# Convert three phase SPA heater to single phase

#### Hugofilipe

Joined Aug 3, 2022
17
Hi,
I've a 6kw water heater that according to the specs should work on single phase, however I'm not sure how to wire it.
I've read here on the forum similar issues, however the heating element had a different arrangement.
As you can see, mine has like a star shaped common (I tried to connect neutral to it without sucess).

The old three phases are connected in parallel to single phase 220v.

Looking for some help, thanks!

#### Dodgydave

Joined Jun 22, 2012
11,234
If you remove the Star connection, and measure the elements individually to see what resistance they are, then you can put them in parallel across the single phase, you might only need one set of elements.

#### Hugofilipe

Joined Aug 3, 2022
17
If you remove the Star connection, and measure the elements individually to see what resistance they are, then you can put them in parallel across the single phase, you might only need one set of elements.
Thanks for the reply, sorry for such newbie question but what kind of resistance will I be looking for? If there is measurable resistance they are the same element? Should I wire neutral and phase on that element?

The connections are marked as 3 pairs of Red, Blue and White. There is a phase for each of them and them connected in common.

Joined Jul 18, 2013
28,488
As you can see, mine has like a star shaped common (I tried to connect neutral to it without sucess).
The old three phases are connected in parallel to single phase 220v.
If I read this right, this is exactly how it should be connected to 1ph, IOW, the connections that were connected to the 3 phases should be paralleled and connected to the 220v, and what was the single star point, is now the single phase neutral.

#### LesJones

Joined Jan 8, 2017
4,171
Is the heater rated at 6 KW when supplied with three phase with 220 volts phase to phase or 220 volts phase to neutral ?
If you can't answer that question I suggest that you do the resistance test that Dave suggested.
Are you in north America where a 220 volt domestic supply has the center tap connected to neutral or are you in Europe where one leg of the 220 volts is neutral ?
When you say "without success" do you mean that it does not work at all or it works but does not provide 6 KW of heat ?

Les.

Joined Jul 18, 2013
28,488
In UK Inc some of Europe, the 230v is one phase of a 3ph Star connected transformer with the Star point neutral.
N.A. is 240v

#### panic mode

Joined Oct 10, 2011
2,636
6kW three phase load means 2kW per phase.

P=U^2 / R

or R= U^2 /P

so resistance of single element (in operation) is supposed to be about 24 Ohm. this is a good ball park value to keep in mind since cold element resistance will be different.

and why don't you post picture of the product nameplate and state in which country this is installed?

#### Hugofilipe

Joined Aug 3, 2022
17
Is the heater rated at 6 KW when supplied with three phase with 220 volts phase to phase or 220 volts phase to neutral ?
If you can't answer that question I suggest that you do the resistance test that Dave suggested.
Are you in north America where a 220 volt domestic supply has the center tap connected to neutral or are you in Europe where one leg of the 220 volts is neutral ?
When you say "without success" do you mean that it does not work at all or it works but does not provide 6 KW of heat ?

Les.
I would assume its 6kw phase to phase, however I attach now the heater label (sorry about the picture, it's a hard to reach position)

Will do the resistance test, what values should I be expecting?

I'm in Europe with one leg of 220v is neutral (the blue wire in the previous pictures)

By without success I mean that I did not get any heat out of the heater. I have a new contactor working and sending 3 x 220v (they are paralled before the contactor) and the neutral attached to one nut that secures the star shaped metal piece connecting the 3 heating elements (i assume).

Joined Jul 18, 2013
28,488
So when the contactor picks up you have nothing from the 220v to neutral on the elements?
I would expect that to be 2kw on each original phase.
Were they originally connected from phase to phase>? What voltage?
Or more likely from each phase to star neutral.

#### LesJones

Joined Jan 8, 2017
4,171
If the heater is designed to work with 220 volt phase to neutral voltage and star connected then connecting them in parallel as you have done should work.
I would expect the resistance reading between the star point and any phase to be about 24 ohms. (The reading between any two phase connections would be about 48 ohms.)
Have you measured the current in each of the switched lives between the contactor output and the element ?
Have you verified that AT THE TERMINALS ON THE HEATER that the voltage between the star point and and each phase connection is about 220 volts ?
The fact that you have to ask what the expected resistance readings should be makes me think that you should not be working with mains voltages.

Les.

#### vu2nan

Joined Sep 11, 2014
341
Hi Hugo,

It's clear from the photographs that it's a 3 x 400 V, 6 kW heater with no necessity / provision for a neutral connection.

If you intend connecting the three elements, in parallel across a 230 V single-phase supply, you need to connect a neutral cable of adequate size, using a ring-type lug.

Nandu.

Last edited:

#### Hugofilipe

Joined Aug 3, 2022
17
6kW three phase load means 2kW per phase.

P=U^2 / R

or R= U^2 /P

so resistance of single element (in operation) is supposed to be about 24 Ohm. this is a good ball park value to keep in mind since cold element resistance will be different.

and why don't you post picture of the product nameplate and state in which country this is installed?
Thanks! Just missed your reply while writing the previous message. I'm located in Europe and just posted a picture of the label.

So when the contactor picks up you have nothing from the 220v to neutral on the elements?
I would expect that to be 2kw on each original phase.
Were they originally connected from phase to phase>? What voltage?
Or more likely from each phase to star neutral.
I haven't actually measured at the heater terminals, I've measured at the contactor 220v between each L and the N, and the contactor actuates when the water pump is activated and water temp is bellow the selected temperature.

When connected in a 3 phase configuration, they were connected from phase to phase, the N wire was not connected to anything. Here is a picture how it was, 3 phases connected and the blue N wire just thrown in there, not striped neither connected.

If the heater is designed to work with 220 volt phase to neutral voltage and star connected then connecting them in parallel as you have done should work.
I would expect the resistance reading between the star point and any phase to be about 24 ohms. (The reading between any two phase connections would be about 48 ohms.)
Have you measured the current in each of the switched lives between the contactor output and the element ?
Have you verified that AT THE TERMINALS ON THE HEATER that the voltage between the star point and and each phase connection is about 220 volts ?
The fact that you have to ask what the expected resistance readings should be makes me think that you should not be working with mains voltages.

Les.
You are right as I probably should not be working with mains voltages, I have some experience with low voltage dc circuit boards but not at all confortable working with mains voltage.

Due to the lack of confidence dealing with it, I have not measure the voltage at the heater it self, I've measure at the contactor. When I get home I will make sure that the readings at the heater elements are the same as the contactor.
Will also check for current between the contactor and the heater, I've a 'clamp' type current meter, that should work?

Once again, thank you!

#### Hugofilipe

Joined Aug 3, 2022
17
Hi Hugo,

It's clear from the photographs that it's a 3 x 400 V, 6 kW heater with no necessity / provision for a neutral connection.

View attachment 273074

If you intend connecting the three elements across a 230 V single-phase supply, you need to connect a neutral cable of adequate size, using a ring-type lug.

View attachment 273094
Nandu.
I did connect without the ring lug, would the weak contact of the wire behind a nut be the reason for it not heating? I have a ring lug, will clamp it to the neutral and try again. Is there a reason for the 3 neutral wire instead of only one connected to the star shaped metal piece in the center? That would be the same, is it correct?

#### LesJones

Joined Jan 8, 2017
4,171
I suggest connecting some twin wire to neutral and one phase connection AT THE HEATER and putting a connector strip at the other end so that you can safely measure the voltage without the risk of shorting anything out with the test probes.

Les.

#### vu2nan

Joined Sep 11, 2014
341
I did connect without the ring lug, would the weak contact of the wire behind a nut be the reason for it not heating? I have a ring lug, will clamp it to the neutral and try again. Is there a reason for the 3 neutral wire instead of only one connected to the star shaped metal piece in the center? That would be the same, is it correct?
Improper contact would have resulted in arcing at the terminal, Hugo.

A single cable, having a cross-sectional area that is three times that of the other cables, would do for the neutral.

Nandu.

#### Hugofilipe

Joined Aug 3, 2022
17
Improper contact would have resulted in arcing at the terminal, Hugo.

A single cable, having a cross-sectional area that is three times that of the other cables, would do for the neutral.

Nandu.
Understood, thanks.
If I get it to work, do you see any problem by using just one or two heating elements? I got thinking that, since I have solar power, I could control the power output by turning the 2kw heating elements independantely and therefore heat it as the PV supply increases or decreases. This would control my surplus solar production and keep costs down.

Joined Jul 18, 2013
28,488
There should be no issue of selectively using any combo.
May mean separate contactors.

#### Hugofilipe

Joined Aug 3, 2022
17
Yes, three independant contactors, or since the load decreases, maybe I could get away with 3 10A or 16A wifi relays and control it remotely. Just have to make sure they cannot be turned on without the pump being on.

Joined Jul 18, 2013
28,488
Yes, three independant contactors, or since the load decreases, maybe I could get away with 3 10A or 16A wifi relays and control it remotely. Just have to make sure they cannot be turned on without the pump being on.
Many contactors, especially DIN style have the option of fitting interlocks to the front of the contactor, actuated by its armature.
Then used to interlock the pump relay/contactor coil.

#### LesJones

Joined Jan 8, 2017
4,171
You would only need 2 contactors. One would drive 1 element, the other would drive 2 elements. You would still have the option of 1, 2 or 3 elements being on.
The interlocking could be done using the power to the pump as the supply to the contactor coils.
If there was no power to the pump then the contactors could not pull in.

Les