House rewiring

[Uncle Peter]

Have you ever had 20 computers plugged into one or two breakers?

There is in a school, because some dimwit paperpusher thinks that kids need more protection.

[Uncle Peter]

You don't need an electrician to change a fuse or push a circuit breaker. That would be like calling an electrician to change a lightbulb. The tenant should pay of course, for being an ignoramus.

[Uncle Peter]

I don't have that problem. Either get more sensibly spaced strips, or stop using those old transformer based wallwarts. All my wallwarts weight about as much as the plastic housing and are half the size of my hand.

[Uncle Peter]

State reasoning for EIGHT computers.

[Uncle Peter]

"in liquidation" - is that because of this problem?

[charles]

Do tell us which ones.

[Uncle Peter]

Post a link or STFU.

[Uncle Peter]

Anything powerful I have has a seperate wart that's on a wire from a normal plug.

They are sold in varying spacings, FACT.

Not if you add up the wasted electricity.

I've got loads.

[Uncle Peter]

Presumably less sensitive ones.

Incorrect, look it up.

[Uncle Peter]

In a school there are more regs.

[Uncle Peter]

"Nuisance trips. Compared to fuses, modern MCBs react more quickly to very short term overloads, and may result in loss of power to a whole lighting circuit when a bulb blows."

Which is what I was saying earlier but nobody believed me.

"Discrimination: it can be harder to ensure that the circuit protective device nearest to a fault will be the only one to open when you have cascaded MCBs - sometimes upstream fuses interoperate better with downstream MCBs"

Why on earth would you cascade them?

"Extra work: Fitting a CU with RCD can often result in the installation not working initially due to hitherto unnoticed faults in circuits such as a borrowed neutral or higher than expected earth leakage. While discovering these faults is not a bad thing, it can force the investigation and repair of a number of other issues not directly related to the original task planned, causing unexpected cost and delay."

Agreed, if it ain't broke, don't fix it.

[Uncle Peter]

You made the claim that they don't exist, you do the work.

[charles]

There might be a local authority's own regulations. In Surrey, it was decreed that all stage lighting installations in schools were to have 5 Amp sockets instead of the normal 15 Amp ones - because "they were safer".

[Uncle Peter]

When safety comes before the possibility of the thing actually functioning, something is seriously wrong. Far too many paperpushers out of touch with reality. I bet they never even saw a stage.

[Uncle Peter]

You can show the regs that aren't what I say they are. There will of course be regs of some sort.

[John Rumm]

As you say plugging in the devices alone was causing the trip, then you must have been seeing RCD trips. The correct fix would have been to split the circuit into two or more, and ensure that each was wired using high integrity earthing techniques. "Fixing" it by changing to RCDs with a higher trip threshold simply defeats the purpose of having an RCD for shock protection in the first place.

[John Rumm]

You don't. Motor rated MCBs (Types C & D) are specified by the circuit designer when protecting large fixed motors (typically induction motors). A large induction motor's inrush will pop a fuse just as easily as an unsuitable MCB.

Then fix the faulty installation or design, not the symptom.

No, that is because you are an imbecile.

[John Rumm]

Fit a type C MCB to lighting circuits and it becomes a non issue.

I have also seen mains halogen GU10 lamps fail and take out a BS3036 rewireable every time - so its not a problem fuses are immune to.

When feeding a submain to another CU typically - an outbuilding, or garage etc.

More correctly it was broke, but you were previously unaware.

There are plenty of positive reasons for changing consumer units:

[John Rumm]

And there is the key point. You probably don't need them to reset a circuit breaker. However you may well need one to safely rewire a fuse these days.

So as owner of the property, what you are saying is that when a rewireable fuse pops, you would like someone with no understanding even of how to change a plug, to be let loose on your property making it up as they go along. Brave decision.

[John Rumm]

Why do you keep making these daft claims?

There are three types of Miniature Circuit Breaker, denoted as type B, C, & D.

A circuit designer is free to choose whichever is appropriate for the circuit.

A "normal" type B breaker will have a nominal trip current, which is provided by a thermal mechanism (i.e. like a fuse), and a fast acting magnetic trip mechanism for clearing "fault" currents (i.e. overloads many times the nominal rating).

All the different types of a given nominal rating will have the same thermal response characteristic.

Since inrush currents can "look" like momentary faults even a type B breaker will tolerate short duration loads of 3 to 5 x its nominal rating before tripping.

A type C will allow 5 - 10x, and a type D up to 10 - 20x its nominal rating.

The designer should choose the appropriate one for the circuit. So if you are switching a large bank of strip lights with magnetic ballasts, then a Type C will be more sensible than a B. For circuit with a 5kW blower motor, a type D may be more appropriate.