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Caravan electrical hook up?

I've been asked to install a supply to a hook up for a caravan in a garden.

I see that the connection of a PME earthing facility to any metal work is prohibited, is there anything else I may have overlooked?

Thanks in advance :)

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0 gkenyon over 4 years ago

mapj1:

I do not think we should talk about 'the' earth voltage as if there is some 'plate at the end of the universe' (apologies to fans of Douglas Adams) at zero volts and we must connect to that by putting an electrode far far away. This is a simplification that makes text books easy to write.

Rather I think there are many things we can refer to as 'an earth', but these are not always at the same voltage as each other.

What I think is more important for the shocked user is the local voltage gradient - we need the car, caravan or boat to have the smallest sensible offset voltage relative to whatever else is in touching or stepping range.

Mike,

The gradient depends on the electrode arrangement, but in the case of one to three rods in line uniform soil, drops off over a relatively short distance of 2.5 m by a drop of about 70 % (See Table 16 in BS 7430).

So yes it depends on where the electrode is, but if it's one side of the van, the influence of the electrode at the other side of the van is only 30 % of what it was ... but you can touch any metal frame earthed via the rod !

This is important, if you just happen to be standing over any buried metalwork connected to the PME earthing system, and there's nothing connected to PME on the other side of the van to help equalize the rod potential with the PME system ...

I think in this case Zoomup's comment regarding the high resistivity of driveway materials is probably more pertinent to shock risk reduction.
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0 gkenyon over 4 years ago

mapj1:

I do not think we should talk about 'the' earth voltage as if there is some 'plate at the end of the universe' (apologies to fans of Douglas Adams) at zero volts and we must connect to that by putting an electrode far far away. This is a simplification that makes text books easy to write.

Rather I think there are many things we can refer to as 'an earth', but these are not always at the same voltage as each other.

What I think is more important for the shocked user is the local voltage gradient - we need the car, caravan or boat to have the smallest sensible offset voltage relative to whatever else is in touching or stepping range.

Mike,

The gradient depends on the electrode arrangement, but in the case of one to three rods in line uniform soil, drops off over a relatively short distance of 2.5 m by a drop of about 70 % (See Table 16 in BS 7430).

So yes it depends on where the electrode is, but if it's one side of the van, the influence of the electrode at the other side of the van is only 30 % of what it was ... but you can touch any metal frame earthed via the rod !

This is important, if you just happen to be standing over any buried metalwork connected to the PME earthing system, and there's nothing connected to PME on the other side of the van to help equalize the rod potential with the PME system ...

I think in this case Zoomup's comment regarding the high resistivity of driveway materials is probably more pertinent to shock risk reduction.
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Caravan electrical hook up?

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