3 Phase vs. Single Phase Heating Elements

Would be nice to view the wiring diagram for your heaters, (before and after.) but, for wiring three phase heating elements you normally wire them in series, while for single phase you'd wire them in parallel.

As a lot of people know, on the when wired in series, if one element would fail, all would fail like the old Christmas tree lights. But on heaters the loss of a single element in a series connected with three phase floating wye configuration, will immediately cut the input power to the furnace in half and that the loss of a second element will cut the furnace input power to zero.

Here is a link of heater wiring configuration for comparison.

http://www.rayteq.com/series_vs_parallel.shtml

Thank you Phoenix for your answer

All i know for the moment is that the furnace was using 90A from each phase with a delta wiring before renew. but now it uses around 130A from each phase and each zone of furnace is connected to one phase. the company claims that the current has increased but total time has decreased and so the energy consumption is the same. Also i know we had 432m of 3mm diameter heating wire before and 144 m of 3.5 mm heating elements. elements are the same type and just weigh has decreased by 2.2 factor.

Hamids740

There have been discussions simular to on this site. I just did a quick search, but there seems to be some differences in the wiring that can play a big part.

http://cr4.globalspec.com/thread/67458/3-Phase-Heating-Element-Problem

There are other members here that either has the knowledge and expertise or excellent research abilities that can help better then myself.

But I'm sure they would request more details.

Thanks for your through complete answer

Dear sir

I think your reply is irrelevant now.

Original configuration of elements was either delta or star formation. Generally it will be star formation for three phase input supply

Revised configuration is for single phase supply. In this case all elements will be in parallel only and there will not be series connection.

Naturally in single phase formation,the total current drawn by the lead cable will be more than in 3 phase formation.

But power consumption and heat generation will be same.

In three phase system even if one phase supply fails 66% of elements will be on and some heat will be generated, but in single phase formation if single phase fails, no element will be on and no heat will be generated.

In single phase the looping cable size to be rated that of lead cable.

For example, assume there are 3 elements of 5 kw each connected in star formation in three phase system of 415 volts.

Total load 15 kw

Line current of each phase will be (15x 1000)/(1.732x415) =20.86 Amps

If the same elements are connected in single phase formation, the line current would be 15 x 1000/230 = 65 Amps.

In this instance the led cable and looping cable are to be rated for more than 65 Amps.

Please check whether this aspect is considered while changing to single phase formation.

Thank you for your answer. This is actually what i am looking for.your answer is completely helpful for me. but increasing the current in that case mean more current in each single heating element and then less life time?

Again thanks for your answer

Whatever current your heaters run at, it is assumed they are designed and rated to work continuously at that temperature - thus you would not expect them to burn out.

I am not a heater expert, but looking at my domestic cooker, the grill pan is rated at 2kW and glows red hot and will run continuously red hot at that temperature without burning out because that is what it is designed to do.

My 2kW electric kettle, on the other hand, without any water to take away the heat fast enough, or if it boils dry, will glow red hot for a few minutes and then likely burn out, but the auto thermostatic cut-out works to protect the heater because the element, although consuming the same current, and thus the same heat, is not designed or rated to run at red hot temperatures - and will soon burn out if the rated current is not reduced.

In other words, your elements, however connected, should be rated for the temperature they reach - and should last just as long - life is shortened when they 'overheat' - which is as much to do with heat dissipation in the process as it is to do with the current in the first place (eg. kettle without water),

I wanted to clarify here that the current drawn by individual element will be same in both single phase and 3 phase arrangement.

Taking the example from my previous post,

In single phase, each element is 5 kw, therefore current drawn by this element is =5 x 1000/230= 21.7 Amps.

In three phase system the Current drawn by individual element will be=(15 x 1000)/(415 x 1.732) =20.86 amps.

I am afraid your numbers are adrift. You have used 415v 3-ph and 230v 1-ph in your calculations.

415v 3-phase gives 240v single phase, or 230v 1-phase gives 400v 3-phase.

Which is it?

Apart from the precision of the result, the only difference as I can see, is you need a 2 large cables to feed 3 single phase heaters in parallel, or 3 smaller cables to feed 3 heaters in Star. Nothing has changed total heatwise. Temperature control is a separate issue.

One of your statements is way off. You state single phase heaters are all in parallel. Then you turn around and state that the power goes to zero if even one element fails. WRONG. You need to back-up there, cowboy, and take another shot at that tin can.

If this is an industrial plant making some parts that are heat bonded, the whole thing is getting ready for a big ol' oops. If this is someone's home toaster oven, good luck, and don't burn the bread.

Thanks again, i have request from the for wiring diagram and all details, as soon as i recieved it i will upload it here.

What reason did the company give for altering the wiring?

A drawing would be a great help to us.

The reason that did it was a mistake actually. When they brought new furnace and started it for the first time, they understood with the same wiring of past furnace need around 270A because of probably less amount of heating elements, so not to change the whole heating elements they decided to change to the wiring connection.

and now i want to know whats the disadvantage of it.

Resistance heating is pretty much you get what you pay for,, watts used = heat produced...If the total amps drawn is the same then you have the same amount of heat produced...If you are drawing more amps then you are producing more heat....So it takes the furnace less time to satisfy the thermostat by producing more heat...this is generally an energy saving strategy, as long as the more rapid heating has no ill effect...

I am not able to come up with an explanation because I have no knowledge or experience of working with industrial heaters. But you refer to the affect on heat, and you have a lot of answers to help you, but I am puzzled because no mention has been made of the actual working temperature you wish to achieve.

Different ways of connecting elements might have an effect on the working temperature you want. Perhaps that's the reason.

the working temperature is around 1250 C and the volume of furnace is about 1 cubic meter.

In general terms, Rixter and Ramvinod have given good answers; but in specific terms we do not have enough information from the OP to determine what is really going on. There are several combinations of star/delta/series/parallel in which a multitude of heating elements can be wired. We haven't even been given the ratings of any of the individual elements.

The correct destination for this query is the company that carried out the modifications.

who's the joker giving Ramvinod #10 a GA for an answer that is mathematically wrong.

415v 3-ph is not 230v 1-ph