Power tool tripping (MCB) in garage

WabbitPoo · 31 Aug 2009

My garage has its power circuits on a ring from a CU in the garage, protected by a 16A rcd*. I have one particular tool, a planer thicknesser which, when you start it, more often than not trips said rcd. Annoying.

The manual states it is an 1800W device at 240V.

When it doesn't trip the rcd*, it runs fine for extended periods.

1800/240 = 7.5A, by my schoolboy physics, so is there likely to be a tool fault rather then a "power circuit design" fault?

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* Edited by moderator - see below - seems to be MCB tripping not RCD
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PrenticeBoyofDerry · 31 Aug 2009

Is anything else plugged in, on this circuit at the same time using power?

BS3036 · 31 Aug 2009

I am assuming you meant to say MCB instead of RCB.

A motor, when starting up, takes a lot more current than when running. A possible solution is to use a type C MCB but this is not something to do without first measuring the circuit Zs and checking that it will be safe.

WabbitPoo · 31 Aug 2009

Sorry, I am a landscaper, not an elec, so got the terms wrong! The CU has two CB cartidges, one for the lighting and one for the ring main. The switch on the latter is tripping, not the switch on the CU itself. It still trips when nothing else is plugged in to the power circuit.

PrenticeBoyofDerry · 31 Aug 2009

so it's the breaker tripping not the rcd?
BS3036 has answered your question, the inrush current at start up is tripping your breaker, when it's running, will work fine but at start up current is too high, Type C needed

ban-all-sheds · 1 Sep 2009

Or a B32.

WabbitPoo - what size is the cable for the socket circuits, and is it just clipped to the walls?

WabbitPoo · 1 Sep 2009

ban-all-sheds said:
Or a B32.

WabbitPoo - what size is the cable for the socket circuits, and is it just clipped to the walls?

Its 1.5mm and is inside insulated walls.

ban-all-sheds · 1 Sep 2009

It should not be a ring, in that case. How long ago was it installed?

WabbitPoo · 1 Sep 2009

That's by using a ruler to measure across the ends of each strand, by eye, so not entirely sure its bang on. So, each strand is approx 1.5mm in diameter. See, I told you I wasnt an electrician!

Don't know when installed and by whom.

What cable size is required for a ring, then? I could replace it all if necessary. Or rather, I could get it replaced.

ban-all-sheds · 1 Sep 2009

WabbitPoo said:
That's by using a ruler to measure across the ends of each strand, by eye, so not entirely sure its bang on. So, each strand is approx 1.5mm in diameter.

Cable sizes are specified as the cross-sectional area of the main conductors:

//www.diynot.com/wiki/electrics:flatpvccables

What cable size is required for a ring, then?

2.5mm², which you may already have.

Is the cable surrounded by insulation? Do you know how thick?

BS3036 · 1 Sep 2009

ban-all-sheds said:
Or a B32.

I think I'd want to know more about the circuit feeding this CU first, though.

WabbitPoo · 1 Sep 2009

ban-all-sheds said:
WabbitPoo said:

That's by using a ruler to measure across the ends of each strand, by eye, so not entirely sure its bang on. So, each strand is approx 1.5mm in diameter.

Click to expand...

Cable sizes are specified as the cross-sectional area of the main conductors:

//www.diynot.com/wiki/electrics:flatpvccables

What cable size is required for a ring, then?

Click to expand...

2.5mm², which you may already have.

Is the cable surrounded by insulation? Do you know how thick?

Just removed boards from wall. the cables lie next to battens, and on the inside of foil-backed kingspan ie internal pb, cable, kingspan, outer ply.

Just compared the cable with some known 2.5mm cable and it looks to be the same physical size. Deffo a ring, too.

ban-all-sheds · 1 Sep 2009

BS3036 said:
ban-all-sheds said:

Or a B32.

Click to expand...

I think I'd want to know more about the circuit feeding this CU first, though.

I am seriously hoping that a cable supplying a garage with it's own CU is properly protected at the source, and isn't relying on the load end to provide overload protection...

ban-all-sheds · 1 Sep 2009

WabbitPoo said:
Just removed boards from wall. the cables lie next to battens, and on the inside of foil-backed kingspan ie internal pb, cable, kingspan, outer ply.

That will be Installation Method 102.

Just compared the cable with some known 2.5mm cable and it looks to be the same physical size.

Therefore the cable will have a capacity of 21A.

Deffo a ring, too.

And therefore should be OK for a 32A breaker, but reluctantly I must agree that BS3036 is right - the circuit supplying the garage needs to be established as OK - what sort of cable is it, what size, how long, and how is it supplied?

WabbitPoo · 1 Sep 2009

Will contact an elec. thanks for help, all

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Power tool tripping (MCB) in garage

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