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Standby generator earth?

Advice required on the connection of a mobile standby generator. We have a sub station with a LV Earth to which the star point of the supply transformer is connected. The supply to is 415V 3-phase + Neutral. Also connected to the LV earth is the earth bars & metalwork of the LV switchgear. We have a separate earth for the HV switchgear metalwork. We have a connection point for connecting a standby mobile generator when required, and this connects to our LV board and supplies power by way of a changeover switch. This is interlocked with the mains supply so that only one source can be on at any one time. Now we have had a visit by some copper thieves and all the earthing has been nicked. I am in the process of installing the earths again, but not quite sure what to do with the generator earth. I thing I'm right in saying that a standby generator should have its own independant earth, but I am concerned that this will get nicked again. What I'm thinking of doing is running an earth connection from the generator point to the LV earth inside the sub. If I need to connect a generator to supply standby power if mains power is off, then the generator earth would be connected to the LV earth, and I would remove the link connecting the transformer neutral point to the LV earth. Replacing this link and disconnecting the generator when mains is to be restored. Is this OK?

Reply to
BIGEYE
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---------------------------- If I read you right, the original connection should be fine. The neutral of the 415V net is tied back to the LV earth and you have apparently had no problems with this before. The extra connection won't hurt but is it necessary?

However: Check local code.

Don't fiddle with opening and closing ground connections-most code systems frown on any form of switching of the neutral or ground. It is not necessary to do so and it could lead to problems.

Reply to
Don Kelly

Is your transfer switch 'solid neutral' (always a connection between normal power neutral, standby power neutral, and load neutral), or 'switched neutral' (4 poles that transfer)? If solid, consider this,

From the genset run 3 hots plus neutral to your transfer switch. That is it. Do not install a dedicated ground for the genset. If the genset neutral (star point) is electrically connected to the genset 'ground' connection point and the genset frame etc.; and the genset neutral connects to the normal supply neutral; and the normal supply neutral connects to the LV ground at some point (LV earth at transformer secondary); then you already have a connection from the genset star point to ground. Making another connection might actually be bad as now your neutral current can (will) flow over ground.

I have some concern over your proposed solution above because, what are the chances that everyone will do the correct switching, safely, every time, for the next forty years? I don't know. It feels to me like a loose end hanging out there. However, it appears you are in the UK and I do not know what is and is not OK in UK. You guys seem to be on top of your earthing though, with all the 'TE' and other connections your standards spell out. Where I am there seems to be a lot less focus on it, and a lot done differently from one install to the next.

j
Reply to
operator jay

My view (ignoring "code" for the purpose of discussion) is that the utility neutral should never be switched. It would be bonded to ground at the service entrance panel(s).

The generator should have a ground rod near the installation and everything metal should be bonded to it. But the general set ground should also be connected to the utility ground.

The transfer switch would transfer the hot load wires from utility to generator and in the "generator" position it would connect the generator neutral to the utility neutral. If you will, the "neutral" load connection will be permanentsly bonded to the utility neutral.

The advantage of this is that when the transfer switch is in "utility power" position, the generator is completely disconnected. The cabinet would be grounded but all the generator wires would be "floating" and available for testing.

Reply to
John Gilmer

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