Lighting MCB on CU works when 'off' and not when 'on'? pics

[coolhands]

OK about 3 years ago we had a kitchen extension done (all properly and signed off etc). But, while I'm looking at my CU re my other thread about running a cable to my shed, I've noticed that one of the MCBs on the CU is unmarked, and appears to (somehow) work in reverse!

By turning if off and on, I've found it operates the kitchen lights (ie in the new extension). When the MCB is up (ie should be off - as indicated red) the lights work. (This is how it has been presumably since they did the extension). If I flick it down, i.e. on - green, the lights are inoperative.

So, it works in reverse. How is this possible? I haven't yet taken the front off the (Siemens) CU but might have a look tomorrow.


EDIT: or, it's the other one (the washing machine) that is the wrong way round. But the washin machine works fine too. What's going on?

See pics

Untitled

• coolhands
• 29 Apr 2011
• 1

Untitled

• coolhands
• 29 Apr 2011
• 1

It can't be the fact that the MCB is not Siemens since the other one works as it should.

Also, here's the board just for interest! The 'bell' unit is still powered, even though the output wires are cut off and simply lay below the floorboards.

Untitled

• coolhands
• 29 Apr 2011
• 1

 

[RF Lighting]

Up is on.

Green means safe, red means live.

 

[coolhands]

but how can those two be different from each other?

edit: ok I can only think I need to check the washing machine one IS actually the washing machine. Perhaps it isn't used?

 

[RF Lighting]

Which is the circuit breaker which is different? Is it shown in one of your photos?

What does it supply?

 

[sparkwright]

Are you sure it's not the one marked 13 amp wasing machine that isn't turned on?

I think green means OFF.

 

[sparkwright]

The unmarked one seems to be on in the pic. 10 amp (lighting?)

The 13 amp washing machine one appears to be off in the pic.

 

[sparkwright]

See if the one marked washing machine isolates anything.

 

[coolhands]

Which is the circuit breaker which is different? Is it shown in one of your photos?

What does it supply?

the middle pic. 'blank' Number 6 (though there are two 6's!) and 5. One is up, one is down. But if both systems (i.e. lighting and washing machine) are operating properly, surely one of them is wrong!!

 

[coolhands]

See if the one marked washing machine isolates anything.

yep just realised that. I will check tomorrow.
thanks both

 

[ericmark]

I have had this with Siemens distribution units in the past. For some reason better known to Siemens than anyone else their RCBO's and MCB's switch in reverse direction to each other. They can't be fitted wrong way around which was what I thought my apprentice had done. In my case the distribution unit was vertical so there is no convention as to which direction MCB/RCBO should switch.

With light switches down is considered as on. However with isolators down is always off so anything dropped on it will never cause them to switch on. One always switches on against gravity.

Since in a consumer unit the MCB/RCBO is single pole it is not an isolation device so there is no convention on which way you should switch on.

Table 53.2 in the BRB shows which devices can be used as isolators.
BS EN 60898
BS EN 60947-2
BS EN 61009-1
Can all be used but BS EN 60947-2 needs to have the sign for isolation printed on them. I don't have any Siemens MCB's to look at but would guess not isolation devices?

The picture shows a number of different devices. Consumer units unlike distribution units are type tested and one can only officially fit MCB/RCBO's recommended by the manufacturer. It is unlikely one manufacturer will recommend the use of items made by another so normally to comply you have to use only items made by the manufacturer of that box.

For an indicator green means safe i.e. Off however for a switch Red is safe i.e. Off with the window on a MCB therefore when Off it should show green.

 

[coolhands]

ok thanks. Should I change the odd make the electrician used (probably as he couldn't get original ones) for genuine Siemens?

Is it acceptable to buy secondhand mcbs on ebay like this one?:
http://cgi.ebay.co.uk/Siemens-5SX21...UK_BOI_CircuitBreakers_RL&hash=item33621a92bd

as tlc etc don't list them.

 

[sparkydude]

Yes its perfectly acceptable to change them for secondhand units. Much better than using the doepke units currently fitted to your unit .

Just make sure you feel competent to work inside the consumer unit bearing in mind that there will still be live parts inside even with the main switch off !!!


Nick

 

[coolhands]

Understood.

thanks

 

[kevindgas]

When the MCB is up (ie should be off - as indicated red) the lights work. (This is how it has been presumably since they did the extension). If I flick it down, i.e. on - green, the lights are inoperative.

its a strange anomaly of mcb's that they show red (for danger) when live and Green (for safe) when off! i've often thought that it should be the other way round as well!
but as a general rule they fail to safe in a downward movement (or sideways in 3 phase boards)