100 ma Main Switch

[EddieB]

I have an overhead supply coming in to the property with a PME , there are two Consumer units with 100ma Wylex RCD's as main switches. Why 100ma ?

 

[DWCOCKBURN]

Why not?
If you have circuits to protect with flexibles or extension leads, you could use 30mA RCBO's and cure nuisance tripping of the entire board.

25amp for ring final circuits please.
20amp for 4.0mm sequentially wired.

 

[DWCOCKBURN]

100mA are great for lighting circuits, if it is a split load board use a 30mA as the second main switch.

 

[mainline]

I have an overhead supply coming in to the property with a PME , there are two Consumer units with 100ma Wylex RCD's as main switches. Why 100ma ?

I assume there are 30ma rcds / rcbos fitted ?

Was this previously TT earthing ?

 

[mainline]

100mA are great for lighting circuits, if it is a split load board use a 30mA as the second main switch.

411.3.4 requires that, within domestic (household) premises, additional protection by an RCD with a rated residual operating current not exceeding 30 mA shall be provided for AC final circuits supplying luminaires.

 

[DWCOCKBURN]

Why?

 

[EddieB]

Why not?
If you have circuits to protect with flexibles or extension leads, you could use 30mA RCBO's and cure nuisance tripping of the entire board.

25amp for ring final circuits please.
20amp for 4.0mm sequentially wired.

There are no RCBO's or 30ma RCD's, that was the reason for my question, given that this board is around 15 yrs old I'd have. expected a 30ma RCD main switch.

 

[EddieB]

I assume there are 30ma rcds / rcbos fitted ?

Was this previously TT earthing ?

There are no RCBO's or 30ma RCD's, it may have previously been a TT but I could see no sign of an old earth rod outside

 

[EddieB]

100mA are great for lighting circuits, if it is a split load board use a 30mA as the second main switch.

There are no RCBO's or 30ma RCD's, and its not a split board, so I'll probably change it in the near future

 

[EddieB]

411.3.4 requires that, within domestic (household) premises, additional protection by an RCD with a rated residual operating current not exceeding 30 mA shall be provided for AC final circuits supplying luminaires.

Yes, I'm going to change it, I was wondering why it was a 100ma as opposed to a 30ma

 

[DWCOCKBURN]

Why does a lighting circuit require a 30mA RCD?

 

[PS Electrics]

Was this previously TT earthing ?

That was my initial thought and I see there is a thread on this forum of a presumed converted overhead supply to PME.

I see the OP looked for an old Earth Rod which was something I was going to recommend the other option is to contact the DNO and see what history they have.

Don't see too many overhead supplies where I am and I know from college that there was an automatic assumption that overhead is normally TT. I know in the thread mentioned the pole was accessible and the poster could see the pole was pme though the DNO had not connected the Earth cable they had installed at the property but it had TT Earth Rod in place. I presume they installed the cable and left the it unconnected for a future conversion of the house to PME.

The other thought was the 100mA RCD was for fire protection.

 

[EalingBadger]

Why does a lighting circuit require a 30mA RCD?

Arguably, the greatest risk on a lighting circuit is somebody accidentally stuffing their fingers into a live socket whilst changing a bulb.

So, require? Probably not. Wise? I think so.

 

[EddieB]

Why does a lighting circuit require a 30mA RCD?

I'm afraid that BS 7671:2018 requires that all lighting circuits without exception are protected by a 30ma RCD/RCBO

 

[EddieB]

I assume there are 30ma rcds / rcbos fitted ?

Was this previously TT earthing ?

No, I'm afraid not

 

[Risteard]

I'm afraid that BS 7671:2018 requires that all lighting circuits without exception are protected by a 30ma RCD/RCBO

Domestic ones only...

 

[EddieB]

Domestic ones only...

Yep you're right, but seeing as this post was about a domestic scenario I didn't think to add that.