VOLTAGE DROP???

[noteinstein]

Hi All,

Come across something unusual (for me at least).

Picture This;

220v 60 hz 3 Phase Supply ...
This supplies a Distribution Board from a 20amp CB with 4mm cable ...
This Dist. Board then supplies (among other circuits) from a 2 Pole 16amp Circuit Breaker a 16amp outlet on 2.5mm cable approx 25 metres in length...
Plugged into this outlet is a single phase 2.2kw compressor...

Heres the problem;

This compressor when switched on would get to 200bar and cut out on overload (it should go to 300bar easily) ...
I assumed the compressor was faulty and had it replaced ...
The new compressor would not even start without tripping its 10amp overload ...
On this compressor I measured the startup voltage/current which was 140v and 40amps respectively ...
So I took this compressor to another socket on a different DB but same main supply and it worked fine ...
I then took the old compressor to the same socket and it went to 300bar no problems ...

The only thing I can think of is Voltage Drop however the voltage at the first Socket is 217v ... hardly significant...
Plus everything else on the first DB seems fine as does anything else I plug into the first socket...

Any ideas???

 

[eeprom]

Well I've never heard of a 16A receptacle....but it sure sounds like a typical voltage drop issue. I'd measure the voltage at the breaker when the compressor is starting. The most culprit is the 75 m conductor. Another less favorable possibility is that somewhere in your circuit you have a poor connection, which is likely to be heating up.

One quick check would be to calculate the voltage drop of a 2.5mm conductor at 75m carrying 40A.

If it were my problem I would check voltage and current during start at the main panel board, at the sub panel, and at the compressor. The location of the voltage drop should be obvious.