6amp Garage circuit upgrade - can't run power tools

jzee · 17 Sep 2010

Hi, I need your advice. I bought a brand new house 6months ago, with a detached garage at the bottom of the garden - the fuse for this says NSB06 - so I assume 6amps.

Now whenever I run my pressure washer (1500watt) or lawn mower (similar wattage) it trips the switch - which is very very annoying. I have to use a long extension from the house.

Can I change this fuse for something like 8amp? When I moved in it only had a light and a double socket in the garage.

I also re-did the whole garden, and when digging I found the cable to the garage (you can also see it inside the garage) - this cable looks like one of those 30amp armoured cables you get (approx 3/4 inch thick) (also in it's own sleeve underground).

So, can I just change the fuse?

jzee · 17 Sep 2010

Oh, just to be clear. It trips the RCB.

Also, I can't see if the big bertha armoured cable goes all the way to the RCB, as the wires from this are behind plaster board.

PrenticeBoyofDerry · 17 Sep 2010

We need to know the CSA (size) of cable and the distance between the house and garage also the size breaker protecting the garage CU from the house.
Does the Garage CU have any spare ways and what rating is the isolator?
As much info possible!
Pictures could help too!

TicklyT · 17 Sep 2010

If it's tripping an RCD rather than an MCB, that suggests a fault that needs further investigation.

A Neutral to earth fault will trip an RCD whenever a significant load is used, no matter what size MCB is protecting the circuit. A relatively small load, like a single light may not generate sufficient fault current to cause it to trip, but anything more power hungry will. Finding the cable with a spade may have done enough damage to cause the fault.

If it's a brand new professional installation there's probably a good reason a 6 Amp MCB is installed. Both the size and length of the conductors are significant to the selection of, and the correct operation of circuit protectiive devices (MCBs etc) There is no such thing as a '30 Amp cable', no matter what the labels in DIY sheds may say.

jzee · 17 Sep 2010

This one is from when the house was being built:

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RCB (that's a energy monitor on the top of it)

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How the cable comes into the garage. The main switch turns all elec off in the garage, the one to the left is the light switch. The cable to the power socket goes into the garage loft, and back down right next to it.

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Close up of cable

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jzee · 17 Sep 2010

Ok, the distance is approx 15-20meters away.

I couldn't have hit the cable with the spade, it is protected in a tube that you cannot crush. I only really saw it where it came up into the garage, as the cable goes into the garage above the damp proof course.

There is only one double socket in the garage, the one in the pic above.

Oh, looking back at my electrics there is a 100amp fuse after the meter (on the wooden board in the first pic) which then leads to the RCB (the 2nd pic). The wires then go from the back behind the plaster board.

I shouldn't have said 30amp earlier, I'm just saying that as the site forman said that - but take whatever they say with a pinch of salt. The black cable is armoured, I've seen it before it was put it.

Monkeh · 17 Sep 2010

The only thing those photos show is that the SWA is not three quarters of an inch thick.

Please tell us exactly what is tripping. Is it the 6A MCB or one of the RCDs? Is that MCB labelled garage or is it for another circuit?

jzee · 17 Sep 2010

Hi, thanks for all your replies.

I've just measured the black cable and it is half an inch - sorry for the error earlier.

The switch that is tripping is the 6a switch, the black one in the 2nd pic (middle of the right set of black switches). This trip switch is just for the garage (it says NSB06 on it).

Monkeh · 17 Sep 2010

There are four of them but I'm going to assume it's the one with the pictogram which looks vaguely like an attached garage.

Changing it is not a DIY job, however it's likely you can replace it with a 16A breaker safely. Hire an electrician who will make sure and do so for you.

sparkwright · 17 Sep 2010

I would have expected the switched fused spur unit on the right to isolate the lighting without isolating the sockets.

Could the sockets have been added later?

sparkwright · 17 Sep 2010

Change of mind.

The switched fused spur on the right must have been designed to isolate the whole of the garage (which probably only consisted of lighting), the 1 gang switch simply to turn on the light.

I think perhaps the sockets were added later, and were tagged onto this lighting feed.

mikeyd · 17 Sep 2010

If that fused switch turns all the power off in the garage then presumably the fuse is not just there to protect the lighting in the garage.

If you upgrade the MCB in the house then the fuse in the garage will just blow when you plug your lawnmower in. You can't put a 13A fuse in it because the lighting circuit must be fused maximum of 6A.

You could get an electrician to check it all and put a 16A MCB in the house and rewire the garage socket into the incoming side of the fused switch but you are getting him on site anyway I would seriously consider getting him/her to put a small 4 way consumer unit in the garage. That way makes it easier in future if you want security lights or a pond feature.

EDIT: Sparkwright: Didn't see your post before I finished my reply (getting pizza out the oven) but good thinking, sockets added later makes sense to me.

jzee · 17 Sep 2010

I won't touch the RCB, I just want to know what's needed before I ask an electrician.

The fused switch turns off all power to the garage, socket & light.

Edit: They had to put a socket in the garage as it was in the advertising.

Now you mention it sparkwright, you're probably right. However that was how it was when I bought it and moved in. I'm guessing the electrician forgot to do it, then added it later. Also, the unit should really be the silver casing rather than the white box.

Monkeh · 17 Sep 2010

The electrician will determine what's needed.

And please, stop calling it an RCB. You have a CU, with a main switch, two RCDs, and nine MCBs.

jzee · 17 Sep 2010

I see what your saying Mikeyd, now I do think the builder messed up. I'll have to ask my neighbours how their setup is.

I plan to put an automatic garage door opener in (depending on cost), so that might be the best option. I'd also quite like another double socket, and outside light over my drive too.

What do you think I'm looking at for the cost? all the cables are easy to get to, and are just tacked to the wall. £100 - £200?? I do have an electrical safety certificate when I moved in, so all is safe at the mo.

Edit: Sorry, Monkeh. I'll get the terminology right.

Thanks once again for everyone's your help.

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6amp Garage circuit upgrade - can't run power tools

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