Chartered engineer required for a small job

Hi Zoe,

Why are two separate systems required? Are any of the supplies at HV (or sharing the earthing system with an HV supply)?

Or radio (e.g. HAM rig) or just TT for an outbuilding or EVs?

Morning

The earthing system coming into factory at present is TNS system. However the process installation team have put 4 control rooms in using 3 ph N&E but other control rooms that they have installed are only using 3ph & E - no Neutral.

We have given our opinion to the client and also the process installation team have had their opinion heard by the factory. However the client/project manager wants an independent view/opinion on this and a report of the findings/opinion/best way forward.

To conclude, not using a neutral in the other panels will cause any conflict in the earthing system.

There is generally no issue with 3P and E without N, actually it is quite common for single items of machinery , but only if none of the loads connected require a neutral connection - i.e. have a single phase aspect.

What should ring alarm bells is if someone is hoping to use the earth as a substitute for the missing neutral for some load that is not perfectly 3 phase balanced. This would cause current to flow in the earthing even in a non-fault condition. In the UK this is a big no-no, although seen in imported kit sometimes, and often the easiest fix for a small single phase load is to add a transformer wired between 2 phases on the primary to step down to the single phase supply voltage needed to supply the out of balance load(s).
Obviously if more than a little current is needed then it is better to supply a 'real' neutral.
Mike.

There is generally no issue with 3P and E without N, actually it is quite common for single items of machinery , but only if none of the loads connected require a neutral connection - i.e. have a single phase aspect.

What should ring alarm bells is if someone is hoping to use the earth as a substitute for the missing neutral for some load that is not perfectly 3 phase balanced. This would cause current to flow in the earthing even in a non-fault condition. In the UK this is a big no-no, although seen in imported kit sometimes, and often the easiest fix for a small single phase load is to add a transformer wired between 2 phases on the primary to step down to the single phase supply voltage needed to supply the out of balance load(s).
Obviously if more than a little current is needed then it is better to supply a 'real' neutral.
Mike.

Thank you so much for your response - it is much appreciated, and is along the same thinking as us. The site in question just needs this information in a report form following a site visit.