current question

[JOHN908]

i am working with a 24kw heating element on a kettle. the element is 208 3ph 24kw,my question is if the supply voltage is 240 3ph which way does the current go,up or down. They do make a 240 element but not for a thousand dollars. the data tag for the 208 states 66.6 amps with 208 supply.

 

[JMOR]

UP

 

[Roger Tomfohrde]

24000/208=116 ohms.
240*116=27840 watts
27840/240=116 amps
Up a lot

 

[will-max dairy]

I can't make sense of the units in the post above.

I agree with JMOR's statement about "UP"... but the math in the next post isn't consistent units-wise.

I also don't know how a heating element is connected in a 3 Phase system... is it three elements? One on each phase? Delta? Y?

This definitely falls into the F around and Find out category... I know enough to know that I don't know enough to give someone a nice, comfortable, quantified answer on this.

 

[will-max dairy]

So... to me, the only way the math works is...

With your 208, 3phase, 24KW, 66.6A element... what that means is...

Three elements... each drawing 66.6 Amps (AC, rms) on one phase, which is 120 Volts (AC, rms)...

120Volts (AC,rms) times 66.6 Amps (AC, rms) is around 8KW.

Three of these 8KW elements... one on each leg (phase)... gives 24KW... probably a Y configuration.



Now... what does 240 three phase mean??? I have no clue, because you could be talking about your average 240 Split Phase power... which might only have one heating element (like your average clothes dryer at home)...and, that single element won't even wire to your three phase system.

Or a true 240V on each phase...


I'm thinking out loud here and purposely showing that I'm stumbling, because I have a Master's in Electrical Engineering; and I can't tell you what's gonna happen, other than... F around and Find out... or actually... find an electrician that can see what you got going and give you a good answer...

 

[will-max dairy]

Worst case... if you truly have 240V on each phase...

You now draw 132.2 Amps on each element... at 240V... which is...32KW... per element. X three elements...

You now have a 96KW pot.... a pot that smelts itself...

 

[will-max dairy]

A thousand dollars? Burn your building down? Smelt your pot?

Decisions, decisions...

So, please, please... get a good answer from someone that you can trust that can lay actual eyes on your situation.

 

[JMOR]

I can't make sense of the units in the post above.

I agree with JMOR's statement about "UP"... but the math in the next post isn't consistent units-wise.

I also don't know how a heating element is connected in a 3 Phase system... is it three elements? One on each phase? Delta? Y?

This definitely falls into the F around and Find out category... I know enough to know that I don't know enough to give someone a nice, comfortable, quantified answer on this.

If it matters to you, power will increase by 33% and current by 15%, whether delta or wye. Difference between delta and wye, for same power is that the resistors will be 1.732 larger with the delta connection than with wye

 

[will-max dairy]

If it matters to you, power will increase by 33% and current by 15%, whether delta or wye. Difference between delta and wye, for same power is that the resistors will be 1.732 larger with the delta connection than with wye

If 240V 3 Phase means a true 240Vrms per phase... and you connect the loads (which were rated for 120Vrms per phase in a 208V 3 Phase system) in the same configuration, then current in each of the three elements doubles, power quadruples... and you have some seriously bad consequences.

But... I'm no expert in 3 Phase... especially what the post means by "240V 3 Phase"... the math works out for the description of a 208 3Phase, with 120VAC per phase, three elements drawing 66.6A each, and a total power of 24KW... whatever 240V 3 Phase means... all bets are off to me...

The two configurations could have different usages of the neutral, could be three wire? four wire?...

Too many variables for my liking.

 

[JMOR]

If 240V 3 Phase means a true 240Vrms per phase... and you connect the loads (which were rated for 120Vrms per phase in a 208V 3 Phase system) in the same configuration, then current in each of the three elements doubles, power quadruples... and you have some seriously bad consequences.

But... I'm no expert in 3 Phase... especially what the post means by "240V 3 Phase"... the math works out for the description of a 208 3Phase, with 120VAC per phase, three elements drawing 66.6A each, and a total power of 24KW... whatever 240V 3 Phase means... all bets are off to me...

The two configurations could have different usages of the neutral, could be three wire? four wire?...

Too many variables for my liking.

If a delta, no Neutral involved..

 

[will-max dairy]

If a delta, no Neutral involved..
View attachment 99945

I don't doubt your math. What I'm saying is...you have a three heating elements wired a certain way in a 208, 3Phase system...and I'm assuming that the wiring is all essentially setup for this... so it's somewhat idiot proof to use as intended.

And now, you take those three heating elements and connect them in a 240, 3 Phase system... Which has a different phase to phase and phase to neutral scheme...

If you don't keep track of how you treat both ends of those elements, you can get some surprising results.

If a person is coming here to ask a basic question about whether current goes up or down... then I worry that they might not have the wherewithal to take three elements wired as a Y with a neutral that carries no current... and then re-wire them as a delta...

So... I agree with "UP"... and I'm not disagreeing with how far "UP" it goes, if it's configured correctly, like you show... I'm just saying that it could go much further "UP" if any mistakes are made with how the elements are wired between the phases... especially if, for the original rating for the 208V system, they are 1.8 Ohm elements connected in a Y...which, when I did my sanity check on the current/power rating... I think they are.

With think (or guess) being the operative term, in my case.

Even my assumption of three elements is just an assumption based on 120V per leg of a "Y" at 66.6 Amps producing 8KW... per element (at 1.8 Ohms)... requiring three to make the original 24KW rating.

I really can't make the numbers of 66.6A and 24KW work out any other way.

 

[JMOR]

I don't doubt your math. What I'm saying is...you have a three heating elements wired a certain way in a 208, 3Phase system...and I'm assuming that the wiring is all essentially setup for this... so it's somewhat idiot proof to use as intended.

And now, you take those three heating elements and connect them in a 240, 3 Phase system... Which has a different phase to phase and phase to neutral scheme...

If you don't keep track of how you treat both ends of those elements, you can get some surprising results.

If a person is coming here to ask a basic question about whether current goes up or down... then I worry that they might not have the wherewithal to take three elements wired as a Y with a neutral that carries no current... and then re-wire them as a delta...

So... I agree with "UP"... and I'm not disagreeing with how far "UP" it goes, if it's configured correctly, like you show... I'm just saying that it could go much further "UP" if any mistakes are made with how the elements are wired between the phases.

You make a leap that he going to disassemble the unit and re-wire the insides, don;t ya think? Why not throw in more irrelevant 120/240v center tapped high leg delta?!

 

[will-max dairy]

You make a leap that he going to disassemble the unit and re-wire the insides, don;t ya think? Why not throw in more irrelevant 120/240v center tapped high leg delta?!

I mean.... If we start with three elements wired as a Y...especially internally... and you don't mess with any internal wiring...


Then I can't quickly come up with a diagram of how to wire the four externally available leads to what is shown, which is supposedly common in the US.

There are some ways of wiring it that would possibly result in less power than rated? But some really odd currents on the internally wired neutral?

Some that result in more power than rated?

Granted, I gave a worst case scenario.

I don't know.

It all sounds like a very, very bad lab assignment from ECE 201 back in my college days. I remember Delta to Wye and Wye to Delta conversions resulting in resistor changes to get the same power, and they were all done on paper, where you could magically undo the center connection of the Y and reconfigure it as a delta... as opposed to dealing with fixed resistors and wiring.

 

[Janicholson]

If a delta, no Neutral involved..
View attachment 99945

I agree amps go up when running a pure resistance load on either delta or wye. A three phase transformer with the correct KVA and turns ratio to lower 240 to 208 would do it. But might be way more expensive than the correct heater. Jim

 

[47fivewindow]

i am working with a 24kw heating element on a kettle. the element is 208 3ph 24kw,my question is if the supply voltage is 240 3ph which way does the current go,up or down. They do make a 240 element but not for a thousand dollars. the data tag for the 208 states 66.6 amps with 208 supply.

Mr ohm says at 208 volts and 66.6 amps resistance is 3.123 ohms. At 3.123 ohms and 240 volts current should go up to 76.8 amps.

 

[will-max dairy]

Mr ohm says at 208 volts and 66.6 amps resistance is 3.123 ohms. At 3.123 ohms and 240 volts current should go up to 76.8 amps.

Mr Ohm doesn't know if the 66.6 Amps is in a Delta connection at 208 Volts (3.123 Ohms)... or in a Y connection at 120Volts (1.8 Ohms)... so Mr Ohm's answer is conditional, and uncertain, at best. In this case, Mr Ohm's middle name is Heisenburg ... or maybe Schrodinger... lol

 

[JMOR]

I'm sorry that I was baited into being so derailed into all the BS discussion of circuit configuration/wiring of elements/etc. , as the man's only questions was "does current go up or down if he applied 240 vs 208 volts?". My first response is all that should have ever been said, "up". Almost all the rest is a derailment. Sorry.

 

[Phill Tibbetts]

I got lost after the first post.

 

[BarnyardEngineering]

I got lost after the first post.

I can't stop wondering how much tea the OP drinks that he needs a kettle like that...

 

[MarkB_MI]

Assumption 1: This heating element is in fact three phase, and is intended to be used with a phase-to-phase voltage of 208 volts.

Assumption 2: We'll assume that the heating element is delta, although what it looks like internally doesn't matter. It could actually be wye with a disconnected neutral.

Assumption 3: You wish to power it with three phase power with a phase-to-phase voltage of 240 volts.

When performing three-phase calculations, we always convert a delta configuration to its wye equivalent. That way we can just work with a single phase. The wye equivalent of 208V phase-to-phase delta is 120V phase-to-neutral wye. (208 divided by the square root of three)

Checking our work against the published specs for your heater, at 66.6 amps the power per phase is 8040 watts. (120V times 66.6 amps) The total power is 24,120 watts, which agrees with your 24 kW spec.

The wye-equivalent phase resistance is 1.8 ohms. (120 divided by 66.6)

The wye-equivalent phase-to-neutral voltage for 240 volts phase-to-phase is 139 volts. (240 divided by the square root of 3).

The current per phase is 77 amps. (139 divided by 1.8)

The power per phase is 10,700 watts. (139 times 77). Total power will be 32 kilowatts. (10,700 times 3)