Discuss Generator changeover switch installation in the Electrical Forum area at ElectriciansForums.net

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Morning all,

Before I start I don't need all the "you're supposed to be a qualified electrician, you need to go back to college' brigade to jump in as I am asking for advice! I am fully qualified however I haven't done much with generators since my training.

I have had a potential client ask me about installation of a generator to power the house in an emergency when the mains suffers a power cut. Living out in the sticks this can happen 2-3 times a year for them.

They are wanting to install a 6KVA 5.2kw generator which is mainly there for lights and some power to keep them tied over until mains is restored. This one is what they're looking at: Generator

So the way I am looking at approaching this is as follows.

1. Install a generator changeover switch in a separate enclosure next to the consumer unit. Something like this: Changeover switch

2. I will then feed the supply from the mains and generator into this and then run a set of 25mm tails into the existing board

3. I will also install something like this of the correct amperage to protect the generator cable: Double pole MCB

4. So the generator cable will go from a female commando socket on the external wall, to the double pole MCB which will be in an enclosure. From the double pole MCB I will then run the feed to the changeover switch.

5. Double earth rod for generator to get the reading below 200ohms. Experience of installing rods around this way usually means sticking in 2 x coupled 1.2m 16mm earth rods to get the desired reading. This usually gives somewhere around the 50-70ohm reading. There is an earthing terminal on the generator so I intend to connect this to a earth bar, along with the cable from the rods and then run a 16mm cable to the MET inside the CU. This should then ensure the operation of the existing RCDs or have I got that wrong? Earth terminal can be seen here.

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They don't want a big bulky box outside the house hence looking at this all being internally mounted apart from the female commando end.

Is there anything I am missing? Happy for any advice/better ideas.

Thanks in advance.

Carl.
 

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Lucien Nunes

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There is an earthing terminal on the generator so I intend to connect this to a earth bar, along with the cable from the rods and then run a 16mm cable to the MET inside the CU. This should then ensure the operation of the existing RCDs or have I got that wrong?

That will depend on whether the neutral of the generator output is earthed. If not, the system will run as IT and RCDs will not work. You will need to check and connect appropriately.
 

pc1966

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As Lucian says, you need to be sure the generator is a TN-S supply. At that rating I would imagine it is, but you really should ask / test it. Unfortunately the documents offered for download are not telling you much. Some give you enough of a manual to tell, for example:

Also I would be very surprised if the generator did not have output protection in the form of both a MCB for over-current and a RCD for the sockets. It will be 30mA (unless hard-wired, etc) so you need to consider total house leakage when on standby-power. They might need to consider opening a few non-essential MCBs to control that. If you have a suitable clamp ammeter then you could do a quick check on the existing tails to see what it runs at normally.

Good to see double rod! Generally getting deeper helps more than doubling up (if soil type permits) as less drying or freezing of the top half meter or so to impact on the rod's effectiveness.
 

James

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one thing to note, That generator is NOISEY, i have a similar one that i have mounted in a sound proofed outhouse with an extra silencer to keep the noise to acceptable levels.
outside with no extra sound proofing, will annoy you even when you are indoors.
 

brianmoooore

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Installed loads of tractor driven emergency generators for dairy farmers back in the day, when there were government grants available for them.
There should be a isolator switch fitted beside the changeover switch, in the main supply. This gives a second layer of isolation between the generator and any power company worker that may be working on the line, and allows you to ensure that the change over switch is not operated under load. A useful addition to the isolator switch is an indicator lamp, that allows the customer to see when mains power has been restored.
These generators were in the range 5kVA to 15kVA, and were always supplied with a rotary change over switch matched to the output of the generator. Had many arguments/discussions with customers convincing them that in most cases these switches were useless, and that they needed an (expensive) larger replacement, matched to their total supply capacity.
 

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