Help with freezer units start up current

 Hi All,

Is there anyone who deals with refrigeration  in the forum who could possibly help me with cable sizing ?.

We have 2 freezer units on trailers at work which are currently  running off of 2 13 amp  sockets  with commando plug to 13 amp plug adaptors .

Cable length is around 5 metres  going to each and they run fine on this circuit and have for some time.

Work want to move them and run a swa cable around 55 metres and put them on there own mcb .

Plate details are 

Minimum current  7 amp s

Maximum current  12 amps 

Start up current  40 amps 

Monobloc refrigeration unit .

I don't have a lot to do with motors and compressors so am I sizing the cable based on start up current which seems  odd to me , however  I would like to understand this if anyone can put me right I would be most grateful. 

Regards .

I'm no expert in refrigeration  Sirsparkabit     but I would say do your calcs on the run current  ,  the start-up at 40A as with most things , only lasts a  second as the motor overcomes the inertia of the compressor  .  

Recommend  type C  MCB  though .    

Best see what others say though ,  I'm not sure about those refrigeration  compressors  .  Can you take a start-up reading on the existing  set up?  

I would only caution that if the volt drop at start up is too high, it might not start, leaving a stalled motor drawing a lot of current.  You will only know that by trying it.

I would do the cable size calcs based on 1 compressor starting, and see what massive size it spits out.

Thank you both ! had a look at volt drop and have gone for 2 x 10mm swa to be on safe side with 2 40 amp c curve mcbs. 

2 x commando sockets with 45 amp isolators at other end .

Hopefully jobs a good un. 

Didn't want both starting on same circuit  so maybe a little overkill but safe and sound.

Thanks Again.....

Where is the overcurrent protection for the (16A - I assume) commando sockets?

Also there are probably very few instances where both would be trying to start at the same time, only one I can think of is after a few hours of power failure and a loss in temperature, they'd both need to start ASAP, but would they overlap starting? most fridge trailers same to have some kind of electronic control module and they seem to go through some checks on pwoer restoration, rather than start straight up, I I suppose if they were the same model, the delay could be identical between them.

I think my starting point would be one 10mm SWA on the 40A C curve*, to a weatherproof unit with two 16A commando sockets each fed from a C16 rcbo (or 2x  mcb and RCD combination). Its unlikely you'd be able to avoid installing RCD protection, but what you should avoid is installing one RCD for both units, the cost of the extra RCD is tiny in comparision with the difference between the lost stock in one fridge trailer vs two fridge trailers if a compressor goes pop

*D curve if possible, if you make this a submain to a downstream unit, then the zs values for 5s are quite forgiving, and because you are relying on the thermal element, its likely that a fault on a downstream circuit might not be of sufficent magnitute to hit the intantaneous trip on the submain breaker, and you might be just able to achieve discrimation between MCBs (which simply doesn't happen if you hit the threashold for the magnetic release on both breakers)

{the above shouldn't be considered a final design, but rather a pointer in where I'd start from before I started verifiying that the resultant installation would be compliant)

Many Thanks 

A lot in there I hadn't thought about !

Will take a closer look at design Tommorow .

Cheers again .