Voltage Drop

[Philpatton]

Hi everyone,
Just a quick post about an issue we recently had with our Thetford Fridge. When we plugged the caravan into the mains supply on site, after a few minutes, we got an error 8 message on the screen. So, I switched to gas and thought nothing more about it, other than to get the 'van booked in for a repair.
As the evening wore on, I realised that we were 50m from the power supply. One cable was 2.5mm2 at 25m and the next cable we used as 1.5mm2. The following morning, I made a bee line for a nearer power source, and plugged the 2.5mm2 cable into the closer supply, and voila, the error message disappeared.
I know this is voltage drop, and I know that using 2 cables of varying cross sectional area would lead to this, but until I pieced it all together, we could have ended up with running the fridge on gas for the next 2 weeks.

 

[ProfJohnL]

Hello Philip,
According to Thetford's trouble shooting notes I understand if the supply voltage at the terminal of the fridge falls below 20% of a nominal 230V (184V) then the display will show code 8. That is a voltage drop of 46V.!

Whether your extended EHU cable was the main culprit is uncertain, because the Thetford's threshold level of 184V will be a fixed value, whereas the mains supply will vary not only because of your extended cable, but also dependant on how much current all the other pitches are using, How long the sites infrastructure cable is and the actual supply voltage entering the caravan park. It could be you saw the fridge during a high demand time at the site which dragged the voltage down.

Just out of interest, your 25M long 1.5csa Ehu will have an effective resistance of .665 Ohms and the 2.5csa EHU a resistance of 0.399 Ohms adding 1.1 Ohms to your circuit. Bearing in mind that the voltage drop is proportional to the current being drawn in a circuit and is given by V = I x R where V is Volts, I is the current in Amps and R is the resistance in Ohms.

If you were using the full 16A the volts drop due to the two EHU would be 1.1 x 16 = 17V IF you were only using the fridge which consumes no more than 200Watts which at 230V is 1.1A, the voltage drop due to the EHU's would only be 1.21V

Neither of these EHU wold be enough to drop the supply voltage to the fridge by 46V so its either down to supply issues on the site or voltage sensing circuit in the fridge being faulty.

 

[GStockton]

Agree with the Prof. But was this a UK site? If so the Electrical regulations BS 7671 AMD 3 state that the Maximum distance from a Bollard to a Caravan pitch is 20 metres and the Maximum length of hook up cable is 25 metres, Regs Also State Min CSA of the lead to be 2.5mm.

So where is this site? and does it have its yearly Electrical Condition report?