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Joined: Jul 2007
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What are the voltages at thes points? Also. Humor me for a moment. Which heat elements are heating?

Greg, I think you may have your ground fault at the wrong end of the element


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Originally Posted by LarryC
Greg,

Since there is no contactor for the third phase, they may be using a corner grounded delta. In that case, the heating element will see the full 400 V across it and the current will be approximately double of the calculated. That comes a bit closer to the measured values.


Even with a corner ground, I would imagine the voyages will be the same between the legs. By the readings, the heater lost the top contact likely to a ground fault between top contact ant first element and lost LS3 or bad connection on the jumper betwen LS1 and LS3. A compound problem

Last edited by sparkyinak; 03/27/16 01:31 PM.

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Quote
Even with a corner ground, I would imagine the voyages will be the same between the legs.


True. However the voltage between each phase to ground would be different. If the return path is ground instead of the other phases, the one working heater would see 400V across it instead of the expected 230V.

A floating 400V delta would see about 230V from each phase to earth. Ground one corner and now two of the phases would measure 400V to earth and the grounded phase would read 0V to earth.

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I just realized we are all going down the wrong path.

6.9 KW total heater output = 2.3 KW per phase

2.3 KW per phase / 230 V phase to neutral / earth = 10 A

Measured current ~ 10 A.

Element resistance when hot, is around 23 ohms.

Top element is open, middle element is fine, bottom element is either opened or unpowered. Somewhere along the common connections is grounded. Probably at the top heating element, near the common connection point.

Last edited by LarryC; 03/27/16 03:24 PM.
Joined: Dec 2002
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Originally Posted by LarryC
I just realized we are all going down the wrong path.

6.9 KW total heater output = 2.3 KW per phase

2.3 KW per phase / 230 V phase to neutral / earth = 10 A

Measured current ~ 10 A.

Element resistance when hot, is around 23 ohms.

Top element is open, middle element is fine, bottom element is either opened or unpowered. Somewhere along the common connections is grounded. Probably at the top heating element, near the common connection point.


Agree! Without the calculations, I think that's what I suggested at first.
Whatever, I think you can safely say you need some new heater elements.

Last edited by geoff in UK; 03/27/16 04:40 PM.
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this is the UK, no corner grounded delta here!

its plain old 400/230. No neutral even to the isolator on this either

Ill get my multimeter out on Tuesday when I'm back


I took my time, I hurried up, The choice was mine, I didn't think enough
Joined: Sep 2005
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Originally Posted by LarryC
I just realized we are all going down the wrong path.

6.9 KW total heater output = 2.3 KW per phase

2.3 KW per phase / 230 V phase to neutral / earth = 10 A

Measured current ~ 10 A.

Element resistance when hot, is around 23 ohms.

Top element is open, middle element is fine, bottom element is either opened or unpowered. Somewhere along the common connections is grounded. Probably at the top heating element, near the common connection point.


this is exactly what I think is happening. I think the top element is shorted to ground, but on the left hand side, but I cant explain why!


either way, its definitely fubar, just need to find somewhere to replace the elements on it


I took my time, I hurried up, The choice was mine, I didn't think enough
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I disagree with the way that the diagram by OP was originally drawn....
For a start, it would be pretty poor form for an equipment supplier to wire a 3 phase 400V heating circuit in this manner, irregardless of the load or voltage.
What I mean by this, is the fact that under any electrical regulations, this configuration would not fly.
In any country that uses 230/400V, you need to feed your contactor coils with no more than 24VAC and make sure that the wiring through them is "straight through", as in no extra contacts outside of your main contactor.

This is obviously an extra heat circuit, when the weather gets really cold, with it being near 7kW, it seems to me like the contractor low-balled on the heat capacity of the original unit?

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Originally Posted by Trumpy
I disagree with the way that the diagram by OP was originally drawn....
For a start, it would be pretty poor form for an equipment supplier to wire a 3 phase 400V heating circuit in this manner, irregardless of the load or voltage.
What I mean by this, is the fact that under any electrical regulations, this configuration would not fly.
In any country that uses 230/400V, you need to feed your contactor coils with no more than 24VAC and make sure that the wiring through them is "straight through", as in no extra contacts outside of your main contactor.

This is obviously an extra heat circuit, when the weather gets really cold, with it being near 7kW, it seems to me like the contractor low-balled on the heat capacity of the original unit?


its drawn as the manufacturer manufactured it, its an assembled unit that just wires straight into the L1L2L2 terminals, the contactor (although the manufacturer calls it a relay) is 24v from the heat pump control circuit.

Its a 15kW heat pump, and this is just the accessory heater for it, designed for the unit, and fits inside it.


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Trumpy,

I suspect the switches drawn as LS1, LS2, and LS3 are actually over temperature switches. I would expect to see them on the line side of the heating elements instead of the common. I am also surprised the contactor is not a three pole device. The lack of the third contact enables the bottom heater to be always on if the common gets grounded.

Assuming the system got approved by the relevant authorities, we can only offer opinions on a safer design.

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