Help with main switch/RCD on CCU tripping

[justjust1]

Hi all,

I have just finished my level 2 City & Guilds 2330 Technical Certificate so am relatively new to electrical installations but loving every minute of it.

Before i start a new business or get a job in the electrical world and before i finished my Level 3 and test and inspection course i have been doing some electrical work at home in an extension we are building.

I have installed a separate CCU with an 80Amp Main switch/combined RCD(30ma) because there was not enough room on the current CCU. This CCU has 32Amp ring circuit, 6Amp Lighting circuit and a 50Amp Shower circuit.

Everything has been working fine i have tested all the circuits and they are all good, but the other day i plugged my circular saw in (brand new Makita) which i have been using in the past fine and the main switch/RCD tripped!!!!! this then happened every time i turned the saw on 3 or 4 times. So i left all switched off for around 2 hours had some lunch, came back and all worked fine and had done ever since!!!!

Can anyone explain whats going on and why this happened?

As i said, i am a newbie so please forgive any terminology i have got wrong!

JG

 

[telectrix]

could be surge on saw start up. . i have a similar problem with a 3kva 110v tranny. even when not loaded, it occasionally trips the MCB/RCD when first plugged in.

 

[Chr!s]

initial leakage current on saw, moisture or carbon build up?

 

[justjust1]

Thanks, this puts my mind to rest, sounds like its not anything i have done wrong! The weird thing is that the 32Amp (ring circuit) MCB stays on but the mainswitch/RCD goes off!!

 

[telectrix]

must be RCD trip then. damp saw, or earth leakage on saw. if it's only the saw that causes trips, i wouldn't worry.