Permissible inrush current single phase


I have had the misfortune to buy a Lincat Combination Oven for my Hotel.

These normally come in 10kw three phase.  3 x  13amps That's not too bad.

I have the single phase version 1 x 39 amps. Not so good.

It is operating at 1 second on 39 amps

                          0.2 second off  0 amps

                          Cycling continually. for hours.

I have a 40kva single phase supply and can hear the current hammering away incessantly. Lights flickering etc. I asked the manufacture for details of soft starting

and duty cycle. They say this is the way they were designed to work. Bang on and Bang off --1 second cycle continually.

I don't have a current (Hee Hee)  Reg book. So I ask is there a reg in place that covers the single phase load criteria.

To add insult to injury-- I have a three phase 65kva standby set.-- I would not put that destructive abuse on one of my 20kva phases.

it would shake it apart. So I cannot run it.

Regards -- Tony

  • The control method used is fairly common, a fixed loading of the element which is cycled on/off very frequently to maintain the desired temperature. Similar in principle to the "simmerstat" controls used on domestic cookers, but with a shorter cycle.

    A better design would control the three elements separately. Too cold=all three on, Nearly up to temp=two elements on, reached set point=one element on, exceeded set point=all off.

    That would add to costs though. 

    BTW, 50 KVA is unusually large for a single phase supply. 24 KVA or exceptionally 30 KVA is the usual limit for single phase service.

  • However, any maker hoping to sell to the UK must take account of the kind of loads the DNOs will and will not permit to be connected, and any importer must CE or UKCA mark and declare that it meets the relevant standards for the market.

    Such short cycling precludes such a load from connection to the vast majority of single phase installations.  To stay within the 61000-3 flicker pulse load limits,  with 1Hz flicker. requires the voltage to drop by less than 2,3 volts p-p - a source impedance below
    2.4/40 or  0.06 ohms.

    That is well below what the DNO will normally guarantee even on what sounds like a 200A supply.
    If the duty cycle was the same but 100 times slower it would stand some chance as you are then permitted much larger disturbances.