Consumer Unit - opinions wanted!

[riph72]

Hello all,

My (new) house was built in 1970, I have taken a photo of the consumer unit (see below), I was wondering if people think it all looks ok? I intend to replace the fuses with MCBs, but apart from that, is there anything else I should be worried about?

Regards,
Richard.

Consumer unit etc

• riph72
• 4 Jan 2012
• 1

 

[jj4091]

No obvious sign of bonding for gas & water pipes.

 

[ricicle]

What is your reason for wanting to swap to MCBs ? Do you have frequent fuse blowing ? If so that would indicate a problem that requires investigation. Also if you have an electric shower then is there any 30mA RCD protection for it ? You may also want to think about RCD protection for your socket outlets.
The list can get longer if you want to bring your installation up to current requirements. eg satisfactory main protective bonding.

 

[riph72]

No obvious sign of bonding for gas & water pipes.

Is that a good or a bad thing?

 

[riph72]

What is your reason for wanting to swap to MCBs ? Do you have frequent fuse blowing ? If so that would indicate a problem that requires investigation. Also if you have an electric shower then is there any 30mA RCD protection for it ? You may also want to think about RCD protection for your socket outlets.
The list can get longer if you want to bring your installation up to current requirements. eg satisfactory main protective bonding.

No problem with fuses, I guess I can change them if/when they blow... I would definitely consider RCD protection - I understand that a single unit can be fitted by the consumer unit, to cover all circuits?

 

[PrenticeBoyofDerry]

No obvious sign of bonding for gas & water pipes.

Is that a good or a bad thing?

The fact that it is not obvious is not a concern.
But if you have no bonding to gas/water etc.
That is a bad thing!

 

[PrenticeBoyofDerry]

. I would definitely consider RCD protection - I understand that a single unit can be fitted by the consumer unit, to cover all circuits?

It could but you would still need to have your system inspected and tested before it could be deemed suitable for RCD protection to be installed.
If I was going down that route, I would consider a complete upgrade with new RCD protected board.
That does not mean I am saying there is anything wrong with the board or installation you have, as safety is concerned. Inconvenient when fuse blows in comparison to the ease of resetting MCB though. Either go for upgrade or stick.

 

[riph72]

No obvious sign of bonding for gas & water pipes.

Is that a good or a bad thing?

The fact that it is not obvious is not a concern.
But if you have no bonding to gas/water etc.
That is a bad thing!

The gas/water pipes are located in the same room (garage) - should be as simple as connecting an earth from them to the board shown? I presume this is normally done on newer builds?

 

[riveralt]

No problem with fuses, I guess I can change them if/when they blow... I would definitely consider RCD protection - I understand that a single unit can be fitted by the consumer unit, to cover all circuits?

Well you can do this but it is not advised since a problem on one circuit would deactivate all circuits.
You wylex board should take the push in wylex mcbs - they cost about a tenner each nowerdays.
http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Standard_Range/index.html
I feel that they are more sensitive than the standard wired version but then they are easier to reset. Though a note of caution - whenever a wired fuse or mcb goes it is normally because something has gone wrong with the circuit. If it is just a bulb blowing then okay but if not.....
Check out wiki for bonding to your utilities //www.diynot.com/wiki/electrics:main_equipotential_bonding
I won't do any work on a circuit unless the bonding is up to scratch.

 

[riveralt]

The gas/water pipes are located in the same room (garage) - should be as simple as connecting an earth from them to the board shown? I presume this is normally done on newer builds?

Yet but it would be better to connect everything to a main earthing terminal outside the consumer unit since there is not much room inside that wylex board and if you have not got an isolator you will be working very close to live cables which is not good.

 

[JohnW2]

Is that arrangement of connection between cutout and meter common - it's not something I recall having seen before?

Kind Regards, John.

 

[ericmark]

To replace the fuse for a MCB only requires the holders to be changed which is one screw. Does expose live parts so do switch off before changing. In the main a good thing. You may find the lighting MCB trips when a bulb blows as more sensitive than a fuse.

In theroy one should test the earth loop impedance before changing. With a fuse the graph time v current is a curve and although if the earth loop impedance is a little high it will take a little longer to blow the fuse the few seconds delay is not really an issue.

However with a B type MCB there are in fact two devices built into one. A thermal trip which will in the fullness of time trip at the rated amps. And a magnet trip which will trip with hardly any delay at 5 times the rated amps. So what we have to ensure should there be a short circuit that at least 5 times the rated amps will flow. We ensure this by measuring the earth loop impedance and either calculating or look up in tables the value permitted. For example for a B32 MCB it's 1.44 ohms.

In theroy a 30A fuse to blow in 0.1 seconds needs something like 450A where a B32 MCB needs 160A so the MCB is better. But as we move to 5 seconds then the fuse will blow at around 87A but the MCB still needs 160A. At about 10 seconds the MCB still needs 160A to open after which a curve has to be followed as the thermal part takes over so at 100 seconds a 32A MCB will trip at 70A the 30A fuse will still beat it blowing at around 60A.

So if the ELI is within limits the MCB is better. But if out of limits the humble fuse can clear faults quicker. Today we rarely rely on either and for earth faults we use a RCD however the name RCD covers many devices. Where we have a poor ELI for example with a TT supply (Means you have an earth rod) we can use a S type (Has small delay) RCD with a trip value of 300mA (Although 100mA would be the normal) this will open the circuits with an earth fault but the current required and time delay is too large and long to save live. The RCD is really there to reduce fire risk.

So today we use a RCD which will trip at just 30mA and will trip in 40ms however these are so sensitive that if too many circuits are feed through the same RCD then natural leakage can cause them to trip. So for a caravan supply having all from one RCD is fine but as the installation becomes larger then we need to use multi-RCD's to stop it tripping when it shouldn't.

There are number of methods commonly used.
1) 2 Way split board using 2 RCD's
2) 3 Way split board using 2 main RCD's and some RCBO's or MCB's with special wiring to feed items like freezer.
3) 2 Way split with one main RCD and a series of RCBO's similar to above.
4) No split and all RCBO's
The RCBO is a MCB and RCD combined often only switching the line so not suitable for a TT supply.

To fit any of these options requires the main fuse to be withdrawn and there is some danger involved. So the rules say it needs notifying under Part P which in real terms means it's not a DIY job.

The same really applies to the simple change from fuse to MCB but not quite as defined in rule book and I am sure there are arguments both ways.

It is like most DIY electrical jobs the physical work is easy it's the inspection and testing before and after which causes the problem.

The old saying is still valid "Fools rush in where angles fear to tread".

 

[JohnW2]

Yet but it would be better to connect everything to a main earthing terminal outside the consumer unit since there is not much room inside that wylex board and if you have not got an isolator you will be working very close to live cables which is not good.

Agreed, but everyone is guessing about what goes on behind that bording. There might already be bonding in place and there might even be a MET external to the CU hidden there. If the cladding comes off easily, a photo or what happens behind it would obviously be helpful.

Kind Regards, John.

 

[riph72]

. I would definitely consider RCD protection - I understand that a single unit can be fitted by the consumer unit, to cover all circuits?

It could but you would still need to have your system inspected and tested before it could be deemed suitable for RCD protection to be installed.
If I was going down that route, I would consider a complete upgrade with new RCD protected board.
That does not mean I am saying there is anything wrong with the board or installation you have, as safety is concerned. Inconvenient when fuse blows in comparison to the ease of resetting MCB though. Either go for upgrade or stick.

That seems fair advice - I'll leave it as it is then, I'm not actually having any trouble, I'll just upgrade to MCBs as and when the fuses go, just for confidence that they are new and shiny etc.

 

[riph72]

No problem with fuses, I guess I can change them if/when they blow... I would definitely consider RCD protection - I understand that a single unit can be fitted by the consumer unit, to cover all circuits?

Well you can do this but it is not advised since a problem on one circuit would deactivate all circuits.
You wylex board should take the push in wylex mcbs - they cost about a tenner each nowerdays.
http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Standard_Range/index.html
I feel that they are more sensitive than the standard wired version but then they are easier to reset. Though a note of caution - whenever a wired fuse or mcb goes it is normally because something has gone wrong with the circuit. If it is just a bulb blowing then okay but if not.....
Check out wiki for bonding to your utilities //www.diynot.com/wiki/electrics:main_equipotential_bonding
I won't do any work on a circuit unless the bonding is up to scratch.

I'll read that wiki, thanks. I'll always treat tripping MCBs as a warning that something isn't right, unless I have good knowledge to the contrary, but thanks for the warning