Really Need Some advise Urgently

moggy1968 · Sep 25, 2012

I've never done a 2 inverter install, but am interested as to why 2 MCBs. That would require 2 meters. When we have discussed this before it was suggested to run the inverters in parallel at the isolator, then to the meter and on to a single MCB.

Looks a neat job, which, as above bodes well. there should be a second AC isolator at the DB, where you would usually also have the meter. I am guessing there is a space issue there.

6 mm cable is almost certainly fine.
The number od DC isolators suggests each array is split into 2 strings. I don't understand why they would do that. I would have thought each array to a single string to the inverter..

personally I would have gone for a single 2 MPPT inverter but thats just a matter of choice.

sedgy34 · Sep 25, 2012

screwdriver said:
I suppose the 2nd ac isolator is there somewhere???? DC isolators could be classed as being a little close to the top of the inverters and so may cause a little bit of airflow restriction, doubt if it would be that bad on an east/west roof though. Gen meter by inverters has never really been our preferred location, especially if the client is elderly and can't climb into the loft every quarter to read the thing!

i agree with the 2nd ac isolator but everything else (behave)

SolarCity · Sep 25, 2012

moggy1968 said:
I've never done a 2 inverter install, but am interested as to why 2 MCBs. That would require 2 meters. When we have discussed this before it was suggested to run the inverters in parallel at the isolator, then to the meter and on to a single MCB.

Not if you connect the meter before a consumer unit supplying the inverters only.

crazygraham · Sep 25, 2012

moggy1968 said:
I've never done a 2 inverter install, but am interested as to why 2 MCBs. That would require 2 meters. When we have discussed this before it was suggested to run the inverters in parallel at the isolator, then to the meter and on to a single MCB.

Looks a neat job, which, as above bodes well. there should be a second AC isolator at the DB, where you would usually also have the meter. I am guessing there is a space issue there.

6 mm cable is almost certainly fine.
The number od DC isolators suggests each array is split into 2 strings. I don't understand why they would do that. I would have thought each array to a single string to the inverter..

Would the system preform better as one large string as aposed to 2 smaller stirngs ?

personally I would have gone for a single 2 MPPT inverter but thats just a matter of choice.

And yes it is very tidy job that has been done in the loft but only after I had stopes them when they started to do it and ask for it to be done very neat with everything planed out rather than just chucked on so with that they removed the inverters and sorted out the level of the back board.
I just wish the panels where as neat as it is the first thing you seen when you turn the corner into my street. I have been promised that all the panels will get removed and the rails will get lowered and levelled to a flawless standard.

I really want to get the photos up for you guys to see and comment. For all I know he used a cheaper fixing bracket or the wrong fixings and that could be why it is so high off the roof.

BruceB · Sep 25, 2012

To answer Moggy's point on why two mcbs, it is because if you only have a single mcb it might be too big to:
- provide fault protection for the cable to a single inverter;
- provide overload protection for a single inverter; and
- you would not have discrimination.

Now you can argue the detail of all those points in any particular situation, but I cannot think of any other reasons the manufacturers would specify it.

Another point on the installation is that it has been in done an over complex and expensive way (probably because that is what they had on the shelf). As it is east/west with neither side pushing out full power simultaneously then a single 5000TL inverter would have done it. Indeed depending on the precise panels used a 4000TL could do it according to sunny design.

moggy1968 · Sep 25, 2012

yes, I would argue the detail! Single 20amp MCB would provide adequate protection of all circuits. Discrimination I think is not really a big issue on this type of install. Discrimination is to ensure that for safety reasons in a house you have at least lights or sockets working in a room if a fault causes a shared RCD to trip or is switched off. You could take it to it's ultimate conclusion and say every socket should have it's own RCBO to provide discrimination!
but I wouldn't argue with the rest of what you say, I too would have gone for a single inverter. I suspect the issue of the second hand inverter answers the question on this. As you say, it's probably what they had on the shelf. A 5000TL would work much nearer to it's max for more of the time than 2 3000s, which means greater efficiency.

trev · Sep 25, 2012

My question is why have they used a second hand inverter? Is it all they can afford (which would be an appalling concept) or have they taken it out from somewhere else owing to a fault

telectrix · Sep 25, 2012

a fault, or possibly a non-payment .

trev · Sep 25, 2012

Either way, putting in second hand kit when a customer is, quite reasonably, expecting new is inexcusable

moggy1968 · Sep 25, 2012

or decomission?
A company we did some subbing for had to decommission an install and refund the money because they were so rubbish. We spent as much time trying to placate irate customers as doing the electrics! In the end we stopped working for them.

Thats a lot of expensive kit to throw away, so I would guess they have tried to reuse it.
interesting you say the panels aren't the ones you requested. Not related to the inverter issue I'm sure:lipsrsealed2:

BruceB · Sep 25, 2012

moggy1968 said:
yes, I would argue the detail! Single 20amp MCB would provide adequate protection of all circuits.

I agree it would - probably. But it would be specifically contrary to the installation instructions, so you have to ask yourself one question, "Do you feel lucky? Well, do you?" - as a well know police character would say.

Gavin A · Sep 25, 2012

I see no need at all to use 2 separate MCBs as long as the MCB is suitable for both the cable size all along the cable length, and the power supplied by the 2 inverters.

particularly as IIRC DTI guide requires a seperate dual pole isolator per inverter, with the MCB not being dual pole usually, that'd mean both an MCB and isolator per circuit.

to answer the question, yes I feel lucky... well, I feel that SMA's guidance is there to remove the potential for installers doing something particularly stupid, but if using 6mm2 cable throughout and a suitable MCB to protect the entire circuit, and a dual pole isolator per inverter I don't see the problem.

And as we have to protect the circuit from the mains end with an MCB, doing a seperate MCB per circuit would mean either 2 cables from the mains, or an MCB at the mains, the subboard near the inverters, which is a fair amount of extra work and expense for no actual benefit.

moggy1968 · Sep 25, 2012

gotta go with Gavin on that. Manufacturers instructions aren't the law, but if you deviate from them you need to be able to justify why, so yes, in a case like this, I feel lucky!!

Gavin A · Sep 25, 2012

same as we've done most of our installs using 30mA RCD on a dedicated circuit, and had both confirmation from Aurora that their guidance was really related to shared circuits, and that for a single inverter a 30mA RCD would normally be ok.

sedgy34 · Sep 25, 2012

telectrix said:
a fault, or possibly a non-payment .

i agree tel,
Theres probably a genuine reason they had fitted the inverter previously and changed it to reinstall on this job
they could have cocked up on the design etc,been sent the wrong inverter which happens and it was fit for this purpose on this job what ever reason its been working and clocked up 600w its still brandnew.looks a neat install from the pics