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32a distro build
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snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
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Points: 3122 		Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 25 October 2019 at 3:24pm
I do understand the difference between RCD and RCBO - sorry for being unclear. I meant should I put a 30A (or 25A) RCBO in place of the 32A RCD so that I have current protection in the rack? I say this in response to kedwardleisure question - the outlet will of course have 32A MCB protection so I assumed he was suggesting something else and this was all that I could think of.

why would having a defeat switch on the rack RCD help?

I am quite confident in the person who built this distro and the people responding aren't 'randoms' but people I have known on here for several years or have done business with.
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RoadRunnersDust View Drop Down
Young Croc
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Points: 561 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 25 October 2019 at 3:45pm
Both questions are answered in the 1st and 5th paragraphs of my previous post. :)
www.guildfordcablecompany.co.uk
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snowflake View Drop Down
Old Croc
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Points: 3122 		Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2019 at 12:26pm
I can't see that a bypass on the rack RCD introduces any discrimination into the system. It means that any fault will definitely take out the main board rather than just possibly. Wouldn't changing to a 10ms device be better (assuming that the RCD on the main board will usually be at least 30ms)?
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RoadRunnersDust View Drop Down
Young Croc
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Points: 561 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2019 at 12:45pm
A bypass takes you from two devices with no discrimination (which is bad) to a single device.

A situation wherein a fault can trip one of two devices at random is worse than a single trip point further upstream.

You could fit a 10mA device in your distro but the nuisance tripping you’ll get from PA gear, etc. would likely be an issue, especially since it’s a global device instead of per output
www.guildfordcablecompany.co.uk
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snowflake View Drop Down
Old Croc
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Points: 3122 		Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2019 at 7:51pm
after reading a few old threads I am going to change to

32A d-type double-pole MCB on input
c-type RCBO per output (will try 10mA ones and see if I get nuisance tripping) 10A,2*16A,20A
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RoadRunnersDust View Drop Down
Young Croc
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Points: 561 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2019 at 8:37pm
Why would you fit a 32A MCB to the input on a distro that can only be safely fed from a supply that already has a 32A or lower limit?

Unless you fit it with something stupidly inappropriate like an A or Z curve device you’re still going to have poor discrimination and two breakers to check in the event of an over-current trip
www.guildfordcablecompany.co.uk
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snowflake View Drop Down
Old Croc
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Joined: 29 December 2004
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Points: 3122 		Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2019 at 5:44pm
Originally posted by RoadRunnersDust RoadRunnersDust wrote:

Why would you fit a 32A MCB to the input on a distro that can only be safely fed from a supply that already has a 32A or lower limit?

Unless you fit it with something stupidly inappropriate like an A or Z curve device you’re still going to have poor discrimination and two breakers to check in the event of an over-current trip


not strictly necessary as long as what I am plugging into is functional. As usually plugging into things that I am not 100% have been checked properly would rather have my own 32A.

Also, as there is a common neutral in the unit, shouldn't the incomer have doulbe pole isolation to be safe under fault conditions? this won't necessarily be provided by the supply output - so doesn't this mean I SHOULD have a double pole RCD on the incomer.

EDIT - replacing all the MCBs with RCBOs will of course necessitate removal of the common neutral. all I NEED is a double pole isolator to switch on/off.


Edited by snowflake - 30 October 2019 at 1:04am
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RoadRunnersDust View Drop Down
Young Croc
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Points: 561 		Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2019 at 6:22pm
If you are that unsure about the quality and integrity of the supply you are connecting to then you quite simply should not be connecting to it. 

An MCB or an RCD does not guarantee your safety.
www.guildfordcablecompany.co.uk
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