Isolators

[Jon.berry]

As i said before i have spoken to SMA technical directly about this and they themselves were adamant that using the ESS as the primary DC isolator was not a good idea (i suggest you speak to them directly to satisfy yourself). They said that if you have a string with the wrong polarity (accidentily one hopes) then if you use the ESS you will get big sparks and a bang, and of course the inverter then goes into mainenance mode and you wouldn't be able to do anything until dark, they said also you would potentially void any warranty.

The bottom line is that they said due to their design and how the ESS works it is not designed to cope with acidental wiring or other short circuit occasions and seperate DC isolators are recommended.


The ESS is a protection device for the inverter and not a maintenance switch for facilitating maintenance of the DC cable run and inverter.

 

[SibertSolar]

Precisely, the ESS is an ELECTRONIC device, not a mechanical disconnect, additional/external mechanical disconnection is recommended. That's my understanding too.

 

[SolarCity]

I agree also. Missing the DC isolators out seems like a pointless shortcut.

 

[BruceB]

Well, I seem to be a minority of one here!
Why do you say the ESS is an electronic device? It looks like a physical make/break device to me.
What is the point of it and what protection does it provide if you do have external dc isolators?
Has anyone come across written guidance form SMA saying add an external isolator?

Regards
Bruce

 

[SibertSolar]

Hi Bruce,

Actually, I may have misunderstood the nature of the ESS. I was sure I read somewhere on the SMA documentation that it was an electronic device rather than mechanical but on closer inspection it seems that it is a combination of both. At the end of the day, it appears that the ESS is a load-disconnection switch compliant under DC21B utilisation with EN 60947-3 so that does suggest that an external/separate DC disconnector is not required. I think I stand corrected!

 

[moggy1968]

can the inverter isolator be labelled in the on and off position?
If not, then it doesn't comply with DTi guide.

 

[poheZ]

I am sure that the ess switch is single pole and the DTI guide requires double pole isolation

 

[moggy1968]

If it is single pole then that is correct, but I don't know if it is single pole or not.

 

[edexlab]

In the TL manual technical details the ESS is listed as an all pole disconnection unit DC side ,and they are rated for a minimum of 50 disconnections under load conditions on systems under 800v per string (pg71) over this and the arcing is too severe and results in the ESS switch port being destroyed ,hence the advice to wait until darkness on the larger systems

However my vote is with the separate isolators , just simplifies things for anyone electrician or joe public who is unfamiliar with these systems ,most people will recognise separate isolators and know how to operate them, and speaking from experience I've never seen any other equipment with a similar type of pull out disconnector switch.

 

[SibertSolar]

Seems to be the trend though, I've seen more new models of inverters recently with built-in DC switches. I think the points made about simplifying post-install maintenance etc are valid though, even if it is technically belt-and-braces.

 

[Gavin A]

I've always seen the ESS as a back up in case someone's silly enough not to switch the isolator off before opening the inverter.

I don't see how it replaces an isolator, as anyone needing to replace the inverter will still have to be working live as the DC won't be isolated. OK, so we'll all have worked with live DC at various points, but it's not likely that the regs would allow it IMO.

 

[BBS]

Hi from France (so excuse me for mistakes).

In France, there are many reasons to use external disconnector :
- electronic disconnectors are not recognized
- safety for maintenance (as most of you seem to agree with)
- firemen may require one unique push button for all DC part, and most integrated isolators do not accept external commands
- you will probably replace the inverter twice during installation lifetime : how to be sure there will still be an isolator in the approaching model in 20 years ? You will also have payed three over-sized isolators instead of one that fits exactly.

The next european regulations will probably take this into account.

 

[moggy1968]

all makes good sense to me.
when working live with DC only one terminal is stripped at a time before being put in it's final location, so risk is zero. When changing an inverter without a DC isolator however you would be working live with 2 stripped terminals which significantly increased risk.
I can see no justifiable reason for not having a DC isolator.

 

[cryo]

Hi all a simple reason is cost, a burnt connection on seperate isolator cost ₤30 easy and quick to obtain and repair a burnt connection on a inverter isolator possibly ₤K depending on collateral damage and possibly difficulty and time to source parts plus a unhappy customer who is not generating elec/fit's.

 

[Dal]

Hi

There is nothing wrong with not using an external DC isolator.

If correct shut down procedure is followed why would you ever have to disconnect the built in isolator under load?