RCD question

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12 Jan 2010
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Hi, I have a new installation. The power went to some circuits the other night because the boiler tripped out. The RCD switch on the CU flipped, that's all. The downstairs lighting went off, but upstairs lighting stayed on. The ring main upstairs went off but downstairs it stayed on. The boiler switch on the CU did not flip. Is this all normal? Why would some circuits stay on? Does it just mean that the boiler is on the same RCD circuit as the downstairs lighting and upstairs ring main?
 
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Does it just mean that the boiler is on the same RCD circuit as the downstairs lighting and upstairs ring main?

It sounds that way. You probably have a recently installed 'high-integrity' consumer unit with dual RCDs. The breaker for the boiler will only trip in an overcurrent situation. A high resistance earth fault will trip the RCD but not the MCB, and even a low resistance high current earth fault may still trip the RCD first in some situations. Other than whatever fault caused the installation to trip in the first place, there is no major cause for concern.
 
Your installation is divided like you say so that if a fault occours on your wiring which can not be easily fixed, you are not left completely without power.
 
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Thanks for the replies. The fault was an earth fault by water backing up in the boiler and shorting out the cabling.
 

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