iDRY Vacuum Kilns

Sponsors:

voltage/electricity

Started by bedway, November 12, 2007, 08:58:00 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

bedway

I hope we got some sparkys here who could give an opinion on this. My son in law just bought a used pizza oven for his  pizza/ice cream shop. We got it in and wired. Fired it up and cooked two pizzas in it. It seems to be working fine. We noticed the tag on the oven calls for 3 phase 208 volts. His shop has 3 phase 240 volts. Will the difference in voltage hurt the oven?,,,,thanks,,bedway

DanG

Should be ok.  There is quite a large tolerance range on those voltages.  I bet if you measured it, you wouldn't find 240 volts there unless you measured "peak to peak" voltage.  The 208 figure is the RMS, or average voltage.  Basically, it's all the same stuff. ;)
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

TexasTimbers

I think you will see premature motor and element failure. Are you sure there isn't a wiring option for 240v? On a pizza oven I would think it would have a multi-tap transformer that allows for 240v. it is common for industrial equipment to have this.

In general, motors are rated for no more than 10% less voltage than stated on the nameplate. i forget about too much voltage but think it is also 10% - stand to be corrected.

If you are getting power from a delta wound transformer which I believe you are since you are seeing 240v you better make sure the wild leg is not feeding any of the loads or they will open quickly.

it's been a long time since I have worked in this field but my memory says you should not connect a 208v load to 240v service.
The oil is all in Texas, but the dipsticks are in D.C.

beenthere

Are we talkin heating elements only here, or did I miss something that includes a motor??
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

TexasTimbers

bt, I am just assuming a pizza oven has a blower motor and if it has a conveyor it has another motor as well. I am also assuming the element itself is a single phase 240v tapped off the 3 phase so a wild leg would knock it out sooner than later if it is rated for 208v.
The oil is all in Texas, but the dipsticks are in D.C.

logwalker

I would be calling the manufacturer. You might need a stepdown transformer. Joe
Let's all be careful out there tomorrow. Lt40hd, 22' Kenworth Flatbed rollback dump, MM45B Mitsubishi trackhoe, Clark5000lb Forklift, Kubota L2850 tractor

bedway

There is at least a conveyor motor and a fan motor. Thats all the particulars i know at this time, sorry,,,,,,,,,bedway

Slabs

The "Wild" (sometimes called " power") leg is only above ground  never used in single phase connections (Delta wired power).  Between any of the other phases there will be 240.  The fan and conveyer motors are probably small and may well be single phase.  The Wild leg will probably be the one on the far right at the main entrance and read about 175 volts above ground.  If your power is "Y" there's no wild leg.
Slabs  : Offloader, slab and sawdust Mexican, mill mechanic and electrician, general flunky.  Woodshop, metal woorking shop and electronics shop.

TexasTimbers

Slabs refresh my old beanbox here, I am not trying to say something with a question I am truly asking because it has been a long time since i studied for and took my SBCCI exam. Max voltage on a 120/208 wye from any line to ground is 120v and across any two legs is 208. He is saying he has 240v 3 phase. It could be a center tapped delta 120/240 so no wild leg and control voltage (or single phase low) from any leg is available. It could also be a pure Delta so a wild leg to ground is there. Those single phase motors getting their power from the 3phase supply in that case are going to be looking to let out some smoke if he unknowingly hooks 'em up to wild leg eh? ???

Like I say it has been a long time but I know I am in the ballpark here although certainly no expert. Where is my memory medicine!

I just re-read your post and where you say "above" ground the only term I have ever heard used is "to" ground but I assume you are saying the same thing.
The oil is all in Texas, but the dipsticks are in D.C.

Slabs

Waaal now there Tex, It's also been a long time since I did any three-phase power work.  I agree "to" ground is probably more correct than "above" ground and most of my experience has been with DC and I'm not even sure of the most universal terminology there.  We seem to go with early esposures even though in error.  I am assuming "wild leg" to be a delta thang.  I had a humiliating experience in learning about the wild leg when I was quite young and tried to "balance" the load among three phases by connecting some single phase appliances to that one.  A few blown bulbs was the only damage.

It is also my understanding that all phases in Y are 120 "to" ground.  My exposure to that fact is on military bases where Y is common for lighting.  Yeah, Y or delta balanced or center-tapped wasn't specified.  I couldn't walk up th the box even with a meter and tell what was there.  Moreover I'm not a certified electrician.  My license is in communications.  It's good to know that we have someone like you to back us up in instances like this.
Slabs  : Offloader, slab and sawdust Mexican, mill mechanic and electrician, general flunky.  Woodshop, metal woorking shop and electronics shop.

TexasTimbers

The Lord have mercy on us if I am the guiding light on electrical on this board!

I was hoping, for once in my life, an actual Electrical Engineer would chime in. Man we blue collar types can't stand those engineers until we need them! :D
The oil is all in Texas, but the dipsticks are in D.C.

Woodwalker

I ain't no double E, but I can tell you 120/208V WYE ain't 120/240V DELTA. 
There is more than one three-phase secondary voltages used as industry standards in this Country.
120/208V WYE is a four wire service that will read 120V from any one of three phases to neutral. It will read 208V across any two phases.
You will also see a 277/480V WYE four wire service that will read 277V from any one of three phases to neutral. It will read 480V across any two phases.
There is 120/240V Delta four wire service that reads 120V from either one of two lighting legs to neutral, 240V across the two lighting legs (the same as residential voltage) and from the ("wild leg" "high leg" "power leg") third leg to neutral you will read something like 208V. Think the square root of three times 120V (or what ever the base voltage is, it could read from 116V to 124V)  This is not 208V WYE, which is measured across two phases.
There is 240/480V Delta four wire. There is 480V Delta three wire, corner grounded.  These are usually used in large industrial applications with a Delta connected secondary.
Don't worry if the voltages vary 5% one way or the other. The equipment operating ranges will account for this. A Power company cannot supply a completely steady state voltage.   
There are other secondary voltages out there, even other number of phases (read about a six -phase system in a mine somewhere). It all depends upon the application and what can be supplied.
Just cause your head's pointed, don't mean you are sharp.

TexasTimbers

Quote from: Woodwalker on November 12, 2007, 10:30:21 PM
I ain't no double E, but I can tell you 120/208V WYE ain't 120/240V DELTA. 

Who said it was?! 
The oil is all in Texas, but the dipsticks are in D.C.

trim4u2nv

Best to consult the manufacturer.   If you are out of specs, you can usually use a buck/boost or line transformer to keep voltages within tolerance.  This is pretty common when using european equipment (230-240) on american lines which can be 208 or 240 or 480.

Gary_C

bedway

I'd go with DanG's answer. Should be OK.    ;D

I read all the others and now I am confused too.    ::)

Actually most heating elements are made for 240 volts anyway. At higher voltages it will heat up faster. The thermostat keeps it from letting out smoke.

As far as the motors, they will use less current at higher voltages so they should be OK too.

Yep, should be OK.   8)
Never take life seriously. Nobody gets out alive anyway.


TexasTimbers

I am not arguing this Gary but simply seeking counsel from those wiser than I.  :)

IMHO the thermostat could theoretically prevent a heating element from opening if it has a slightly higher amperage going through it than it is rated for but thermostats are not designed as current limiters and don't really offer any protection for that if the sees too much voltage over the longrun. Damage to the element is cumulative and premature failure will result if it continues to see more voltage than it is designed for.  But as you say maybe it is also rated for 240v so it would be a moot point.

Now as far as the motors, the windings offer a fixed resistance to current flow which will decrease slightly as they heat up but for all practical purposes the resisitance of the windings is not going to increase. Current is directly proprtional to voltage as long as the resistance remains constant. Increase the voltage in a load and you will increase the current going through it. Like instructors like to teach voltage is the water pressure and current is the water. open the hydrant more, get more water.

Maybe you  are saying a 460v motor uses less current than a 240v current all things being equal. That is true. Higher voltages are more efficient because the motors take less current to make them turn. But in a motor rated for 240v, if you increase the voltage, the current is going to also increase. That's why unwary American travelers who go to Europe fry thier 120v shavers and blow dryers in the 220v outlets.  :o
If I am wrong on this you gotta fix my brain . . . if that is even possible.  ;)
The oil is all in Texas, but the dipsticks are in D.C.

Gary_C

Power = Voltage x Current

The current that a motor uses is related to the load on the rotor, plus some winding losses. In other words it will draw whatever current it needs to keep that shaft rotating. So if you increase the voltage the current needed to maintain rotation will decrease.  ;D

Never take life seriously. Nobody gets out alive anyway.

TexasTimbers

Ooooohhhhh you sly dog. Boy oh boy how my head Hertz. ;D

I have a rheostat for my router and I have a amprobe. I am going to check it out in a bit. I think as I increase the voltage (turn up the water pressure) that the router is going to spin faster. As it does it needs more electrons to accomplish this so I think it is going to suck alot more of them from ground. I think the amprobe is going to reflect an increase in amperage as I increase the voltage but I am prepared to be suprised!
The oil is all in Texas, but the dipsticks are in D.C.

scsmith42

Kevin, I think that Gary is correct.  When voltages increases, current is reduced, and thus the size of the wire is reduced as well.

I just bought some large 3-phase equipment at auction - all 480V 3 phase.  The  wiring feeding these 15HP motors is only 10 guage, due to the lower current on the higher voltage.  That's one of the reasons that many high HP industrial motors are higher current - to reduce the size of the wiring and related costs.  To operate the same motor on 220V 3-phase would require a significantly larger wire, due to the increased current.

The ultimate wattage consumed is the same though, as watts is volts x amps (current). 

Clear as mud?!

Scott
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

TexasTimbers

On that we agree Scott. I even stated that so as to (try) to be clear. Higher voltages allow for  less current to do the same amount of work. We all agree on this.

I am trying to address the situation at hand really and I am thinking that if the element in the pizza oven is rated for 208v max, and 240v (or as is so often found even more like 248 etc.) is applied to it then the element will have an increased amperage flow because it is seeing more voltage than it is designed for. Am I wrong on this. ???
The oil is all in Texas, but the dipsticks are in D.C.

RichlandSawyer

Heating element. We need "ohms law" I=V/R  (current=voltage/resistance)

The resistance of the heating element will be constant. If you look on the nameplate for the amp rating of the element at 208 volts then we can calculate the amp draw at 240 and i think you will find it is not a significant difference. For example if it draws 8 amps at 208 that is a resistance of 26 ohms. Now working backwards if we take 26 ohms at 240 volts we get 9.23 amps. i would be more concerned about cheese dripping on the element and causing premature failure. And a side note, I said earlier that the resistance is constant. That is not entirely true as the element heats up the resistance goes up and since the increased voltage will cause it to get a little hotter then the resistance will increase which according to ohms law will cause the amps to drop so the actual amperage at 240 will be less then the calculated. Call the manufacturer and they will tell you it will work fine with no ill effects.

RichlandSawyer
Every log i open up, a board falls out!!!

Gary_C

You are right, but you keep jumping from the heating element to the motor and getting confused. One is a resistive load and the other is an inductive load and they behave differently.

For heating elements, yes, operating at higher voltages and higher currents will somewhat shorten the life of the elements. But in this case it probably is designed to handle that 240 volts anyway.

As far as the motor is concerned, we are talking about no change in the power the motor needs to move pizza's so if you increase the voltage, the current will drop (at constant power).   

OK?
Never take life seriously. Nobody gets out alive anyway.

RichlandSawyer

Thats a good point Gary. As for the motor, inductive loads work similar to resistive loads in that induction is the building of a magnetic field. In the case of a motor it is a rotating field or pulsing field. As the magnetic field builds the "resistance" increases and yes it will reduce the current to a certain extent. The problem is the field takes time to build and collapse and with increased voltage that propagation time increases causing the current and voltage to go farther out of phase. This is also called slip and will generate heat in the motor and will actually increase the amp draw of the motor. The voltage rating of a motor is determined by the number of windings in the armature. This particular motor was wound to work most efficiently at 208 volts. If you were operating a hundred of these motors you would want the windings to match the voltage because the power company would charge you for having voltage and current out of phase. This measurement is called power factor and for there grid to be efficient you have to be efficient. Yes if the nameplate voltage matches the actual voltage your motor will cost less to operate and will run cooler but as long as you are not operating 100 to 110% of nameplate amps the life span of the motor will not be effected.
Every log i open up, a board falls out!!!

TexasTimbers

Well thank you RLS and Gary for straightening me out. I do appreciate it. Now you know how my wife feels she has to keep me straight all the time - poor lady. ::) ;)
The oil is all in Texas, but the dipsticks are in D.C.

Thank You Sponsors!