Street lighting

A specification for street lighting requires an earth electrode at the beginning of the circuit and at the end of the circuit both having an Ra of not more than 20 ohms (Is this a common spec?.) The single phase circuit will be lifted off a DNO PME supply and supply 16 columns of galvanized steel construction.  My view would be that the columns will offer a relatively good connection with earth when considered globally. I intend to measure the arrangement using the two clamp method which we use for lightning system earthing. I would be surprised if it didn't offer something below 10 ohms.

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  • It sounds like the specification in BS 7430 for TN-C-S arrangements to street furniture, but there are subtle differences e.g. BS7430 requires an electrode at the point of supply (not necessarily the start of the circuit) and at the far end of the circuit, and the objective is to bring the N-E resistance down to 20Ω at any point in the circuit not just the electrode resistance, with additional electrodes being added as necessary.

    Disclaimer: This isn't my ballpark, just looked it up out of interest. I don't know if there are ENA or DNO specs that supersede this.

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  • It sounds like the specification in BS 7430 for TN-C-S arrangements to street furniture, but there are subtle differences e.g. BS7430 requires an electrode at the point of supply (not necessarily the start of the circuit) and at the far end of the circuit, and the objective is to bring the N-E resistance down to 20Ω at any point in the circuit not just the electrode resistance, with additional electrodes being added as necessary.

    Disclaimer: This isn't my ballpark, just looked it up out of interest. I don't know if there are ENA or DNO specs that supersede this.

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