Mains Connection?

[T0M0]

Hi All,

I suspect this has been covered many times but I cannot find a definitive answer.

I am undertaking my first install which will be used for assessment. The inverter is a SB2500 with electrical separation so does not need RCD protection. My AC cable to the loft will be buried in, so Part P requires an RCD.

I believe a double pole 100mA class A or AC is required, as a 30mA may trip due to fluctuations. My intention for this and other installs is to install a separate CU with the above RCD feeding a 16A MCB as standard. Does this sound correct?

Also, I am mounting the inverter in the loft onto firerated plywood attached to the trusses. Does this sound good and are there any issues with noise with the SMA inverters?

Sorry if this is repetitive and any help appreciated - Thanks for reading,

T0M0

 

[T0M0]

Just answered my own question regarding RCD's. Can't use 100mA for part p - doesn't offer personal protection!

Just going to have to use 30mA but read so many stories of them tripping. How do you guys fare with them? Guess cheaper inverters may not smooth the fluctuations as much and cause tripping?

Thanks - T0M0

 

[Ramjam]

Hi TOMO,

I always connect with a 30mA RCD in the circuit. THe additional protection is always wise and I reckon my 18th edition you won't be able to have a circuit without.

I believe that the correct way is to install an second CU cut into the tails on henly blocks. Then have a 30mA RCD as the main switch and a 16A MCB. Mark the CU as Generation CU then clip on monitors on the tail can easily show generation on one meter and consumption on the other, the difference is then either coming from or going to the grid. Much easier way to optimise self consumption.

I've not got long term experience but so far I've not had any nuisance tripping with SMA inverters.

Fire rated plywood sounds like the right job to me, that's what I use.

 

[T0M0]

Thanks Ramjam, that's exactly the info I was looking for.

Out of interest, have you had any problems with noise or vibration from the inverters, particularly when attached to trusses?

Thanks again for the clarification - T0M0

 

[Ramjam]

I try to screw to a wall when I can, that said next weeks install sees me fasten to the trusses for the first time. I've not had any noise from a running inverter but it might take 15 years for a transformer to break down to start the plates vibrating. Perhaps we should consider a shock absorbing mount of some sort? Any ideas?

 

[T0M0]

I pondered the idea of shock absorbing but decided against it because I haven't seen any installers debating it. I think if I were to do something, I would use some sort of rubber bush at each fixing point. The problem would be how to isolate the bolt and stop the noise transfering through it. How about you - overkill perhaps?

I welcome advice from installers with experience in this method of mounting. Is there an issue with noise and vibration with SMA inverters?

Thanks - T0M0

 

[edexlab]

I pondered the idea of shock absorbing but decided against it because I haven't seen any installers debating it. I think if I were to do something, I would use some sort of rubber bush at each fixing point. The problem would be how to isolate the bolt and stop the noise transfering through it. How about you - overkill perhaps?

I welcome advice from installers with experience in this method of mounting. Is there an issue with noise and vibration with SMA inverters?

Thanks - T0M0

Inverters with fans can be noisy so best avoid stud walls or near main living areas
sb 2500 does'nt have a fan and is quiet just slight buzzing
I've never fixed to trusses but have seen a job where they used a cement fibre board to mount on , personally i never fix to plywood etc and always rawlbolt to the wall
most of the inverters even tl / hf are 18 kg plus and i like to know they can't be pulled off easily

 

[T0M0]

Thanks for that edexlab - great to know.

 

[sean_ork]

just a note - some roof spaces get VERY hot, the SBs don't like heat

be warned

 

[T0M0]

hmmmmmm - wondered about heat and brought it up on my course. They weren't impressed by the point and advised inverters are designed to operate at temps of upto 60 degrees C.

Have you had issues with sunny boys in lofts?

Cheers - T0M0

 

[sean_ork]

yes - random shuts downs, resetting and 2 complete failures

all due to being installed within supposedly cold roofs

 

[T0M0]

not good - with this one I can position in garage but didn't want to run DC out of loft! How do you run DC? Do you take it externally in SWA?

Also, if you have no real alternative to loft, what do you do - specify a temp friendlier inverter if they exist?

Thanks for the help - appreciated

 

[claypole]

Can I just ask if the enclosed schematic for addition of block and sub main looks like a reasonable proposal? Would pm one or two of you but can't find a way to attach a file pic that way so apologies for thread hijack, albeit related. My meter and main fuse seals are intact. I believe splitting the meter tails on a block would be cleaner but in order to avoid breaking seals does this look like a reasonable way to add a block and sub main for the pv from the mains switch in the existing CU? I have no isolating switch between meter and CU (if I knew then what I do now I would have requested one when meter was changed last year!). Existing CU has one spare way on the 30ma RCD and SB4000TL guidelines clearly state it will trip 30ma RCD. I should add I have no intention of doing this work myself just wishing to avoid looking like a complete ar.e by suggesting something stupid to my installer if he doesn't initially suggest it himself. I believe this is going to be the best way to install but it also has the incidental benefit of being easily able to monitor house consumption with a clamp on the neutral wire feeding the existing CU neutral bar from the new block. Any comments?

 

[edexlab]

I try and avoid lofts as I've posted before I tend to run pv cable in separate conduits , although 2 core swa is fine, but I have read the Germans will only use swa if there are string fuses because if the cable does get damaged then you have the shock/ arcing factor and there is no short circuit protection on Dc side.


Re heat most inverters have electrolytic capacitors which wear as do most electronic components, these have a reduced lifespan and can fail if used in high temps, the rating on an inverter of 60 C will mean that when its at max temp the inverter will reduce power or shut down, while the fan operates to cool it down to a temp where the inverter
will start up again and so on, this will mean in the best irradiation conditions the inverter is reducing power resulting in reduced output ,so you should give it some consideration when deciding the position