Mobile Crane Grounding

[lee5]

We have an old dockside crane which was converted from diesel to electric 20 years ago. It is supplied with 3 ph and earth (combined earth and neutral) the IEE would class this as a TN-c system. The crane runs 50 meters either side of the supply point. An inspector has called this into question and has stated that TN-C is only applicable to fixed installations. I have checked out BS2452:1954 but the only thing in their about earhting is "The earthing shall be provided independently of the contact between the track wheels and the rails."

Can anyone help on whether a combined earth and neutral is acceptable in a mobile system such as this or should we have a seperate earth and neutral

 

[RajT]

A combined earth and neutral is perfectly acceptable and I assume that you have earthed the neutral some where along the track with say a "fastoon" type cabling or a reeling drum arrangement.
The inspector is incorrect in his statement in that no legislation states that the TN-C is ONLY applicable to fixed installation.