UK Generator connection to mains supply questions

[Chris Wilson]

I want to use a manual change over switch to safely connect a 21kVA single phase tractor PTO powered generator to my mains supply in case of power outages. The cable run from the generator to the outside mains incoming box will be about 40 meters. I intend to use 16mm SWA for that run. The generator control box has metering, fusing and an RCD. It's modern and made entirely by Mecc Alte. Not some Ebay Chinesium device.

Once the SWA is at the outside wall box where the underground feed from the supply company exits and the meter and master switch, 100 Amp utility company fuse is located, can I delete the two pole fused master isolation switch and use the two pole 125 Amp break before make change over switch and separate fuse as both an isolation switch to the house distribution panel and as a change over switch? I see a similar question was recently covered, but it was unclear as to whether doing this was advised against or regulated against.

Space inside the wall mounted outside box is limited. The alternative is to bring tails outside the box, to another water proof cabinet with the change over switch in, and return the cables back to the utility company box. Messy...

The property, a domestic bungalow, and has a PME earth system, how should the cabling from the generator be wired with regard to earthing at either end?

Thanks.

 

[davesparks]

Can you post a picture of the meter box so we can be clear on what switchgear is currently installed in there?

 

[Chris Wilson]

Can you post a picture of the meter box so we can be clear on what switchgear is currently installed in there?

I should be able to do that tomorrow, but basically incoming SWA service cable from underground to 100 Amp service fuse, then meter, then to a two pole fused switch and onwards to the consumer unit within the house. There are a couple of junction boxes in there, too, where outputs FROM the CU in the house splice into SWA cables to outside lights and to the garage. Thanks for your reply.

 

[Chris Wilson]

Here's a photo of the inside of the supplier's wall cabinet, the fused switch to the consumer unit inside the house has an 80 Amp fuse in it. The other fused switch has a 63 Amp fuse in it and serves a dedicated panel in the garage for a 63A socket for my TIG welder.

 

[UNG]

Looking at the wiring in that meter box I would suggest you employ an electrician as I doubt that the additions in that meter box have been ever been tested and parts do not appear to be compliant with the regulations

With a 2 pole changeover switch I would have concerns about the earthing still being connected to a PME system in the event of a power cut as it could be unreliable as an earth point and in the event of a fault could introduce fault currents into other properties located nearby

 

[pc1966]

That looks rough, and there are boxes feeding various bits that kind of look like no over current protection, etc. As @UNG says you really should be getting that lot tested and documented before considering anything new.

As a first point of principle you should get an isolator switch that isolates everything, so all of the various things are down-stream of that including any transfer switch. It is the only safe and above-board means of working on the supply side of any CU to fit or fix the transfer switch, etc.

You must have an independent means of earthing any generator as you cannot assume the supply earth connection would be intact in the event of a fault that made you need to use the generator. A generator of that size would still be a TN supply (earth and neutral common at the generator) but that needs to be referenced to the true Earth by means of a rod or similar.

 

[snowhead]

Althought the wall cabinet is owned and maintained by the property owner, the space inside is (supposed to be) reserved for the DNO and Energy supplier, apparently it's a condition of supply and is mentioned in their terms and conditions.

So if you are proposing altering any of what's there (excluding meter and fuse cutout) the simplest thing to do would be to move all the switch fuses to a new adjacent box and install the changeover switch in there.

If the meter needed to be changed to a "Smart Meter", either by request or the existing one going past it's use-by date or it failing, then I suspect the supplier would refuse to fit one as there would not be enough space.

 

[loz2754]

there are boxes feeding various bits that kind of look like no over current protection,

OP says they are fed from the consumer unit in the house.
But I agree, it looks very amateurish.

 

[Chris Wilson]

OK, thanks for then replies, I imagine various things have been added on over the years and it has become somwhat of a pig's ear in there. What sort of secondary box would be required, are the regulations about that? I would like to have one mounted and ready for an electrician to populate, with any cable gland holes drilled to suit. Do cables between two boxes need to be SWA, or can T&E or tails in conduit be used? The SWA cable feed to the garage would really need to remain as it goes straight down into concrete and I will not be wanting to start digging up the concrete...

 

[UNG]

You could fit a similar box to what you have now

You are being redirected...

They have a few different sizes available so you should be able to get one to fit all the equipment you need