Pv on rcd

[GEOFF S]

LV 3 phase inverters.
In particular the ABB Trio range.
Although there are separate connections for each phase, neutral and earth, the earth and neutral are connected together internally.
In fact it appears that the neutral is nothing more than another earth conductor, as there is no internal connection from the neutral to any other part of the inverter.

Hi

Im not able to coment on abb trio, unless you can give an explanation?

This unit has no seperation, so requires RCM, secondly it will require a type B RCD on the a.c outlet, so no seperation d.c to a.c.

Cheers

 

[Deleted member 26818]

What's to explain?
Earth and neutral are connected together at the inverter.
Don't know what you mean by seperation and needing an RCM?
Why would it require an RCD?
Would existing RCDs (if there are any) in the installation, require changing from A/AC to B type?

 

[davesparks]

What's to explain?
Earth and neutral are connected together at the inverter.
Don't know what you mean by seperation and needing an RCM?
Why would it require an RCD?
Would existing RCDs (if there are any) in the installation, require changing from A/AC to B type?

RCM - residual current monitor.

The type b RCD would be needed between the inverter and the final circuits as it will operate in the event of DC residual currents flowing due to the lack of DC/AC separation in the inverter.
All normal RCDs in the installation can remain as they are, the type b will disconnect the source of the DC (inverter)

Normal RCDs are prevented from operating by DC as it saturates the core balance transformer, which is one method used to prevent RCDs tripping during EFLI testing

 

[Deleted member 26818]

Why is an RCD required between the inverter and final circuits?
Inverter is connected to the incoming supply from the grid via SY cable through trunking to a meter then to an isolator , then to fuses (can't remember the ratings) then via SWA to to a busbar chamber in the intake room.
Not sure if there is d.c./AC separation at the inverter, though there is an indicator led for if there is an earth fault on the d.c. side?

 

[uksparks]

I have to say this is a really interesting thread!

if we need to disconnect both ends, how about this.

from the main db, circuit starts with an RCBO, then connected to that would be a 6A MCB on a shunt and that circuit holds open a NO contactor which the inverter end is connected to (the one that runs back to the main db).

so by doing this, should there be overload or earth fault on that circuit, thevRCBO will trip and disconnect the line at the board end and open the contactor disconnecting both line and neutral from the inverter. But would this disconnect or open the contactor in the right time to comply?

Just a thought?? No idea if it would be ok or not

 

[GEOFF S]

Why is an RCD required between the inverter and final circuits?
Inverter is connected to the incoming supply from the grid via SY cable through trunking to a meter then to an isolator , then to fuses (can't remember the ratings) then via SWA to to a busbar chamber in the intake room.
Not sure if there is d.c./AC separation at the inverter, though there is an indicator led for if there is an earth fault on the d.c. side?

Hi

Without simple seperation between d.c and a.c, a fault on dc could transfer to the a.c side, so a type B RCD must be installed.

Cheers

 

[Deleted member 26818]

Seems a bit complicated when just two RCDs will suffice.

 

[uksparks]

Seems a bit complicated when just two RCDs will suffice.

Not two normal ones?

 

[GEOFF S]

What's to explain?
Earth and neutral are connected together at the inverter.
Don't know what you mean by seperation and needing an RCM?
Why would it require an RCD?
Would existing RCDs (if there are any) in the installation, require changing from A/AC to B type?

Hi

How you know the N-E link is internal and its purpose?

Cheers

 

[Deleted member 26818]

As far as I am aware, these particular inverters do not require type B RCDs.
I know that the earth and neutral are linked by visual inspection.
I was interested in why there is a neutral for 3 phase inverters, when to my mind there would be no need, as there is no transformer to connect a neutral to the star point.
As no one I asked could provide an answer as to whether a neutral is required, I thought I would investigate the next inverter I got hold of.
There is a wiring block to connect the output conductors, then some short lengths of conductors to over voltage surge arresters, with blank modules for the earth and neutral, the other side of the surge arresters, is where the earth and neutral are linked, with only the earth and phase conductors continuing into the innards of the inverter.

Something that puzzles me, is how the inverter knows there is a connection to the grid?
Does the inverter pause the output from the inverter to measure the grid, or is there some manner that the inverter can differentiate between the grid voltage and the inverter voltage?

 

[davesparks]

I have to say this is a really interesting thread!

if we need to disconnect both ends, how about this.

from the main db, circuit starts with an RCBO, then connected to that would be a 6A MCB on a shunt and that circuit holds open a NO contactor which the inverter end is connected to (the one that runs back to the main db).

so by doing this, should there be overload or earth fault on that circuit, thevRCBO will trip and disconnect the line at the board end and open the contactor disconnecting both line and neutral from the inverter. But would this disconnect or open the contactor in the right time to comply?

Just a thought?? No idea if it would be ok or not

How is a 6A MCB with a shunt trip going to hold a contractor open?

 

[davesparks]

Why is an RCD required between the inverter and final circuits?
Inverter is connected to the incoming supply from the grid via SY cable through trunking to a meter then to an isolator , then to fuses (can't remember the ratings) then via SWA to to a busbar chamber in the intake room.
Not sure if there is d.c./AC separation at the inverter, though there is an indicator led for if there is an earth fault on the d.c. side?

It is required if the inverter does not provide suitable separation between the DC and AC.
The basic outline of the theory is that if DC can get into the AC circuit then it will prevent a A or AC RCD from operating as the DC saturates the sensing coils these preventing the RCD from operating.

Injecting DC into an AC RCD is one method which can be used in 'anti-trip' Zs testing to prevent an RCD from tripping.

I'd be surprised if a non-domestic unit wasn't provided with appropriate separation, but it really isn't my field so I don't know.

 

[davesparks]

Seems a bit complicated when just two RCDs will suffice.

Two RCDs are unlikely to suffice, but we've strayed so far in this topic I'm not certain what you are saying the two RCDs would doing?

This started with the provision of 30mA RCD protection to a PV inverter circuit (in a domestic setup if that makes any odds) in a situation where regs require it for the usual shock protection reasons. But now it's strayed into type B RCDs and N-E links so I'm getting a little lost!

 

[Deleted member 26818]

If the cable from the inverter to the mains requires RCD protection as you said because it may be concealed in a wall less than 50mm.
Then two RCDs, one at each end of the cable would suffice.
One will disconnect the power from the inverter, and the other the power from the mains.
I mentioned the fact that the neutral and earth are linked because someone asked if all inverters are separated from earth.

 

[davesparks]

If the cable from the inverter to the mains requires RCD protection as you said because it may be concealed in a wall less than 50mm.
Then two RCDs, one at each end of the cable would suffice.
One will disconnect the power from the inverter, and the other the power from the mains.
I mentioned the fact that the neutral and earth are linked because someone asked if all inverters are separated from earth.

Two RCDs may not suffice, if the inverter is earth referenced through a solid link then it should work, but if it's earth referenced through a resistance or through fortuitous connection it may not.

The bottom line that most of us were getting at is that the circuit should be designed so that RCD protection is not required, which isn't exactly difficult really.