just been wondering....the 100amp company fuse doesn't seem much for a large household. what happens if:

1. someone is using 10.5KW shower (45amps)
2. cooker is on say 10KW (40-45amp)
3. couple of 2bar heaters 4kw (16KW
4. TV, microwave etc etc

you could easily go over the 100amps

also how do you remove the 100amp fuse if you want to isolate the consumer unit mains switch. For example if you wanted to put in a new box. Our cooker ring only has a 32amp fuse, seems abit low, we are on gas so it doesn't matter but still seems wrong ??

Cliff

Firstly, the 100A Board's fuse is usually rated at 100A but wiil probably carry up to 140A before going "pop". I think they are "slow blow" types as well ,which are far more likely to fuse with a sudden overload, like a dead short, than with an overload of the type you are describing.

Strictly speaking, you have no legal right to remove that fuse, as it is in with lead seals, but I've "modified" mine, so I can remove it, and did so when I fitted a split load for a new disribution box.

If in doubt, contact a sparky.

I don't need to remove it, just wondered how you isolate the RCD mains throw if the need ever arised.

Cliff

As above, the types of fuses used by regional leccy companies are dsigned to withstand a certain overload beyond their rating, its how they behave when you chop through a cable that matters.

If you do decide to cut the seals ( illegally ) and remove the fuses you MUST ensure all the breakers are open and the main distribution board incomer is open so you are not pulling fuses under load.

Also depending on how old/where/how many houses etc.. the installation is, there will not be any kind of real shrouding on the live side of the electric board fuses when they are pulled - bear in mind, that you will could potentially be in contact with live terminals that are backed up by fuses rated at maybe 300 - 400A at the local substation.

Ideally, to isolate your main RCD you would get the leccy board involved- -IIRC the last time we had to get them in there was no charge.

also whats the difference between an RCD and MCB, I know what they stand for.

I would not attempt to remove the company fuse as its not mine to touch.

Cliff

Best to call the board mate I know we don’t charge for resealing if asked but we do if the cut-out or meter has had the seals cut without prior conformation. BTW if you have one of the old metal-clad "Bill" cut-out’s I wouldn’t even bother going near it mate as MJ said you could get quite a bad "Pi55er" off it if you start fumbling about inside it, some don’t even have fuse carrier’s and fuses have to inserted and retracted with insulating gloves. If you house is quite new you might have a "KMF" (fused isolator) so you wont even have to touch the cut-out or meter.

MCB = Miniature circuit breaker = Trips when there is a sudden current overload

RCD = Residual current device = Same as above but also detects phase to earth faults and leakage.

The RCD will trip quicker than the MCB but they don’t like lighting circuits they end up tripping every time a lamp blows, hence split load consumer units.

From memory - 14 years since college :eek:


An MCB relies on how much current flow is passing through it - the current is passed through a bi-metallic strip - a strip made from two different metals stuck together. As more current flows so the temperature of this strip increases, and as the two different metals expand at different rates the strip starts to bend. At a certain point of overload or fault the strip will bend to such an extent that it will physically hit a "trigger" this in turn will "trip" the MCB.

An RCD works on a similar principle, except it compares the current flow between the live and neutral cores - if there is more current going through the live than the neutral then there is a fault somewhere, i.e, a leak so to speak. That leak might be a loose wire touching earth somewhere or a live current flow through a person - in any event they trip. they only need to see a difference of .003 amps ( the same amount that is required to kill you ) and they will trip out.

You work for the MEB Tim?

our lighting MCB blows when a bulb goes, but i thought that was down to the fact that just before the bulb blows the current passing through it is massive due to the melt down of the filament. Hence the trip goes.

So in theory if I am earthed and I accidently touch the live then the RCD will trip?????

how does an RCD work

also whats the point in having a separate RCD like you can buy to plug in the wall

Cliff

yeah

just found out how RCDs work, they use a small tranformer to drive a relay if there is a current in-balance

Cliff

just been wondering....the 100amp company fuse doesn't seem much for a large household. what happens if:

1. someone is using 10.5KW shower (45amps)
2. cooker is on say 10KW (40-45amp)
3. couple of 2bar heaters 4kw (16KW
4. TV, microwave etc etc

you could easily go over the 100amps

And as for you first question mate, it’s called "diversity" mate they hope that you don’t use everything at the same time:D. Hears a little graph so u can see how much and how long it takes to blow a 100A fuse.

http://www.kenegie.pwp.blueyonder.co.uk/fuse.GIF

You on the board up in manc MJ??

no, we supply & install diesel generators up to 2.5MVA & gas turbine CHP's up to 100KW, and anything else that comes our way - mecchie or eleccy :D

Ok how do i know if my consumer box main isolator has a built in RCD or if its just a standard double pole switch ???.

Cliff

An RCD should have something like a disconnection time rating and a fault sensitivity rating and a overload rating, e.g. 30mS 100mA 100A

A normal MCB will just have an overload rating on it e.g. 100A

Well that’s my good deed done for the day:D, best get ready got work at 7pm:(.

cliff-vtr: An RCD will have a button marked "test" somewhere on it, and pushing said button will cause it to trip. DON'T do it in the dark:D:

Can anyone who has responded to this thread answer the question I posed in my thread about RCD's:

What is the difference, if any, between a "TypeA" RCD, nd a "Type AC" RCD??

Cheers for answers.
Alcazar

There are a few MCB's and MCCB's that have a trip buttons.

Type A protects against AC earth faults only

Type AC protects against AC and pulsating DC earth faults.

Type B protects against DC only earth fauly

Ah-ha! Thanks Tim Grove, that makes sense, as they want me to use a type A, the one that protects against AC,and DC to protect circuits for the hob, dishwasher, and washing machine, where there could be some DC present.
Cheers.
Alcazar

Along the same lines....

Currently got a 60amp fuse coming into the house. Is there any way on getting this uprated? Costs?

piece of string question - make a note of your meter No and ring your local utility Co. It will be fused at 60A for a reason - if they just uprate the fuses this may overload the main feeder cable on the street.

Why do you want a bigger supply ? are you having problems?

<<Why do you want a bigger supply ? are you having problems?>>

Why do we all want more power?:D:

orbv: put a new dumpvalve, and bigger alloys on your incoming cable..........that's always good for more power:D:

Alcazar

wrong section :)

anyhow small wheels give more power but less torque with respect to the wheels.

Ditch the turbo and go for a s/c :)

Cliff

Why do you want a bigger supply

In the process of putting an extension on the house so adding around 40% to the size. As the electrics are going to be re-done as we currently only have one ring with one socket in each room. If the house was already 100amp would not have asked the question

Got no idea how to phone nowdays :(

phone your leccy company

Cliff