2 inverters

[bumcrack]

If we lived in B&Q world where solar inverters plugged into a bedromm wall socket, great !

But we don't. It's a dedicated circuit to a fixed piece of kit, that is akin to an immersion heater, cooker, burgular alarm..

you dont howl 2 cookers into the same mcb?

 

[moggy1968]

depending on your definition radial circuits apply to all kinds of circuits.
A storage heater is a radial circuit, a cooker is a radial circuit, a lighting circuit is a radial circuit. A radial circuit is just a circuit with a begining and an end, not just a socket radial circuit.
as I said, it depends on whether you regard the PV array as one installation or not, if you regard them as 2 seperate installations how do you get around the 2 meters and 2 installations at the same address problem?
I wouldn't combine the PV at the MCB, I would combine them either at an isolator or in a suitable enclosure with appropriate connectors, then connect them to a single meter and from their to an MCB.
not had to do it yet but I think thats how I would do it.

 

[BruceB]

I suggest it is generally better to have the inverters on separate mcbs. A fault on one is less likely to affect the other. But it is not always essential, for instance micro-inverters have many on a single mcb. Read the installation instructions. You will find that for instance on the SMA TL series (and perhaps others) that the manufacturers require them to be on separate mcbs.

There are similar considerations about sharing rcds.

Regards
Bruce

 

[johndpar]

Hi Bruce (Hic! here)

I bow to your experience as always, but...

I know what it says in the SMA installation manual but I'm not sure they mean it!

Load disconnection unit
You must install a separate line circuit breaker for each inverter in order to ensure that the inverter
can be securely disconnected under load.

And by Line circuit breaker they do mean MCB as explained in http://files.sma.de/dl/7418/LSS-UEN114031.pdf

However the intent of their statement is that each inverter can be securely isolated and here in the UK at least we would be fitting a lockable AC isolator to each inverters AC connection. After all, MCBs should not be used for functional switching which is what the sentence above implies.

I reckon MCBs are just protecting the wiring. It is up to the equipment to protect itself (internal fuses) so as long as the wiring is rated for the total load and the MCB is the right rating for the wiring I see no problem with a single MCB.

Am I wrong?


Regards

John

 

[BruceB]

Not necessarily wrong. German/English translation can leave ambiguity! Some inverters specify a maximum mcb size and by doubling up you may exceed that. An extra mcb does not cost much. On a point of detail I think you will find that mcbs CAN be used for functional switching. For instance many shop lights around the country.

Regards
Bruce

 

[sharpener]

i think i'm just going to put 2 radials in and be done with it , the C/U is only a couple of meters away from the inverter location anyway , would you consider 2 meters one for each inverter?.

Lee

Surely the place for the sub-board (with a separate MCB for each inverter) is between the inverters and the meter. This side-steps any question of needing two meters. You could then just use a two-module enclosure as there is no need for a main switch in addition to the AC isolator required by DTI Guide. The one lockable isolator will isolate both inverters for maintenance, you can still isolate one defective inverter using its MCB so long as the case is not open. The additional length of cable is as you say negligible and might even be of smaller cross-section depending on Mastervolt's recommendations about cabling and overcurrent protection.

 

[johndpar]

Hi Bruce

Yup I accept that MCBs can be used for functional switching but not sure they should be used that way, especially in this case.

I also agree that mcbs do not cost much but the problem comes when you want to put both inverters on the same meter. One way of course is to put the meter on the tails of a small ccu with the tails connected to henley blocks, but that is a different arrangement to that which is normally recommended.

I do see that there can be a problem with 2 inverters on one mcb in some circumstances. With the original poster specing 1715kWp on each inverter I guess they would have to be something like the Sunmaster XS3200 which has a rated current of 15A at full power but I can't see a max mcb rating.

All things considered I reckon one mcb per inverter is right after all, and as for the meter I reckon it would have to go on the tails.

This sort of configuration should be in the various guidance notes of course!

Regards


John

 

[bumcrack]

314.2 ?

 

[lee foster]

Thanks for all the replies and information , it's much appreciated.

Lee

 

[flamefix]

Out of interest what do you put on the FIT application do you just list each inverter or the combined output?

 

[lee foster]

I'm planning on listed the combined output but will need to list both inverter serial numbers.