question

Hi,

I found it was easier to have the ET112 receive the line meter tail directly and then loop over from the ET112 line output to the main switch line input with an off cut of meter tail. But have the neutral meter tail go direct to the main switch neutral connection. Then you'll need a 315mA 250V+ rated fuse either in a DIN rail carrier if you can find one or just as an inline glass fuse between the ET112 neutral connection and the main switch neutral connection.

Note that you must NOT connect the ET112 neutral to the consumer unit neutral bar because if you do that then when the main switch is turned off, the neutral bar will rise to 230V since it is being fed via the ET112. This is obviously dangerous.

If you do it like above then the bus bar coming out of the main switch can just feed the bottom of the MCBs/RCBOs as normal. If you're using a split RCD board then a different arrangement might be better though.

Some might argue that the main switch should always be the first device in the consumer unit and that all other devices need to be isolated when the main switch is off. I personally don't see an issue as long as you heed my warning about not using the neutral bar and also assuming you have a way to isolate the meter tails upstream of the consumer unit of course. Anyone know if there is a reg that says the main switch must isolate everything contained in a CU?

The alternative is to wire to the main switch first as normal and then have a link wire between main switch line out and the ET112 line in and then another link wire between the ET112 line out and the first MCB/RCBO line in where you would also install the bus bar to link to the other devices. There is nothing inherently wrong with this approach but I just preferred to use the standard bus bar arrangement rather than having extra link wires. If you do decide on this latter arrangement then obviously the ET112 would get its neutral connection from the neutral bar, again via the 315mA fuse.

Last option is to install the ET112 in a separate enclosure where you don't need to worry about bus bars etc. But in that case it would be upstream of the CU and again would depend on having an isolator switch further upstream.

Hope this helps,

Craig.

ps. I'm not qualified to advise you in any official capacity so as always, check with an electrician.

RS Components fuse holder I used: https://uk.rs-online.com/web/p/fuse-holders/2375259/

And fuses: https://uk.rs-online.com/web/p/cartridge-fuses/0563677/

Fit it after consumer switch, easier and safer to fit. Ensure you switch off any inverters/chargers, PV generation as well!

Good Luck.

It does seem a surprising question - "I've designed my system, so where does the energy meter go?". As such, I would prefer to say, it depends - what are you using it for? Especially given, there are, for example, some ESS scenarios where a meter is not required.