Generally transformers do not require an earth. But as an earth tail is part of the product, read the instruction that come with the equipment. If no instructions then the sensible thing is to connect to earth and bond to any metallic pipework connected to shower.
A copper pipe is NOT an electric cable, so it should not be used as such. Connect the earth wire to the Earth the the transformer is supplied from. (The transformer will use live and neutral, but where this is connected there will be an earth) Obviously you will need to extend the transformer earth wire.
[quote="murph78"]Thanks kbrownie The transformer will not be too close to shower so can i connect earth cable from tail loop to metal pipe of shower or is it better to earth it another way? CIrcuit is RCD protected[/quote]
You still need to connect the earth tail to the earth of the circuit, not just use copper pipework,supplementary bonding the copper pipework is normally required, but there must by a CPC(aka earth) connection to the appliance. If the circuits entering the bathroom are RCD protected, supp bonding under most circumstances can be excluded.
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