connecting single phase to three phase delta heaters 2

[lippy]

Hello,
I'm in need of electrical help as I'm a Mechanical Engineer who knows enough electrical to be dangerous....if you know what I mean.

I have electrical distribution all set up for 230V 1 phase power to be delivered to resistive defrost heaters. The equipment unfortunately is designed as 3 phase delta arrangement. Could some one explain to me what would happen if I just power 2 outta 3 terminals? Is there something I can do to make this work? I thought we were getting 1 phase 230V @ 4500watts/19.6 amps but instead the equipment tag specifies 3 phase 230V @ 4500watts/11.3 amps. Thank you my electrically savvy friends. Joe ME

 

[jghrist]

If you just powered 2 terminals, you would get 1/3 of the heat output and draw 6.52 amps.

 

[rcw retired EE]

If you supply 230 V across two terminals you will power up one heater element at 230V and the other two in series. The two elements will draw about 3.2 amps, the single one will draw 6.5, and total power will be about 2250 watts. You may have a problem if control power for the heater control comes from the same terminals.

If the heater has three 1500 W elements connected in delta, it may be possible to reconnect the elements in parallel, single-phase to two terminals. Each element draws 6.5 amps for 19.5 total. It would depend on the configuration and rating of the controller, the size of wires, UL listings, etc.

Best bet is to ask the supplier to suggest a modification that would not void their warranty.

 

[lippy]

Hello rcwilson,
Thanks for the explanation. I get it. I will reconfigure as 3 heaters in parrellel at a total amperage of 19.6 since this is what I originally planned for anyhow. The two outta three idea without re-terminating the three heater leads is not the way to go but I do appreciate your calculated answers regarding what would happen if I did in fact try this. Like I said, I'm an ME with enough electrical knowledge to be dangerous. Thanks again, Joe.

ps-is there a good source of formulas that would allow me to work this out for myself....I think I have an UGLY reference around but can't locate it right now.

 

[itsmoked]

You should ask the maker how to convert it. There are other details like the controls that may matter.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[lippy]

Controls are seperate thru ssr and contactors.
But I did find out there are in fact 4 seperate heaters in a delta configuration for 3phase 230V heat. How in the heck is that done? Does this mean that not all the heaters are the same? Thanks, your humble student of reason....Joe.

 

[itsmoked]

Four heaters doesn't hunt.

We don't have enough info say much more.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[rcw retired EE]

Lippy - Those SSR's and contactors will have more current through them on single phase (19.6 A) than they would 3-phase (11.3A). If the devices are rated for 25 amps, you may be Ok. (25 A = 20A load +25% safety factor). If they are only 15 amp rated devices, you have a problem.

Check with the vendor. Four elements?? We would need to see a wiring diagram to comment.

With heating elements there are many ways to connect them in series/parallel configurations to get the desired heat output. This flexibility also means there are many ways to do it wrong and let the smoke out so it doesn't work anymore. There are definite safety issues involved.

As far as calculaitons: P = V x I, V = I x R

 

[lippy]

Thanks All,
Here is an attachment from HEATCRAFT who makes the units. They use 4 defrost heaters and can arrange them for 230v/1p or 230v/3p or 460v/1p.

 

[itsmoked]

Funky!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[NeonJohn]

>lippy (Mechanical)
>22 Oct 08 16:17
>Thanks All,
>Here is an attachment from HEATCRAFT who makes the units. >They use 4 defrost heaters and can arrange them for 230v/1p >or 230v/3p or 460v/1p.

In addition to everything else I've been involved with, I owned a small chain of restaurants for about a decade. This is an extremely common configuration.

Near the center of the attachment are the diagrams for wiring the 4 heaters to various voltages. The heaters themselves are 240 volt rated. For single phase 240 volts, wire 'em all 4 in parallel. For 240 3 phase, wire 'em in delta configuration with the 4th resistor in parallel with one of the others as shown in the center diagram. For 460/480 single phase, wire them as two series strings in parallel as noted in the right diagram.

Most restaurant/food service oriented equipment has a terminal block somewhere, usually near the incoming power connection, where all these different connections can be done. If this is new equipment then both the terminal block and the wires should be clearly marked. (grease tends to cause the markings to come off old equipment.)

If you get confused, just drag out the old ohmmeter to identify each pair of heater leads. All four heaters will have the same resistance.

With my restaurant equipment connections, especially the equipment we designed and built in-house, I labeled the wires using a Brother label maker and then heat-shrunk a sleeve of clear heat shrink tubing over the label to make sure it stays in place permanently. Brother uses a thermal dye transfer process in making the type so it stays in place regardless of the heat or grease involved. At least until the heat shrink gets hot enough to melt :-(

John

 

[itsmoked]

NeonJohn welcome to Eng-Tips.

Nice posts man.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Compositepro]

I would love to hear the story of how and why a nuclear engineer comes to operate a chain of restaurants. I agree - very practical advice, welcome.