30 Ma Rcd Discrimanation
- Thread starter Harris786
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314.1 (i) possibly omitted at the design stage me thinks..??
Maybe a diagram of how YOU have already got it configured would assist....
THEN....
once you have your drawing have a close look at how you have your final circuits, distribution circuits, CU's and incoming supplies arranged...
THEN...
have a look at the regs to see which circuits NEED 30ma RCD protection....
THEN
redesign your circuit arrangement accordingly......
:C
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I am confused....what exactly have you done regarding the connections
Post some pics please
Post some pics please
I also do not understand if you have already done this or are planning it. Does the flat have access to the shop ?
I will make an assumption that the flat is a sub off the shop (dual arsedeee) board and the flat does not have access to the shop 
should be split at the head and on separate meters
:C but what do I know?
As as for assumptions they are the mother of all ****ups.
should be split at the head and on separate meters:C but what do I know?
As as for assumptions they are the mother of all ****ups.
Methinks someone might have dropped a small clanger??
What are you trying to discriminate against / with / for??
edit: a diagram would be appercated ( sic)
What are you trying to discriminate against / with / for??
edit: a diagram would be appercated ( sic)
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If these are two,separate installations of one "service". Why do,they need discrimination......surely they would have been designed to be independent, independent fuses, ditto submains, ditto MCB boards and off one service head split at source
But what do I know
But what do I know
I see trouble ahead........
But in an effort to not be like other forums where the 5ww are bashed relentlesly.........granted most deserve it but we are the friendly forum.
As per the others im assuming one supply for both shop & flat.
From the meter put the tails into a henly block > one set of tails from henley to shop cu > second set of tails to switch fuse (correctly rated for your submain) > swa submain from switch fuse to flat cu.
Ive not mentioned the suppliers or TT earth (which ever it is) but it will need connecting to both cu's and meb you should know about.
Upto you how you design cu circuits and the mcb/rcd/rcbo make up.
Just out of curiosity are you a fast track taught sparks?
But in an effort to not be like other forums where the 5ww are bashed relentlesly.........granted most deserve it but we are the friendly forum.
As per the others im assuming one supply for both shop & flat.
From the meter put the tails into a henly block > one set of tails from henley to shop cu > second set of tails to switch fuse (correctly rated for your submain) > swa submain from switch fuse to flat cu.
Ive not mentioned the suppliers or TT earth (which ever it is) but it will need connecting to both cu's and meb you should know about.
Upto you how you design cu circuits and the mcb/rcd/rcbo make up.
Just out of curiosity are you a fast track taught sparks?
Harris786
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shop DB1 is a dual RCD consumer unit, from db1 40A MCB to to upstairs flat. It's a only one bed flat. DB 2 in flat RCD trip same time as down stairs in shop. I never work under any experienced sparky cos no one want improver in my area, this is the my only way to learn the trade.
install the submain in a way that doesnt require RCD protection. or is that too simple?
DB1 may be able to be reconfigured to have a non rcd way, so wire to that or fit a extra small board with no rcd for the flat
Photos would be a help, but as slips has said can DB1 not be reconfigure to be a high integrity board, where the first way after the main switch is in fact just an mcb?
The mcb would then be the ocpd for the sub to DB2 (dependent on the installation method used for the sub of course).
AS the installer the easiest way forward for you would be (as slips has again said) change DB2 for a non-rcd board & rely on the rcd located at DB1. will be a pain in the bum for the flat tenant if the rcd trips & the shop is locked up.
Me I'd have split the tails plonked in a sub meter, put in a correctly designed submain & used an all rcbo boards in both the flat & shop...................................but that's just me & having had a few years at college & on the tools before taking money off Joe public to do their electrical work.
You CAN NOT learn all that is needed to work in this trade by taking a fast track 5 week course, but at least you will get the basics (discrimination included hopefully) & you will definitely end up in hot water trading with only knowledge gained from forums.
So I think I've given enough info to you on this job & fulfilled the forum obligations of being polite & helpful, but you do need to go & get some recognised training........cant believe I'm going to say this......even some 5ww course might help you not cause death & mayhem by poorly planned & executed electrical work for your customers.
The mcb would then be the ocpd for the sub to DB2 (dependent on the installation method used for the sub of course).
AS the installer the easiest way forward for you would be (as slips has again said) change DB2 for a non-rcd board & rely on the rcd located at DB1. will be a pain in the bum for the flat tenant if the rcd trips & the shop is locked up.
Me I'd have split the tails plonked in a sub meter, put in a correctly designed submain & used an all rcbo boards in both the flat & shop...................................but that's just me & having had a few years at college & on the tools before taking money off Joe public to do their electrical work.
You CAN NOT learn all that is needed to work in this trade by taking a fast track 5 week course, but at least you will get the basics (discrimination included hopefully) & you will definitely end up in hot water trading with only knowledge gained from forums.
So I think I've given enough info to you on this job & fulfilled the forum obligations of being polite & helpful, but you do need to go & get some recognised training........cant believe I'm going to say this......even some 5ww course might help you not cause death & mayhem by poorly planned & executed electrical work for your customers.
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I would do as post #9 and install a switch fuse.
Even if the design load current for the flat is only 40A, I would size the submain for at least 60A and put a 60A fuse in the switch fuse.
This way you keep the two instalations separate.
Even if you can make one way of the shop CU a high integrity one, that still means whenever the shop CU is turned off for maintenance / alterations in the shop that the flat loses power. Not good. a completely separate submain from a swich fuse solves that problem.
Even if the design load current for the flat is only 40A, I would size the submain for at least 60A and put a 60A fuse in the switch fuse.
This way you keep the two instalations separate.
Even if you can make one way of the shop CU a high integrity one, that still means whenever the shop CU is turned off for maintenance / alterations in the shop that the flat loses power. Not good. a completely separate submain from a swich fuse solves that problem.
Doc Hudson
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Did you get your NICEIC registration you were asking about back in March http://talk.electricianforum.co.uk/topic/25749-niceic-registration/ Whilst I admire your have a go attitude, I honestly hope that this is not "the only way to learn the trade". (i.e. Have ago - Make a mistake - Ask on a forum - Have another go - Maybe rectify mistake). The problem you discuss is a basic understanding of electrical science. Do you understand the concept of how RCD's work compared with how MCB's work. (i.e. The current involved in making a device trip and the fault path to cause the trip?) Just asking how to wire something up is not the correct way to get a practical working knowledge so that you can then design installations correctly and randomly fitting some electrical equipment that you think needs to be connected is not a good design method. Your design process should have been something like: Establish what final circuits you will need, loads, cable sizes, over-current protective devices etc. Then consider what size and where any CU's will be physically located and if one or more CU's are needed and any distribution circuits between them and/or the incoming supply. Then with a basic loading & CU layout understood, establish what circuits need RCD protection and if you are using integral RCD's external RCD's RCBO's and what ratings are needed. Then ensure all of your MCB's, RCD's, RCBO's have appropriate discrimination with your proposed design layout ensure only the correct single device trips not a whole chain of devices or a random selection of one device out of group of two or more. This same principal apples to over-current protection as well as earth leakage. If you look at BS7671 and numerous electrical guidance and educational books, discrimination is a topic thats covered. I honestly think that a majority of customers would be shocked to think that so called electricians are learning the trade by using their properties as a training school while doing on-line fault finding via internet forums. Lets all hope this is not the only way to learn the trade as it is a very bad advert for electrical competence to any members of the public who may read on-line forums such as this one.
Doc H.
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