replacing an MCB?

[Palmerston5]

Help needed from those in the know, please!

I am trying to add a new double socket in the kitchen, but am rather alarmed to discover that the existing sockets are on a circuit with a 15amp MCB. I thought it should be 30 amp, and think this explains why the circuit trips each time the dishwasher and kettle are on at the same time.

Am I right to think this is wrong? Can I simply change (or get an electrician to change) the 15 amp MCB for a 30 amp MCB to make everything alright?

Many thanks in advance for any replies.

 

[dingbat]

As always, it depends. It sounds as if your kitchen circuit is a radial, in which case, if it's wired in 2.5 sq mm twin and earth cable and serves a floor area less than 50 sq m you can change the circuit breaker for a 20 amp one, but NOT a 32 amp; that would only be possible if the circuit was either a ring or a 4 sq mm radial.

And, yes, if you have a 3kW kettle and 3kW dishwasher, they will draw around 26A together, which will trip your 15A breaker. The fact that you say it's a 15 amp MCB (not 16) suggests it's a Wylex plug-in fuse replacement. If this is the case it might be wise to get an electrician to check everything over anyway because it's not unusual to find all sorts of additions to older installations.

 

[plugwash]

it all depends on what is there already

best case: just the breaker needs changing

worst case: replacement of CU and rewire of kitchen

a photo of your CU would be very helpfull here (and one with the cover off would be even more usefull but if you don't know what you are doing then wait until we've seen the outside and pointed out any dangers before taking the cover off the CU)

 

[Palmerston5]

Thanks guys, I will take a photo and try to post it (though I'm sure I don't know what I'm doing as far as putting a picture on here is concerned!)

 

[breezer]

(though I'm sure I don't know what I'm doing as far as putting a picture on here is concerned!)

see the forum information thread, beleieve it or not that is what it is there for

 

[Palmerston5]

Thanks Breezer, I guess it was obvious. Here is a photo of the inside of the CU. Unfortunately because of the flash it's a bit bright. The relevant MCB is second from the right. You can't see because of the flash but it is 15 amp. And there are TWO red wires going in, which suggests to me this is a ring! Which can't be right...can it?

It's all 2.5mm cable.

The CU is made by MK.

Any help gratefully received.

[/img]

 

[plugwash]

ok there is something odd about that CU

i see no main switch?!

is there a main switch placed seperately or something?

also that CU is an old style MK they do sell a retrofit kit though to allow you to use modern MK mcbs in them

 

[ban-all-sheds]

Is that pyro I see on the right? What part does that play in the installation?

EDIT - no it's not, is it. Now that I see where it is, and peer at the screen through the right part of my glasses, I can see the ribbing on them. Sorry 'bout that...

Also I note that that 45A MCB is not at the end of the busbar closest to where the incomers are....

 

[Palmerston5]

Oh dear this all sounds very ominous...

Here is a pic of the setup on the outside of the CU. THere is a separate RCD switch on the right - hence I was brave enough to open the CU.

On the outside of the CU there is a sticker with writing on it, which says that the system was checked in 1994. God knows who by, though.

[/img]

 

[ban-all-sheds]

Oh dear this all sounds very ominous...

Not necessarily - I'm sure we'll get the circuitry identified, and that misplaced MCB will be easy to move...

Here is a pic of the setup on the outside of the CU. THere is a separate RCD switch on the right - hence I was brave enough to open the CU.

Wouldn't have done you much good if you'd formed a live-neutral fault path, but we won't dwell on that. Would be interested to see a close up of the RCD - is it an old voltage-operated type?

Secondly, can you confirm the path that the tails take? The service head is just visible on the left - I guess they come from there, into the meter and out to the RCD, but it does look as though they curve downwards into the RCD enclosure.

#3 - where's the main earth connection? Is there something above the CU, hidden by the open lid?

#4 - what are those unsheathed conductors disappearing behind the mounting board above the meter?

#5 - it's probably just the combination of camera angle and twisted wires, but it looks as though the rightmost MCB has 2 conductors of different sizes coming from it...

 

[Palmerston5]

Okay, to answer your questions as best I can:

The tails do indeed come fromt he service head above the CU then down through a tight squeeze below the metre into the RCD. Then up from the RCD into the metre (just visible in the photo). Then presumably the two grey wires take the feed into the CU from below. You are right, it does look odd in the picture but that is just the tight fit.

As for the main earth connection, um, I'm afraid I'm not sure what I should be looking for. As you can see from the new pic below of the overall arrangement, there's an earth wire coming out of the top of the CU which disappears to the left. It then vanishes behind some plasterboard - could the main earth connection be behind that (this is all in the cellar - behind the plasterboard is the rubble/foundations of the front of the house).

The unsheathed conductors...I wish I knew. They don't disappear, they just stop and have been bent up "out of the way". I haven't dared touch them. They run off with another 2.5mm cable (A), and disappear into the floor above. I am assuming that they were originally one end of a ring which the muppets who lived here before disconnected, then connecting up the ring with a new cable (B) (A and B both go into a 30 amp MCB).

As for the rightmost MCB - since reading your comment about live-neutral faults I am a little wary of opening it up again! But I think that is just the camera angle - from what I remember there was only one wire going into that MCB - 15amp for the boiler.

Phew! And here also is a pic of the RCD close up. I feel quite ashamed by the extraordinarily shambolic state of our electrics.

[/img]

 

[Palmerston5]

I'm not sure how to insert an 'edit' as ban-all-sheds did, but I've just realised I got it all wrong about the tails in the last post - they come from the service head and then go UP to the metre in the tight squeeze place, and then down from the metre to the RCD.

I got it all upside down before. Sorry.

 

[ChrisRogers]

your RCD is only rated at 40amps? and you have a shower or other appliance running on a 45 amp breaker. I would recomend the RCD be changed to a higher rated one.

 

[ban-all-sheds]

Oh poo -that'll teach me to wander off for a cup of tea part way through doing that, and not check for new replies before posting....

Ignore my questions about the tails, then, but the other comments still stand.

 

[Lectrician]

Looking good this post

Keep it up lads

I do have some of those MK breakers if required. Type C mainly though.