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Discuss Working on electrics with 2 supplies. in the Electrical Forum area at ElectriciansForums.net

happyhippydad

Member
Electrician's Arms
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.

20190520_110347.jpg 20190520_110340.jpg 20190520_110333.jpg 20190520_110328.jpg
 

Rob

Control System Engineer
Respected Member
I would be isolating both supplies.
 
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littlespark

Electrician's Arms
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

Forum Mentor
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
 

happyhippydad

Member
Electrician's Arms
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?
 

Strima

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

Gary K

Regular EF Member
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

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

Rob

Control System Engineer
Respected Member
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?
 

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