Garage supply and solar panels / battery

[Mikey D]

Ok so I have a 10mm2 3 core armoured cable that I've laid underground. To my garage , I'm getting solar panels on the roof and battery storage too ...
The armoured cable is coming from the house consumer unit which has a 30 ma RCD .

Now question is what size MCB or indeed rcbo do I need and do I need an RCD on the new garage consumer unit ? I mean I don't think it's ideal having RCD in garage unit as well as being fed from the house consumer unit via RCD .

Or do I just have main switch on garage unit and use rcbo on the circuits ?
I'm just gonna have a couple of lighting circuits and a 13 amp socket ring main , possibly a couple of 16 amp sockets ..
Also I'm not sure what circuit protection the solar/ battery would require

Thanks in advance for any input ,Mike

 

[Kram]

Does your house unit have a RCD that feeds all MCB's or seperate RCBO's? If its the former, then an issue in the shed will shut off the house and cause great shouting
It is a great regret that the idiot that fitted out new unit used an overall RCD rather than RCBO's.

I'd highly recommend having the shed fed from a seperate RCBO or MCB without and having the RCD/RCBO in the shed unit.

 

[MetalMonkey]

The way I would do it would be to split your incoming tails from the meter, to feed your existing house CU and a separate mini consumer unit with a main switch, and then use this to supply your SWA.

Then in the garage you can install a consumer unit with RCBO as required, appropriately bi directional rated for the solar obviously.
That way you will avoid problems with selectivity for RCDs tripping and just generally make the install easier and neater.

 

[Mikey D]

Thanks both for the suggestions The small consumer unit used to be for economy seven feeding storage heaters and emersion heater .so I could get a smaller consumer unit (the same make with a double pole main switch for the garage supply and use that one in the garage ?

 

[RaceDiagnostics]

Like this one I used to supply my 10mm swa to the garage.

 

[Jelly_Sheffield]

The correct MCB to protect your spur will depend on the length of the cable run, calculations are in the 18th edition and have doubtless been reproduced online.

I would strongly recommend that you have a sub board in the garage which is fitted with either RCBO's or a High Integrity setup to ensure lighting is split from other circuits, from a safety standpoint.



I have a very similar setup to yourself and the workshop feed is connected to a 40A type C MCB in a dedicated mini consumer unit with it's own meter tails (split in a pair of 150A connector blocks) under the main CU.

That feed goes into a sub board (in the form of another CU) in the workshop which has a high integrity setup, with a main switch and 3 RCD's.

RCD1: 1 × 6a Type B MCB for the left hand lighting circuit, 1 × 32a Type B MCB for a ring main feeding 13A sockets

RCD2: 1 × 6a Type B MCB for the right hand lighting circuit, 1 × 32a Type C MCB feeding a Commando switch socket for Welders which is interlocked to two extraction fans (turn on the socket, and the fans come on automatically),

RCD3: 1 × 32a Type C MCB feeding a dedicated commando socket for the Rotary Phase Converter, 1×16a MCB for a radial circuit feeding the humidistat and dehumidifier.

It's overkill, but:
- I knew I wanted to have the lighting to be redundant (hence splitting into two circuits each of which lights the whole length of the workshop on one side, each on separate RCD's).
- I also wanted to ensure that a trip on the "regular" sockets from the normal sockets couldn't unexpectedly cut the RPC power whilst a machine was running.

 

[Jelly_Sheffield]

I mean I don't think it's ideal having RCD in garage unit as well as being fed from the house consumer unit via RCD .

It kinda of is ideal...

They won't prevent each other from tripping, but the RCD closest to the fault will trip first. So if you accidentally trip something in the garage, you won't cut power to any other circuits in the house.

Also and perhaps more importantly, if you have an old-school installation with a single Voltage-Operated RCD that protects the entire house, that isn't offering the same level of protection as modern Current-Operated RCD's do, which would definitely be desirable in a workshop environment.

 

[Misterg]

It kinda of is ideal...

They won't prevent each other from tripping, but the RCD closest to the fault will trip first.

No.

For the same rated RCD, which trips first will be essentially random, depending on the exact characteristics of each RCD at the fault level and operating temperatures prevailing.

Better to feed the garage from a non RCD circuit and fit RCD / RCBO in the garage CU as already stated above.

 

[Jelly_Sheffield]

No.

For the same rated RCD, which trips first will be essentially random, depending on the exact characteristics of each RCD at the fault level and operating temperatures prevailing.

Better to feed the garage from a non RCD circuit and fit RCD / RCBO in the garage CU as already stated above.

I agree that the garage CU should be fitted with RCBO's or RCD+MCB's in a high integrity configuration.

I also agree that having multiple modern current operated RCD's protecting a single circuit would be largely pointless.

However if the main incomer is going through a single "Voltage Operated RCD" (more correctly called an Earth Leakage Circuit Breaker, but often described as an "RCD" as they do the same job) which is a configuration common to installations of a certain era, then the presence of the ELCB shouldn't be seen as a reason not to install modern RCD's downstream (and the modern RCD/RCBO will trip first for almost any fault that occurs on a final circuit it protects).

 

[MetalMonkey]

However if the main incomer is going through a single "Voltage Operated RCD" (more correctly called an Earth Leakage Circuit Breaker, but often described as an "RCD" as they do the same job) which is a configuration common to installations of a certain era, then the presence of the ELCB shouldn't be seen as a reason not to install modern RCD's downstream (and the modern RCD/RCBO will trip first for almost any fault that occurs on a final circuit it protects).

Id suggest it would be fairly unlikely to be a voltage operated circuit breaker. They are somewhat of a rarity, done away with in the 80s IIRC.

RCDs are, IME, likely to be found on 16th edition single or split boards and will be "current detectors". In which case daisy chaining them is not the best idea because you can't guarantee which will trip. In addition, if solar generation is to be installed in the garage, back feeding some RCDs has the potential to damage them so that also needs consideration (and is now a requirement of amendment 3)

Obviously without all the details of the existing installation it is impossible to say anything for definite.

 

[aesmith]

Not mentioned, maybe because I'm wrong. I believe that if you have armoured cable (SWA) for the whole route from house to garage DB then there's no need for RCD at the house end.

I have the same layout as you but the SWA is split off before the house CU protected by a fused isolator. The garage has a main switch DB with RCBOs for each circuit.

New suitable RCBO was installed in the garage DB by the guys installing the solar. Just one circuit because the battery is on the DC side of the inverter rather than having a separate AC connection.

You will probably also need a data cable to the house so that the system can monitor import/export at the supply point and control the battery to suit.

 

[addjunkie]

You will probably also need a data cable to the house so that the system can monitor import/export at the supply point and control the battery to suit.

If you haven't put the swa in yet to the house you can get SWA with power and data cables in it used for car chargers etc. saves a lot of mucking about if your digging trench anyway.

 

[Gareth J]

The suggestion to not have an RCD at the house end of the SWA is further reinforced by the fussiness of some solar inverters. some will trip out a 30ma RCD. Indeed a couple of ones here specify 100ma. So they are best fed from their own mini CU and appropriate protection with non RCD stuff protecting the cables before them.

 

[Robotstar5]

Not mentioned, maybe because I'm wrong. I believe that if you have armoured cable (SWA) for the whole route from house to garage DB then there's no need for RCD at the house end.

That's what I did when I replaced my CU some years ago, I fitted a high integrity CU with the garage fed off a non-RCD protected MCB.

 

[brightspark]

I agree that the garage CU should be fitted with RCBO's or RCD+MCB's in a high integrity configuration.

I also agree that having multiple modern current operated RCD's protecting a single circuit would be largely pointless.

However if the main incomer is going through a single "Voltage Operated RCD" (more correctly called an Earth Leakage Circuit Breaker, but often described as an "RCD" as they do the same job) which is a configuration common to installations of a certain era, then the presence of the ELCB shouldn't be seen as a reason not to install modern RCD's downstream (and the modern RCD/RCBO will trip first for almost any fault that occurs on a final circuit it protects).

and thats why you put a 100ma time delayed rcd at source to feed the garage if its a tt supply

 

[Onoff]

overkill

Would "overkill" have been all RCBO? Or should that have been "ideal"?

 

[dobbslc]

and thats why you put a 100ma time delayed rcd at source to feed the garage if its a tt supply

That's probably what I'm going to do what I get time.

 

[aesmith]

Would "overkill" have been all RCBO? Or should that have been "ideal"?

It would same space to have six RCBOs instead of three RCDs and six MCBs, a well as giving more discrimination.

I do vaguely remember some criticism of all-RCBO when they are SP so don't disconnect N from the failing circuit. Whereas typically RCDs are two pole. I don't know how big a deal that is, but if it matters the using SPSN RCBOs would answer that point.

 

[Misterg]

However if the main incomer is going through a single "Voltage Operated RCD"

It isn't - see photo above: 30mA RCD

 

[Misterg]

How far is the garage from the house, and what is it made of (metal or not)?