Mitre saw trips rcbo Ask questions and find answers to many subjects relating to electrics and electrical work

[Tim Mawer]

I have a new consumer unit fitted with rcbo's. When i came to use my old mitre saw it caused the rcbo to trip. I was able to exchange the saw for a new one, thinking that it was the fault. Tried the new saw out but it wouldn't work either. Went back to the shop and exchanged this one for a different make to see if that might help. No joy!! Im on my third saw now and it looks like i may have to cut all the timber by hand. Is there anything i can do to prevent the rcbo from triping. Tim.

[kuzz]

What size is the rcbo? Probably just tripping because the saw needs a surge of power to get it going. (starting current)

[sparx]

Hi,
If you are using the same sockets each time ie in the garage/shed or using the same extension lead I would suspect a wrong connection.
This may have been wrong for ever as it won't blow fuse/trip mcb but will show up when RCD/RCBO installed, eg reversed N/E in lead.

This is why we are advised to test circuits before changing cons. units or adding an RCD to existing installation.
Usual customer reaction is "it was alright 'till you fitted that thing, now you want to charge extra for fault finding? you're one of those rogue traders".
happy hunting,
Sparx

[Tim Mawer]

Hi Sparx.
Thanks for your reply. With regard to the socket/extension lead that i have been using. The rcbo doesn't trip when i use other power tools such as my saw bench.
Tim.

[Tim Mawer]

The rcbo is 32A.

[sparx]

Hi again, it may be as KUZZ suggests starting current, unfortunately with RCBO's there is no easy way of knowing if tripped by earth leakage or overcurrent, one reason I don't care for them.
It is usual for most RCBO's to be type C however yours may be type B, if so it may be possible if circuit length/impedance allows to have it changed , still 32A but greater inrush current.
The leckie who changed the board must have given you a set of test sheets on which you will find a reading of Zs for the circuit which will tell if chane possible,
regards Sparx