Home Electrics - Fuse Rating

[Mr-H]

I have recently had a couple of occasions where the ring main has tripped out; it is rated at 15 amps. A friend of mine suggests that whilst the lighting circuit should be rated at 5 amps (as it is), the ring main should be upped to 30 amps. He says that given the modern consumption of electricity, e.g. Microwave, tumble dryer, kettle, toaster could all be on at the same time, along with tv, sky box, wifi router, telephone etc. etc. 15 amps is simply too low. He seems to suggest that I need not worry about the occasional trip, but that this would not happen if the fuse rating was lifted. What about it please, Ab-ers?

[Dizmo]

Most modern ring mains are on a 30amp RCD.

[Dizmo]

Given that yours is on a 15mA circuit I'd probably want to make sure that the ring is safe beyond said mA. Old wiring could be an issue?

[Dizmo]

Is your cooker spurred from the ring (does it have its own fuse spur)?

[Dizmo]

If it is actually a ring and the cable is 2.5mm then 32a is the maximum.

[bhg481]

Are you sure it's a ring main?

VERY old houses used to have a single wire to each socket and were rated at 15 amps. If yours is a old (guessing more than 70 years) house that might be the case.

[The Builder]

Yes, it may be a radial circuit. One cable from the fuseholder.

For re-wireables, 30 amps is usual for a ring circuit.

BUT ............... do not just uprate the fuse until you're sure you have a continuous ring.

When you say "tripped out", do you mean the fuse blows?

[Mr-H]

Dizmo - yes, the cooker is separate. It is rated at 30amps separately at the box, as is the shower (30amp and separate). bhg481 - the house is no more than 50 years ok'd. divebuddy - you are on my wife's side about getting a sparky in. I think that I would have done that anyway, but now I can tell him what I think I need, rather than ask "can it be done?". I can speak with perhaps just a little knowledge!

[Dizmo]

Mr-H: the age of the house is irrelevant in my opinion. The idiot who wired my house was a complete cowboy. My brother and I had to rewire the entire house :/ The 'builder' decided to wire both upstairs and downstairs on the same ring and wire some of the lighting off the ring. Nightmare.

[Mr-H]

Dizmo -My house has just 6 trip switches in the box in the garage. They are labelled: 1 x 40amp for cooker; 1 x 40a for shower; 2 x5a for upper and lower lights (separately); 1 x 15a for immersion (not used, and hasn't been for years) and 1 x 15amp labelled 'plugs', which can only be all sockets, upper, lower and garage. Builder - trip switch moves to the off position. Certainly time to ask the neighbors if they can recommend/warn-me-away-from someone to look at it I think.

[buildersmate]

You need to have a properly qualified person look at your power circuit to see whether it is installed as a ring main or not. If it is, using the normal 2.5mm squared conductor cable, 30 amps (A) maximum can be drawn through it, so the MCB (miniature circuit-breaker ) can be uprated to 30A, but this work is Part P modifiable under Building Regs, so you will have to have an electrician do this work.

If the circuit is radial, only 15A can be drawn through the single conductor so you won't be able to have the circuit uprated to 30A at the Consumer Unit without some additional cabling being installed.

It is ridiculous that any modern house was designed with only 15A capability from the power sockets, so no wonder the breaker is tripping regularly from your regular domestic power consumption.

Dizmos advice is generally good but contains a glaring mistake in his first post that needs correcting. Modern ring mains circuits may additionally be protected by a 30 milliamp (mA) RCD. This is an additional protection device to the MCBs, which your installation does not have (from what you say), that detects earth leakage and breaks when the leakage current exceeds 30mA (not amps). It is not an overcurrent detection tripping breaker (MCB) and assists in preventing electric shock from faulty appliances.

1000mA equals 1 amp.

[Dizmo]

buildersmate: Is it not normal now to use RCDs on rings?

[BRIGHT SPARK]

You guys must have some old distribution boards if they include 15a and 30a breakers.

[buildersmate]

Dizmo. Yes, but not instead of MCBs, they are an additional protection device. And you seem to be confusing amps and milliamps.

[Dizmo]

buildersmate: It was a long day/night. I'm not the sparky, my brother is. Apologies for giving incorrect information.

[buildersmate]

No problem. Grateful that someone puts their hand up to mistakes. Most on here don't. I'm not a registered electrician either - Bright Spark is, I believe.

To clarify his comment for the sake of the OP, the European harmonised MCB ratings primarily used for domestic power circuits are 16A and 32A, that replaced 15 and 30. I went with the flow of others comments to try to get some sense into the important elements of the thread without rejecting everything that had gone before.

You can still get old rated breakers but they would not be used on a new installation.

Completing the commentary, someone else said you can drive up to 100A from a domestic installation. That's only true of one with a supply feed cable appropriately rated. You may find a 63A main isolator switch or indeed some other lower capacity main breaker.