But, that's not our trade. Suffice it to say: don't waste your ears on steam table travails, and wails. Just juice 'em and move on... for the whiner is overwhelmed by the physics of boiling water. 

BTW, ANY temperature switch in a steam table can only function during a temperature excursion: either it's sensing that the temperature is too low (most likely) or is a cut-out (Klixon style) for excessive temperatures. 

( If you've looked, no-one building these puppies ever seems to install Klixon style cut-outs / alarms. I'd say they're aiming at the replacement market!) :laughing:


----------



## A Little Short (Nov 11, 2010)

telsa said:


> If this underslab work was done before your arrival...
> 
> Then imagine this: A strut rail system anchored with concrete forming stakes (the round steel ones) attached with stirrup style strut straps -- with two (2) rails in each row of stubs -- tops and bottoms -- so as to keep all of the GRC/ RMC straight up and down -- perfectly -- before the mud covered all. In the second rank, additional strut rails, twinned, so as to keep them in perfect alignment -- and a SET spacing between all of the stubs -- just 'so.'
> 
> ...



Whatttttttt?????

What does this have to do with a steam table running on 240V vs 208?:blink:


----------



## telsa (May 22, 2015)

Dang Java & Cross posting


----------



## JRaef (Mar 23, 2009)

I agree, you are over thinking this. If the heater elements were configured as line-to-neutral, they are 120V anyway, so not a problem. If by chance they were configured line to line, the ratings will change, but it's still not a problem. A heater element is just a resistor. The resistance doesn't change, so if you increase the voltage you increase the wattage dissipation of it. The formula is P = E^2/R.

So you may not know the resistance of the heaters, but you probably know the wattage. Let's say for example it is 1000W, 208V. To find the resistance, it is E^2/P, so 208 squared is 43264, divided by 1000 = 43.264 ohms. Now if you increase the voltage to 240V, the new wattage is 240V squared, = 57600, divided by 43.264 = 1331W. So your heater elements went from being 1000W to being 1331W each. _(Side note: MOST heater elements will be sized based on 240V in the first place, so it's more likely that they would use a 1000W 240V element, which at 208V would have been REDUCED to about 750W)._

What does that meant on a steam table? It just means that _*the water will heat up faster*_ with 240V applied to it, so the thermostat will be turning on and off less often. Not a problem.


----------



## Electric_Light (Apr 6, 2010)

JRaef said:


> What does that meant on a steam table? It just means that _*the water will heat up faster*_ with 240V applied to it, so the thermostat will be turning on and off less often. Not a problem.


If it's wired line to line 208v 24A for use on a 30A circuit, it will draw 27.7A on 240v, so it wouldn't be allowed on a 30A branch anymore.


----------



## A Little Short (Nov 11, 2010)

Electric_Light said:


> If it's wired line to line 208v 24A for use on a 30A circuit, it will draw 27.7A on 240v, so it wouldn't be allowed on a 30A branch anymore.


What are you talking about?

If 24A @ 208V on a 30A circuit is ok why wouldn't 27.7A @240V be ok on a 30A circuit?


----------



## Tsmil (Jul 17, 2011)

A Little Short said:


> What are you talking about? If 24A @ 208V on a 30A circuit is ok why wouldn't 27.7A @240V be ok on a 30A circuit?


Maybe because 27.7 is more than 80% of 30.


----------



## A Little Short (Nov 11, 2010)

Tsmil said:


> Maybe because 27.7 is more than 80% of 30.


That rule is only for circuits that supply two or more receptacles or outlets. I highly doubt the steam table is on a circuit with other loads.


----------



## mikewillnot (Apr 2, 2013)

OP, outcome:
I'm conservative on the matter of running anything on a higher voltage than it's nameplated for. I don't want to wind up replacing an $8k piece of equipment, or even shelling out part of that for a service call to replace a burned out anything. It's not built-in to my quote.

Factory techs were useless, but the 3rd party field service techs were very helpful. The lower section of this table, with the controls and the main heating elements, did not require a neutral at all (120/208), only 208v power. The upper section of the table had 208v elements and a sub-circuit for 120v light bulbs; that was it. 

I put in a buck-boost connected for 120/240 in, 208 out, wired the neutral straight through for 120/208 (120+88) output, connected it so that the upper section light sockets got the 120v leg. Good to go.


----------



## ponyboy (Nov 18, 2012)

What a waste of time and material. 


Sent from my iPhone using Tapatalk


----------



## mikewillnot (Apr 2, 2013)

ponyboy said:


> What a waste of time and material.


Agreed. Next time I run into something like this, I'll just have them call you.


----------



## telsa (May 22, 2015)

Your nic...

Heh.:laughing::no::laughing::no::laughing::no:


----------



## Southeast Power (Jan 18, 2009)

Wait a minute.
I want to get back to this auto transformer.
Tell me more about this 120 + 88 = 208.

I want to learn something today.


----------

