Hi all
Cable type selection question
I'm looking at running a 500m cable underground to a farm water pump station. (Pump (4 amps) + Lights + GPO)
My plan was to run 4 core Neutral screen 95mm AL but have discovered that is not a common cable.
I don't trust the farmer not to cut the cable via Mole plough so we are going down 1m plus I was going to have the supply on RCD.
Based on price and my current thinking i'm going to run 70mm 4 core Circular TPS AL and run a separate Earth Wire. (reduce the supply fuse size)
The other way is to forget the RCD and just drive in a Earth at the pump shed.
Is this how others would do this job?
Farm pump - underground power supply cable type
Re: Farm pump - underground power supply cable type
So MD approx 15A, x Run approx 500 m; amounts to 7500 Am.
Max permitted V-drop of 11,500 mV, but allow 50% for mains etc to origin of this circuit so 5,750 mV available
That means you need a cable with max impedance of 7.666 mV / Am
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as for whether to run as PEN submain; over this distance I probably would, provided there won't be any parallel paths.
Not to save the cost of the PEC; but because you want the earthed equipment at this remote part of the installation to be at similar potential to the ground at that location.
Max permitted V-drop of 11,500 mV, but allow 50% for mains etc to origin of this circuit so 5,750 mV available
That means you need a cable with max impedance of 7.666 mV / Am
------------------
as for whether to run as PEN submain; over this distance I probably would, provided there won't be any parallel paths.
Not to save the cost of the PEC; but because you want the earthed equipment at this remote part of the installation to be at similar potential to the ground at that location.
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Re: Farm pump - underground power supply cable type
InterestingNot to save the cost of the PEC; but because you want the earthed equipment at this remote part of the installation to be at similar potential to the ground at that location.
I thought supply via RCD would have been a greater safety factor
Re: Farm pump - underground power supply cable type
In that long run, there will be quite a bit of capacitance; and that = leakage current if there's a PEC running close alongside.
There's certainly enough even on much shorter runs to make CF & LED lights flicker.
Hard to say whether the capacitance would be enough by itself to cause 'nuisance' tripping, but it will certainly lift the 'standing leakage' level closer to the trip level.
Remember the RCD doesn't trip at 30 mA, generally it's down around 24 - 27 mA; and isn't considered unsafe unless it trips at / below 15 mA.
So regardless of PEC or PEN submain, I would make it a submain rather than a subcircuit; and save the RCD for the final subcircuit(s) at the pump shed. If you want some level of protection for the submain cable, maybe a 100 mA unit. And if you want discrimination between the RCDs, a Type S.
There's certainly enough even on much shorter runs to make CF & LED lights flicker.
Hard to say whether the capacitance would be enough by itself to cause 'nuisance' tripping, but it will certainly lift the 'standing leakage' level closer to the trip level.
Remember the RCD doesn't trip at 30 mA, generally it's down around 24 - 27 mA; and isn't considered unsafe unless it trips at / below 15 mA.
So regardless of PEC or PEN submain, I would make it a submain rather than a subcircuit; and save the RCD for the final subcircuit(s) at the pump shed. If you want some level of protection for the submain cable, maybe a 100 mA unit. And if you want discrimination between the RCDs, a Type S.
- Rating: 33.33%