UK MCBs for Inverter-Supplied System

[Phil1234]

My house is off-grid and supplied from an inverter. Max power output of the inverter is about 6kW (25A). Max fault current is 100A. The highest rated Type B MCB that can be tripped by this max fault current is 16A, so I cannot use MCBs with higher ratings than that. I cannot have a circuit with loads totalling more than 16A even though the inverter can supply the power. Is there any way around this? Is it acceptable to run an MCB above its rated current? Any ideas would be appreciated!

 

[Julie.]

You have three options, the first is to split all loads into smaller 16A radials, so you can distribute it, however this would realistically have to be at the inverter not at a distribution board/cu.

If you can get an older type 1 mcb which has a lower instantaneous trip, then you could use a 25A mcb, alternatively if you obtain manufacturer's data for a type B, careful selection would give you a 20A mcb which will operate within time on 100A.

Lastly, it is permissable to use a rcd/rcbo if the fault current is insufficient, however you need to ensure the inverter is correctly earthed and can provide earth fault current.

 

[Phil1234]

You have three options, the first is to split all loads into smaller 16A radials, so you can distribute it, however this would realistically have to be at the inverter not at a distribution board/cu.

If you can get an older type 1 mcb which has a lower instantaneous trip, then you could use a 25A mcb, alternatively if you obtain manufacturer's data for a type B, careful selection would give you a 20A mcb which will operate within time on 100A.

Lastly, it is permissable to use a rcd/rcbo if the fault current is insufficient, however you need to ensure the inverter is correctly earthed and can provide earth fault current.

Thanks for the advice Julie, I'll look into the manufacturer's data for MCBs.

 

[davesparks]

Does the inverter have one pole of its output reliably connected to earth? Ie is it providing a TN system or an IT system.
If it does not you should be installing double pole mcbs.

 

[Phil1234]

Does the inverter have one pole of its output reliably connected to earth? Ie is it providing a TN system or an IT system.
If it does not you should be installing double pole mcbs.

It's a TN system. Neutral and Earth are connected at the inverter output and are also connected to an earthing rod.