separate consumer unit

[solgen]

I have a job where the easiest solution is to provide a separate CU dedicated to PV (Incidentally this is the recommended way according to NICEIC ).

In the attachment is the drawing of how I this is to be connected. I assume this is correct?

Thanks

 

[JulianC]

Looks OK. However because of.....

this is the recommended way according to NICEIC

...I would be tempted to fit it on a new breaker in the existing CU. Then phone them up and tell them. Tee hee.

 

[solgen]

So what do you think of this arrangement?

 

[Marvo]

Yeah, I'm sure the supply authority will love that arrangement....

 

[JulianC]

Naughty naughty. That side of the utility meter is the DNO's responsiblity and not yours to mess with. Technically known as 'bypassing the meter'.

Is this some sort of test? Do I pass? What's my prize?

 

[solgen]

Ha Ha - yes you've passed congratulations! No prizes I'm afraid just my thanks for confirmation.

If the PV CU is only supplying electricity, then technically bypassing the utility meter isn't a problem! But better safe than sorry to not do this, besides feeding the PV supply (which is already being metered by its own total generation meter) then feeding it through the utilities meter doesn't make much sense. The whole point of the PV generation is to supress what is coming in via the utilities meter!

Cheers

 

[Marvo]

I thought the second schematic was a joke at first...Is the PV system exporting power during low local demand periods?

 

[solgen]

Potentially exporting yes!

 

[SolarCity]

I actually think a seperate consumer unit is a good idea - space permitting.

However, it is news to me that this is what the NICEIC recommend. It certainly wasn't mentioned on their shoddy course.

As has been mentioned, fiddling with suppliers side is a no-no. From what I gather, inverters DO draw a tiny amount of power so you could technically be charged with defrauding the supplier. Even so, you shouldn't mess with it and there is no need to do so.

We have enough problems with pulling their sodding fuses!

 

[malcolmsanford]

I wonder if the NICEIC have a department created called "The Regulations as we see them" I know the Regs are written by a consortium that include the NICEIC but if there is a spare way in the existing CU and it's RCD protected,why give the client the extra expense of installing a small single way board, as the chances are if there is a spare way that is where your going to pick up the supply of that new board.

 

[JulianC]

If you did connect up your PV the naughty way as per diagram 2, you'd be paying your utility supplier for all the electricity you generate and use as it would be passing through their meter.

I tend not to pay any attention to NICEIC recommendations, mainly due to their overinflated idea of their own self-importance. I'm with Elecsa for a start and tend to base my decisions on what it says in BS7671 or what they tell me.

The only time I fit PV on a new CU is if the existing CU is full or if it is some ancient decrepit thing that I really don't want to mess with. Don't even need RCD protection for the vast majority of jobs.

 

[solgen]

NICEIC may publish a document "recommending" separate CU's for PV, however, it will only be a recommendation as far as I know. So providing you are confident in what you are doing the usual standard according to MCS guidlines will suffice.

 

[malcolmsanford]

If you did connect up your PV the naughty way as per diagram 2, you'd be paying your utility supplier for all the electricity you generate and use as it would be passing through their meter.

I tend not to pay any attention to NICEIC recommendations, mainly due to their overinflated idea of their own self-importance. I'm with Elecsa for a start and tend to base my decisions on what it says in BS7671 or what they tell me.

The only time I fit PV on a new CU is if the existing CU is full or if it is some ancient decrepit thing that I really don't want to mess with. Don't even need RCD protection for the vast majority of jobs.

Isn't that reliant on the type of invertor you use, as per reg 712.411.3.2.1.2 (whew what a reg). It may have changed but I thought the majority of the invertors did not have this capabilitiy, but if wrong do apologise.

 

[JulianC]

I've used SMA Sunnyboys and Fronius IG inverters in a domestic setting, and am soon to use the Mastervolt XS range - all these contain transformers for 'galvanic isolation' and therefore don't need a (rare and expensive) type B RCD. For these situations you'd only need a standard type AC RCD if it was called for under the regs. as per usual (cables sunk less than 50mm in a wall and so on.....)

Also, it transpires that a lot of SMA's transformerless inverters don't require the use of an RCD either. More info here: http://www.electriciansforums.net/p...11-transformerless-inverters-type-b-rcds.html

 

[PeteC]

In your arrangement, the PV supply doesn't bypass the meter, but does tap onto the utility wiring (upto the consumer unit). The PV connection wiring would have to meet supply rating ie.100A 16kVA pfc (probably not cost effective). If supply connects to isolator before consumer unit, than thats fine to connect onto. Recommendations for separate DB for PV connection come about because of continuous load de-rating factors of the mcbs. Some manufacturers derate their mcbs (check proteus specs~ 75%!) with cont' load because of operating temp. ranges~ they can also de-rate the adjoining mcbs (could cause nuisance tripping if the adjoining circuits are under continuous high load themselves: not that probable on domestic installs)~ try to incorporate a spacing (blank) either side of the mcb(s) used to connect the inverter(s). If you find no spare positions on board, you can remove 1 or preferably 2 circuits, and move them into the new DB, giving you spare ways for the DB protective device. Shuffle the mcbs so you have the DB at end (with space to one side)~ if a 2nd removed, then you have space either side (the DB protective device can be at continuous load as PV device). Doing this has one drawback~ the circuits moved to the new DB have been altered (by introduction the distribution circuit) and they become part of the "altered" installation, and those full circuits have to be included in the installation certificate ie inspected and tested to verify they meet current regs. You may need to choose the circuits to move, so they avoid needing major upgrades to meet regs~ need to add additional protection (RCD) most common outcome.