Good morning all,

I have a quick garage electric question. Over the summer I had new electrics installed in the garage at the end of my garden. There was nothing in there before but I now have 2 x 2 gang sockets, one strip light, an external light and a weather proof 2gang socket under the adjacent car port and a security light on a pir. This is all fed by approximately 35m of armoured cable connected to the house consumer unit.

Anyway, when it was installed I said I wanted the sockets so that I could run power tools in the garage.

Fast forward to last night and I spend some time setting up the sliding mitre saw so I can start making some raised beds from decking planks. As soon as I pull the trigger everything goes off (at that point only the strip light and the saw). I go into the house and it has tripped the switch for the garage on the consumer unit. I turn it back on, walk down the garden to try again and the same thing happens. Cue giving up for the might.

Following that my question is – does it sound like a fault or just that the saw is drawing too much and there’s nothing to be done? I’ve run the saw from an extension lead from the house before and from some external sockets on the back of the house with no problem. I’ve just to try and other tools but at present it doesn’t do what I want it to do. I’m happy to get the electrician back if there’s an issue but he’s a friwdns brother in-law so don’t want to cause a fuss unnecessarily.

What would Singletrack do?

I presume the garage is on it’s own circuit from the house consumer unit. Is it on an mcb with local rcd in the garage or an rcbo? What rating? Is it tripping due to an earth leak or over current? That said probably the first thing to do is get the electrician back to check it.

What trips? Mcb or rcd?
If it’s the mcb, what size is it?

Basically mcb trip = too much current. (Possibly by the saw starting up, you can get “c” type mcb’s that hold a little longer before they trip out)
Rcd trip is an earth fault. Probably your saw.

If its the MCB tripping it’s probably because the MCB is a “B” curve. What happens is that the mitre saw has a large inrush current when it first starts which is too great for the MCB to carry. Changing to a “C” curve will sort it.

A 32A “B” curve MCB will instantaniously trip at 5* it’s rated current – 160A. A “C” curve 32A MCB will trip at 10* – 320A – They’re still rated at 32A and perfectly suitable for task.

A word of warning though. What is known as the Zs – the earth fault loop impedence required to trip the MCB in the max. allowable time of 0.4 seconds – is lower for a “C” curve mcb than a “B” curve. Your electrician, when he changes it, should retest to ensure it’s ok.

Any questions, ask.

Rich.

Cheers for replies guys. Most of those have gone over my head but have confirmed that I probably need to get the electrian back to tale a look. He’s a decent guy and I’m not suggesting he’s done anything wrong, just didn’t want to waste his time if it was likely the saw.

P.s. these isn’t a separate unit in the garage as far as I can tell, think it all just connections the house consumer unit but I’m at work so can’t check details

It could be the saw – try it in a socket in the house.

Cheeky question OP – How much did the work cost you just out of interest, I had a post on here recently about doing similar work.

Ta

i’d call him back.. i thought this kind of set up had to have a second consumer box at the garage end.. in my house it does, but iirc it does trip at the main consumer box too. my garage is converted to a ‘man cave’ and if i turn too much equipment turned on at once (via gang sockets) it would trip. so i’ve set it up so i can turn on in stages (limit the inrush)

also, i take it the work was “part p” certified?

Yep all tested and certified, got the bits of paper and everything. As for how much it cost, I honestly don’t know. I know that sounds stupid but it was done in stages as we had the whole house rewired 4 years ago when we moved in and some of the prep and the armoured cable were installed then to avoid too much disruption post decoration. We would have done the garage then but it needed a new roof to keep Tue rain out!