Help understanding my friends garage set up

[gazdkw82]

Just having a conversation with a non electrician frown of mine who did a Feed to his garage 15 years ago.

when he was explaining it I was bemused

his house cu has a 63amp 400v RCD protection

the garage is fed by 6mm swa into a cu with 6a mcb for lights (1.5mm t+e) and 16a mcb for sockets (2.5 t+e)

the garage cu has a 100a 400v rcd

isn't the garage RCD majorly overated? And why 400v??

 

[Marvo]

RCD's are designed to detect earth leakage currents in the range of milliamps. Usually if an RCD is rated at 100A it means it is capable of disconnecting a 100A load if an earth leakage fault is detected. RCD's often don't sense the load current and don't detect overload faults.

When looking at an RCD check the 'IΔn' figure which is the sensitivity to earth leakage currents, not the 'In' figure which is the max current rating.

Discrimination in RCD's is achieved by either a higher downstream IΔn rating or a time delay.

 

[davesparks]

Maybe you could explain to us why you think there is a problem with the garage RCD? You have missed out the information as to the RCD's tripping current so it's impossible to say.

As for the voltage rating, it sounds odd for 15years ago, I'd expect it to be 415 in those days.


Sent from my iPad using Tapatalk

 

[gazdkw82]

I think I'm confused by the fact his RCD in garage is rated 40A higher than his house cu.

plus why are they both 400v and not 240v? Is it normal to have 400v in domestic installations

 

[gazdkw82]

Thats the garage cu

 

[Bobster]

That isn't an RCD kid, that's a main disconnect switch.

It is literally just a switch that is rated to 100A. It has no thermal or magnetic tripping capability.

 

[gazdkw82]

Ah...now I feel a plank ha

just assumed he was on about an RCD.

Still confused why it's 400v?

 

[Richard Burns]

The switch is designed to be able to be used in a system that has a maximum voltage of 400V.
Therefore it is suitable for use for any system below 400V.
It is just that the switch has been made slightly better than it needs to be for its current application, but the specification allows the switch to be purchased for use in a variety of requirements (up to 400V).

A similar situation is in place for the current rating of 100A, can be used in any situation up to 100A. One product many uses.

 

[hightower]

Hope he hasn't got kids that like to go round licking shiny things. :laugh3:

 

[gazdkw82]

Makes more sense now.

Thanks for the info J

 

[Marvo]

As a general rule you can always spot an RCD (or RCBO) because it will always have a test button on it that's accessible from the front to allow the property owner to periodically check it's operating correctly.