440 Volt heaters

[jrk]

I have 3 440 volt 2500 watt (total) heating elements. Can I put these heating elements in parallel and run them off of a 120/208 3 phase system. When using them with 440 volts they are in a "Y" configuration.

 

[charlie b]

If you do, then each element will get 120 volts, instead of its rated 440. That will cause the heating power of the element to drop by 93% (i.e., each will only give you 7% of its rated heat). Not a good plan. Probably also not within the manufacturer?s instructions, so it is not allowed by the NEC either.

Why would you want to do such a thing anyway? :-?

 

[don_resqcapt19]

If they are wye connected in a 480 volt system then they are 277 volt heaters. You could use them on 208 connected in delta, but you would only get about 56% of the rated wattage.
Don

 

[jrk]

440V heaters

440V heaters

If they are configured in a wye configuration isn't that presenting themselves as a two equivelent resisters in series? So therfore the voltage drop across each heater is 240V which of course equales the supply voltage. So then I should be able to configure them in a delta configuration with each heater having a voltage drop being equiveant to supply voltage which is 240V between phases. Ohm's law also supports this. The reason I want to do this is because this is used equipment and I have to convert it from 440V to 4 wire 120/208V system.
Thank you very much.

 

[winnie]

If you have three equal resistors, connected 'wye' to a 480V system, then the voltage on each resistor will be 277V. This is not the 240V that you might expect by dividing 480V by two, because each resistor carries current from _both_ of the other phases. You have to do the vector math to correctly calculate the voltage drop.

If you have a 208V three phase system, then the voltage between the phases is 208V, not 240V.

So as Don says, if you have 277V heating elements, and you connect them in delta across your 208V supply, you will only operate these elements at about 56% of their rated power.

Note: if you have a _240V_ three phase system, then the elements will operate at 75% of their rated power. Since 240V center tapped delta gives 120V and 208V line to neutral voltages, as well as 240V line-line voltages, perhaps this is what you have. Usually this would not be called a 120/208V three phase system, which to most of us would imply a wye system with 120V line-neutral, and 208V line to line.

-Jon

 

[charlie b]

If they are configured in a wye configuration isn't that presenting themselves as a two equivalent resisters in series?

To Jon?s explanation, let me add something to help you understand series and parallel.

A series connection is like a line of people holding hands. My left hand is holding your right hand. Your left hand is holding Jon?s right hand. Jon?s left hand is holding someone else?s right hand. And so it goes down the line. At each point of connection, there is one person?s right hand, and one other person?s left hand, and no other hand is touching the two.

Current flowing through a set of series components will see a similar situation. Specifically, current gets to one connection point, and starts flowing through the next component in line. At the end of that component, it gets to another connection point. It discovers at that point that it has one, and only one, place to go from there.

That is the essence of a series circuit. Current flowing through the circuit will find, at each connection point, one and only one path to follow.

Suppose, back at the line of people holding hands, someone new walks up, and with his right hand he grabs the point where my hand is touching yours. It is like taking a series circuit, and connecting one additional component, but not at the end of the line. Rather, you connect the new component at the junction point of two existing components. Now, as current flows through one component, and gets to the next junction point, it finds two different paths that it can follow. This is no longer a series circuit.

In this same sense, a WYE connection is not a series circuit. Current flowing into the center point of the WYE, let us say it is coming from Phase A, will have two choices of where to flow next. It can flow into Phase B, or it can flow into Phase C. That is not a series circuit.

 

[jrk]

440V heaters

440V heaters

Once again, thank you. By the way it's been over 30 years since I did real electrical work. Been in electronics for the last 30 years with very little power with exception to DC. Iunderstand everything that was stated and agree that a wye connection is not in series. We do have a center tapped delta system with 2-120V legs, 1-208 leg and 240V between phases. By the way these forums are a great resource for information and makes my job just that much easier.

 

[al hildenbrand]

We do have a center tapped delta system with 2-120V legs, 1-208 leg and 240V between phases.

run them off of a 120/208 3 phase system

I think we're being confused by a less than rigorous statement of what you have.

Based on your last post, I believe that your power company supply, where the machine is, is 120 / 240 Volt 4-wire 3 ?. There's no "208 3 phase" in that.

Others can talk about the "high leg" voltage measurement.

I'm interested in your machine.

You call it a 440 volt machine. Is the machine actually labeled 440 volt?