481th consumer unit question??

[lizzieg]

Evening All
No doubt in those 480 posts that came up is the answer to the question I am about to pose...I looked at first three or so pages and thought" I will be here all night??", so here goes:-
Ventured down the cellar and opened up CU and noted it said 60A just below main switch.
Counted along the MCBs, which are as follows:- 30A, 15A, 5A, 15A,and 5A.

mmmmm.....now I live in the house that jack renovated, and we have not covered above at college yet, (except I am sure I read that MCBs are supposed to be 6A, 32A etc...)
After all that I suppose I am asking is above okay......

 

[Softus]

Hi lizzieg

The rating of any fuse or breaker is dictated by the type of circuit that it's serving, so you haven'yet t given enough information on which anyone can base an answer.

For each of the breakers that you've listed please could you say what its circuit does? Then you'll get an abundance of helpful and informative replies!

S.

 

[lizzieg]

Hi Softus
So far all I know is that that the two 5amp are for the upstairs and downstairs lighting circuits. 1 of the 15amps is to a double socket in the kitchen, looks like it's been put in as an afterthought, I would need to check the others tomorrow, thanks
Lizzie

 

[lizzieg]

So it does not matter that the amps come to more than the number of amps on the box ie 60A.......

 

[andy]

So it does not matter that the amps come to more than the number of amps on the box ie 60A.......

my house hasa 40A service fuse. often has 9.5KW shower on along with other things. neverblown in the 10 years ive lived here. so i wouldnt worry about it.

 

[slippyr4]

lizzieg,

"Diversity" is the principal whereby you don't actually use every electrical appliance all at once. Although all your fuses add up to more than 60A, you don't ever use them all to the max all the time.

Diversity is applied all over an electrical installation. For example, your cooker has a cable and MCB chosen by the electrician to be appropriate to expected demand. It's quite likely that if you turned all the rings on max, as well as the oven and grill, and plugged a kettle in the socket on the cooker point, you'd blow the fuse. Thing is, you never have everything on like that.

Its that same with ring mains. These are normally fused at 30 or 32 A, but it doesn't take many irons or electric fires to reach that.

slip

 

[lizzieg]

Thanks Slip
Everything else has gone wrong with this house, I am probably looking for problems that are not there!!!. Doesn't help when every switch/ socket I have had to undo has not had an earth sleeve in any of them??
I am still wondering why the MCBs are rated at 5A, 30A instead od 6A or 32A etc......

 

[TraineeSpark]

Lizzie, the MCB's you have are of the old type. Modern MCB's are type B,C or D depending on the usage and installation. Domestic Installations usually have type B's. The old type breakers however, Type 1, 2 or 3, (which are approxiamte equivalents to b,c or d) have old ratings equating to fuse ratings. I.e 5A lighting, 30A ring main.
As for the ratings adding up to more than your 60A incomer, the earlier posting on diversity was bang on the money. For example, you may have say, 8 lights on your downstairs lighting circuit. Even allowing that each was a 100W lamp, you would only use just over 3A.
P = IxV =
I= P/V =
I = 800W/240V = 3.33A
Therefore you are never using the full 5A capacity of the breaker.
However a house I went to a few weeks back, the woman of the house wondered why her breaker kept tripping when she put a certain amount of downstairs lights on. She said the kitchen seemed to be the problem, and no wonder. She must of had 30 lights in the kitchen alone. Track lighting, spots, you name it she had it. Just to show her the problem I put my clamp meter on the circuit at the c/u and switched each light on while she watched the current rise. I think we got to 7 or 8A (again on a 5A breaker) before the penny dropped for her.
Anyway hope all that makes sense, cause reading some of it back it don't make much sense to me, and I wrote it.
TS

 

[lizzieg]

Hey TS
A bit of transposing of algebra there.........impressed...LOL
No seriously, thank you for answering my question, much appreciated
Lizzie

 

[Darkness]

If say for example, you have a 40A MCB in your CU which is for power to say a garage. Why on some CU's in a garage or whatever have a 100A Isolator?

 

[Steve]

If say for example, you have a 40A MCB in your CU which is for power to say a garage. Why on some CU's in a garage or whatever have a 100A Isolator?

1. because it came with the board
2. it is cheaper than a 40A isolator, as i expect 40A ones are seldom used anywhere
3. it is like having a 10A switch on a 5A lighting circuit. Does no harm to use overrated accessories.

 

[Darkness]

Cheers for answers.

 

[TraineeSpark]

No Probs Lizzie, could talk electrics all night, thats my problem. If you have any questions feel free to ask. If it is easier 4 you, take my msn messenger number and use that

 

[slippyr4]

If say for example, you have a 40A MCB in your CU which is for power to say a garage. Why on some CU's in a garage or whatever have a 100A Isolator?

The rating of the isolator is simply the maximum current it can safely handle. The isolator is NOT the current limited safety device