Working on electrics with 2 supplies.

[HappyHippyDad]

I have little knowledge of PV.

When working on circuits supplied by a domestic CU, is it fine to just have the main switch off in the CU or should you be isolating the PV as well?

The stickers all over the CU's in this example all say to disconnect both supplies.

 

[Bobster]

I would be isolating both supplies.

 

[littlespark]

Use your tester.

If what you are working on is dead, then good to go.

I have never worked on PV, from what I can see, sometimes the pv power comes in on a regular mcb, so even if mainswitch is off, you can get power on the bus bar.
Other way is it’s on its board, and connects through a Henley block before the DB.

I don’t know if one method is more “right” than the other.

You could always do your work in the middle of the night when there is no pv power being generated.

 

[Pete999]

I have little knowledge of PV.

When working on circuits supplied by a domestic CU, is it fine to just have the main switch off in the CU or should you be isolating the PV as well?

The stickers all over the CU's in this example all say to disconnect both supplies.

View attachment 49460 View attachment 49461 View attachment 49462 View attachment 49463

it's not just PV you need to worry about, UPs and Standby sets need isolation prior to working on, many organisations with multiple Supplies operate an AP, LV, PtoW system to allow for safe working

 

[Wilko]

All off please !
Otherwise the inverter may kick in and liven up the CU ...

 

[Tony Reidy]

I have little knowledge of PV.

When working on circuits supplied by a domestic CU, is it fine to just have the main switch off in the CU or should you be isolating the PV as well?

The stickers all over the CU's in this example all say to disconnect both supplies.

View attachment 49460 View attachment 49461 View attachment 49462 View attachment 49463

 

[Tony Reidy]

If it says isolate all supplies then that's what to do

 

[HappyHippyDad]

All off please !
Otherwise the inverter may kick in and liven up the CU ...

If this did happen then if I have the MCB switched off on the circuit I am working on, is there any way this circuit could become live? I can't see how? This isn't a reason not to isolate both supplies it's just for me to understand it better.

Is the worst case scenario the busbar becoming live in the CU (assuming all mcb's are off?

 

[DPG]

Don't forget the MCB is not isolating the neutral.

 

[Strima]

Isolate ALL supplies. As mentioned before there is a very slim chance the inverter could power up due to a fault.

 

[HappyHippyDad]

Thanks for all the replies guys

 

[buzzlightyear]

Get in the loft and bolly turn the red rotary switch off or where ever it is .

 

[Gary K]

In theory, the inverter will not power up when main switch is off as it need a reference, power wise so to output marginally higher than mains power.

 

[PEG]

I thought all grid-tied inverters,had to shut down,on the loss of supply,to protect supply personnel,on an outage...

 

[Bobster]

I thought all grid-tied inverters,had to shut down,on the loss of supply,to protect supply personnel,on an outage...

I believe you're correct.

However, for the sake of flicking a switch, would you risk it?

 

[PEG]

I believe you're correct.

However, for the sake of flicking a switch, would you risk it?

Definitely not ...but if someone did not know that already,they need to pass the tools along...

 

[Lucien Nunes]

The inverter itself should shut down so that it does not backfeed AC to the DB when the mains is off, although as mentioned one should not rely on that. Because its output neutral is not referenced to earth (until it is tied to the DNO supply) the SP MCB does not make it 100% safe if it did start up, as a difference in leakage could make the N more live than the L.

But, the main point of the '2 supplies' stickers around the inverter is to remind that with the AC off, the DC from the panels is still live unless it's dark. So before working on the inverter, both the DC and AC sides need to be isolated.

 

[Pete999]

The inverter itself should shut down so that it does not backfeed AC to the DB when the mains is off, although as mentioned one should not rely on that. Because its output neutral is not referenced to earth (until it is tied to the DNO supply) the SP MCB does not make it 100% safe if it did start up, as a difference in leakage could make the N more live than the L.

But, the main point of the '2 supplies' stickers around the inverter is to remind that with the AC off, the DC from the panels is still live unless it's dark. So before working on the inverter, both the DC and AC sides need to be isolated.

Also see post 4

 

[Lucien Nunes]

Pete makes a very good point. It's easy to fall into the trap of thinking that the second supply 'must' be the PV, when there's an automatic backup set ready to spring into life the moment you pull the public supply main switch, and a hidden UPS in what used to be the computer room but now isn't, etc etc.