3 PHASE 32AMP

[leighv]

Hi - I bought (foolishly?) a smoker oven that has the above plug attached.

Question: how can I connect this to a UK power supply. I don't really want to change any underlying electrics in the house, as we are renting, so any recommendations welcome, so I can start using it

Thanks.

 

[electronicsuk]

If you only have a single phase supply, you very likely can't use it. There is a small possibility that it can be rewired to run on single phase, but you would need to consult the instructions and/or manufacturer. Furthermore, if the FLC is anywhere near 32A/phase then it's too big to run on a domestic supply anyway.

Oh, and there's absolutely no way you can run it from a 13A socket, so if you can't touch the electrics in your rented house, forget it.

 

[plugwash]

What is the make and model of this device?
Does your place have a cooker outlet available?
Where did you get this from? was it new or secondhand?
Does the device have a rating plate? if so what does it say on it?

 

[Steve]

Question: how can I connect this to a UK power supply.

By plugging it into a UK 32 amp 3 phase socket?

You cant use it as it. But if you can find details of voltage, wattage, amps per phase, frequency, we'll try to find out if it can be used on single phase.

And what is the model and make?

 

[ban-all-sheds]

It may just have a 32A plug...

12.75kW sounds enormous, when you think how much electricity a regular oven uses. Even with hot smoking you don't want a temperature of more than 85°C, and with cold smoking you can put your hand inside, it's that cool.

Furthermore, if the FLC is anywhere near 32A/phase then it's too big to run on a domestic supply anyway.

Wouldn't 32A per phase equate to 55A single phase?

 

[ricicle]

Wouldn't 32A per phase equate to 55A single phase?

No - if the heating load was rated at 32A per phase (3 phase) then to make it work at the same power single phase it would be 96A (excluding any fan or control loads)

 

[ban-all-sheds]

So is an "X amp" 3-phase appliance not (X x 400) watts?

And why is the multiplier for current 3 when for voltage it's √3?

 

[ricicle]

So is an "X amp" 3-phase appliance not (X x 400) watts?

And why is the multiplier for current 3 when for voltage it's √3?

Because when you work with 3 phase power it is basically 3 lots of single phase power. If you had a 3 phase oven rated at 13A you can safely assume its 3kW per phase/9kW total (approx)
Now for an equivalent single phase oven it would still be 9kW but single phase so 39A (approx)

 

[ban-all-sheds]

Because when you work with 3 phase power it is basically 3 lots of single phase power.

But not all in phase, so at no time do all the currents sum to 3x the per-phase, surely, any more than voltage does?

If you had a 3 phase oven rated at 13A you can safely assume its 3kW per phase/9kW total (approx)

9kW total.

This is where my understanding goes fuzzy - maybe it's too late...

Voltage between phases is 400. If that's giving you 9kW then isn't the current between phases 22.5A, not 13?

Conversely if the current per phase is 13A why isn't the power 5.2kW?

 

[ricicle]

Because of the star point each phase current is flowing through a load connected across a voltage of VL/1.73 ie 400/1.73V = 230V

 

[ban-all-sheds]

Yes I know.

I'll revisit this after I've had a lie-down...

 

[plugwash]

Ok lets start with the simple case to understand, a star connected load with a neutral.

Each phase has a voltage of 230V RMS relative to the neutral So if we put a load that draws 13A RMS per phase then each of those loads will get about 3KW. We have three such loads so they are drawing a total of 9KW. There will be no current in the neutral since the instantanious currents in the three phases sum to zero.

Now lets consider the case of a star connected load without neutral. It turns out the circuit will behave exactly the same as above, since there was no current in the neutral removing it will have no impact on the voltages in the system. Each of the loads will still have 230V RMS across it and they will still draw 3KW each for a total of 9KW

Finally consider a delta connected load (each of our loads is connected between a pair of phases, one to L1 and L2, one to L2 and L3 and one to L3 and L1). This time we have 400V RMS across the load so each of our 3KW loads would be drawing 7.5A RMS.

You might think this would give a total of 15A per phase but you would be wrong! because the two loads are drawing currents from the phase that are 60 degrees out of phase with each other and so partially cancel giving us 13A (you can treat a magnitude/phase pair as a 2D vector or a complex number for the purposes of adding them together).

Note: i'm rounding in the above post (but then electrical engineers tend to round anyway, the phase-phase voltage for a 230V phase-neutral voltage is actually 398.37 iirc)

 

[Stoday]

BAS — the formula for three phase power is P = √3.VL.I
Where VL is the line (between phase) voltage.

So whereas single phase, 230V 13A supplies 3kW, 400V 13A three phase supplies 9kW.

 

[electronicsuk]

Furthermore, if the FLC is anywhere near 32A/phase then it's too big to run on a domestic supply anyway.

Wouldn't 32A per phase equate to 55A single phase?

I suppose the easiest way to consider this is in terms of three 32A single phase 230v loads fed via a 3P+N supply. If you were to take these loads and run them on SP, they would still consume 3x 32A.

 

[ban-all-sheds]

Righty ho.

I guess what I was thinking was that although the current in each phase would be 13 amps, because they never coincide you wouldn't simply add them up when considering a single phase equivalent, i.e. that the 3-phase power calculation would be 400 x 13 = 5200, not √3 x 400 x 13.

So if the OP's oven does take anything approaching 32A per phase it makes it even more odd - I just googled for commercial smoking ovens, and the first link I looked at was an Australian company, and they have a 21kW model.

It's 1.2m wide and deep, 2.4m tall, and takes 380kg of meat. I imagine all others of that sort of power will be similar.

[lloyd-grossman-accent]Who would buy something like that to use in a rented house?[/lloyd-grossman-accent]

A? - nobody. It can't be a 22kW oven, or anything near. It may not even be 3-phase - it's possible it was somewhere where only 32A 3P+N 60309 sockets were available so someone just stuck a plug on it.

As plugwash says, we need the details of make/model/rating plate info etc.

Another Q leighv - how does it make its smoke? Do you also need to connect it to a flue so you don't die from carbon monoxide poisoning?