Solar panel circuit MCB size?

[driverman]

Hi guys,
I have asked this in another Electricians thread here. Firstly what size MCB usually required for lets say a 4kw solar panel load? Also it has been mentioned about RCD's protecting the solar panel circuit may not be a good idea. Any thoughts please? It's a brand new house build.i was planning to install RCBO's to each and every circuit. Thanks http://www.electriciansforums.co.uk...orum/98430-solar-panels-circuit-mcb-size.html

 

[Leesparkykent]

#14 in your last thread and a 16amp normally for a 4kw system. What more clarity do you want? Lol

 

[driverman]

#14 in your last thread and a 16amp normally for a 4kw system. What more clarity do you want? Lol

Just bored at work! It has come to light also about RCD protection. so thought I'd try this forum who put Solar panels in daily. But i have taken on board what has been said. thanks

 

[whinmoor]

See below for info from Samil's product manual. Other inverter manufacturers may have different ideas.

 

[BruceB]

A 16 A mcb is a reasonable starting point for a system that has a nominal 16 A output.
But it could mean running the mcb near maximum for many hours in the summer.
When in doubt read the manual!
ABB recommend 20 A for the 3.6TL and 25 A for the 4.2TL
SMA recommend up to 32 A for their range from 3000TL to 5000TL

 

[davesparks]

But it could mean running the mcb near maximum for many hours in the summer.

Is there a problem with that?

 

[whinmoor]

Is there a problem with that?

The could be a problem with discrimination...

 

[Leesparkykent]

Discrimination of what?

 

[BruceB]

There can be a problem with mcbs running hot near maximum rated current. Manufacturers' websites go into more detail. As the cable size for 4 kW PV is generally recommended to be 4 mm2 or larger, there is normally scope for a larger mcb.

 

[driverman]

I will be installing 6mm as I have that on site. No point getting 4mm. Any thoughts about 30mA protection? Am I asking for trouble?

I could always install a 20A MCB if 16A near the limit.

 

[davesparks]

The could be a problem with discrimination...

How does discrimination change due to the amount of current flowing through the mcb?

 

[driverman]

See below for info from Samil's product manual. Other inverter manufacturers may have different ideas.


View attachment 27461

Thanks, according to graph, i could in fact use 2.5mm cable as the inverter is next to the consumer unit. Having said that, installers mentioned 4mm. I've got 6mm, so will use that. I doubt if the circuit will more than 1m.

 

[Leesparkykent]

What about the dc side of the installation? How's this being run?

 

[whinmoor]

"Thanks, according to graph, i could in fact use 2.5mm cable as the inverter is next to the consumer unit. Having said that, installers mentioned 4mm. I've got 6mm, so will use that. I doubt if the circuit will more than 1m."

No, the graph is for the 3300TL model and is given as an example only!! 6mm cable is definitely fine though in a 4kWp domestic situation.

 

[driverman]

What about the dc side of the installation? How's this being run?

The DC side of the installation will be run in galvanised 20mm steel conduit which has been flushed into the corner (150mm). Inverter will be housed on ground floor. 2 x isolators have been installed in the loft by the installers.

 

[Gavin A]

A 16 A mcb is a reasonable starting point for a system that has a nominal 16 A output.
But it could mean running the mcb near maximum for many hours in the summer.
When in doubt read the manual!
ABB recommend 20 A for the 3.6TL and 25 A for the 4.2TL
SMA recommend up to 32 A for their range from 3000TL to 5000TL

I don't think we've had a single case of nuisance tripping on any of the 16amp MCB's we've installed on 16A generation limited systems, which would be all of those hundreds of systems.

I've had to swap out a couple of 30mA RCDs for nuisance tripping, but that's it.

 

[davesparks]

Of course you won't have, a 16A mcb will handle 16A, that's the whole point of it being a 16A rated device.

 

[Leesparkykent]

The DC side of the installation will be run in galvanised 20mm steel conduit which has been flushed into the corner (150mm). Inverter will be housed on ground floor. 2 x isolators have been installed in the loft by the installers.

i think burying DC cables in the wall is an awful idea IMO

 

[driverman]

i think burying DC cables in the wall is an awful idea IMO

How would you normally install DC cables in a new build house? Surly, not surface in say trunking? The Solar people wanted it done that way and agreed the route which is basically straight up from main / inverter area to loft space. They wanted it in steel conduit. I went galvanised, even though it was behind dot dab. I even used female /male brass bushes. Would be interesting to know how you and others would do the job though?

 

[Leesparkykent]

i would of tried getting the inverter closer to the array or used micro inverters.